CMP Extra 300S .90-.120 trouble

Hi guys

I bought a Extra 300S from China Models and converted i to electric. S far so good. The bird has a flying-weight of apx. 4 kg. The setup fo this model is a Hyperion 4035/12 with the Hyp. 80A OPTO ESC running o a Hyp. 1P5S 3700mAh battery-pack. I have until now only used a AP

17"x10" prop. This is more than enough power, so that is not the issu here. (just some info ;) )

The thing is that the model is a little bit tricky i the air. It flick to one side when it got some speed. When I do a loop, it flicks aroun on the back in the last 1/4 of the loop. I almost lost it a couple o times trying out different setting on my radio to get a clue on this. The EWD is OK. The CG says 135 - 145mm. I set it up on 130mm. I als did set the throws on both elevator and the ailerons less that wa suggested in the instructions. Sometimes when I fly it it seemes t have the CG too far back, but other times it seemes like it is to nose-heavy :confused: I have tried both linear stickmovement and wit

20-30% expo. Still it seemes crazy ..... I have no mroe ideas at the moment on what to change. Is it someon that has experienced the same thing with this plane ???

-- geirstr

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On Wed, 7 Mar 2007 14:47:00 -0600, geirstro wrote in :

It sounds like it is snapping out of the loop.

It may be that you're just using too much elevator throw for that maneuver. Do you have hi-lo rates? Can you test it with milder throws?

Snappy planes are often tail-heavy rather than nose-heavy, I think.

Don't have that one in my hangar ...


Reply to
Martin X. Moleski, SJ

Marty is right

While it almost sounds more like a control throw issue than a CG issue, playing intelligently with both can't hurt. Snap happy planes live short lives. Add a couple ounces of easily detatchable weight to the nose, make the elevator travel 1/2 of whatever you are using now and test fly it. If it no longer snaps, put the control throws back in and try again. If it no longer snaps, the CG was wrong. However if it snaps now you have proven the issue is a control throw problem.

Good luck and let us know

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I'm putting in my vote for excessive elevator throw. With enough elevator deflection you can make an Extra stall at any speed. The worst part of it is that Extra-type planes suffer from high speed stalls so suddenly and unexpectedly. That's why these planes make me so nervous. Just back off on your elevator input and see what happens.

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Robert Reynolds

On Wed, 07 Mar 2007 19:52:02 -0600, Robert Reynolds wrote in :

Good point.

I think they call these "accelerated stalls," although perhaps that term is used more often in the context of stalling out of a banked turn.

3-D aircraft are sort of designed to produce (and tolerate) high-speed stalls. In a snap roll, one wing loses lift (stalls) before the other, which is what helps to throw the airplane around the sky.

I'm not sure "suffer" is the right word. It seems to me that this is an intended result from the design of the aircraft and the use of very large throws and large control surfaces. (I don't know whether the model in question was designed for 3-D maneuvers--I just mean as a general rule for the planes I have seen.)

I have flown a lot of combat Gremlins. I've got them set up, for good or for ill, with enough throw so that I can make them snap out of a loop when I want to, just by pulling a little harder on the elevator. Unfortunately, in the excitement of combat, I have sometimes crossed that line inadvertently. I came real close to auguring in last September at a fly-in breakfast. It was NOT pretty. :o(

Bottom line: accelerated stalls are fun to play with when you expect them and a whole world of hurt when you don't.


Reply to
Martin X. Moleski, SJ

If everything the other guys say looks ok, then it's worth checking the wing for warps. I once had the joy of test flying a friend's model which snapped to the right with even the slightest up elevator input. Got it back to the ground rather untidily and found a twist in the right wing effectively giving it a few degrees of wash-in, enough to stall the wing with any increase in AoA.


Reply to
Kevin Manley

"Martin X. Moleski, SJ" wrote

Ever manage to recover one from a flat spin?

A little story, here.

At one fly-in YEARS ago, as things were winding down, and only a few regulars were left, some of the guys asked if the hot-shot JR pilot (who was also a friend of someone there) if he had ever flown a gremlin. He said no, but he would like to, so that is all it took for about 5 of them to suddenly appear.

They didn't have any paper to pull (for cuts) so they just decided to do some mock pylon racing.

Well, it seems like there was a wide range of speed differences, so to make things more fun, and to keep a tight pack, corner cutting soon became common, and expected. My former instructor was flying mine, and it was the slowest. He said, "Jim, tell me when to turn."

I said, "ready, ready, NOW!"

BLAM!!! A perfect, dead center mid air. Five birds are now three.

A few more laps, and one guy has sudden engine failure, and he is out. Now there are two.

A few more laps, and one guy showing off with a low inverted pass, when he dumb-thumbs it.

THWACK!!! Now there is only one. It is the Hot Shot JR flyer.

He is all proud of himself, and doing twitch wing rocking,, victory rolls, and a few other acro moves, then he puts it into a flat spin.

The owner of the gremlin says, "Oh no, I forgot to tell you not to spin it!"

"Try blipping the gas, try this, try that." All to no avail. It went in flat, still spinning.

Fortunately, the ground was soft, and the grass was high, out away from the runway. No damage.

But, everyone else in the club felt good, that even a Hot Shot could do something dumb-and crash!


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On Thu, 8 Mar 2007 02:31:38 -0500, "Morgans" wrote in :

Hmm. I don't think I've gotten a Gremlin into a flat spin. Letting go of the controls and STAYING off them long enough gets mine out of the spin. My problem in the combat round was that I kept pulling up-elevator before the plane had stabilized. I lost a ***LOT*** of altitude over a stand of hungry trees. Even though I did recover and fly away, I am ashamed of losing control for so long. :o(

LOL! BTDT and have the pix to prove it. ;o)

OOOH, it gives me the shivers ... It must have been a little tail-heavy. I follow Eric's instructions: CG 1.7" from the leading edge.

I'm glad that the owner got the plane back in one piece.

I loaned three planes to an excellent pilot to fly at a pig roast while I went on a road trip to Montreal. When I came back, all three planes were broken. Stuff happens, don't it? :-O


Reply to
Martin X. Moleski, SJ

This reminded me of the old Kittywake kit. Ever see one fly twice? There was an apparent error in the plans for the location of the CG. Look too hard at the elevator and it was snapping. Never even got to the doing loops part. I saw several die while being test flown by very competent pilots. One almost made a landing before it snapped. That flight by that guy convinced me to sell my kit...

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