Great Planes Curtis P-6E Hawk ARF

VIDEO FILES

Just judging by the left side photo above, most new RC pilots would think that there is no possible way that Great Planes’ new scale ARF, the Curtis P-6E Hawk biplane, could ever be considered as a Sport Aviator review aircraft. Sport Aviator exists to help new and newer RC pilots progress in the sport of model aviation with the fewest problems and greatest success. Obviously, an aircraft the size (76-inch wingspan) weight (nearly 14 pounds) and complexity (it is a biplane with cabanes and struts after all) just can’t be a beginner’s aircraft.

Honestly, until Bob Karasiewicz reviewed the Great Planes Tiger Moth, right side photo, I would have very strongly agreed with anyone who said the P-6E Hawk was not for Sport Aviator’s readers. But the Tiger Moth’s gentle handling, honest flying habits and slow landing approach speed proved it was a great second airplane. While more complex to build than the more common low –wing second airplane, the Tiger Moth could do everything a low-winger could and still handled like pushing a baby carriage.

The Tiger Moth and the Hawk are both large aircraft but the Hawk is bigger. The Tiger Moth is more complex to build but lighter by 3.5 pounds. However, the Hawk has a bigger wing area and a flat bottom airfoil. The Hawk’s 22 oz. / sq. ft wing loading is heavier than the Tiger Moth’s 17.4 oz. / sq. ft. But its flat-bottom airfoil has more lift than does the Tiger Moth’s semi-symmetrical one. In the end, both aircraft fly at about the same airspeeds and both handle much like big trainers.

But because of the Hawk’s larger size, and heavier weight, the Curtis has more momentum in flight requiring the pilot to be just a little further “out in front” of the airplane. For that reason, the Hawk is best suited as either a third aircraft or as a second airplane for a pilot that has been flying their basic trainer far longer than normal and is extremely comfortable with it while flying all aerobatic maneuvers.

Great Planes’ ARF scale aircraft, airplanes that are miniature copies of a full-size airplane, have a reputation of being very easy to build. As complex as the P-6E Hawk looks, it builds quickly and straight. It requires almost no more building ability than would any low-wing ARF Sport Airplane. The wings assemble the same “ARF” way even though there are two of them. Building the tail is the same as is the engine installation. Radio installation can also be identical if the builder wishes (but we made a small change).

Photo 1 Photo 2

The only real differences are wheel pants and the top wing alignment and struts. Great Planes makes these two extra tasks easy even if this is the pilot’s first biplane. Plus, this airplane looks so much better than a standard sport low-wing aircraft that it is not possible to intelligently compare them.

Building the Aircraft – Both Wings

Photo 3 Photo 4

Both wings assemble in the same, ARF typical, manner. Photo 3 shows all the parts as they arrive in the kit. Each wing uses a front and rear spar. The front spar is made by laminating three plywood pieces together using 12- minute epoxy resin. Photo 4 shows this lamination process. The square is used to insure that the three plywood pieces are perfectly aligned and square to the flat surface. If one of the pieces is warped, note the bent plywood piece on the lower wing, put the warped piece in the middle to insure the spar is straight.

Photo 5 Photo 6

The front spar with the dihedral is used in the bottom wing. The straight laminated spar and the thicker rear spar are used in the top wing. Allow the laminated spars to dry at least one hour. Use this time to seal the covering around the aileron servo’s mounting box edges (photo 5). Then cut the covering away leaving enough to overlap into the box as shown in photo 6.

Photo 7 Photo 8

The string seen in photo 6 extends to the wing center section as shown in photo 7. This string is eventually used to pull the aileron servo wire through the wing to the center exit hole in the bottom of the top wing. Make sure that this string stays in place during the wing’s construction. Use the remaining spar dry time to install the hinges into the precut slots in the wing halves. Use a high-speed rotary tool to drill a 3/16 inch hole in the center of each wing slot in both the ailerons and wing trailing edges. This hole allows the thin CAA adhesive to flow completely into each end of the hinge.

This is probably a good time to mention that it is just not possible to build this aircraft without using a high-speed rotary tool. There are several cowling cutouts that must be made (details later) plus numerous holes to drill that just cannot be done without this tool. If you don’t have one, you will need it in every aspect of your modeling career so now is the time to get this indispensable tool.

Instead of describing each hinging operation, please check out the Sport Aviator article “Installing Mylar Hinges” in the Flight Tech Section if you have not installed such hinges before. Mylar hinges are used on most every ARF model aircraft so it is a good idea to learn their installation completely now.

The top wing is a BIG WING! It is 76 inches long and nearly 14 inches in width, its chord. Make sure there is enough room on your workbench to assemble it. A flat surface is important in this step so locate one if your building board is too small. It does not have to be level, but it must be flat.

Photo 9 Photo 10

By now, the laminated spars should be dry. Mark the bottom of the spar on both sides (photo 9). Note that the part with the slight “V” is the bottom. Draw a center line on the spar as shown. Also draw a center line on the rear spar. Photo 10 shows most of what you will need to assemble the wing. The tape is a low tack masking tape to protect the covering.

Insert the spars into each wing half to be sure that they will slide into place at least to the center mark. If not, there will be a gap at the wing’s center. It is usually a good idea to have one wing half that will extend exactly to the center line, but not past it. The other half should allow the spar to be inserted just about 1/32 in. past the center mark. This small clearance insures that the wing halves will fully meet in the center. Enlarge photo 10 by clicking on it and you can note that the front spar fits exactly to the center mark. The other side had the clearance. This keeps the point of the “V” exactly centered for proper dihedral.

Photo 11 Photo 12

Before assembling the wing, make sure that the string is reachable through the small hole in the bottom of the wing near the center (photo 11). Once the wing halves are joined, this string is reachable only through this hole. If you are good at wing assembly, use 12-minute epoxy throughout the process. If not, like me, coat the inside of both spar boxes and the spars with 30-minute epoxy. Insert the spars into the wing side that exactly fits the spar centers and remove any excess epoxy using a little, just a little amount, of 91% rubbing alcohol.

Coat the other wing half with 12-minute epoxy. Then slide that half onto the spars and firmly against the other half. Lay the wing upside down on the workbench and run two or three pieces of tape span-wise to hold the halves together. Then remove any excess epoxy using the alcohol cloth. Turn the wing over, apply two pieces of tape and clean the top half as well.

