BP Hobbies Sand Bird
At the November, 2006 JR INDOOR RC FESTIVAL Terry Nitsch, the Event Director, set up a water tank approximately 60 X 15 feet and several inches deep. From this tank, many micro size RC electric aircraft were able to take-off from and land on the water. But with a new twist — the flying was indoors. One of the little airplanes that caught my eye was a tiny, Almost Ready-to-Fly (ARF) RC electric that is now being offered by BP Hobbies (http://www.bphobbies.com/). The airplane is called the Sand Bird and has a 21-inch wingspan, with 89 square inches of wing area and a total weight of 5 to 7 ounces depending on the equipment used. The Sand Bird requires full, four-channel control of ailerons, elevator, rudder and the electric motor’s throttle.
The Sand Bird meets all the aircraft requirements of the Academy of Model Aeronautics’ (AMA) Park Pilot Program. The aircraft weighs less than 2 pounds (the Program’s upper weight limit) and has a level top speed under 60 mph (the Program’s upper speed limit). For complete Park Pilot aircraft details, follow this link.
The AMA Park Pilot Program offers non-AMA members the opportunity to become AMA members at a much reduced cost. Park Pilot membership includes a great magazine “Park Pilot”, $500,000 personal liability insurance, $2.5 million liability insurance for all outdoor or indoor flying site owners (see insurance details) and membership in the world’s largest sport aviation association – the AMA. For complete information and details about Park Pilot membership, just click here.
Photo 1 Photo 2
The list price of this built from balsa and factory covered ARF model, including the electric motor, is just $59.95. The Sand Bird has a typical flying boat configuration, with the motor mounted up on a pylon above the wing and two tip floats for stability when taxiing on the water. This is what it looks like floating in the water.
Photo 3 Photo 4
All of the Sand Bird’s flying surfaces come pre-covered with an iron-on material that resembles BP Hobbies SO-LITE (actually Solarfilm, a low-temperature heat-shrink covering). These kits are available in light green (as was mine), orange and purple. The control surfaces (aileron, elevator and rudder) come pre-hinged but I’ll say more about that in a moment. The fuselage is basically one big float with a step to help the airplane get off the water. It is covered with an opaque iron-on covering.
Despite the excellent construction and covering job, I did find that the fuselage takes on some water. To correct this situation, I ironed on a second layer of covering on the bottom of the fuselage, right over the first layer. I used BP Hobbies clear SO-LITE which is a transparent material. That seemed to “plug” any holes and proved a fast fix.
Photo 5
The motor supplied with the Sand Bird kit is a 12 mm diameter, brushed variety. I was advised by the folks at BP Hobbies that, if I intended to fly off water, I should consider a stronger motor. I’ll talk more about the substitute motor in a while.
Photo 6
The two wing tip floats are made from balsa and are thoughtfully factory painted with a clear coat of some form of urethane to make them waterproof. They install easily into slots cut in the bottom of both wing panel. The wing, by the way, comes already assembled (one piece, right out of the box).
Photo 7 Photo 8
The airplane comes with a fairly complete hardware package. But my kit did not come with a wing mounting screw (Ed. Note: I don’t know Bob, but that brass-colored bolt looks suspiciously like a wing mount bolt to me.). I assumed it was a 2-56 thread but found out that it was likely a metric thread. So I quickly passed a 2-56 tap through the supplied “T” nut and used a 2-56 X ½-inch Allen head screw to hold the wing in place.
Photo 9
At the front of the radio compartment (by the wing’s leading edge) is a small notch that accepts the wing hold down peg. I found it necessary to “open up” this slot so that the peg would fit more easily. You best try this fit right at the beginning of your assembly job. Make sure it is tight with no “play” either vertically or horizontally. If you accidentally sand it too large, use 1/64- inch ply shims to tighten the fit.
Photo 10
Photo 10 shows the wing hold down peg just referenced. It is located on the bottom of the wing and projects forward just enough to fit into the slot noted in the previous photograph. This plywood peg was not secured with much cement, so make sure to add a coat of your own 5-minute epoxy. If that peg breaks off, good-bye wing!
Photo 11 Photo 12
As mentioned earlier, the control surface hinges were quite stiff. I wasn’t sure if it was the hinge material or the fact that too much cement was used. But if I had left the hinges as is on the ailerons, the little servos might have stalled from the extra load. To correct this situation quickly and easily I just cut off the ailerons and then reinstalled them using SR Batteries Gapless Hinge Tape (http://www.srbatteries.com/). I did only the ailerons at first, but later found that my rudder was having a tough time moving and so I redid those hinges also with the SR tape.
