[Guest]

This weekend I was very lucky with my Kingcat.
I was flying around hard and fast as usual when Dean W yelled out from the crowd "slow it down your wings are flexing bigtime!"
So I pulled the throttle back and landed, we checked the wings and all looked fine. I think that was warning number one....

The next 5 flights I kept the turns wider (I have 44lbs of blow on the Kingcat) and slowed it down a bit. On the landing of the 5th flight, as I taxi'd back I noticed my main gear had twisted out a bit, no big deal I figured, I'll just straighten them.

Now, before every flight, I check my control surfaces to make sure everything is tight. My ailerons have had just under 1/16" of play for a long time now, but I chalked that up to a little linkage slop, maybe gear train slop, who knows, pretty rare to find surfaces that don't have a little slop even with brand new servo's.

Well, while the jet was upside down, I grabbed the left aileron, it was moving almost 3/16" of an inch!!!
So I pulled off the servo hatch cover and found that it was the control arm moving on the servo output shaft! I did not build this airplane, it had the grey dubro servo horns on all the servo's except the elevators (changed those when I put new servo's in with the bigger motor). I decided to check ALL the horns after that and ALL the horns except the elevators were loose on the output shafts. I have never liked the dubro horns, but they had been working so I foolishly left them.
When I pulled off the right flap servo cover, I also found that one of the 90 degree flap servo mounts that BVM supplies had broken right at the 90 degree bend. The servo was able to move in the pocket, I think the ONLY thing that kept it from failing totally was it was the rear mount so when there was pressure on the flap in the down position it was still pushing against the flap mount.

Needless to say, I decided to pack up for the weekend and give the airplane a thorough check over. I do preflight things, but this is stuff that I missed, just wiggling the surfaces I guess isn't enough.

Anyway, she gave me all the warning signs, I'm glad I listened! No more dubro arm's for me!

[SpaceCowboy]

Lots of learning material there.

Thanks for sharing.

.

[atiger]

That is very lucky Jeremy, seems Dean W. made a great call.

Now I will check over my jets ....... again.

Thanks for sharing

Allan

[powerjets]

[QUOTE=LGM Graphix;721165]This weekend I was very lucky with my Kingcat.
I was flying around hard and fast as usual when Dean W yelled out from the crowd "slow it down your wings are flexing bigtime!"
So I pulled the throttle back and landed, we checked the wings and all looked fine. I think that was warning number one....

So answer me this question, you're not gonne like it.Yes, c'mon guys start bashing me....
Why was Dean yelling at you to slow down ?

[reo]

That does it....the used Elan I purchased used last year has some Dubro arms on it and they're coming off today.....never did like plastic arms on any high performance airframe, that's what metal arms were made for.....Ron

[Guest]

[QUOTE=powerjets;721195]

Originally Posted by LGM Graphix

This weekend I was very lucky with my Kingcat.
I was flying around hard and fast as usual when Dean W yelled out from the crowd "slow it down your wings are flexing bigtime!"
So I pulled the throttle back and landed, we checked the wings and all looked fine. I think that was warning number one....

So answer me this question, you're not gonne like it.Yes, c'mon guys start bashing me....
Why was Dean yelling at you to slow down ?

Um, I thought it was pretty clear, because my wings appeared to be flexing.
What does that have to do with anything? We're flying at a wide open location, the airplanes get checked over between flights. Guess how many Kingcats I've seen fail in flight, none, but I've seen other jets at well below 200mph come apart in flight. Don't get into your high and mighty don't fly so fast BS, there are plenty of airplanes out there that will exceed 200mph, maybe we should all just go back to flying parkfliers..... oh wait, my vapor wings flex when I turn too, I guess we should quit flying altogether right??

Ever seen heli blades flex in flight?

[Angus]

That's Dean's old Kingcat didn't he build it?

AM

[powerjets]

[QUOTE=LGM Graphix;721216]

Originally Posted by powerjets

Um, I thought it was pretty clear, because my wings appeared to be flexing.
What does that have to do with anything? We're flying at a wide open location, the airplanes get checked over between flights. Guess how many Kingcats I've seen fail in flight, none, but I've seen other jets at well below 200mph come apart in flight. Don't get into your high and mighty don't fly so fast BS, there are plenty of airplanes out there that will exceed 200mph, maybe we should all just go back to flying parkfliers..... oh wait, my vapor wings flex when I turn too, I guess we should quit flying altogether right??

Ever seen heli blades flex in flight?

Thanks, that was good !

[AJCoholic]

jeremy, i am unclear of one thing, were the wings really flexing or was it something to do with the loose servo arms and mount

[Guest]

Originally Posted by Angus

That's Dean's old Kingcat didn't he build it?

AM

Yes he did, and he did a fantastic job. Back when he built it there hadn't been much negative said about the Dubro arms and I certainly don't blame him for using them. I take responsibility for not changing them sooner, but it was all part of that "if it ain't broke don't fix it" deal. Like most things in life, it's pretty rare that there is an instant catastrophic failure, if you check things over, especially after you see ANY change in flight, or otherwise, you'll probably find it before something really bad happens.
Dean did an awesome job of the build and install on this airplane, that's a huge part of why it does stay together at high speed.
I was probably a little bit lax in my preflights, or maybe those arms really did develop that much extra slop after that last flight (when something starts to wear, it doesn't take long to wear to the point of failure after that) but I caught it thanks to the warning signs, and I posted about it to remind others to check all of those things especially when you get a warning sign.

I don't like metal arms at all, I don't like using the ball links on them, but I have never had a JR heavy duty plastic arm wear on the spline or fail, so I will be using those from now on. I think the problem with the dubro arms is they never really fit properly to begin with. I remember buying a pack of them when I built my Exocet years ago, I didn't use them in the end because of how they fit on the output shafts.

So again, yes, Dean built the airplane, and did an exceptional job, the airplane is 6 years old and has 125 flights on it now, approximately 25 when Dean owned it, and around 100 since I've had it, 51 of which were made with a 44lb thrust engine. I don't know too many people that check over the servo horn itself, they check the linkage, maybe the control horn on the surface, but how many actually pull the servo's to check the horns for wear.
In 25 years of flying, I have never though to replace a servo horn unless it was the white nylon ones that were turning yellow, and only once in my flying life have I had horns do that.
However, it will now be something that is on my winter maintenance schedule all the time.

The Carbon servo mount on the other hand is something I've never seen break without a big crash preceding it.