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Electric Stunt => Gettin all AMP'ed up! => Topic started by: Andrew Borgogna on May 28, 2012, 07:27:45 PM
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Well I got to the point on the Continental where I wanted to test the motor system it was then I found out my cool idea for removing the motor turned out to be a really bad idea. I built vertical rail slots into the fuselage and mounted the motor front and back to bulkheads. The bulkheads then dropped down into the rail slots. It looked so good. y1 But it worked so bad. ??? When the motor got up to speed the torque litertally started to take the front end of the plane apart. I got things shut down before an serious damage happened, but it was a bit scary. The bulkheads must be glued in to hold everything together, I just hope I don't need to remove the motor in the future. Oh well, live and learn. I think it was Dean not to long ago who warned us about how much torque these motors can generate. I can testify he was right. HB~> HB~> HB~>
Andy
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you can still do it your way - but brace the nose outside the box - ie - some warren trusses below, and maybe a light ply doubler or two in front and behind your slots - just to keeop it rigid with or without the motor in place
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Can you add a screw-on shear panel of ply over the top of the motor well?
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most likely any method of reinforcinng the box would have helped. You could have an upper and lower longeron tied to a screwed down plate top and bottom to do the same. The key is to maintain rigidity . (sp) to keep the torque from twisting the box.
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"keep the torque from twisting the box." That's the main point here, and as dumb as it sounds I really didn't give it much attention. Well that's a mistake I won't make again! Thanks for all the input.
Andy
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Ah grasshopper, you have so much to learn. ;D
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Yes Zen Master! HB~> HB~> HB~>
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Andy:
Did your motor plate just slide in or were they retained some how? Rick Sawicki up in Detroit has been using slide in plate mounts for years with good success, he uses 2 sheet metal screws on either side to hold the plate against the fuse doublers.
Among my new fleet I have a profile with a front mounted motor, a profile with a rear mount, a full fuse with a front mount (motor comes in from behind) a full fueslage with a rear throughthe-firewall mount, and a front mount with rear bearing that drops in from the front. Each seemed to make sense for the installation at hand...
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Dennis
Then just slid in, the idea was the top cover would hold it in place. The problem was the side walls of the fuselage around the motor compartment were not strong enough to hold back the torque. The entire motor system rotated about a quarter turn before pulling one of the motor wires and shutting everything down. The front fuselage side wall let go from the front of the fuselage and freed the motor mounts to rotate. Two things that contributed to the problem, one the top was not on the fuselage to hold down the motor mounts, and second I didn't put the prop insert into the prop and it was slightly off center. No excuses, anyway I glued in the bulkhead mounts and balanced and centered the prop and all is working well. Tomorrow the Continental will get it's first flight. ~^
Andy
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Andy, I see we are still learning. If we don't try things, how can we learn. Of course Dad always told me to learn from others mistakes. I didn't listen to his statement enough at times. H^^
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First flight was successful in that the plane is totaly unscratched. It is a bit noseheavy and there wasn't enough cooling to the motor. Both easily fixed. It does hunt. Andy is using 1:1 flap to elevator. Does that tend to cause hunting? Where else can we look to smooth it out. His controls are very free.
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Larry and Andy,
A 1:1 flap/elev. ratio should not cause hunting. What I would look for is motor thrust line alignment and that the flaps and elevator are at neutral at the same time. If the flaps and elevators are out of alignment, it could cause hunting as the flaps and elevator will try to fight each other.
Stan
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Assuming that Andy laid in the stabilizer at exactly 0-0 to the wing, would a hint of down elevator relative to the flaps be of aid?
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Larry,
Just a touch of down elevator relative to the flaps is generally OK. It should help getting a groove in level flight.
Stan
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Well additional cooling was added for the motor. Larry modified the spinner per Dennis Adamisin's suggestion to open the nose of the spinner and reshape the openings on the back plate to turn it into a fan. I also opened up air passages to the motor for better air flow around the motor. The CG was way off, mind you there is no mention of CG on the plans. So my "Zen Master" Larry Renger explained I needed to locate the aerodynamic center of lift on a swept wing, then locate the CG at 20%. I was going for 25%, but Master Larry suggested I start with 20%. It to a full ounce of additional lead to get the CG right, assuming that the calculator I used on the internet was good and more importantly I was feeding in the right data. Anyway I am ready for flight number two. Tally Ho!
Andy
P.S. The power system, over heating motor aside, performed very well. Line tension was exceptional at all angles.
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All sounds pretty T'rrific Andy. Do you have any "nose lightening" tricks you can use in case the CG has to go futher aft? BTW, I recently flew an OTS bird that hunts with a heavy battery but grooves well on a lighter battery (CG slightly aft) This was the first time I had ever encountered this oan a CL model, but used to (routinely) have a similar issue when I was flying sailplanes where aft CG's flew better. Hopefully you will similarly benefit...
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Dennis when it was all said and done I had to add another ounce of lead to the tail, ouch! ~^ I think your mention of a heavy battery contributing to hunting has merit. I have been thinking about this for some time. I'm not a physics major, but I wonder about the inertia from the larger mass causing some type of ringing when trying to stabilize the plane. Any physics majors out there for comment. I actually went out on the net yesterday in search of a lighter battery, but what I have is the best I could find. I will work to drop the revs down a bit at a time and increase the gain on the KR timer to try and save power in level flight. Slower lap times but still have the needed power for maneuvers. I might then be able to go to a smaller capacity batter and hopefully save some nose weight.
Andy
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Well if you are at the "flyable" stage then you should be able to quickly determoine how much battery you are using - HOPEFULLY you can go down a size or two.
If you can downsize the motor that can save weight and quickly make the CG move. Next do what ever you can to lighten the spinner and prop adapter.
The only other trick left to s to make sure the battery is as far aft as possible.
BTW what about the hunting issue - under control?
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Dennis
Going flying tomorrow and will have more information on the hunting. I had the handle spacing very wide and I a very nose heavy airplane. I am not sure hunting is the correct term more like porpoising from the heavy nose. I will know more tomorrow.
Andy