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Old May 27, 2010, 10:59 PM
Some epoxy & it flies again...
Low Pass's Avatar
Santa Cruz, California
Joined Sep 2008
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First of all: Jumpy, great work, I love it. I am totally interested in the plans at some point.

Second: LuvEvolution & MaxThrottle, interesting discussion. I would always vote for extending the ESC wires on the input side to not cause any problems on the motor side with the sensing etc. Maybe I'm over cautious with this. But it also seems easier to extend 2 wires than 3 and the ESC is normally closer to the EDF than to the battery.
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Old May 28, 2010, 01:15 AM
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Quote:
Originally Posted by Low Pass View Post
First of all: Jumpy, great work, I love it. I am totally interested in the plans at some point.

Second: LuvEvolution & MaxThrottle, interesting discussion. I would always vote for extending the ESC wires on the input side to not cause any problems on the motor side with the sensing etc. Maybe I'm over cautious with this. But it also seems easier to extend 2 wires than 3 and the ESC is normally closer to the EDF than to the battery.
You are right that many models are setup that way usually due to scale etc.
Actually the reason for the battery side being the shorter is the battery always gives all its got, full volts and amps. For this reason you want to minimize resistance from the wire, thus gage is becomes important. The Resistance results in heat and reduced watts.

Also its how an ESC handles throttle control; ESC has to deal with starting and stopping electricity flow from the battery. The ESC does the work of regulating the pulses at full amp rating of the ESC and volts of the battery to the motor. At the same time the ESC is reading the motor to time the pulse.
The motor just received the pulse of electricity. So there is a little more work happening on the battery side.

What surprised me was Castles comment that running at half throttle is more taxing on the ESC and battery than at full throttle.At full throttle the ESC only deals with the motors timing not regulating the throttles on off pulse.

The only time I'd be really concerned with the motor side is continuous full throttle and over volting; pushing the motor to its limits.
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Old May 28, 2010, 02:28 AM
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well, if you think about it, it makes perfect sense that it puts more pressure on the ESC at part throttle, because the ESC among other things, is basically a big resistor. it also has to do double duty, by not only resisting the direct flow from the battery, but it also has to convert DC voltage from the battery into AC voltage for the motor to use. so at part throttle, it has to work harder to do this. it's the same with all electrical circuits that have some form of resistor in the middle of it. remember the old mechanical speed controls for RC cars?......................if you ran them at part throttle for too long, they would get insanely hot and occasionally, just burn out for the hell of it. or so it would seem, but the very same thing was going on here too. at part throttle, the resistors in the circuit would kick in and allow less voltage to the motor. the trade off for resistance is heat, which is why they burned up. sometimes you could get away with just replacing the resistors on the speed control, but if you were unlucky enough, as most were, you'de have to replace the whole thing cause it melted to nuthin. you were often left with a huge molten glob of crap. LOL. modern speed controls are better at handling the heat, but they still operate in much the same way. they are way more efficient at handling the heat these days, so usually you fry them when you are putting through more power than they can handle. an interesting experiment would be to do a couple of runs while holding a temp gun to the ESC. I would bet money that if you did a full run at WOT, you'de have less temp than the same run, but done at say half throttle for the entire run.

this is also the reason why you can extend the ESC to motor wires, is because it's running pulsed AC current/voltage instead of constant DC current/voltage from the battery. it's far less harsh on the wires than the DC current/voltage coming from the battery. you can also run less AUG wires on the motor side of the ESC because of this reason.

I love discussions like this, cause it allows everyone to learn at least something, without resorting to the battles that go on, on some of the other threads. I say keep this type of stuff coming. sorry Phil, didn't mean to go too off track from you awesome Froggy. now quit lollygaggin and finish the thing already. yeah yeah, I know, I'm one to talk, right? LMAO

Rich
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Old May 28, 2010, 03:58 AM
smithy
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With information like this you can go off topic as much as you like. Like you said ,you learn something new every day, thats the beauty of forums like this. Thanks guys, until now i wouldn't have thaught it made any difference which one you extended, not being electrically minded. Now that i have control snakes and ducting installed i can press on and finish skinning the frame, also need to make plugs for the vacformed canopy, nosecone and tail cone. Need to get this weekend out of the way first, stacked out at work for the bank holiday weekend, it gets pretty manic down here this time of year. Thousands desend on Newquay for the 'Run to the Sun' event, custom cars and general partying!!!

