HobbyKing.com New Products Flash Sale
Reply
Thread Tools
Old Dec 10, 2005, 02:13 PM
Team Cobra!!! Ssssssss!
lmopar69's Avatar
United States, NE, Doniphan
Joined Feb 2005
7,853 Posts
The 7' twin is dead.. flutter, flutter, flutter --- BANG! RIP

Well, maiden flight went great, until that fatal moment! Wish I woulda had video! Nice smooth takeoff, couple laps to get it trimmed perfect. Man it flew smooth with lots of control authority. Decent power with the S400 DD with 5x5 props. Top speed maybe 30ish, not really fast.

Then the sequence of events that followed, well, it looked cool at least... did an aileron roll, pretty quick roll too for nearly 7' wing span. Decided to try a roll followed by a loop... ugly, ugly, ugly. Did the roll and into a dive, pulled back and FLUTTER, FLUTTER, FLUTTER... BANG! Ailerons and rudder fluttering like mad all the way down from about 150'. Tried everything to save it in that 5 seconds too. Oh well, back to the drawing board.

Too bad, it was a neat plane. Wonder whats next.
lmopar69 is offline Find More Posts by lmopar69
Reply With Quote
Sign up now
to remove ads between posts
Old Dec 10, 2005, 02:41 PM
United Kingdom, Leighton Buzzard
Joined Sep 2004
548 Posts
Wow, that sucks!

But, you can't stop there, you have to re-build it and get her flying right!
littleport2003 is offline Find More Posts by littleport2003
Reply With Quote
Old Dec 10, 2005, 03:13 PM
Balsa is for doll houses
Skrogg's Avatar
Texas, San Antonio
Joined Aug 2004
1,647 Posts
HAHAHHAHAHAHAHHAHA
wait, um sorry for the loss!
NO VIDEO! NO VIDEO?
Skrogg is offline Find More Posts by Skrogg
RCG Plus Member
Latest blog entry: Babymetal!
Reply With Quote
Old Dec 10, 2005, 03:17 PM
An itch?. Scratch build.
eflightray's Avatar
South Wales U.K.
Joined Mar 2003
13,399 Posts
Great concept, nice build, good looking model.

The flaw is one that many people fail on, myself included, not designing to withstand the intended flight envelope. I assume you intended to do aerobatics.

If we intend to do aerobatics, we need to consider the stresses involved not just pulling 'g', but speed as well. I have seen plenty of light weight models, gliders especially, go into a self destruct when diving. Flutter is a very difficult thing to design out for light weights.(edit - and big spans).

I know that if I try to bring my electric glider down too fast the wings will start to flutter, I am pushing it outside it's design envelope.
I now like to scratch build semi scale models, and they are build to withstand flying, but only gentle non-aerobatic flying.

Flutter is a nasty one that can take you by surprise, hope you can rebuild the model, it doesn't look too bad from the pictures. Just remember that next time it flys, no aerobatics.
eflightray is online now Find More Posts by eflightray
Reply With Quote
Old Dec 10, 2005, 04:32 PM
Ascended Master
Sparky Paul's Avatar
Palmdale, CA
Joined Oct 2000
13,468 Posts
6 reasons:
1) elevator chord WAY too much!
2) elevator pushrod insufficiently stiff
3) booms insufficiently stiff
4) Aileron chord WAY too much
5) Aileron pushrods not stiff enough
6) Wing way too flexible due to 4)
Sparky Paul is online now Find More Posts by Sparky Paul
Reply With Quote
Old Dec 10, 2005, 05:39 PM
Team Cobra!!! Ssssssss!
lmopar69's Avatar
United States, NE, Doniphan
Joined Feb 2005
7,853 Posts
Quote:
Originally Posted by Skrogg
HAHAHHAHAHAHAHHAHA
wait, um sorry for the loss!
NO VIDEO! NO VIDEO?

Thanks for the words of encouragement there Skrogg! You shoulda seen it, it was cool! And this after having to wait 3 days to fly it because I had to order my props and adapters. The suspense KILLED ME!!

Yeah, I know the ailerons and elevator were too big... but they were SUPPOSED to be too big, the idea was supposed to be over kill on control authority. It worked, cuz man it was quick and sensitive, but they ailerons/elevator just werent stiff enough. I knew it would be a problem, and figured it would flutter, but didnt think it would be THAT bad! The intent was to adjust as necessary until I got it all to work right. Guess that wont be happening!

