Author Topic: Fuselage design for electric stunters (Read 1132 times)

Christoph Holtermann · « **on:** June 06, 2007, 05:21:14 AM »

Hi all electric maniacs,

I wonder wether there is the first plan published for a purely dedicated electric stunter. My next project will be to design an electric stunter and it seems that not much developemnt was done yet to design an optimal fuselage.
Many issues have to be looked at:
- Fastening the motor on a front ring or on a former (option to change engine, different lengths, diameters etc.)
- Loads on bearings in function of these two options of attachement
- Cooling of engine
- Position of the controller either for good cooling (if necessary), short cable length and quick accessibility (if needed?)
- Battery compartment, fastening the battery, space needed to shift battery in order to adjust CG
- Location of timer and accessibility in case of programming
- Reduction of cable length in the whole system
- Equipment cooling vs. sealed system in case of flying in rain and humidity

There might be some more issues that I forgot.

Past design were mostly suboptimal conversions from IC to electric. These worked well but none of us has the long years experience we have developed with IC engines.
Could someone publish here the nose design of his new electric stunter in order that this serves as a discussion basis?

Thanks!

In order to display some information of my current setup:
- Cobra 60 (Henk de Jong design, converted from ST-51 to Graupner Compact 480 12V, equiv. to Axi 2820/12)
- weight 58 ounces after conversion, 54 ounces before with ST-51
- MGM controller 44A, Heli mode and brake
- Zigras timer set to 5.5 min
- APC-E prop 11x5.5
- 4 cell LiPo 3200mAh, I draw max. 2400mAh in 5.5min
The model has a very constant laptime, the engine breaks nicely after 5.5min with the prop stopped for landing, plenty of power but I needed to give 1.5° engine side thrust for better line tension in turbolent circles. I don't see what I should improve with this setup. I never had this feeling with any IC stunter :-)

Regards

Christoph Holtermann, Germany

Alan Hahn · « **Reply #1 on:** June 17, 2007, 05:38:34 PM »

One thought I've had about motor attachment (basically related to a profile mount) would be to have a bearing glued between the location of the original motor mounts that you would have for a normal IC engine. A lot of the motors have a long shaft coming out the front (or back depending on the point of view) that would fit into the bearing. This would allow a two point vertical mount at the front of the fuse, but give lateral support at the rear. This would opposde any gyroscopic forces on the motor in a sharp corner.

I am not too worried about cable lengths (making them shorter for example) from the battery/ESC, primarily because these are pretty low resistance compared to the motor winding gauges and lengths anyway. Plus we aren't really drawing extreme currents anyway compared to some RC electric use.

I do think providing good cooling to both the motor, ESC, and battery can only prolong lifetimes of these somponents. I think I have seen magnetic field loss in my permanent magnets over the length of a flight. I always have flown with a data logger and have noticed that my level lap current consistantly rises through the flight, even though the rpm has been kept constant by the ESC (governor mode). This has only been at the ~10% level (at the end of the 5 minutes) and seems to be reversible (next flight starts back at original current value---after a little time for cool off). I may be mistaken to the explanation--anything which makes either the permanent field or the electromagnet field less would give the same readings.

Dean Pappas · « **Reply #2 on:** June 18, 2007, 08:31:07 PM »

Hi Alan,
You are not seeing demagnetization. Constant RPM and lap time require constant Watts. As the battery voltage drops during the flight, the "internal throttle" the governor uses to maintain RPM gets set higher and higher, so that the currrent will rise by the same percentage that the voltage drops. That maintains the wattage.

Motor warming and magnet strength change are real, but it is a small second-order effect.

later Sir,
Dean

Clancy Arnold · « **Reply #3 on:** October 06, 2007, 10:22:36 AM »

While rereading the posts on C/L Electric reminded me of my tests back in the mid 1980's.

The first thing I learned was that an electric motor powered model does not react like a IC engine model. The nearest comparison to Electric power is Rubber band power.

Stop and review what I just said. Smooth even power, with little or no vibration.

The electric model is better than the rubber powered model in the amount of power available, length of run, adjustment of power applied and cutoff at a pre selected time. Then if you add a throttle control it is even safer than any other form of power.

Now when you design your Electric Only Stunter, remember these things and you will produce a lighter, cleaner model. Remember no hardwood engine bearers, heavy plywood nose doublers, heavy gusseting at the wing to fuselage joint.

Just my observations, yours may vary.

Clancy

Dennis Adamisin · « **Reply #4 on:** October 16, 2007, 08:02:15 PM »

Clancy - well done!

As an alternative I gotta beleive the best way to build an e-power fuselage will be FIBERGLASS with the motor front mounted.

I think Clancy is right -on in saying wood fuselages - will have more in common with rubber power than with traditional CLPA structures.

Author Topic: Fuselage design for electric stunters (Read 1132 times)

Christoph Holtermann

Fuselage design for electric stunters

Alan Hahn

Re: Fuselage design for electric stunters

Dean Pappas

Re: Fuselage design for electric stunters

Clancy Arnold

Re: Fuselage design for electric stunters

Dennis Adamisin

Re: Fuselage design for electric stunters