EXP 1r - by Chris Martindale

16 Jun 99 - WCL figure added.

Exp-1r #1 Exp-1r #2 Exp-1r #3 EXP-1r #4 Exp-1r #5

I originally built this model around 7 years ago, from the Radio Modeller free plan. It was under-powered by a 540 motor and didn't fly too well due to being too heavy. It was eventually scrapped for other projects. I have finished building another, paying more attention to weight.

The 1st photograph shows the 2nd model as originally built. The remaining photographs show the model after the fitting of the new wing. The 3rd photograph shows the positioning of the aileron servos in the wing.

N of launches / Time 154 16 hours 15 mins Note: Not all flights included
Wingspan 39.2 " 0.995 m    
Wing Area 334 in 21.5 dm    
Flying Weight 2 lb. 12 oz 1.26 kg    
Wing Loading 19.2 oz/ft 60 g/dm    
Wing Cube Loading 12.6 - Scale  
Motor Modified Graupner Speed 600 Race 8.4V
Propeller Aeronaut Elektro Glas 6 x 5 (White)
Batteries 8 Sanyo RC-2000
Speed Controller Jeti JES35 - 35A - 6 to 10 cells, BEC & Brake
Receiver Futaba FP-R116FB - PPM - 6 channel - 35 MHz
Servos Ailerons - 2 Volz Wing-Maxx
Elevator - Hitec HS-101MG
Static motor parameters  8 RC-2000 or NiMH 2200 cells gives 13600 RPM @ 26A, estimated 88W/lb. (output)
Flight performance 5th motor - Graupner Speed 600 Race modified with ball races and reverse rotation with Graupner CAM 6 x 6: Slightly faster than before and quieter. Takes longer to accelerate from launch but performs everything as before. With the Aeronaut Elektro 6 x 5 propeller the model is even quieter and accelerates better with little loss in top speed. I think this propeller is the one I'll stick with.

4th motor - Graupner Speed 600 Race with Graupner Super 7 x 4L: Not quite as fast as with the T-Tech motor but much more respectable currents. Duration is improved and the ESC doesn't cut out due to overheating.

3rd motor - Trinity T-Tech 17T with Tornado 5 x 4L: Faster than ever, especially on 8 cells. estimated level flight at faster than 50 mph. Full power duration is about 4 minutes on 7 cells and 3 minutes on 8 cells. The ESC shuts down after about 2 minutes on 8 cells due to overheating - more ventilation needed.

2nd motor - MFA Hummingbird 20 with Graupner Super 8 x 6L: Climb has reduced & now is approx. 25. Slower in the air, needs more throttle for level flight and struggles to loop from level flight. Duration about the same.

1st motor - Goldberg 550 Turbo with Graupner Super 7 x 4L: Climb out at approx. 30 and really grooves in level flight at high speed. Will maintain height at 1/2 throttle. Rolls and loops extremely well. Will just maintain level flight inverted (flat bottom wing section). Duration is about 4 minutes at full throttle and 7 minutes at cruise.

I have only flown this model from a hand launch of which almost all self launches. It is not difficult to launch despite being a pusher, even when the 8" propeller was fitted. In calm conditions and 7 cells it needs quite a good throw, but with 8 cells or into a breeze it needs little effort.

The first motor was a Goldberg 550 Turbo with a Graupner Super 7 x 4L (pusher) propeller. The motor suffered a terminal brush failure due to overheating and has been scrapped.

I have temporarily fitted my MFA Hummingbird 20 motor (all I had in my goodie box) pending the purchase of a suitable motor. This has now suffered a rear bearing failure due to being used in the pusher configuration (the back bearing wasn't designed to take any thrust load). I have repaired the motor by enlarging the bearing hole in the rear plate and bonding in a ball race. I have also fitted a nylon washer, coated with lithium grease, between the propeller adapter and motor boss to act as a thrust bearing. This has reduced to motor speed by a little and therefore reduced to model's speed in the air. It still flies well but really needs a good motor with a ball race as a thrust bearing. I have replaced the Graupner Speed 8 x 6L propeller with a Kyosho 8 x 5 to see if the motor performs better with a little less pressure on the thrust bearing.

When landing once I was a little low and one wing tip caught in the 18" high grass surrounding the landing square. This caused the model to cartwheel removing the tailplane. It actually did very little damaged and it will take lass than 30 minutes work to repair. I added a couple of pieces of triangular stock to the inside of the tailplane / fin joint to stiffen the joint.

I wanted to try and improve the top speed of the model so I tried a Graupner CAM 6 x 6 propeller (increased pitch / smaller diameter). To use the CAM propeller I had to run the motor backwards and I think the motor timing caused the poor performance. The Graupner Speed 600 Race I am using is fixed timing and I think advanced for normal rotation at something like 25A. On the first launch the model slowly descended to the ground about 25m away. On the second launch I threw the model a little harder and it managed to get away, but didn't want to accelerate at the normal rate. If have reverted to the 7 x 4L propeller until I think of a better way / motor.

Whilst driving to my parents the other day my toolbox fell over and broke the wing in several places. It is less effort to make a replacement wing than to repair. In the new wing I am again including a few new modifications. I've decided to fit an aileron servo for each aileron and to mount them in the wing, and I have bought some Volz Wing-Maxx servos for the job. I am also increasing the changing the wing planform of the model very slightly for convenience. As the original aileron servo has been removed the elevator servo is now mounted sideways inset into the wing top skin, and operates a bellcrank as shown on the plan. I have now completed the rebuild of the model and it is 3oz (90g) lighter than it was before, a saving of about 8%. Half of the weight loss was in lead ballast from the nose which could be removed as I managed to get the battery further forward. The remainder was from the lighter grade balsa used for the wing skins & ribs.

The removal of the aileron inboard of the booms has reduced the aileron surface area by about 30%, however, the roll rate is just as good now as it was before. I'll have to experiment with the effect of the flap functions now available. On the 2nd launch after the rebuild, I hand launched the model and felt the battery move back as I did so. The battery could move back about 0.5" and this moves the CofG position rearwards by about 0.2". Other than having to apply almost all the forward elevator trim the model flew quite well, but was a little twitchy on elevator. I must put a removable block in behind the battery to prevent this happening again. The block needs to be removed to get the battery out.

28 Aug 99 - I have become fed up with the restriction of using a left handed propeller as there is little choice of sizes. The stock Graupner Speed 600 Race motors are probably the best motor in this class, but unfortunately have well advanced timing for normal rotation and do not work well in reverse. I therefore decided to retime the motor by cutting new locking tabs in the case. Whilst I had the motor apart I decided to fit ball races in places of the original plain bearings (as I had suitable ball races in my spares box). This allows me to use the motor with a conventional (right handed) propeller. I have set-up a web page of the modifications made.

1 Sep 99 - I had chance to flight test the EXP-1R with modified motor tonight. It was slower accelerating away from the launch, but the extremely coarse pitched propeller explains that. Once it had reached a good speed it maintained it without effort and was probably slightly quicker than before. The one good point is it has reduced the noise a little, but it is still a noisy electric model.

13 Nov 99 - I have been using an Aeronaut Elektro Glas 6 x 5 propeller for a short while now and I'm very impressed. The noise of the model is further reduced and acceleration has improved again as the propeller is not stalled at launch. I'm going to stick with this propeller for the moment for further assessment.

Return to Electric Aircraft Models page