The Dorothy II Basic Trainer ARF
VIDEO FILES
| (Windows Media Player) Part 1 – Engine Out Landing - Dial-Up / Cable/DSL Part 2 - Normal Landing – Dial-Up / Cable/DSL Part 3 - Training Sessions – Dial-Up / Cable/DSL |
When the description “trainer-airplane” is used with a model Radio Controlled airplane, the words immediately conjure up the images of learning to fly and a model airplane that makes everything easy. It is rarely thought of as a device to train and to educate the beginner in the fundamental skills of model building and design concepts of radio control flight operation. What if you could buy a model airplane that did both?
The advent of Almost Ready to Fly (ARF) airplanes, especially the basic trainer type models, has rapidly introduced a lot of new people to the wonderful sport of RC flying. But there is a more traditional school of thought that feels that many steps have been left out in the education of a new pilot. Before the “ARF Revolution” most Radio Control pilots earned their wings after going through hours and hours of building, assembling, covering, painting and finally flying the models that they built. They know how they were built and learned why model airplanes fly during the assembly process. They are familiar with the structures and what to look for in general assembly as well as the effects of wear, over time.
A lot of trainer-airplanes come very brightly covered and as Ready-To-Fly (RTF) aircraft complete with installed radio and engine systems. They look very sporty, but the operator really does not know structurally what goes on inside. The Dorothy II is an airplane that might well bridge that knowledge gap and earn the respect of the “school of hard knocks” brigade. You may have met that slightly older generation who tells you how hard they had it in the “old days”. They walked to school in the wind, ice, snow, and rain, uphill, BOTH WAYS! Well, we know that was a bit of an exaggeration but there was a foundational belief behind that storyline.
Could the Dorothy II be an ARF that meets the standards of the older beliefs and yet still successfully develops the new breed of trained pilot? With this ARF, there is the usual and reasonable amount of ARF-construction that is still required. A significant difference is that the airplane is pre-covered in an attractive translucent iron-on film. The builder can clearly see how the parts such as the wings, stab and fin have been constructed. The ailerons, elevator and rudder are not just solid pieces of wood. They have been made out of several pieces of wood and then covered. This forms an open-looking structure that is generally referred to as built-up construction. This type of construction is strong, yet lighter than sheets of balsa. Another side effect is an educational benefit that lets you clearly see how the parts have come together. It may also promote understanding of the design and how it was made. It will certainly help in any future repair activity.
CONTENTS
Photo 1 Photo 2
The Dorothy II came in a plain white box which contained a complete, but no frills, model airplane that is clearly designed to be a basic trainer. It looks like a well proven trainer-design that has stood the test of time. It will have a familiar look to those RC pilots who built and flew their way into RC in the days gone by.
The construction manual is fairly rudimentary. A less experienced modeler would be well advised to seek assembly advice. This would be best obtained by joining a Radio Control Flying Club (go to the Academy of Model Aeronautics website www.modelaircraft.org to find a club in your area). These clubs are where you will find the more experienced modelers who will no doubt revel in the opportunity to pass on their “hard-earned” knowledge and past experiences.
Photo 3 Photo 4
To complete the Dorothy II, additional equipment needs to be gathered and purchased. The radio system you choose does not have to be very sophisticated or expensive. A simple four-channel radio will more than do the job. For this review, a Futaba 9CAP was used so that the airplane program could be copied over to several other club members’ radios for subsequent test flying.
These are the supplies not packaged with the ARF kit that were used to complete the model:
- Futaba 9CAP and FM receiver
- 4 JR Sport ST-47 standard servos
- JR switch with charging lead
- JR 1100 mAh NiMH receiver battery
- 30-minute epoxy resin
- Thin CAA adhesive and kicker
- O.S. Max® 40 LA 2-cycle glow motor
- 10 x 5 APC propeller
- Dubro 1/4 x 24 spinner nut for starter motor action
- 4-40 allen-head engine mounting bolts, washers and blind nuts
- 8” silicone fuel tubing
- Fuel filter
- Extra rubber bands
Building the Wing
Photo 5
The manual begins with advice to re-shrink the covering to remove any wrinkles induced by storage temperature changes. The wing needed this treatment. This may well not be the easiest of tasks for a beginner. It is strongly advised that new “builders” seek the help of an experienced modeler or their local hobby shop for this task. It is far better to use a hobby iron for this job than a heat gun. The iron will not cause corners or seams to shrink apart or lift like the heat gun, in inexperienced hands, might. Most RTF and ARF aircraft need this treatment so the Dorothy II is no exception.