Then turn the wing upside down on the workbench and fully tape the bottom and the top (photo 12). Weight it down if possible so that the wing top is firmly against the flat surface. Align the leading and trailing edges and clamp in place as shown. Then allow the epoxy to dry. The end result should look like photo 12.

Even though the top wing has no effective dihedral, putting the wing upside down on the workbench provides what is popularly known as “airfoil dihedral” although I am sure it also has a technical term but I don’t know it. As the wing gets narrower towards the tip, the chord gets smaller, the airfoil shape also gets slightly thinner since the thickness of the wing is expressed as a percentage of the chord. The smaller the chord for a given airfoil, the thinner the wing becomes.

Since the wing is slightly thinner at the tip than it is at the center, and the top of the wing is built against the flat surface, the bottom of the wing tapers upwards by the amount the tip airfoil is thinner than the center airfoil. This is airfoil dihedral and has two major benefits. First, it does provide a slight amount of effective dihedral to help steady the aircraft’s slow speed flight. It also eliminates a common optical illusion. For some reason, our eyes do not want to see a curved, tapering surface in a straight line. If the wing were actually perfectly straight, it would appear, appearance only, as if it were drooping downwards. This makes the wing look like it has anhedral; the wingtips look lower than the center section. Avoid this.

Photo 13 Photo 14

The bottom wing assembles the same way but there are no ailerons to install and no strings to manage. A no-string wing for a change! However, there is a catch. The bottom wing has for-real, honest dihedral. Make sure to mark the bottom of the spar and accurately draw the centerlines. This is critical to obtaining the exact dihedral specified. As became evident during the entire assembly process, Great Planes has gone the extra step and made this process foolproof.

Photo 15

Photo 14 shows one wingtip supported by two small blocks. You can see these blocks in photo 13 as well. The idea is to put one block under each wingtip during wing assembly to insure getting the proper amount of dihedral. My work bench is a little short for that so I weighted one wing half flat on the board and propped the other wingtip up by both blocks. Everything comes out the same. Note that the bottom wing is built with the wing bottom against the workbench.

Except for this, assemble the bottom wing exactly as you did the top. Tape the wing together and clamp the leading and trailing edges in perfect alignment. Weight the wing as before but only in the center and at the wingtips. Do not put heavy weights on the unsupported areas. Make sure to clamp the two plywood “extensions” firmly together as this part holds the wing onto the fuselage.

Yes I know, photo 15 shows lots of little lead balls rolling around the building table. So, one of the weight bags broke during assembly. This is one reason why you should use 30-minute and 12-minute dry epoxies for this step, not 5-minute.

Accidents happen, wings take longer to align than planned and who knows what other delays are possible. The slower dry period provides extra time without really prolonging the assembly process. Plus, the slower dry epoxies provide more bond strength since the adhesive has time to penetrate further into the wood.

Photo 16

After the bottom wing has dried, examine the area around that plywood extension. Enlarge photo 16. Note that some excess epoxy seeped out onto the part of the extension that slides into the fuselage. This interior 90 degree angle must be flat in order to correctly mount all the way into the fuselage. Carefully remove any excess epoxy so that this interior angle remains 90 degrees but is flat to the wood on both sides. Remove only the adhesive, not the wood.

Into the Fuselage

The fuselage is almost big enough to get into. I have owned cars with less trunk room than this fuselage has space. Fortunately, without the really big cowl and the large rudder, the fuselage, though wide and high, is short. This makes building easier. I chose to start by attaching the horizontal stabilizer and the vertical fin, minus rudder, first.

Photo 17 Photo 18

Before installing the stabilizer onto the fuselage, mount the elevators and rudder in place. Drill the hinge center holes and mark where the hinges go. Do not glue the hinges now. Remove the rudder and elevators and put aside. Photo 17 shows the one-piece stabilizer and most of the tools needed for its installation. The next step is to adhere the covering to the stabilizer “ribs” around the center section (photo 18).

Photo 19 Photo 20

I haven’t mentioned the instruction book before, but it is excellent. The many photos clear up all potentially confusing construction steps. Photo 19 shows the several photos used to insure that the stabilizer covering is cut just as it should be. There is a difference between the top and bottom covering because of the mounting system used.

The stabilizer does not just lay on top of the fuselage as is true with most ARFs. Instead, it actually overlaps onto the fuselage by about 1/4 inch for extra strength and gluing surface. Identify the bottom of the stabilizer and remove the covering as shown in the instruction book and in photo 20. Then adhere the covering about 1/8 inch into the slot as shown in photo 20. A trim covering iron is a good tool for this task.<!–

Photo 27

Once everything is aligned, take it apart. Apply 12 or 30 minute-epoxy to the stabilizer only. Note photo 27. Keep the epoxy clear of the slot edges. After the stabilizer is attached, this slot will form the base for the vertical fin. Excess epoxy squeezing out onto the fin base will make alignment difficult and weaken the fin’s bond to the wood. Make sure to realign and level the stabilizer before the epoxy sets.

Photo 28

Once the stabilizer is dry, cut away the covering from the fin slot as was done for the fuselage on the stabilizer’s underside (photo 28). Test fit the fin into the slot. It should fit against the fuselage bulkhead in front and be flush with the fuselage and stabilizer in the rear.

Photo 29 Photo 30

However, the fin on this Hawk was cut slightly short. Look carefully at photo 29 and you will note that the rear of the vertical fin is 1/8 in. out of line with the fuselage rear. This was the only misalignment in the entire airplane. The simple answer is to install a 1/8 inch light ply spacer between the vertical fin and the fuselage bulkhead (photo 30). Epoxy the spacer to the bulkhead, making sure there is clearance for the plastic fairing that covers the fin and stabilizer. Epoxy the fin in place, using a modeling triangle to make sure it is square with the fuselage.

Photo 31 Photo 32

Cut out the front of the fairing as shown in photo 31. Make sure the slot clears the plywood spacer as it must butt up against the bulkhead. Then use a round file to bevel the top of the slot so that it fits around the fin’s curved leading edge (photo 32). Cut away the top portion of the fairing to clear the fin. Test fit the fairing until it just fits over the fin

Photo 33

Once the fairing is cut to fit, there will be some white plastic showing at the very edges. Since the pre-painted edges were cut, the white plastic shows through. I used some Top Flite LusterKote Olive Drab paint, sprayed into the can top and applied with a brush, to hide the white edges.

