RE: CMP Hellcat
 

You will still have to worry about elevator flutter.

RE: CMP Hellcat
 

Yep, Richard, you are so right! And is it ever destructive!
hookem

RE: CMP Hellcat
 

I was talking to one of the more experienced modelers at the board meeting last night about the flutter problem and he talked about the normal stuff, changing to 4-40 rods, using carbon fiber rods and putting in braces for the rods. He also talked about counterweights on the elevators.

Richard, did you try counterweights on the elevator?

When I mentioned the whole horizontal stabilizer possibly fluttering he thought pinning the stabilizer was a good idea. He also mentioned that most chinese ARF fiberglass fuse's are made with a polyester resin and that 30 min epoxy doesn't bond well with it and speculated maybe that possibly an improper bond might be the problem. Having the tube through the stabilizer would maybe hold it together but allow the whole thing to flutter. He says the polyester smells different when using a dremel on it.

Personally I wasn't aware that there were different kinds of fiberglass resin... and who has polyester resin...

Anyone have any thoughts on this theory?

RE: CMP Hellcat
 

Yes Big Bird. That is correct. However, my situation was similar to Richard L. in that I had stab flutter. That fixed the problem.

I did use the wood dowels supplied with the kit, and didn't have a problem with elevator flutter. Areyou sure it is elevator flutter and the total stab isn't fluttering... since stab flutter seems to be a common problem with this aircraft. Especially on hot days when the fiberglass towards the rear of the fuselage becomes more flexible.

Oriole

RE: CMP Hellcat
 

Some how I got horizontal stabilizer instead of vertical out of the previous posts, I don't have either problem as I haven't put the thing together yet. I'm just trying to "get the facts" before I do, so I don't have the problems that have surfaced. Especially the fatal ones ;)

Some where towards the begining of the thread Richard L said he had flown his "Tons of times in the past couple of years" and reported no problems, till later. Does it weaken over time, I wonder. Would filling it with expanding foam would do any good or just add too much weight? Seems like it might stiffen it up.

RE: CMP Hellcat
 

just reading thru this post with much interest since I recently purchased a Hellcat and have yet to build it. Bigbird, I have used the expansion foam on other projects with much success. I was thinking of using it in the rear of this plane even before reading your post. It doesn't add much weight at all but care must be taken not to add too much because the expansion can actually destroy your airframe. There are different kinds, some that expand more than others also.

RE: CMP Hellcat
 

That is correct. I flew mine tons of times, but not at full throttle. Most of the time when I went to full throttle with the OS 120 four stroke in the nose, the rear stab would flutter. That was after the plane had around 20-30 flights. I do have a second Hellcat brand new in the box and will do things differently next time.

RE: CMP Hellcat
 

If you don't mind me asking, what specifically will you do differently Richard? I'm looking for the best way to avoid the flutter demon and any help is appreciated.

RE: CMP Hellcat
 

1) Reinforce the area where each rear stab half is glued into, as mentioned above.
2) Use a single internal joiner wire for the elevator and either a stiff carbon fiber rod going to it or a servo mounted in the tail close to the elevator.
3) If I use a carbon fiber rod with the elevator servo mounted up front in the servo tray, then I would mount the servo longitudinally (parallel to the fuse) to reduce servo rocking as the elevator is being deflected.
4) If I don't use a carbon rod for the elevator, then I could use a metal pushrod inside a nylon tube and anchor the tube to wooden cross braces placed across several formers inside the fuse.

RE: CMP Hellcat
 

Has anyone contacted the importer/distributor? If so were they any help?

RE: CMP Hellcat
 

Richard, if I may add to your notes:
Control surface flutter is quite often encountered and is not the flutter of it's mating aerodynamic appendage ie it is of the elevator and not the horizontal stab. Both can ( and often will) flutter and requite different resolutions. Beefing up the aft structure per the preceeding threads should add significant help to stiffen the horizontal stab area. That being said, now about the elevator whose flutter can drive the entire mess! Here are typical causes of flutter, with some fix/prevention suggestions:
excessive air speed---fly slower
excessive gap between the elevator and the horizontal stab---seal the gap,easily done
flexible push rods---choose stiffer design
wrong control horn/push rod attachment---remember-long on the surface, short at the servo
weak servo selected--- go to a proper inch/ounce servo
In my own experience, items 1, 2, and 4 have at one time or another bitten me in the butt and have helped my learning curve. BTW, the above apply equally to the wing/aileron flutter.
I wish y'all the best and a Merry Christmas!!!
hookem

RE: CMP Hellcat
 

Thanks and Merry Christmas to you also.

bigbird

RE: CMP Hellcat
 

Heres the motor I am trying to put in my hellcat !

RE: CMP Hellcat
 

You need to get one of the cut-down flywheel's so it will fit in the cowl.

RE: CMP Hellcat
 

Started on my panel line and rivet job. What a chore! But the result is quite rewarding.

RE: CMP Hellcat
 

For all having a problem with elev. flutter.

I did the following:

I Have the older model with wood push rods.
I used 4-40 wire in place of those supplied.
This reduced the flutter but did not stop it.
I then added a 1/8 ply cross brace on the first former behind the wing saddle. I drilled a hole
in the brace about 1/16 larger than the wood push rod. this stopped the push rod from flexing.
I have since flown the F6F six times with no flutter. I am using a MAGNUM 120 AT FULL THROTTLE.

RE: CMP Hellcat
 

how'd you create that look on the rivets and what would you suggest how to do this for a begginer?

thanks dave trimmer

RE: CMP Hellcat
 

I flew mine again today. I haven't had any flutter problems, and I tend to fly at full throttle most of the time. Magnum 120 for power, spins a 15x6 prop. Hopefully when it gets more time on it, will swing a 15x8. But I've never had any flutter concerns with the plane.

Andy

RE: CMP Hellcat
 

Just bought the Fly Models Hellcat from AK models which I beleive is the same as the CMP version. I was thinking of putting a Super Tiger 90 in mine or maybe a Magnum 120 4 stroke. How does yours fly with the 90 Super Tiger? [email protected]

RE: CMP Hellcat
 

Thinking about putting a Super Tiger 90 - 2 stroke in mine. How does your's fly with the Super Tiger?

RE: CMP Hellcat
 

This is why you are not having any flutter problem. A 15x6 prop won't provide you with enough speed to test out that rear stab/elevator.

RE: CMP Hellcat
 

A friend of mine flies his with a Super Tigre 90 with pitts muffler and his does well.Not unlimited vertical mind you, but flies in a scale manor. He has the fixed gear on his - no retracts so his weighs a little less.
John

RE: CMP Hellcat
 

Hello Richard,
I ordered last week a CMP Hellcat from AK-Models.I will get some retracts for this kit and the engine should be a 4-stroke.
Do you think a ASP 120 with a Nylon 15x8 prop is good enough or should it be a bigger engine?

Thanks and a very Xmas at all

Klaus Stephan

RE: CMP Hellcat
 

Klaus, ASP 120 with 15x8 prop is good enough.

RE: CMP Hellcat
 

Thanks for the info John! I am looking to go with the retracts (added weight) so I might move the Super Tiger G90 to my Extra and put the Magnum 120 in my Hellcat.