Photo 6 Photo 7
When joining the wing, the covering that is wrapped over the root-rib edge needs to be removed. The hardwood spars provide good strength but the surface joint at the edge of the rib is also part of the wing-skin and adds additional strength. Trim the covering off with a sharp knife or razor. Hold the wing halves together using low-tack masking tape (photo 6) until the epoxy is dry. Another tip is to plug the hole in the wing root that leads to the aileron torque-rod/horn. A scrap of balsa wood will prevent any glue running into the cavity and interfering with aileron movement.
Photo 8
To join the wings it is best to use 30 minute epoxy resin. This gives you the time to align the two halves. It also allows you to wipe off any excess glue and tape and clamp the wing joint (photo 7). Clear Scotch-tape was used to seal the joint/seam (photo 8). This tape was left in place as it would not show and gives a better finish to the joint. The wing was left to cure overnight.
Photo 9
Care needs to be taken when fitting ailerons to the wing. No glue can be allowed to touch the exposed torque rod support bearing otherwise it will not rotate later (Ed. Note: Try putting a little oil, the same one used to protect the hinges, into the slot for the aileron torque tubes.). The hinges are slot-and-pin type and are much easier to install if 30-minute epoxy resin glue is used. The hinge pins need to be oiled to prevent binding later. It helps to make a pin-holder type tool to help you insert the epoxy into hinge slots. (Ed Note: I just use a flat wooden toothpick for this task.)
The metal wire holding the two hinge halves together has a 90-degree bend. During final installation, this bend must be inserted into either the wing’s trailing edge or the aileron’s leading edge to lock it in place. I suggest using the Mylar® laminated hinges instead as they assemble faster and more easily. To learn how, read Sport Aviator’s “Installing Mylar Hinges” in the Flight-Tech Section.
The instructions show the ailerons with unequal throws up and down. It really helps the airplane to fly if it is built with “aileron differential”. Differential in this case is when the aileron control has more up movement than down. With a flat-bottomed wing, the down-going aileron has much more drag than the up-going aileron. This causes the airplane to yaw a little when the aileron is applied which tends to cause the nose to pitch up when entering a turn and to dip down when bringing the wing to level. This is called adverse yaw. Making the down-going aileron move less tends to equalize the drag caused by aileron control deflection and to keep the airplane level in the turns.
Aileron-induced adverse yaw is often fixed in models by coupling the aileron to the rudder. Unless you want to buy a computer radio, there is a much easier way to fix the problem. You can mechanically achieve the desired aileron differential. The connector hardware provided with the Aero-Star actually makes it easy to do this task.
The goal is to have more up-aileron than down-aileron – in both left and right directions. Use a servo disk instead of a straight servo arm. Mount the connectors forward of the center screw of the servo disk. It is not too critical how much differential you achieve because all, and any, is helpful with a flat-bottomed wing. By using a servo disk, instead of a straight arm, you can achieve as much as a 2:1 ratio. That is half an inch up and a quarter of an inch down.
It is a very good idea to use an aileron extension lead coming from the receiver. This avoids plugging and unplugging of the aileron servo directly into/from the receiver socket. This will prevent accidental loosening of other receiver connections.
It is a good idea to position the wing on the fuselage. Mark the center of the fuselage at the front and rear of the wing saddle. Position the wing as shown in photo 9 and then measure the distances from each fuselage side to its respective wing tip. The distances should be equal.
There were no problems assembling the wing. Everything fit exactly as it should.
Building the Fuselage
Photo 10
The fuselage is pre-drilled for the wooden dowels that will be used by the rubber bands to hold the wing in place.
Photo 11 Photo 12
All wooden dowels, regardless of the airplane involved, will wear and bend over time. It is a good idea to make them “serviceable”. The dowels, in the review model, were held in place with silicone sealant (photo 12). This stops them from falling out but still allows you break the seal and twist one out if it needs replacing.