After the paint dries, position the fairing and draw a line on the vertical fin and stabilizer where the fairing edges are. Use a fine felt tip marker. Remove the fairing and poke some pin holes into the covering, about 50 per section, to make holes for the fairing adhesive. Remove the pen marks with rubbing alcohol. Use canopy glue along all the fairing areas that will contact the fin and stabilizer. Position the fairing and hold in place using cushioned modeling clamps as in photo 33. When dry, cut the rear fairing edges flush with the rear fin edge, stabilizer and fuselage.

Selecting and Installing the Engine

Photo 34

The engine choice for this aircraft basically determines its destiny. It all depends on what the pilot wants this aircraft to do. I knew I wanted this airplane to fly as a scale model. But I also wanted to be able to perform some basic aerobatics. After all, the full-size P-6E Hawk was powered by a predecessor of the famous 12-cylinder Allison engine (the 12-clyinder Curtis V-1570-23) that powered such American fighters as the P-40 Warhawk, the P-39 Airacobra, the P-38 Lightning and the P-51A Mustang. The Hawk’s pre-Allison engine produced 600 to 675 hp and gave the little biplane some impressive performance numbers.

But above all, I needed a powerplant that would be super reliable. My thought was that a 14-pound giant biplane would not make an outstanding glider. The engine had to keep running no matter where the fuel tank was placed and to the last drop.

This airplane was also to be used for local model air shows. That meant that it had to look, sound and fly just right. The need for a “scale sound” eliminated the 2-stroke engines like the new OS 1.20 AX and the OS Max 1.60. Although super-powerful, the exhaust note of these big 2-strokes just would not match the aircraft’s looks. The stock mufflers were much too large and required removing almost one whole side of the cowling. However, “Pitts” style mufflers for these inverted mounted engines are available from J’Tec (http://www.jtecrc.com) and Slimline (http://www.slimlineproducts.com) if you require absolute maximum power and large aerobatic maneuvers.

I thought 14 pounds was already heavy enough, especially for a second or third airplane. The wing loading should be at the low end of the scale, 22 oz. / sq. ft. I also did not want to cut out the cowling more than necessary to retain the airplane’s great appearance. These criteria ruled out heavy gasoline engines. While their sound may be right and they are ultra-reliable, gasoline engines are extremely heavy for their power output. I needed decent power without the weight.

This pretty much left the 4-stroke engines for the Hawk. There are many excellent 4-stroke engines available. But the Hawk was designed around the OS Max 1.20 Surpass series. Everything fits the Max 1.20 and it is a light engine at only 32 ounces. The 1.20 Surpass II, the current version, has proved itself to be nearly 100% reliable over the last decade or so. But I wanted maximum power with my reliability.

So I chose the Max 1.20 Surpass III for the Hawk. Why the “III” version? The Surpass II and III engines are identical with one difference. The Surpass III has a fuel pump. Having a true fuel pump has some significant advantages:

1) The fuel tank can be located anywhere, even back over the airplane’s center of gravity.

2) The fuel pump provides constant fuel pressure regardless of atmospheric conditions. Constantly changing the high-speed needle mixture settings as conditions change is not necessary. Even more important, the idle mixture also stays constant adding to the engine’s reliability. Once the mixtures are set, very few changes are usually required unless the altitude (or density altitude) changes by 1,000 ft. or more.

3) Best yet, the pumped engine produces a little more usable horsepower. How? On non-pumped engines, the needle valve must be set 4-500 rpm on the rich side of peak rpm. This procedure protects the engine from “lean runs” once airborne as the propeller “unloads” in flight. Most RC model engines will turn faster in the air than on the ground, sometimes by as much as 500 rpm. The high-speed mixture is set rich to insure that the faster turning engine never runs lean, even in vertical climbs.

But with a pumped engine, the faster the engine turns, the more fuel is pumped meaning the in-flight mixture settings more closely resemble the ground settings. A pumped engine only requires a 200 rpm off-peak setting. In practice, this means that the Surpass III, even though it is otherwise identical to the Surpass II, will produce 200-300 more useable rpm. I wanted that extra power and greater reliability.

4) A pumped engine requires only two fuel lines to get fuel into and out of the tank.

Photo 34A Photo 35

Locate and cut out the engine alignment guide in the instruction book. Use a hobby razor knife and make the edges straight (photo 34A). Actually, straight edges are not important but it does look more professional. But you must make sure the dotted alignment lines reach to the edge of the template. There are four dark alignment lines on the firewall as shown in photo 35. Align the engine mount template with these marks as shown in photo 35

Photo 36 Photo 37

Use an awl or scribing tool to indent the exact center of the four engine mount bolt holes as shown in photo 36. Drill out the holes using a 7/32 in. drill bit.

Photo 38 Photo 39

Use a modeling razor chisel to carefully remove any wood flashing from the holes on the back of the firewall (photo 38). Then use a pair of pliers or a curved surgical clamp (photo 39) to install one blind nut to the engine mount bolt (photo 39). Before inserting the blind nut, apply a very small amount of epoxy to the rim of the nut where it will contact the firewall. Do not get epoxy into the treads.

Photo 40 Photo 41

Install all four blind nuts by tightening the bolts, with the mount installed, until they are flush against the rear of the firewall. Allow the epoxy to set. After the epoxy is dry, remove the mount and the template. Reinstall the engine mount but allow enough “play” to move it as required. The Hawk uses the popular Great Planes two-piece mount. This mount has alignment lines molded into the top, bottom and sides.

Position your engine (more on this subject later) inside the mount. Pull the sides inwards until the mount beams are evenly against the engine crankcase. This sets the mount’s width. Now slowly slide the mount sideways until the two alignment marks on the mount are exactly centered on the firewall mark as in photo 41. Tighten securely in place. The final step is to remove one bolt at a time. Then apply removable thread locking compound to it and reinstall the bolt. Lock all four bolts in place using this method.

Photo 42 Photo 43

With the motor mount in place, it is time to install the engine. Position the engine on the mount beams (photo 41). Make sure the engine sits flat on both beams. Measure the distance from the firewall to the front of the thrust washer, the part the propeller tightens against. The book says this distance should be 5 5/16 inches. Of course the book also says that the cowling should be taped in place first and the distance from the firewall to the front of the cowling should be 5 7/8 inches.

