Dmacsimum

Well,
I had my first crash ever today, and it wasn't that bad. Yes, I was LUCKY, very LUCKY ! It happened as I flew around for a while, and was heading back to wards me. All of a sudden the plane pulled up vertically. I gave it full down in which it reacted with very little response. I was able to level it out, pass me by, and attempted to bank it in for a landing. That's was where I lost all elevator control. It stuck in a steep dive, I chopped the throttle all the way back and watch her disappear behind a row of cotton gin trailers, and then poof....... ground impact.

As I approached, she still looked in fair condition. Under closer observation the was front fuselages, the wing near the center was damaged, and the engine was impacted with Farmer's Dirt. Oh yeah, and the prop was bent, didn't even break it. I will not however use it again, for it has kept the bend and I do not trust it.

At the first sign of trouble, I thought the battery pack had dumped because I had flown for around for a solid hour non stop. I discovered however that the elevator push rod clevis was missing its pin that fits through the elevator horn hole. I tested power of the battery, and it was able to activate the servos with no problems.

All of the actions of the plane coincided with the failure of the pushrod clevis pin......IE: the climb to vertical, for the plane required down trim for level flight. Once the clevis let go, the lift from the wings caused it to climb, and had no down elevator trim. When I gave it full down, the clevis just pushed on the horn. Once I backed off the throttle, it lost lift and descended to the ground...impact.....

Oh well, I learned..... replace the cheap plastic clevises with good ones.................

Happy flying all,
Dennis

njl

Glad you didn't have too much damage. I learned the same lesson on Tuesday too! I was flying my replacement Home Run. I was just setting it up. The maiden flight was a bit hairy as it wanted to dive and bank right all the time. Once I got that trimmed out OK, it calmed down and was fine.

The next two flights went OK and I was pleased that the plane didn't have any funny trim characteristics unlike the previous one.

On my forth flight of the day I was flying towards my self when suddenly the left aileron started to flutter big time. I slowed it right down and the fluttering stopped. I still had some control but knew something was wrong and as it wasn't handling quite right. I managed to do a circuit at just above stall speed and landed it safely. Once on the ground I could see what was wrong. The plastic clevis had let go even though I had a bit of fuel hose acting as a keeper. The control rod was just hanging on the servo.

The metal replacement clevises arrived in the post yesterday! Why do they sell kits with bits in them that are just not up to the job.

Chunkylad

Why do they sell kits with bits in them that are just not up to the job.

This boils down to economics, I'm afraid. ARF planes are made to a price to compete in the marketplace.

If you buy an ARF plane that comes with cheap clevises and hardware, you are tempted to use it. This will get the model into the air in the shortest time (after all, isn't that why you bought an ARF kit instead of building in the first place?), but maybe not for the longest time!!:cry:

Put yourself into the shoes of someone who has spent umpteen hundred hours scratch building a scale masterpiece, or even a trad. balsa/ply kit; and ask yourself what hardware are you going to fit?

It should NOT be like this, but it is .

You should look hard at ALL the components you choose to put into your models; AND keep checking them with thorough pre-flight inspections.

I have had a "good" brand name clevise let go on the elevator of an Ugly Stik, with the inevitable consequences. I have since "upgraded" my pre-flights to check for such weaknesses. You may uncover only one fault in a blue moon, but it's better than taking your plane home in a bin bag.

Good luck, and enjoy your flying

Cheers,

Chunkylad

ajvpb

My Feedback: (3)

DONT USE THOSE PLASTIC POS CLEVISES. I dont really like using zbend either. What I use are Du-Bro Kwik Klips. Super heavy duty plastic, which I know sounds bad, but it is quite strong, and a metal pin with a retaining clip. Do this on one end, then solder on a threaded coupler to the other. Even if I don't use a threaded coupler, I still always use Kwik Klips on every surface.

njl

Thanks for the advise ChunkyLad, I'll add a physical clevise inspection to my pre-flight checks in future. I guess I was very lucky in that it was only an aileron clevise that let go and not the elevator, otherwise it would have been taken home in a bin bag, thats for sure.

Nick

Montague

You know, there is a good chance that the flutter started before the pin sheared, and the flutter caused the clevis to fail. I've flown in to sever aileron flutter a couple of times with some bad results, including stripping out the aileron servo. I was using all nylon clevises on that one too, and the servo gears failed before the clevises did.

I'm not saying the hardware that comes with many ARFs isn't junk, I know it is. And it's always a good idea to pre-flight as mentioned above.

Chunkylad

Without getting into cause/effect debate about flutter (or whatever the aerodynamicists choose to call it), it's one of the reasons we keep or control runs as short as poss. and slop free.

"Flutter" hugely increases loadings on control surfaces, causing such failures as mentioned by Montague.

I recently built a Great Planes G202 kit. In their manual, they stress the importance of using a small pitch prop (6 inches max.) to minimise the risk of flutter. Small pitch will limit the plane's max. velocity

It's something we have to be aware of, and do our best to minimise by using quality fittings and by keeping slop/freeplay out of control runs. I don't mean that we need to necessarily over-engineer things, just be aware of the forces acting on our models and go from there.

I have to backpeddle a bit though. I said ARFs were built to a price, I meant to say that many (not ALL) ARFs were made that way. I think the people at ZN Line etc might say something about that!

Have fun.

Chunkylad

Dmacsimum

There was no slop at all, what so ever in the Elevator/Push rod assembly so flutter was not an issue. The push rod was stick, and rod which was strong, and stiff.

The control clevis, and elevator horn was being pushed to the limits for I was consistently full throttle, and using down speed to really get her going in certain maneuvers.

The ARF plane is a World Model's 20 Super Frontier in which I had installed a MVVS .28 W/mini pipe. I was using a Master Airscrew 9x4 prop. I had the elevator trim at MAX and the plane would still climb at full throttle......grin. A lot of down elevator was being used to attempt to trim, but with the speed, and the flat bottom foil......lift was incredible....
Dennis

Chunkylad

Yep, cr***y hardware can ruin your day.

Sounds like you may have other issues to deal with. ie being unable to trim out that climb on full throttle. May have been a thrustline issue, or possibly cg?

Anyway, that's all academic now.

Better luck with your next model.

Chunkylad

Dmacsimum

CG was in the limits suggested by the manufacture. If at all, it was a little nose heavy. The MVVS is built fairly beafy, and the mini pipe could be felt at full throttle for the plane would roll on the pipe side due to drag....

I could have her airborn in about 33 feet and at a pretty steap angle of attack. Sure do like the MVVS .28, starts easy, and has power on the pipe.
Dennis