Photo 13 Photo 14
The Dorothy II comes with pre-bent undercarriage wires. These wires fit into a pre-drilled slot in the bottom of the fuselage. It is a good idea to remove just a small amount of wood from the inside portion of each hole to allow the landing gear to rest completely against the bottom of the wood slot.
One other tip for fitting the wheels to the U/C legs is to grind or file a flat spot to prevent the wheel collars from coming off in flight. It is tempting to just tighten them up as much as possible but they will often strip or be very hard to remove for future maintenance. Small notches were filed in the axle locations. There was an allen-wrench included for the set screws in the wheel collars.
Each set screw in the wheel collars was treated with screw-locking compound to further help in wheel retention. The wheels were a good bounce absorbing size for grass runways. The collars were positioned with the set-screws facing rearward to keep the runway dirt out of their sockets.
Photo 15 Photo 16
The metal straps provided a very strong way of holding the undercarriage wires in place. Before actually installing the landing gear legs, brush on a very thin coat of 30-minute epoxy onto the bare wood inside the slot. Make it a very thin coating and let dry completely before attaching the landing gear. Do not get any adhesive inside the two holes. This fuel-proofs the bare wood for added durability.
Photo 17
To get the fuel tank into the fuselage, the opening to the front of the fuselage had to be ground away a little at the sides (photo 17). Make sure to install the fuel tank right side up with the interior vent tube towards the top of the fuselage.
Attaching the Tail Parts
Photo 18 Photo 19
Fitting the tail is the most challenging part of most ARF’s. The Dorothy II II’s fuselage has a flat platform that accommodates the stab assembly and makes alignment much easier (photo 19). Note the lightening hole in the fuselage just forward of the control rod slot (photo 18). This attention to detail will make the airplane fly better and more slowly because it will weigh less.
Photo 20 Photo 21
The easiest way for me to install the tail surfaces is to glue the fin to the horizontal stabilizer first, then install the assembly onto the fuselage. A 90-degree square, held in place with a small clamp, is a good device to help in lining up the fin (photo 20). The whole assembly can then be lined up with the fuselage. Using 30-minute epoxy resin gives you time to make this alignment before you pin the stab in place.
Photo 22 Photo 23
However, it is very important to be sure the vertical fin in not only 90-degreees to the stabilizer, but is also pointed straight ahead. Nothing will ruin a good airplane’s flying ability than a vertical fin pointed off to one side. Mark the center of the stabilizer along the trailing edge (photo 22). Use a square on this mark and draw a straight center line front to back on the upper side of the stabilizer. Mark where this line is on the leading and trailing edges as well. Position the vertical fin with its center directly over the front and rear marks. Draw a line on the stab on each side of the vertical fin (photo 23). Remove the covering 1/64 in. inside this line. Then apply the adhesive only to the part of the vertical fin that contacts the stabilizer and realign the fin, all directions.
Photo 24
The modeling pins secure the parts until the epoxy has cured. Mark the center of the fuselage as shown in photo 24. Remove the fuselage covering as was done with the stabilizer. Level the fuselage and test install the assembly. Center it and again remove the covering from the underside of the stabilizer where it contacts the fuselage mounting are. Epoxy the assembly in place. Make sure the fin is pointed straight down the fuselage and that the stabilizer is level side to side and that both forward tips are the same distance from the center of the firewall (a pin at that point helps with this measurement).
Photo 25 Photo 26
The Rudder is used to drive the spring loaded tail-wire (photo 25). The rudder’s control horn is bolted around the part of the tailwheel wire that is actually inside the rudder (photo 26). The nylon base of the control horn reinforces the balsa rudder.
Photo 27
The tail wheel (photo 27) is a bit larger than usual and improved the Dorothy II II’s ground handling during the taxi tests in the wind.
Photo 28 Photo 29
The control horns and pushrods do not interfere with each other and provide a strong link to the servos. A short section of fuel tubing was added to the clevises to prevent them from coming off under flight loads (photo 28).
RADIO INSTALLATION
Photo 30 Photo 31
The final pushrod and radio equipment installation was very easy to do. It can be difficult to get a drill inside the fuselage once the servo try has been fitted. It is much easier to pre-drill the servo screw holes before fitting servo tray. It might also be a good idea to put some 1/2 x 1/8 in. hardwood strips on the bottom side of the tray where the servo mounting screws will be.