The only problem with this is that it is nearly impossible to tape the cowling in place and center the front crankshaft opening while aligning the fuselage/cowling “feather” design when the engine is not installed. I guarantee that the crankshaft/thrust washer hole will be off-center. This makes the cowling measurement wrong and could result in a misplaced engine.

Photo 44 Photo 45

Instead, temporarily clamp the engine in place on the mounting beams. Remove the valve cover from the engine. Position the thrust washer 6 3/32 inches out from the firewall (photo 43). Locate six of the eight metal “N” strut tabs that will be used to mount the struts to the top and bottom wings. Double up these pieces and place around the engine’s thrust washer as shown in photo 44. With the cowl taped in place and the feathers aligned, install the propeller you intend to use. As photo 45 shows, this process centers the forward cowling opening exactly. Make sure the thrust washer extends 1/8 inch past the front of the cowling.

Photo 46

As the above shows this procedure exactly positions the cowling. It is possible to mount the cowling now, but the engine is still just clamped in place. If its position varies a little during the final permanent mounting process, the cowling could be in the wrong place. It is a good idea to mark the cowling’s position on the fuselage now, but remove it to permanently mount the engine.

Photo 47 Photo 48

Just about the best way I have found in 30+ years to position and mount an engine is by using the Great Planes Dead Center Hole Locator (GPMR8130) (photo 47). I know they are many other tools and ways to accomplish this task, but in my own opinion, and it is just an opinion, this is about the best way ever. This product rates right up there with the invention of the self-tapping drywall screw and computer transmitters. All three are far better than sliced bread!

With the engine still clamped in place, use the tool to mark the four holes. Install the valve cover and then drill the four holes with a 9/64 in. drill bit. Make sure the holes are drilled exactly as marked and straight. If this is your first engine mounting, drill one hole, remove the engine, tap the hole for an 8-32 bolt and install the bolt. Check that the other three hole marks are still aligned and then continue the process until all four holes are drilled, tapped and the engine is in place.

Photo 49 Photo 50

Install the cowling again. Well, install it as far as it will go. The valve cover hits the top of the cowling. Fortunately, you can still reach inside the cowling with a long set of surgical clamps and mark the area where the cowl collides with the engine’s valve cover. Mark this area as shown in the above photos.

Photo 51 Photo 52

Reach inside the cowling and push a sharp modeling pin through the cowling at the four corners you marked. The result should be as shown in photo 51. Use a high speed rotary tool with a metal cutting bit to cut out the square as shown in photo 52. Make sure you wear a mask to protect your lungs from the fiberglass dust. Vacuum the dust after each cutting operation. Wear eye protection as well. If you can’t see anymore, it gets very hard to fly an RC aircraft.

Protect the engine with a plastic bag during the cutting process or make the cuts far from the airplane. Once the first hole is cut, Slide the cowling back onto the engine. It will go a little further this time. Again mark the area for the second cut as shown in photo 52. Continue this process until the cowling reaches back to the marks you made on the fuselage. As a last test, hook up the glow plug connector you intend to use to the glow plug in the engine, without electrical power. Make sure the connector clears the rear of the opening. If not, remove enough cowl material to allow it to connect with at least 3/16 in. clearance all around.

Photo 53 Photo 54

Install the cowling, using the N-strut hookups for centering the thrust washer. Tape the cowling in place. Check everything out, especially the thrust washer centering and the “feather” alignment. When everything is perfect, remember that the thrust washer must extend 1/8 inch past the cowling, start drilling the cowling mounting screw holes.

Photo 55 Photo 56

Once the cowling is permanently mounted, remove it again. Make up a high-speed needle valve extension from some 1/16 in. music wire, available in any hobby shop. Attach the muffler header to the engine. Get two pieces of cardboard, tape one side to the fuselage, behind the rear of the cowling, and make two holes where the cardboard overlaps the header and needle valve extension (photos 55 and 56).

Photo 57 Photo 58

Remove the cowling. Protect the engine with a plastic bag (photo57) as before. Remove the exhaust header and needle valve extension. Install the cowling and mark the location of the two cardboard holes onto the cowling (photo 58). Reinstall the exhaust header and plug it with a paper towel. Plug the needle valve hole as well. Cut out a 3/8 in. hole in the cowling for the needle valve extension. Cut out the square area for the exhaust header.

Test fit the cowling in place. Continue to slowly and carefully relieve the cowling around the exhaust header until it and the muffler clear the cowling. Allow at least 3/16 in. clearance all around so that the exhaust heat will not damage the cowling. Remove the cowling.

Photo 59

Since the Hawk has a completely cowled engine, we need to find a way to get fuel into the tank without removing fuel lines. A pumped engine makes this easy. Just two lines are required and one fuel line “T” fitting. If a non-pumped engine is used, the instruction book shows a great way to manage this task using a double line system inside the tank.

Either way, the best external fuel fittings are the now universally popular, among competition flyers anyway, “Fuel Dot” system. This foolproof system uses decorative outer aluminum rings to hold the fuel lines in place. In a pumped system, just two lines are used. The first is the vent/overflow line. This line extends through one of the aluminum tubes into free space. The other line connects to the “T” fitting between the fuel tank and the pump. This line is plugged with an aluminum “dot” except when filling or draining the tank. With fuel dots, there is no valve jamming or clogging and it works every time. Photo 59 shows the two outer aluminum rings mounted in place on the bottom of the cowling.

Photo 60 Photo 61

Test fit the machine gun barrels in place. The base of each barrel is angled to fit into the cowling and still point straight ahead. Once you get the correct angle, remove a little of the base nearest the cowling and epoxy in place (photo 60). If you are using a 4-stroke engine, cut out the front of the air scoop located on the top of the cowling (photo 61). Make a rough cut using the high speed rotary tool as shown in photo 61. Then use a file to make the opening square but leave the corners slightly rounded to prevent cracking.

This opening will allow cool, fresh air to enter the top of the cowling but not for engine-cooling purposes. Rather it is cool air for the engine’s carburetor. In an inverted engine installation like the Hawk’s, a 4-stroke’s carburetor opening will face upwards. Since the engine is tightly cowled, the only air the carburetor can get is the hot air around the engine. Hot air reduces engine power. The cooler, outside air from the scoop flows easily into the carburetor and restores some of that lost power. This is another little trick learned from the world of Pattern competition.