Phil
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Old May 28, 2010, 03:03 PM
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yeah, when I was a kid, I remember heading down that way at this time of year. although for us, it was always to visit family in Mevagissey and Paignton. I really do miss it down there though. another one I miss is going to watch the tanks on the firing range at Castle Martin, near Tenby.
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Old Jun 08, 2010, 06:28 AM
smithy
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I was looking through some pics of the 'froggy' and spotted this one. Its a pic of a froggy taking off but i just noticed that it has an all flying tailplane, didnt spot that before. Also it has conventional elevators aswell, what's the function of a flying tailplane aswell as conventional elevators. I thought perhaps the elevators might be used for trimming in flight, any ideas?
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Old Jun 08, 2010, 07:44 AM
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Kevin Cox's Avatar
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Jumpy,
I think that is the trim function (all moving). Not uncommon at all.
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Old Jun 08, 2010, 09:09 AM
smithy
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Kevin, Iv'e looked at some more pics and 3 views that i have, they all show trim tabs at the trailing edge of the elevator. So, it has moving tailplane, elevators and trim tabs, im confused!! Could it be that it uses the moving tailplane at low speeds for extra manouverability?

Phil
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Old Jun 08, 2010, 09:24 AM
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Quote:
Originally Posted by jumpy View Post
Kevin, Iv'e looked at some more pics and 3 views that i have, they all show trim tabs at the trailing edge of the elevator. So, it has moving tailplane, elevators and trim tabs, im confused!! Could it be that it uses the moving tailplane at low speeds for extra manouverability?

Phil
Try PMing Pinecone. He flew the actual. Pincone is correct that this is a subsonic attack plane but even old pre sonic fighters found themselves getting in the sonic range so this may serve as multi purpose to maintain control at higher velocities and being a stabilator for load.

Too there are airliners with an adjustable tailplane, elevator and trimtabs so....
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Old Jun 08, 2010, 09:40 AM
smithy
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I see, thanks.
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Old Jun 08, 2010, 12:26 PM
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something to ponder....................

if you've looked at planes like the DC9, it has all moving tailplane with what looks like elevators that are driven hydraulically and also trim tabs. there's a reason for this. the elevators are actually tabs that drive the whole tailplane and don't work in the traditional sense of the elevator. when a surface (tailplane) is too massive to be driven in the traditional sense, they use a smaller surface with less hydraulic power, to help in the aerodynamic assist of the larger surface. the larger surface being basically free floating on bearings with dampers. so in other words, if you look at your picture of the jet taking off, the elevator woud be driven downwards, hydraulically, which then forces the rear of the whole surface up and you get rotation of the plane. the smaller tabs are just that.....tabs to trim for flight.

I would guess that the same thing applies here and they've done the same thing as they did on the DC9...............they are using aerodynamic load by using less mechanical load, to improve the flight characteristics of the plane. that would be my guess anyway.

Rich
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Old Jun 08, 2010, 02:05 PM
smithy
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Actually Rich that seems to make alot of sense. Iv'e just pm'd pinecone to get his thaughts, seeing that he as actually flown one. I think using a system like that would be to complicated for a model, just stick to conventional elevators. Thanks guys.
Just about to start a bit more on the build, will post pics later this evening.
Phil
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Old Jun 08, 2010, 02:13 PM
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I think the problem with the DC9 was more about deep stall conditions, so the tailplane was designed around the considerations and allowed to freefloat, instead of compounding deep stall issues. I'm wondering if the Froggy has the same deep stall characteristics and this is how they solved the problem here also. there's gotta be a reason why the flight surfaces are so huge for the relative size of the airplane........compared to other aircraft, of course. makes sense to me anyway. LOL.

Rich
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Old Jun 08, 2010, 04:05 PM
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from http://warfare.ru/?linkid=1611&catid=256

"Horizontal tail assembly
The horizontal tail assembly consists of two planes and two elevators. The structural assembly of plane is longerons, frames and ribs. Elevator hangs up in three knots. Controls are slanted synchronously, spread from +14 to -23 deg. na by right elevator is located trim tab. Controls are statically and aerodynamically compensated. The planes of stabilizer are established in three positions: takeoff, landing and flight. Stabilizer for an increase in the aerodynamic effectiveness is established above wing and engines."

So it looks like a pilot stick controls movable elevators, and the whole stabilizer can be positioned into various positions.

Speaking of DC9, I watched "Air Emergency" on TV and had an impression that a DC9 stabilizer is moved up and down by a dedicated motor activated by a separate lever. I.e. it is not "free floating", and it does not move together with the elevator, but kind-of similar to a trim function.

Sergey.
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Old Jun 08, 2010, 04:05 PM
smithy
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Well as promised, some more pics of progress so far. Still need to skin the rest of the other side and underneath yet but you can see its starting to look like an su25 at last. Also need to make the 2 fan access hatches. Ive left openings for undercarraige but still haven't really decided yet what im going to use in the way of retracts, air mechanical or electric

Phil
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