Photo 13
I first spotted the stabilizer in position with some thin CA cement. Then the vertical fin came next. I followed that with an application of 5-minute epoxy cement. Make sure the stabilizer is parallel to the wing and that the vertical fin is 90-degrees to the stabilizer.
Photo 14 Photo 15
I used DuBro (http://www.dubro.com/) micro control horns on both the rudder and elevator along with DuBro mini EZ connectors that allow me to adjust both control surfaces.
BP Hobbies recommends the Blue Bird BMS-303 micro servo that weighs 4.1 grams and has an output torque of 10 oz. / in. I had just received two samples of the new, even lighter weight sub-micro servo designated as the Blue Arrow BA-TS-2.5 and decided to try them for the rudder and elevator control application. The weight of this servo with the cable is 2.8 grams, but the output is only 2.08 oz. / in. In all honesty I think this servo was too light duty for this application. I would suggest you stay with the Blue Bird BMS-303. (Ed. Note: With only 2 ounces of servo output power, it is understandable that the factory hinges on the rudder might have been a little stiff.)
Photo 16
You will note that I used DuBro mini EZ connectors on both servo output arms. One arm goes to one side and one to the other. This way the two servo output arms don’t interfere with each other. Although control wires were furnished with the kit, I opted for the Stevens Aero Model (http://www.stevensaero.com/) yellow nylon tubing (.040 inch ID) with .020 inch diameter wire running inside the tubing. This worked out well. The places where both tubes exit to the outside of the fuselage are precut. Just make sure you anchor the yellow tubing just aft of the servos. I added a cross piece of hard balsa and applied some 5 minute epoxy cement.
Photo 17 Photo 18
Photo 17 is the Feigao brushless, in-runner motor that BP Hobbies recommended for use on the water. It is their model number 1208436L and measures 12mm in diameter by 31 mm long. It weighs 17 grams. This motor uses direct drive on a GWS 3 x 2 prop. Photo 18 shows the Feigao motor just before being attached to the pylon. The plastic motor mount is supplied with the kit.
The parameters I recorded using this motor are as follows: Using a two-cell, 800 Li-Poly battery pack, motor current 3.62 amps, voltage under load 7.75 volts, power input 27 watts and motor rpm 20,000. The final airplane weight was 6.4 ounces so the power loading works out to a strong 4.22 watts/oz. The Electronic Speed Controller (ESC) in this case is a Jeti Advance 04-3P available from Hobby Lobby (http://www.hobby-lobby.com/). An alternative might be the Blue Arrow 5 amp ESC.
Photo 19 Photo 20
Two separate aileron servos are employed, one in each wing panel. I chose the Hitec HS-50 (http://www.hitecrcd.com/) for this application. You will also need a “Y” type connector so that both servos can be plugged into the one aileron port on the receiver. For a receiver you could use the BP Hobbies Corona RD-620, which has six channels. Using that receiver, you could plug the aileron servos into ports 1 and 6 and forget the “Y” adapter. That would save weight and allow you the option of flaperons (both ailerons deflect down for flap action, but still can provide roll control). But the connector block exits out the end of the BP receiver (photo 20). I felt the FMA Direct M5 receiver, with the connectors on the side, made for an easier installation. This allowed me to place the receiver on the floor of the RC compartment. That was my final choice!
(Ed. Note: As a dedicated flaperon nut case, I suggest you might want to try mounting the BP receiver on some adhesive backed hook and loop tape. That would raise the receiver off the fuselage floor enough to allow clearance for the connectors. Flaperons on water would slow the landing speed, allow quicker takeoffs and just be fun to use. Make sure that the hull is completely waterproof if using a side-connecting receiver. Just a suggestion.)
Photo 21
Although the instructions show the aileron servos lying on their side on the underside of both wing panels, I decided to mount the servos upright and on top of the wing. My reasoning was that the servos would be less likely to get wet, being on top. The servo cables are easily routed out holes in the ribs and then out a hole in the bottom of the wing, at the center section. Each servo is attached with screws, going into hardwood blocks. A DuBro mini EZ connector was placed on each servo output arm. The control wire is again .020 inch diameter terminating with a Z-bend at the control horn (DuBro micro control horn). Make sure that you place the servo output arms on the correct side so that one aileron goes up, while the other goes down. This is very important!
(Ed. Note: Mounting the aileron servos upright on the wing is a good idea. It keeps them out of direct water spray when the aircraft is “on the step” during takeoffs and landings. It also leaves the bottom of the wing sealed so no water can enter into the wood wing through the underside servo bays.)
Photo 22 Photo 23
Note that the three-wire motor cable and its connector are passed through a hole cut in the center top of the wing, adjacent to the pylon motor mount. The somewhat clumsy part is the fact that the motor cable and ESC, along with the aileron servo cables must all “hang off” the wing. I left enough wire so that the cables never needed to be disconnected when removing and recharging the battery.