Epoxy the exhaust stacks into place. The stacks should point straight out to the sides, not up or down. Use 5-minute epoxy and hold in place until the adhesive cures.

The hardest part of the Hawk’s construction is now complete. After the cowling, almost all the hard work is finished. The rest is fun and feels like sliding down a steep icy hill on a waxed sled.

Attaching the Rear Control Surfaces

Photo 62 Photo 63

Attaching the rudder is easier to do without the elevators in place, so do that control surface first. The idea here is to make sure that the rudder fits tightly against the vertical fin even though there is a steerable tail wheel to install. Insert the tail wheel assembly into the factory-cut slot in the rear of the fuselage (photo 62). Position the rudder in place using two Mylar hinges in the top two hinge slots in the vertical fin. Mark the place where the torque rod will be inserted into the rudder (photo 63). Drill a 3/32 in. hole into the rudder at this mark.

Photo 64 Photo 65

Lay the nylon bearing over the ridge in the center of the rudder’s leading edge (photo 64). Mark the bearing’s edges on each side of the covering. Use a sharp model razor knife to cut the covering below the hole exactly over the center ridge. Carefully peel back the covering to the marks you made. Then use the tail wheel wire itself to cut a channel in the soft balsa deep enough to allow the bearing to recess half way into the rudder’s leading edge.

Photo 66 Photo 67

Once the channel for the bearing is cut (photo 66) use a trim or modeling covering iron to fold the covering back over the leading edge as shown in photo 67.

Photo 68 Photo 69

Do the same thing to the fuselage rear where the tail wheel bearing fits into the factory slot. Test assemble the rudder with the Mylar hinges and insert the torque rod into the rudder. Make sure everything fits as it should. Insert a thin metal strip or cardboard in the space between the top of the vertical fin and the overlapping rudder extension or aerodynamic balancer (photo 68). There should be about 3/32 in. clearance so the rudder can move freely. Once everything checks out put a few drops of a plastic safe oil, or Vaseline into the bearing to protect it during the gluing process (photo 69).

Photo 70 Photo 71

Install all the Mylar hinges into the rudder. Apply 12-minute epoxy into the torque rod hole in the rudder and along the slot (photo 70). Put the epoxy into the slot in the fuselage rear. Insert the tail wheel assembly into the fuselage slot and press into place. Install the rudder. Make sure all the Mylar hinges are in their slots in both surfaces and that the tail wheel torque rod is fully inserted into the rudder. Do not forget the spacer. Press the rudder firmly in place and CAA (thin) the Mylar hinges. The end result will be a tight fitting rudder (photo 71) that will have maximum effect with a reduced probability of flutter. It looks better too.

Photo 72

Make sure that the rudder to fin gap is as shown in photo 72. On a full-size aircraft, the rudder extension over the fin reduces the load on the pilot’s feet by using air pressure to help move the rudder. I am sure this assistance was appreciated by the hawk’s pilots as they maneuvered at airspeeds approaching 200 mph. On a model flying at 50 mph however, it is probably only useful for appearance sake. Just make sure it does not inhibit rudder travel.

Installing the elevator halves is as simple as were the ailerons. Make sure both elevators fit very tightly against the horizontal stabilizer. There should not be any light showing through the hinge gap. This is important. If one side has a gap larger than the other, elevator response will vary as more air flows through the larger gap, reducing that elevator’s effectiveness. The end result is the same as a misaligned stabilizer. The aircraft rolls slightly with elevator input making maneuvers just that much more difficult to control.

Installing the Servos.

Photo 73 Photo 74

The factory cut servo tray is installed next. However, the fuselage has so much space that some mounting blocks need to be installed to hold the tray in place. Epoxy, do not use CAA as this is a high stress area that must stay in place, the front blocks against the fuselage former making sure that the slots above the block are open (photo 73). Epoxy the rear mounting blocks against the rear former, level with the former’s “shelf” (photo 74).

Photo 75

On the bottom of the servo tray, reinforce the servo screw areas with 1/2 x 1/8 in. spruce strips on the front side and with 3/8 x 3/8 in. spruce in the rear. Note that one of the servo areas is not reinforced in photo 75. This area will be epoxied to one of the support blocks which will also serve to reinforce the servo screws. Install the servo tray using eight servo screws into the mounting block; two into each block. Remove the tray and harden the treads with thin CAA.

Before permanently installing the servo tray, assemble the tank according to the directions. Use the twin pickup lines outlined in the instructions if you do not have a pumped engine. Pumped engines require just one pickup and one vent line plus a “T” fitting in the line to the pump. Connect the fuel lines to the tank, mark their function and install the fuel tank into its position. Connect the fuel lines to the engine and route through the cowling.

Reinstall the tray after the CAA has thoroughly dried. The servo tray locks the tank into position.

Photo 76

Great Planes supplies some pretty heavy duty control horns for this large aircraft. These are high quality and yet easy to mount. Screw a metal clevis onto one of the control rods about halfway. Then insert the control rod into its plastic housing in the fuselage and run it up to the servo tray area. Install the clevis in the appropriate control horn hole as shown in photo 76. Hold the horn in place against the control surface, making sure the horn’s screw holes are over the hardwood block in the control surface and mark the four screw holes. Drill with a 1/6 in. drill but do not drill through to the other side. Screw the control horn in place, remove the screws, harden the threads with thin CAA, let dry and reinstall the horn. Do this for both elevator halves and the rudder.

Photo 77

Mount the servos in the servo tray. It is at this point that the instruction book and I part company. The book would have you bend one of the control rods against the other and then hold it in place with two wheel collars (photo 77). This will work but produces a maintenance point that will need to be checked before every flying session and possibly even during a flight day. If those wheel collar screws loosen or one rod slides against the other due to excess elevator application, the twin elevators could become so misaligned that controlled flight may not be possible. That would make a bad day for the Hawk pilot.

Plus, since one of the rods is bent off center, it is nearly impossible for the elevator halves to have the exact same movement. The difference would not be much, but it would be annoying during elevator-heavy maneuvers like loops and slow rolls. If you intend to use an analog transmitter, then you must use this installation method. Remember to frequently check those wheel collars. Double secure the screws with thread locking compound as well.