I would rebuild it, but, there just is too much damage to it to really worry about it. So, I will pull all the electronics, take all my carbon fiber out and build something else.

Any ideas on what I should do with either one or two DD S400s? Im thinkin fan fold pusher jet type thingy.
lmopar69 is offline Find More Posts by lmopar69
Reply With Quote
Old Dec 10, 2005, 06:26 PM
Registered User
Kilsyth, Victoria, Australia
Joined Oct 2003
1,970 Posts
Sorry to see that you had to find out the hard way but can't understand you saying that you knew you'd get flutter. Once it starts it does not normally go away as plenty of full size pilots have found out. If you are really lucky and can slow the aircraft the moment it starts - sometimes hard to recognise - you might get out of the speed range where it occurs but it's unlikely. Frankly if I thought flutter could be a problem on a specific model before take off the flight would not take place. The reason for that being that once flutter on any surface takes place but it seems to usually be ailerons on the aircraft I've seen affected you are going to lose control and hence have a potentially dangerous situation.
David Hipperson is offline Find More Posts by David Hipperson
Reply With Quote
Old Dec 10, 2005, 06:29 PM
Team Cobra!!! Ssssssss!
lmopar69's Avatar
United States, NE, Doniphan
Joined Feb 2005
7,853 Posts
lol Yeah, common sense would say to fix it before its a problem huh. Never claimed to have much of that stuff!

I have had other planes start fluttering and was able to slow it down and recover, this thing, nope, it was gone. Besides, even after the first 3 min of flight, I knew I wouldnt be keeping it as it was long. Didnt do what I was hoping it would. So, a crash was just a nice way to put it out of its misery.
lmopar69 is offline Find More Posts by lmopar69
Reply With Quote
Old Dec 10, 2005, 10:50 PM
I broke my kerpellor.
Artemetra's Avatar
Salt Lake City
Joined Sep 2004
2,430 Posts
Cool, really neat one. What next? It looks way worth rebuilding and beefing it up! Maybe instead of carbon booms, some kind of ladder frame booms or something.

Really nice, thanks for the posts and stuff. I hope you do it some more. It's great to have a unique plane. No one else has one of those, you can be sure!
Artemetra is offline Find More Posts by Artemetra
Reply With Quote
Old Dec 10, 2005, 10:59 PM
Resistered Loser
bicmedic's Avatar
United States, IL, Paris
Joined Jul 2005
308 Posts
Why give up?? That is a REALLY cool design, just needs reinforcement.
bicmedic is offline Find More Posts by bicmedic
Reply With Quote
Old Dec 10, 2005, 11:00 PM
Team Cobra!!! Ssssssss!
lmopar69's Avatar
United States, NE, Doniphan
Joined Feb 2005
7,853 Posts
Yeah, for sure no one else has one like that! It wasnt really worth fixin. Too much damage. So, its been gutted now, and Im about halfway through my next "project". This one is a pusher jet lookin thing. About 32" span. Hope it flies better than that big twin did, well, it flew fine, just not quite "stiff" enough in the control surfaces.

Pics will follow in new thread sometime soon.

Laien
lmopar69 is offline Find More Posts by lmopar69
Reply With Quote
Old Dec 11, 2005, 08:12 AM
Baptised Heathen
batman's Avatar
Bundaberg, Qld, Australia
Joined Jun 2002
1,365 Posts
I tgink Sparky Paul is right. Too much elevator and aiteron chord. Just reduce these in size and you should correct most of your problems.
batman is offline Find More Posts by batman
Reply With Quote
Reply


Thread Tools

Similar Threads
Category Thread Thread Starter Forum Replies Last Post
Help! Eclipse 7 semi dead El Pe Radios 6 Feb 14, 2006 01:55 PM
Question Eclipse 7 semi dead El Pe Hitec/Multiplex USA 4 Feb 11, 2006 08:29 AM
Stephens Akro & D&B 3.7 Twin WLJ Aircraft - Fuel - Airplanes (FS/W) 0 Nov 26, 2003 09:52 PM
H M M Crossfire aileron flutter E SOARER Sport Planes 7 Jul 18, 2001 01:14 PM
Flutter in my zagi x jimbarstow Foamies (Kits) 2 May 14, 2001 03:24 PM