Speed 280 prop/battery questions - RC Groups
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May 31, 2001, 01:57 AM
Registered User

Speed 280 prop/battery questions

Reference the American Airlines glider conversion on my previous post; what's the best prop for a Speed 280 direct drive on eight cells? The Gunther/Zagis seem like too much, draws 8.5 amps on my Whattmeter, two motors in parallel. They run very hot! I have Cox 6 x 3s and APC 5.7 x 3s to experiment with, but any and all advice is appreciated. The model's speed is about like a TwinStar, so I don't think gearing is the answer. Thanks, Russ
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May 31, 2001, 07:56 AM
Registered User
You might be surprized how fast a geared motor will push a plane. I have had geared 300 planes doing about 45 mph. The best prop I have used on a direct drive 280 is the replacement prop for firebird trainer plane. I tried other conventional glow type props, but kept going back to the firebird prop. Of course these are pusher props only.
Jun 02, 2001, 11:40 AM
Registered User
I use the normal Zagi props on a twin speed 280 powered Titanic Attack. The 280s are in a tractor arrangement (not a pusher) on the Attack. The 280s are wired in parallel via a Castle Pixie 14 ESC. This works just fine and does not cause the motors to run hot.

In order to get the props to stay on the shafts you should hold the motor with the shaft pointing down and put a little CA on the shaft. Then spray on some kicker to set the CA. Do this twice. The result will be a slightly thicker motor shaft and the prop can simply be pushed on the shaft and it will stay put.

BTW - New Vreations has the Attack and it is a NICE flying little twin.
Jun 04, 2001, 05:57 AM
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Bill Glover's Avatar
Originally posted by russf:
Reference the American Airlines glider conversion on my previous post; what's the best prop for a Speed 280 direct drive on eight cells? The Gunther/Zagis seem like too much, draws 8.5 amps on my Whattmeter, two motors in parallel. They run very hot! I have Cox 6 x 3s and APC 5.7 x 3s to experiment with, but any and all advice is appreciated. The model's speed is about like a TwinStar, so I don't think gearing is the answer. Thanks, Russ
Those props are all a bit big for a 280 running direct drive. Graupner do a CAM 4.7x2.3 folder which works great. On 7 cells I later fitted CAM 6x3 blades to this hub/spinner which improved performance but the motor got pretty hot (I think the static current was about 4.5A). On 8 cells a 6x3 prop would cook the motor for sure.
Jun 04, 2001, 07:24 AM
Registered User
I've used the Gunther prop on S280's but usually on 6 cells, occasionally 7. Why carry the extra weight ?

Jun 05, 2001, 12:10 AM
Registered User
Thanks for the good input, guys! I made some major mods to the 757 today in the motor department. Originally I merely hollowed out cavities in the foam nacelles for the 280s and glued 'em in, with NO provision for cooling! In a hurry, I guess, I do know better. I tore all that out, made some nice cowls with plenty of gap around the motors, with a sizable exit hole. Also changed to motor mounts to dowells epoxied into the wing LE, secured with a nylon tie wrap. Finally, I put those tiny gold plated Deans plugs in-line, so I can easily swap motors for testing purposes. For now, I followed the suggestion of CA on the propshafts to keep the Gunthers on. But I have proper 280 prop adapters, 5 inch props in various sizes and two Simprop 300 motors coming from HobbyLobby, so I can try and arrive at the optimum motor/prop/battery setup. Ship #1 i the test bed for all these changes, I already bought three more for the staggering sum of 20.00 dollars once I get this prototype sorted out. I'll post pictures as soon as I figure out how...Russ Farris
Jun 05, 2001, 05:19 PM
Registered User

Please do keep us up to date. I picked up one of these gliders for $4.99 at a local discounter with the intent of doing a conversion just like yours.

I guess I'll wait to see what motor combo works best for you and do the same.

Jun 06, 2001, 01:06 AM
Registered User
Update on the American Airlines jet glider conversion! Flew four flights back to back. First off, the mods for better motor cooling made all the difference. After the first six minute sortie with an eight cell 600AE pack, I could hold my finger on the motor(s),as long as I wanted. I couldn't do that before without getting a blister! I then tried a seven cell pack, The performance was the same, for all practical purposes I couldn't tell the difference. Guess the lower weight makes up the difference nicely. The best flight was with a 1100 mah nickel hydride seven cell...11 minutes of mostly full power flying. This brought the weight up to 25 ounces from about 21, but the little airliner flew exactly the same. The wind was blowing 8 to 10 mph, it does much better under these conditions than most Park Flyers (downwind loops look pretty funny, though.) It rolls to the left very fast, probably because of torque/P-factor, not as good to the right, a little more work to make it axial. A passer by, who happened to be an R/C flyer commented that he never saw an airliner do a roll before! The appearance in flight is very scale. The only glitch was that cheap GWS-15 ESC would sometimes cutout at full throttle, and not re-arm, cutting the flight short. I put my old trusty Jeti 18 in it tonight. Still has a pretty nasty stall, thinking of leading edge cuffs on the outboard portion of the wing to help, but overall this six buck foamie flies better than any Park Flyer I ever owned. Thinking of adding rudder, it doesn't really need it but I like spins, snap rolls, and other Boeing 757 scale type aerobatics...Russ
Jun 06, 2001, 06:50 PM
Registered User
Great job Russ!