Photo 78

But if you have a computer radio, there is a much better way; especially in an aircraft this large. Mount the rudder servo in place of the throttle servo. Install two elevator servos next to each other in the two center positions (photo 78). Hook one elevator servo up the receiver’s elevator channel and the other to a non-gear auxiliary channel. Mix the aux. channel to the elevator channel 1 to 1. Reverse the direction of the aux servo so that it moves in the opposite direction.

Photo 79 Photo 80

There is a large hole in the servo tray forward of the rudder servo. It is a perfect size for a mini-servo. These servos have impressive strength but are small and light. The one in photo is from Polk’s Hobby and costs about $20. Futaba also makes these servos as do most other radio brands. I just happened to have the Polk’s servo available.

Raise the servo above the tray using two 1/2 x 1/8 in. spruce blocks. Mount the servo in line with the throttle control rod as shown in photo 80. Set the throttle movement as per usual.

The extra weight of this modification? It probably totals only a few grams. The twin wheel collars weigh almost as much as does the mini-servo. The throttle control rod is shorter than if the servo was located in its original spot so that is lighter. The airplane would never notice the weight difference.

But it will surely notice the difference in performance. Not only will both elevators have the exact same movement (after tuning the servos with the transmitter) but there is now double the servo strength moving those big surfaces. The servo movement can also be adjusted for any slight stabilizer misalignment as well.

Tuning the Elevators

Photo 81 Photo 82

Level the fuselage using a small level placed in the wing saddle (photo 81). Place the level up against the front bulkhead to insure measuring the same curved saddle surface on each side. Check that the stabilizer is also level (photo 82).

Photo 83 Photo 84

Use one or two combination squares to measure the height of each elevator from the flat building board (photo 83). With the fuselage level, both elevators should be the same height above the board. This setting will get you into the “ballpark” matching the elevator halves.

To fine tune them exactly, tape two straight metal rods or warp-free balsa sticks, to the elevators; one to each side. The rods should be angled to meet in the middle, just past the rudder’s trailing edge, as in photo 84. Make sure both rods, or sticks, have the exact same angle on each half. The rods should match exactly. If not, adjust the sub-trims of each channel until they do.

Then slowly move the transmitter control and watch to be certain both elevator halves always match throughout the complete movement range. The amount of movement should match. If there is a difference at the extreme end of up and down, use the travel range adjustment feature to insure each servo moves the same amount. If the movement matches at both ends and the center but differs in the middle, only an advanced transmitter like the Futaba 7CAP or higher can make mid-range adjustments. If you have such a transmitter, great. Make the adjustments. If not, don’t worry about it as the difference must be extremely slight and the airplane will probably never notice it.

George Asteris, famed FAI Pattern pilot and Team Futaba member, taught me this elevator tuning technique and I have used it to tame dozens of airplanes, including my competition birds. It works every time. Thanks, George.

But There Are Two Wings?

Photo 85 Photo 86

Yes, but Great Planes makes the setup easy. Locate the hardwood dowels in the top of the bottom wing. There are two on each side. These dowels have 4-40 blind nuts epoxied to the bottom. Some of the nuts had epoxy inside them. Use a 4-40 tap to clean the threads (photo 85). There are four angle connectors used on the bottom wing (photo 86).

Photo 87 Photo 88

Mount each connector facing outwards as shown in photo 87. Then bolt on an “N” Strut to each connector. The short leg goes towards the front. The strut is mounted to the outside of the connector (photo 88). Tighten these struts but leave the connectors slightly loose in the wing.

There are two center cabane struts. These are mounted to the top wing just like the connectors. The long leg of each cabane strut goes towards the trailing edge of the top wing.

Photo 89 Photo 90

Mount the bottom wing on the fuselage. Position the top wing over the fuselage and connect the two “N” struts from the bottom wing to the top wing. Again, the struts connect to the outside of the metal angle connectors (photo 89). Carefully measure the distance between the two wings (photo 90). All distances should be equal. The top and bottom wings should be parallel.

Photo 91 Photo 92

Then drill a 5/64 in. hole through each of the cabane strut’s mounting holes where it meets the fuselage (photo 91). These holes must be over the hardwood plates inside the fuselage. They will be as my wings fit perfectly the first time. Screw the cabane struts to the fuselage. Check all the measurements and alignments again. Tighten the strut connectors against the wings. Remove the top wing and check that the cabane struts are level (photo 92). Mine were level with no problems.

Final Touches

It reads like a lot of work. But getting to this point took just 22 hours of work time. That is less than a tiny fraction of what it would have taken to build this airplane from a wood kit. And along the way, each step teaches you how to build a complex ARF for strength, reliability and great flight characteristics. Plus, it was fun. So now is the time to finish it up.

Photo 93 Photo 94

The landing gear bolts to the factory installed blind nuts (photo 93). The straight edge of the gear points forwards. The instruction book would have you glue the cover plate in place over the gear. A better way is to drill two 7/64 in. holes through the cover plate as shown in photo 94. Drill matching holes in the gear plate and tap for a 4-40 bolt. Then use these two bolts to secure the gear cover in place. This allows removing the cover to tighten the bolts as they loosen over time. They will no matter how much locking compound is used as grass is bumpy and lumpy.

Slip the factory formed and painted fairings over the gear legs. Bolt on the axle and install the wheels. The fairings are held in place by two 4-40 bolts. 10 minutes and that complicated looking landing gear is finished without hassles.

Photo 95 Photo 96

I installed the receiver and battery pack on the servo tray. The battery pack, a 5-cell 2,000 mAh Nickel Metal Hydride pack is located under the tray and the receiver is held to the top by rubber bands (photo 95). I mounted the switch in the instrument panel. Make sure there is clearance behind it (photo 96).

Glue the windshield and small turtle deck in place using canopy glue. Attach the ailerons to the servos as was done with the tail feathers. Make sure they are centered. Run the aileron wires out of the small holes. A “Y” connector is run out the small fuselage holes, one connector on each cabane strut and cable-tied in place.

Finishing up all the little details and fine print tasks will take about another hour or so. In the end, the airplane requires about 25-28 hours to build. That is not bad for a nearly 14 pound airplane with a 76 x 14 inch wingspan.

After you are done building, perform all the checks outlined in the Sport Aviator article “RTF…Maybe”, especially determining the CG (Center of Gravity). Great Planes provides a weight box if you are going to use a very light engine. While this is a professional addition to an already excellent airplane kit, don’t even think about it.