Photo 32
The pushrod is two pieces of wire that have been joined and wrapped to a 3/8” square hardwood rod. The exit wires had to be bent a little to clear the sides of the fuselage. One pushrod was for the elevator and one for the rudder. Each was the correct length and worked perfectly.
It is important that the elevator and rudder be perfectly straight for the first flight, with the transmitter “trim tabs” in neutral. A good way to do this is to clamp the control surface in the middle using two sticks and soft clamps. Turn on the receiver and center everything. Hook up the control rod to the servo. Then screw on the nylon clevis until it centers in the control horn. Remove the clamps and wood braces and make any final adjustments. Remember to turn off your transmitter after this task is finished.
Photo 33 Photo 34
The 1100 mAh battery was wrapped in foam and fitted right up behind the firewall as near to the engine as possible. It was laid flat under the fuel tank. Half-inch pre-glued foam padding was used to line the inside of the tank bay area. This technique helps prevent any fuel from bubbling and frothing in the tank as a result of vibration from the engine.
Photo 35
The receiver was wrapped in more foam and fitted vertically behind tank to also keep weight forward. The foam wrapping also helped hold the receiver, the tank and the battery in place. The on-board radio system switch was mounted in the fuselage side away from the muffler as shown in photo 35.
Mounting the Engine
Photo 36 Photo 37
The engine was fitted last. The Dorothy II uses factory-installed wood rails, coated to protect against fuel residue, to mount the engine (photo 36). The mass of the engine was used to get the best center of gravity without having to add any lead. As it turned out, the engine needed to be bolted in place at the very front of the airplane (photo 37). The battery and receiver had already been positioned as far forward as they would go. The O.S. Max® 40 LA is not a very heavy engine so the far-forward position came no surprise.
The long engine-bearer rails allow you to position the engine any where you want. The engine and muffler were assembled first and then put as far forward on the engine bearers as possible to see how the center of gravity worked out. The muffler was removed and the holes drilled for the engine bolts.
Photo 38 Photo 39
The high-speed needle requires you to remove some material from the side of the fuselage (photo 38). This is the usual practice since ARF manufacturers cannot know where the high-speed needle valve of every possible engine will be positioned. However, unlike most ARF basic trainers, the Dorothy II’s fuselage side is designed low enough that the muffler clears the side. It was not necessary to remove some of the fuselage side, a real hassle at times. The wood around the needle valve can be fuel proofed by simply dripping some thin CAA onto the balsa wood.
Photo 40 Photo 41
Photo 40 shows the installed engine from the bottom. The provided locknuts were used but “blind” nuts could also be used for mounting. The throttle arm on the carburetor is connected with the wire provided in the kit (photo 41). The rod needs to be kept as far to the side as possible to allow the fuel tank to be fitted. Make sure it does not bind against the fuel tank.
Photo 42 Photo 43
It is important to set the throttle so that it correctly uses the swing of the servo arm. In the low-throttle position it still needs to have some remaining servo arm rotation (photo 42). This will let you close carburetor and turn off the engine using the transmitter’s trim tab or engine shut off switch. Adjustments can be made using the sliding mount shown in photo 43.
Photo 44 Photo 45
The fully-open throttle position should be set just a fraction before the travel-end-stop of the carburetor so that the servo does not “stall” when in that position. This will prevent any excessive current draw and lead to longer battery life and flying sessions.
Once the throttle was connected, there was not much left to do except put it all together with rubber bands and see what it weighed. Fully assembled, the Dorothy II came out, without fuel, at exactly 4 lb 12.8 oz. (Ed Note: Maybe Eric didn’t say it, but this is nearly an unbelievably low weight for a 72-in. wing span, 52-in. long basic trainer. Polk’s must be using some very light wood in this aircraft. Either that, or Eric forgot to install something.)
Construction Summary
By time the builder has put this ARF together, they will have mastered several skills such as hinging control surfaces, the alignment of a stab and fin, installing a glow engine, plumbing the fuel system, wiring up the radio equipment, connecting the control rods, and the setting up of all of the control throws. The owner of the Dorothy II will have earned a substantial set of “builder of the model” credentials from the experience of this model airplane.