Could you re-cap everything you did to this point? I have many questions like: Did you add elevators or cut the scribed ones from the wing? Where did you mount all of the gear, inside the fuse or slot it from the outside (like a sky scooter)? Etc., etc., etc.

Your success has proved to be an inspiration, I really hope to find time to work on mine!

El Rojo
Jun 07, 2001, 12:30 AM
Registered User
Here's the quick and dirty on how I did the conversion. I took the stock fuselage and removed the section directly above the wing.This formed a hatch. I hollowed it out to make room for the reciever and speed control mounted on top of the wing. For the elevators, I mounted two FMA S-80 servos in outside pockets, directly below the wing, just forward of the wing trailing edge. Music wire pushrods to small control horns epoxied directly to the bottom of each elevator. This is all external. The stab is made from "meat tray" foam and was too thin and flexible, so I added medium balsa to the bottom, from the leading edge about 1/3 of the way back, grain paraellel to the L.E. Cut away the fuselage section directly below the stab mount, and sand it down to match the stab bottom, then glue the stab and fuse bottom section in with Titebond. I used the stock scribed elevators, no tape or hinges, seems to work great. For the battery, I hollowed out the bottom of the fuse directly below the wing, I'll measure exactly where if you are interested. Mounted a 1/16 ply plate for the Velcro to hold the battery on...I also glued in two dowels for a couple of rubber bands as extra insurance, since the battery is literally hanging from the Velcro, flush with the bottom of the fuse. Excellent cooling, though! Heat a 1/8 wire with a torch, then run it through the fuse from the tailcone to the rx/esc compartment over the wing, for the antennae run out the tail.

On to the wing! Glue the halves together (I used Titebond) and cut the ailerons out. I doubled the size foward of the scribed on lines, but the next one will be triple - I like lots of control! I used two HS-50 micros for each aileron. I have a computer radio with mixing, otherwise use a Y-harness - same with the elevator set-up. Bevel the front of the aileron 45 degrees at the bottom, so you will have differential (more up than down), hinge at the top with tape, trim Monokote, ect. I used 1/32 ply control horns, mounted on the inboard end of each aileron. The servos are mounted on the bottom of the wing. I used a dremel tool with a 1/8 bit to route all the wiring channels. Strapping tape covers them, and adds a great deal of strength, too. Run it out all the way to the tip.

Motors: Don't make the mistake I did! They need LOTS of cooling with the props and amps I'm pulling. On the next one, I'll cut off the cowling just ahead of the wing. Use a table saw to remove the inside foam, now it looks like a cowl should, lots of room around the motor. Glue two dowels into the wing leading edge, make the thrust lines 0/0 and nylon tie-wrap that baby down. MAKE SURE you cut a slot directly behind the motor for the cooling air to exhaust from, also run the motor wires through there. Spot glue the cowl back on and mount the props. I used 18 gage stranded wire from Radio Shack, run it through the wing center section and up into the rx/esc compartment. For finish, one can of Testor's spray enamel silver gives it that cool AA big jet look. Oh, I almost forgot, before you do all this work stick the gilder together and mark the C.G. location well. It flew right off the board at the toy glider C.G. That covers the basics, if you have any questions fire away! Russ
Jun 07, 2001, 02:22 AM
"Bible Thumper"
AMTJIM's Avatar
I've converted that 737 several different ways. It flies great. I used twin expert 280 gear drives, pusher 400 with the zagi prop, twin graupner 400 fans and made a canard, MD-80, and Dash 8 looking thing. The fuselage is perfect for packing in the equipment. I want to try their 747 looking glider next.
Jun 07, 2001, 06:47 PM
Registered User
Thanks Russ!

I think I'm gonna do mine with a single servo for the ailerons, using torque rods.
We'll see how it goes.

I'm almost tempted to do one for sloping, as there is a good slope here, close enough for lunch-hour flying.

Thanks again
Jun 07, 2001, 11:16 PM
Registered User
ElRojo: It would make a great little slope airplane, no doubt about it. If only I lived near a slope...sure do miss the SF bay area.
I converted one of those Comet three foot foamies 15 years ago to a sloper, and it would stay up in conditions that had the polyhedral Gentle Ladies headed for the ground. The 757 should be similar. One suggestion - have ailerons AND rudder. Under light lift conditions, adverse yaw from ailerons only causes drag - think side slip angles. With a rudder (and knowing how to use it) you will maintain cooardinated flight, reduce drag and stay up. It does make a difference! A full size sailplane has tremendous adverse yaw, due to the large wing span, and if you didn't use rudder and let it yaw all over the sky under marginal conditions, down you go. Russ
Jun 07, 2001, 11:19 PM
Registered User
AMTJIM: What 747 are you refering to? The Hobbyflite one, or is there another out there I can fool around with? Russ
Jun 08, 2001, 07:23 AM
"Bible Thumper"
AMTJIM's Avatar
I think their 4.5 foot wingspan glider looks 747'ish.