First, any weight box can pull free under high-stress maneuvers like snap rolls. Second, you shouldn’t need a lot of weight because you WILL NOT BE USING A SMALL ENGINE! I know the directions say it is possible to use a 0.61 2-stroke engine. Yes, it is possible but a little short of common sense. This is a 14 pound airplane with two wings of drag and a fuselage as wide and high as a jumbo jet. A small engine will fly it, but that is about all it will do.

This is a beautiful airplane and it is a fighter. Only a larger engine like the OS 1.20 Surpass series or the .90 and larger 2-strokes can give it fighter performance. Very little nose weight is needed with these larger engines. This Hawk needed just three ounces screwed to the firewall. A weight box is not needed to bolt a three ounce wheel weight to the lower firewall. It is possible the OS .90 2-stroke engine would require a lot of nose weight to balance as this engine uses a 60-size crankcase. In that case, use the weight box.

I admit to being puzzled as the instruction book says that one pound, 16 ounces, of lead is required to balance this aircraft using the 1.20 Surpass engine. Mine required just 3 ounces and that with an extra servo slightly to the rear of the CG and the battery pack located under the receiver in the middle of the wing saddle. Why the prototypes needed so much nose weight is far beyond my limited mental capacity, but this airplane surely didn’t require any such massive intervention.

Great Planes also provides a really neat handle/strut carrier combination. This is built from plywood and bolts to the top of the cabane struts. It carries the “N” struts while serving as a handle for toting the fuselage around. I didn’t build it as I leave the struts attached to the bottom wing but it is that extra professional touch that has almost become expected in a Great Planes kit.

The instruction book has complete details on how to install non-functional wire rigging to improve the airplane’s realism and looks. For me, it looks too good already. I didn’t install the rigging but might in the future. It looks like it would require about two hours to install and probably another ten minutes field setup time. But the improved looks are probably worth it.

At the Field

Photo 97

Frank Costello, Sport Aviator’s flight photographer, and I loaded the giant biplane into my Suburban and headed out to the field. It was a little windy but the temperature was a comfortable 65 degrees F. It required 20 minutes to assemble the airplane and check it out. That time has shortened to about 10 minutes now as I have gotten used to the procedure. Assembly means installing the bottom wing and then the top wing using four cabane bolts and four top wing strut bolts.

Photo 98 Photo 99

This is one impressive airplane. The looks are just great and so is the size. It is not too big to transport. While impressive, its size is not so large as to require expert piloting skills. Larger airplanes begin to have a lot of “momentum” meaning that control response is not immediate. The pilot must plan ahead while also flying in the “now” and that increases the pilot’s workload. The Hawk is just about at the maximum size for a newer pilot with low-wing experience.

Photo 100 Photo 101

It happened that Bob Karasiewicz was at the field that day along with his beautiful Great Planes Tiger Moth reviewed elsewhere in Sport Aviator. As the photos show, the Hawk is about the same size as the Tiger Moth but is more massive. It is also about 3+ pounds heavier.

Frankly, I wondered how it would fly. The Tiger Moth is a “kiddy car” as it is slow, glides forever and has a medium control response. At just over 10 pounds and with those giant wings, the Tiger Moth behaves more like a glider than a sport airplane. I have witnessed the Tiger Moth glide for over 300 feet starting from only 50 ft. high.

I filled the approximately 16-ounce fuel tank with “YS 20-20” type fuel. Almost all fuel manufacturers offer this fuel. It was originally designed for high-performance YS engines and contains 20% nitromethane for extra power and a reliable idle. The 20% oil content provides extra lubrication but is all synthetic, no castor oil, to prevent carbon buildup on valve trains and cam gears. This type of fuel is one of the best available for all 4-stroke engines. Again, this is just my opinion.

Photo 102 Photo 103

The original propeller was an APC 16 x 8 in. After one break-in run, the 1.20 Surpass III would peak at 8,400 rpm. Since it was new, I richened the mixture to 8,000 rpm. The idle, from the very start, could only be described as superb at a constant 1,600 rpm.

Taxiing this large airplane on grass was easy as the big wheels rolled over everything in their path. The airplane sat there at the runway’s edge, just idling away the time. With the wind about 10 mph and coming from 45 degrees on the left corner, I applied full throttle. The airplane accelerated, lifted its tail (photo 102) after about 20 feet and climbed into the sky using about 125 feet of runway (photo 103).

This airplane definitely flies on its wing. The flight data recorder is out for repair so numbers will have to come later. But my guess is that the climb rate is around 500 ft. /minute. The airspeed appears around 30 mph.

I leveled off about 75 feet up and needed just two clicks, two insignificant clicks, of right aileron trim for steady level flight. Not bad for a biplane with extra wing alignment tasks. The pitch trim was perfect. It was time for a few photos passes.

Photo 104 Photo 105

Wow! Aw, just plain WOW. Stately, easy to point and with no sign of wanting to depart from level flight, the big Hawk drifted over the runway at a stately pace like a king walking through his throne room. Talking stopped, eyes were riveted skyward and there was a hushed tone to the whole flying field. I was so busy watching that I had to keep reminding myself that I was flying this grand aircraft.

The only maneuvers performed on this maiden flight were two loops and one roll. The loops were small because the engine was running rich. The one roll was done slowly, maintained altitude throughout and proved the rudder’s effectiveness.

But about ten minutes into the flight, something fell off the airplane. I was concerned it might have been a wheel. Landing on grass with only one wheel can be a problem (see the SIG 4-Star 60 review video for an example). But then Frank Costello asked how could a wheel have fallen off with those giant wheel pants? Good question as it could not have. That scared me even more. But a quick pass proved that the pilot had bailed out of the airplane.

Photo 106 Photo 107

I didn’t realize my flying was so bad that he had to jump! Guess I was too busy watching this impressive airplane to fly it properly. But I thought this was a good time to land as who knows what else might be coming loose. I brought the airplane around and into the pattern. The landing approach was too simple. The big airplane, with the engine just ticking over, handled the wind with ease.

The initial final approach was steady at around 25 mph. At touchdown, a small wind gust arose requiring some left correction. Nothing to it and the airplane responded like a thoroughbred born to the wind.