All that left was to do was charge the batteries and go fly the Dorothy II. The flying field regulars will see the building that took place before you purchased this ARF and then the work that you did to get it ready to fly.
Construction Likes
1) Very good wheels.
2) Strong and pre-prepared pushrods.
3) Wooden construction very serviceable.
4) Extremely light weight
5) Muffler fits without modifying the Fuselage
6) Easy to Build
7) Factory installed engine mounting beams
Construction Dislikes
1) The tape that was used to hold the pieces in place during transit left a sticky residue that was hard to remove.
2) One color all over was a bit hard to see on a dull day.
3) Directions could have been more complete.
At The Field
Photo 46 Photo 47
After 14 hours of actual assembly time it was imperative to get a break in the weather before winter really set in. November in NJ can be difficult but the weather gods were kind and there was going to be good enough weather for flying the next day. As it turned out, it was the only decent flying day in November 2005.
There were low but bright clouds and it was a bit windier than would be ideal for test flights. The 46 degree F temperature was not bad for late November in NJ. This was no time to hesitate so with all of the batteries overnight-charged it was time to be off to the field.
Photo 48 Photo 49
The wing was attached with the four (4) heavy-duty rubber bands that were supplied with the kit (photo 48). The O.S. Max 40 LA, with a 10 x 5 APC propeller attached and 15% CoolPower fuel in the tank, started immediately and it only took a minute to set the high-end needle and low throttle mixture adjustments. The high-end throttle travel throw was easily set in the workshop, but the idle position is never that easy to determine until the engine is actually warmed up and running.
Photo 50 Photo 51
This engine had been used before and did not need any break-in procedure. It is a good tactic to have a reliable engine in a brand new model airplane and often vice-versa. A simple fill and drain system had been installed. The feed line to the carb was unplugged just behind the filter and the pressure line from the muffler was disconnected (photo 51). It is not a good idea to leave the pressure line connected to the muffler during filling because fuel can easily overflow and go directly into the engine. This is especially the case when an engine is mounted upright.
Photo 52 Photo 53
With the airplane safely secured on one of the club’s upright workbenches, everything was re-checked to make sure the controls moved in the proper directions and nothing was loose. A final preflight and range check is a good idea before each day’s first flight, but especially so before the very first, first flight.
Photo 54 Photo 55
With the engine running like a Swiss watch, at least for now, the airplane was given a taxi test to see how well it tracked on the ground. The Dorothy II did very well in the wind and would turn both directions into and away from the wind. The wind was blowing at about a 30 degree angle across the runway and the airplane could easily be steered straight down the center-line. The larger than usual tail wheel definitely had the authority to do the job.
Flying
Photo 56 Photo 57
With no problems encountered on the ground, there were no excuses left. It was “time to Fly!” The throttle was advanced to about two thirds full power and the airplane accelerated briskly. The elevator had been left at neutral. The tail came up to level very quickly. After about fifty feet a small amount of up elevator was applied. The Dorothy II was airborne. More power was applied and height was gained to allow some trimming exercises.
The take-off run had been dead straight. Initially there was no need for aileron. It did need a healthy amount of “beeps” of down-elevator-trim. The Dorothy II handled the gusty conditions very well and was now cruising around the New Jersey sky with ease. This airplane seemed to like being flown at around 3/4 throttle.
Photo 58 Photo 59
During a downwind pass the OS Max 40 LA suddenly went to low throttle. This was not a good place for this to happen. The airplane was easy to control in this state. Down elevator was immediately applied to gain some speed. A tight turn was made back into the wind and lined up on the runway. Even though the engine was stuck at idle, the Dorothy II stayed responsive and it was easy to guide the airplane and let it settle gently onto the runway. This airplane has excellent glide performance.
Photo 60 Photo 61
Photo 62 Photo 63
This was not quite the ideal landing test. However, the Dorothy II was up to the task. There was still plenty of fuel in the tank so the engine was restarted. It still refused to open up. The throttle arm was still physically connected and was definitely operating correctly. The diagnosis was that there might be some “junk” trapped in the fuel system.
The fuel pump on the flight box was used to flush out the fuel lines, the remote needle and the carburetor, in both directions. The fuel lines were then reconnected. The engine started immediately and throttled up again in a normal manner. The general consensus of those present was that due to the cold temperatures there was probably some old gelled up oil in the fuel system. Once it had been flushed out the engine could function correctly.