Photo 24
The two tip floats are inserted into slots cut in the bottom of the wing, approximately at the mid point of each wing panel. Some thin CA is all that is needed to secure these floats in place.
Photo 25
I certainly didn’t want a 38 inch receiver antenna trailing into the water so I removed the long wire and substituted one of Azarr’s (http://www.ecubedrc.com/) reduced size antennas. You can see it pasted along the upper portion of the fuselage in photo 24.
Photo 26
The choice of a two cell Li-Poly battery pack proved critical in this application. You need to insert this battery as far forward into the nose section of the fuselage to achieve the correct balance (photo 26). The Center of Gravity (CG) is 25% back from the wing’s leading edge!
Photo 27 Photo 28
The battery I finally settled on came from Horizon Hobby. It is their E-Flite, two-cell, 800 mAh pack that is wired with a balance connector. The battery weighs 1.5 ounces. With a motor current of 3.62 amps, the load capability need only be 4.5C. At that load you could obtain almost a 14 minute motor run time at full throttle and much more when flying throttled back.
Photo 29
Initially I just press fit the GWS 3 X 2 prop to the motor shaft. But at upwards of 20,000 rpm, it flew off on several occasions while still doing some ground testing. This naturally concerned me so I obtained this neat prop adapter from Dave Thacker at Radical RC (http://www.radicalrc.com/).
Off To The Flying “Field”?
Photo 30 Photo 31
This is the completed Sand Bird, ready to fly at just 6.4 ounces, a 21 inch wing span and with 89 square inches of wing area. Wing loading calculates to 10.3 oz/sq. ft. That is in the glider wing loading area.
The underside of the completed Sand Bird is shown in photo 31. The orange colored fuselage bottom received that extra layer of clear covering that I mentioned earlier. This stopped some of the initial water leaks, which can’t be tolerated if you expect the RC system to keep working. The orange color shows well in the air and helps the pilot’s aircraft orientation during flight maneuvers.
Photo 32
This is what your Sand Bird will look like when you remove the battery for recharging purposes. The cables from the wing can remain attached. It’s a simple process.
FLYING
Photo 33
The Sand Bird flies well, but it is fast and maneuverable. As such, this is not an airplane for a rank beginner. You will need some flying experience. For land based flying you can easily hand launch the airplane. You might strap on a two wheel forward landing gear, which would make the airplane look like an amphibian. Since this was the winter time, we were able to make touch ‘n go landings on soft snow — believe it!
The flight shots were all taken by my fellow SEFLI club member, Joe Cabana. Photo 33 shows AMA Hall of Fame member and NEAT Fair Event Director, Tom Hunt, hand launching the Sand Bird.
Photo 34 Photo 35
The next sequence of photos was taken at our big Lake Ronkonkoma in central Long Island. This lake has to be at least a mile across. I was able to get the airplane off the water several times. There is more than enough power when using the 27-watt Feigao brushless motor. Unfortunately on the late December day that I did this, I was by myself and so couldn’t get any flight photos.
Photo 36 Photo 37
What follows are some shots taken with the Sand Bird floating and taxiing. My biggest worry was being able to retrieve the airplane if I had a problem. It was after this flight session that I found the water inside the fuselage. That’s why it is important to add that second layer of covering.
Photo 38 Photo 39
The Sand Bird does fly well. Both Tom and I felt that the aileron control throw had to be greatly reduced. We also added about 30% expo rate control on the aileron and rudder control functions. That definitely helped smooth out the flying.
Photo 40 Photo 41
Of course to do that, you need a transmitter with those extra control features. In my case it was a Polk’s TRACKER-II computer transmitter. Final control throws were as follows: Ailerons (3/16 inch either side of neutral), Elevator (1/4 inch either side) and Rudder (3/8 inch either side).
Photo 42 Photo 43
All in all, this proved to be a fun airplane. Despite the fact that this was an ARF model, it did take a little building experience to figure out all the detailed assembly process. The instructions weren’t particularly helpful at some points. But the bottom line is that, with some experience, you can really enjoy this little flying boat and at $60, the price is right!
For more information on how to get one for yourself, visit: website
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Specifications Manufacturer: BP Hobbies Wingspan: 21 in. Cost: $60.00 Special Airframe Features: ARF Construction. Very Light Weight. Good Appearance and Color Choice |
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Notable Positives Notable Negatives |
| Electric Power Specifications
Prop: GWS 3 X 2 Max RPM: 20,000 |
Short URL: http://masportaviator.com/?p=794
Posted by Bob Aberle
on Filed under Park Pilot Airplanes.
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