Photo 108

The roll out was straight and took about 40 feet or less. My first major question was answered. Any pilot with low-wing experience could fly this airplane like a pro. Even a new pilot just out of extensive training could fly it safely. The flat-bottom wing provides all the lift required for safe, steady slow flight. The airplane has no bad habits and is completely honest. Like all biplanes, it will slow quickly in a steep turn without throttle, but it never falls off on a wing or even gets near a snap stall.

Photo 109

The airplane made it back but the pilot just was nowhere to be seen (photo 109). It took a few hours to find the pilot. A large aircraft like the Hawk is easy to see, even at long range. The pilot proved to be further away than we thought. That is something to keep in mind when flying large models. During those first flights, keep the airplane close in in case the engine quits or something drops.

Flying ended for the day. I usually epoxy and then screw a pilot into place with extra servo screws. But this time I had the screw loose. I forgot this important step. Glue a small piece of light plywood under the cockpit floor, epoxy the pilot in place and then drill two 1/16 in. holes through the plywood, the cockpit floor and into the pilot’s base. Two servo screws, held in place with thin CAA, will make sure this pilot never qualifies for jump wings.

Photo 110 Photo 111

Photo 112 Photo 113

With the pilot firmly in place, it was back to the field. I had also added a little more decoration while fixing the pilot problem. I had applied some of the great stick-on decals that Great Planes provided using the soapy water technique. This involves cutting out as much of the decal as possible, leaving just enough “clear” to hold the letters together (photo 110) and then wetting the surface with a spray of “wet” water (photo 111). Wet water has ten drops or so of dishwashing liquid mixed in. Applying the decal over this wet area allows it to be slid into position without tearing.

Then blot up the excess water (photo 112) and use a stiff piece of cardboard or some old playing cards to squeeze out the water from under the decals. After an hour or so, it looks like the letters were painted on.

While I had applied some of the decals like the “U.S. Army” under the bottom wing, I had not applied the scale number “40” to the vertical fin and the nose. Instead, I used some commercial lettering to put the number “162” on the airplane as this was the 162nd airplane I had built and flown. The Great Plane Hawk comes with the correct number “40” decals.

Photo 114 Photo 115

It was time to fly again. I used the “pilot break” to run the engine a few more times. With five runs on the engine, it was safe to set the mixture a little leaner. Performance with the 16-inch propeller was less than I had hoped even taking the rich mixture setting into consideration. The airplane needed a little more airspeed. The propeller was switched to an APC 15 x 8 inch one that produced 9,000 rpm at peak. The high speed mixture was set at 8,700 rpm.

Photo 116 Photo 117

This time the takeoff used only about 90 feet of runway and the climb was a little faster, probably near 750 fpm. The airplane was noticeably faster as well. With the improved performance, it was playtime!

Loops were bigger this time. From level flight, 50 foot loops were easy to do. The airplane remained steady and tracked well. The heading stayed constant throughout. With a short dive, the loops could be expanded to 75 feet diameter or more. If allowed to slow too much at the top, the airplane needed a touch of rudder to keep straight. But that would be true of any aircraft. Moral – keep some airspeed going over the top.

Photo 118 Photo 119

Rolls required about 1/3 of the available “down” elevator to remain level if started from level flight. Multiple rolls from level were possible but rudder was also required after the first one. The roll rate was two rolls in five seconds. That is about perfect for a large scale biplane. Surprisingly, the rolls were close to axial; the nose position did not change much during the roll. Biplanes normally barrel roll. The nose and fuselage appear to rotate as if the fuselage was tracking around the inside of a barrel or drum. Not this Hawk. While not perfectly axial, the roll was impressive and probably better than the full-size aircraft could do.

Snap rolls were quick but positive. The airplane took about 1 second to perform them in either direction. The slower than sport airplane snap rotation made stopping with the wings level an easy task. Stall turns showed that the rudder was powerful enough to perform a good stall turn even with the aircraft 20 degrees off vertical.

Level knife edge flight was not possible. There was just not enough power to hold the airplane level using just the fuselage lift. But in truth, this type of airplane was never designed with knife-edge flight in mind. There was enough knife-edge performance to do some 4-point and slow rolls and that is really all any pilot can expect from a large scale biplane like the Hawk. The Hawk did pull heavily to the wheels when rudder was applied in knife-edge. This could be “mixed out” with the computer transmitter for the rolling maneuvers but more power would be needed for any extended knife-edge flight.

Similarly, inverted flight was extremely difficult with the power available. The airplane would almost stop in the air and stall once the wheels pointed upwards. Inverted flight is a victim of the flat bottom wings. In order to provide the extra lift that turns this 14-pound giant into a pussycat in the air, the wings could not be symmetrical as was the full-size aircraft’s. But the tradeoff was more than worth it.

However, later flights at true full power, 8,900 rpm, proved that inverted flight was possible with careful elevator management. As the engine breaks in further, I expect this problem to disappear.

Photo 120 Photo 121

After getting to know the Hawk a little better, we tried a series of landings. All were non-events that would have proved boring except that this is just one great looking airplane. Have I mentioned that before? It is also easy to fly. How about a true, full-stall, three-point landing like the one in photo 121? The airspeed had to be less than 20 mph yet the airplane flew like it was on a wire. The descent rate remained constant; there was plenty of elevator control left (notice in the photo how little elevator was being used); and the gentle touchdown was the prettiest thing the old field had seen in a long time.

Photo 122

Yes, this airplane can be flown and enjoyed by most any pilot with a few months hard flying experience. With all the hard work already done, and a more than reasonable price, this P-6E Hawk is one airplane that will stay in my hangar for a long time. I’m definitely taking this one home (photo 122).

AIRCRAFT SPECIFICATIONS Manufacturer: Great Planes Airfoil: Flat Bottom Radio: Futaba 7 CAP Servos: 54 in. oz. or larger Engine: OS Max 1.20 Surpass III Length: 60.0 in. . Wingspan: - Top -76 in - Bottom – 63 in. Wing Area: 1441 sq. in. Wing Loading: 22.08 oz. /sq. ft. Weight: 13.81 lb. Cost: $420.00 (-30 rebate)

Special Features Unbelievable Good Looks; Difficult Construction Tasks Made Easy; Easy To Build Straight

Notable Positives The best looking ARF to date Complex assembly made easy Good size and light flying weight Flies like a sport low-wing Excellent glide Stable and honest in the air Notable Negatives Stock elevator linkage suspect Weak knife-edge performance Inverted flight needs improvement

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