(Ed. Note: This was an older, but reliable engine of mine. It had been put away about 6 years ago before I discovered the true joy of using Mobil 1 oil for proper storage. I had loaded the engine up with military issue gun oil that contained a coating agent. The agent must have gelled from age and quickly clogged the carburetor’s tiny fuel passages.)
Flight Trimming
As noted earlier, down elevator trim had to be added to stop the airplane from climbing. This is not unusual with a flat-bottomed wing section. More down-thrust could be added later by fitting a washer under the rear engine mounting bolts. In this case, it was probably more likely to be a slightly rearward CG condition more than anything else. Subsequent flying tests showed that the down elevator trim was not causing any flight problems so the down thrust of the engine was left alone. The CG was also left unchanged because of how stable the airplane was in the air. This indicated that the CG was acceptably close to what was required.
During the second flight, several passes were made to see if the rudder trim was correct. Rudders can have as much rolling affect as the ailerons. The Dorothy II was flown directly away from the pilot, into the wind. The tracking of the fuselage was studied to see if it went in a straight line or showed a slight curve to the left or the right.
The airplane did need a couple of clicks of right-rudder-trim to track in a dead, straight line. When rudder trim is added to a trainer-type it usually also causes a slight rolling effect. This was true for the Dorothy II and had to be corrected with a few beeps of left (opposite) aileron trim.
It is a common mistake to fix the rolling action of a trainer airplane with aileron trim only. The best practice is to get the airplane to first fly level with the aileron trim. Then, check for the straight-line tracking of the fuselage. If this is not done, the airplane may well be flying in a slightly crabbed direction for the rest of its flying life! If you are not sure how to do this yourself, the best thing to do is seek the help of an experienced RC pilot.
The aileron differential was proving to be just about right. The airplane rolled nicely into the banking angle of a turn without dragging either top wing-panel. The nose stayed at the same height. Application of the elevator only held the airplane at the same height all the way around the turn. No aileron input was normally required until the wings needed to be brought back to level. Said another way, the Dorothy II makes lovely wide or tight radius turns without gaining or losing any height or requiring continuous aileron input.
Trainer airplanes are often subjected to quite a lot of wrong-control inputs due to pilot disorientation. To test disorientation recovery the airplane was taken up quite high. The throttle was set at half throttle and the rest of the control sticks released. The Dorothy II sorted itself out in about 50 feet. It would level the wings and enter straight flight path. (This test was done after the airplane had been trimmed in the air for level flight).
To attempt a roll, full power was first applied during level flight. On the first roll test the airplane suddenly did a very tight half loop. The throttle was cut back and the airplane landed immediately. The initial thinking was that there had been some sort of radio interference. But upon closer inspection it could be seen that the wing had shifted slightly. This indicated that the wing had lifted from its seat, in flight, and caused the unplanned half loop.
Photo 64 Photo 65
More rubber bands were added so that a total of twelve were now holding the wing in place. This proved to be just what the doctor ordered and during the rest of the flights, the wing never moved again.
During the next flight, using the same level approach, the nose was pulled up about 15 degrees and then aileron only applied. This resulted in a very respectable barrel-roll with almost no loss of altitude. The result was the same in both left and right rolling directions. A roll was then tried with some down elevator correction during the inverted portion of the roll. This was a much better roll and very pleasing to the eye. The peanut-gallery was most appreciative!”
A fully axial-roll was tried next but proved to not be a practical proposition. Normally, to do an axial roll you add top-rudder as the airplane goes through both of the knife-edge attitudes. This really slowed the roll rate in the first quarter of the roll and rapidly accelerated the roll rate in the third quarter. This is a common trait of all high-wing basic trainer aircraft.
To make a trainer roll without dropping the nose you apply some down-elevator just as the airplane goes over into the inverted position and then adding some up-elevator just as it is getting near the end of the roll.
The powerful rudder on Dorothy II rolls the airplane quite strongly when it is applied, so it was interfering with the aileron rolling action. A slow roll was tried with only elevator correction and the airplane did just fine. The small amount of down-elevator that was applied as the airplane rolled though the inverted part of the roll was enough to compensate for the lack of rudder correction. The elevator action keeps the nose up and makes for a pretty roll that will give a pilot a degree of confidence. A rudder only roll can be done, but it corkscrews through the sky and can use up a lot of room. It is advised to keep the airplane high when playing with that maneuver.
Inverted flight was quite a surprise. The Dorothy II is very stable when flown inverted. Inverted flight was both more than possible and actually quite practical. There was enough flight performance, while inverted, to allow the nose to be raised for a half-roll back to level flight whenever needed.
Loops were next on the agenda. While flying straight and level into the wind, full power was selected and up elevator applied. No dive was needed to gain extra speed. The loop was big and round with no twisting. Decreasing the throttle on the down side of the loop produced a very graceful loop. The Dorothy II performed ten consecutive loops without any problems. No outside loops were tried during this test. Flat bottomed wing sections are not really designed to do outside loops and it was asking a lot of the little OS Max 40 LA, so it was not attempted.
Stall-turns depend upon a rudder that causes a yaw but not a rolling action. By pulling the nose up and going up a vertical line it is possible to make a stall turn-happen. But any application of rudder causes the airplane to roll during the stall-turn. Snap-rolls and spins were not tested. They are not really what this design was intended to do in the air.
Slow flight was very good indeed and the airplane could be made to look like it was flying backwards when flown into the wind. It was very stable and that big wing dampens the small “bumps” in air. It will fly well if you take your hands completely off the sticks. If you apply a couple of beeps of up and rudder trim and she will circle almost all day.
Two other tests were tried with the Dorothy II. A “hands-off” take-off was done by pointing the airplane into the wind and applying about half throttle. The control sticks were not touched again until the airplane was well into the air. This was an impressive display of the tracking and stability of this airplane.
Photo 66
A “hands-off” landing attempt went almost as well. The airplane was lined up for a landing and the throttle cut back to idle. The airplane was allowed to approach the ground unaided. At the last moment some up-elevator was applied to prevent a “bounce” on the runway. It is not a requirement for the Dorothy II to land unaided, but it did show that the airplane needed very little piloting help to make a good landing.
The only thing that would make this airplane better to fly, other than the aforementioned extra rubber bands, would be the application of some highly visible decals on the leading edge of the wing. A couple of times it was hard to see the angle of the wing as the Dorothy II dropped below the background tree-line on certain landing approaches. Other than that, this airplane will most certainly help many a pilot get their wings.
Making a Video December 16 and 17 2005
The flying session for a “video-shoot” had to be cancelled several times. It was either snowing, too windy, or just simply too cold in New Jersey for a video camera to work. Many of the new cameras have a temperature sensor that shuts the system down if it is too cold for the tape to run.
The flying was done at the Pine Barons RC field in Lumberton, NJ. It had rained all through the previous night so the snow had all gone but the runway was very wet and contained a lot of surface water in the short grass.
Several pilots were recruited to fly the airplane for the camera. George Engle did the initial honors. Then the Dorothy II was set up on the buddy box for Tom Emanuel who checked out the buddy-box trims, The Buddy-box was then given to his seven year old son “T.J.” who flew the Dorothy II with ease.
For the second day’s flying session, the airplane was flown by Scott Rafer who has only been flying for a few months. Scott was able to fly the airplane with comfort from the get-go! He performed several take-offs and landings as if he had been flying the airplane all summer.
All of the video-flying is demanding and requires the pilots to fly lower than usual and also fly-by-command. The Dorothy II behaved perfectly and gave the new pilots a lot of confidence. During the testing, the airplane tended to draw a crowd and received many favorable and appreciative comments about the visible built-up structure. With mission accomplished, we all retired to the local café for welcome cups of piping hot-chocolate.
Additional Aircraft SpecificationsManufacturer: Polk’s Hobby Length: 52 in.Cost: $50.00 Wingspan: 72 in. Radio: Futaba 9 CAP Wing Area: 828 sq. in. Servos: 4 x JR ST 47 Wing Loading: 13.4 oz./sq. ft. Engine: O.S. Max 40 LA Weight: 4.81 lb. Airfoil: Flat BottomSpecial Airframe Features: Great Flying Trainer; Very Light Weight; Attractive Transparent Covering; Very Inexpensive |
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Posted by Eric Henderson
on Filed under Hall of Fame.
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