RE: CMP Hellcat
 

Hi, Hookie
Thanks for sharing your Hellcat with us. It's a great looking plane you have there. I am confused with your comment of "horizontal failure" as well. On my Hellcat I couldn't find anything weak on the horizontal stab. Perhaps you could eleborate a little more, like bigbird already mentioned.
Bigbird, try to get "Helmsman Spar Urethan". It is a "MinWax" product. It comes in gloss, semi gloss and satin sheens. Sold at Lowe's or Home Depot. If you don't like the "rattle" cans it also comes in small cans. This is what I am going to use on my Cat.

RE: CMP Hellcat
 

I have started to put together Luke's cockpit for the Hellcat. In the package of small assorted parts there is a small rectangular piece that's blue. Not sure what this is for. Anybody have any ideas?

RE: CMP Hellcat
 

Pull the blue plastic off and use the template sheet with the stick and other things. It's at the bottom, it says "Template for Gunsight glass. Cut from thin clear plastic sheet."

RE: CMP Hellcat
 

For anyone who has used the Sierra retracts, can you tell me if this is a missing screw or not. (see pictures) Both retracts have these threaded holes on both side with no screw in it...

Do you know if this product can be thinned for airbrush use?

RE: CMP Hellcat
 

Bigbird007 Mine are the same way.

Randy

RE: CMP Hellcat
 

Hi Randy,

Thanks, I thought they were probably right but wanted to check.

bigbird

RE: CMP Hellcat
 

Has anyone had a problem with elevator flutter ? If so what did you do about it?

RE: CMP Hellcat
 

bigbird,
this Polyurethan can be thinned with regular paint thinner for airbrushing.

RE: CMP Hellcat
 

I had a problem with the whole rear stab fluttering.

RE: CMP Hellcat
 

Hi Richard, Virginian,
Very interesting, Richard. It was on my 5th take-off that my F6 met its demise! All checked out pre-flight, the usual wiggling and touching to have confidence that all was snug. Lift off was norman, then sudden flutter of the elevators followed by an abrupt dive to the ground.
All was reassembled post-crash and very carefully examined. Xmtr/receiver links were solid, all servos OTHER than elevator operated normally to xmtr command. Elevator servo gears were stripped, symptomatic of flutter. Elevator pushrods had been checked before-no undo slop or flexing.
Findings: Uncertain. Lots ruled out, little resolved. Very similar to war-time flutter crashes, especially of the Curtiss SB2c. I have had other meetings with the flutter devil -a Giant Sweet and Low had springy pushrods but I have long since avoided that problem. Perhaps the OS 1.08 overpowered the airframe, just don't know. I fly lots of different models, no problems like this.
Bumer!!
hookem

RE: CMP Hellcat
 

Hi, hookie,
Very interesting your story, indeed. Maybe it was one of those fatal crashes that you scratch your head over and over again and still don't find the answer you hoped for. I checked the ridgidity of my tail feathers and found no reason for concerns. The fiberglass fuse is strong and so are the horizontal stabs. My kit came with a couple of pretty stiff carbon tubings to be used as the pushrods. I definitely will use them since I feel they are more than adequate. The rudder is going to be on a pull-pull.

RE: CMP Hellcat
 

Hi Richard,

What, if anything did you do?

bigbird

RE: CMP Hellcat
 

I reinforced the inside of the aft fuselage at the areas where the stabs are attached to the fuse with epoxy and glass cloth, but that wasn't enough. I had the original first generation Hellcat, so maybe they have fixed the issue in the later batches.

RE: CMP Hellcat
 

Thanks Richard.
I found this thread after my first flight. My F6F must be old design, it has hardwood push rods.
Has anyone been able to solve the flutter problem?

RE: CMP Hellcat
 

See my post 1182 in this thread.

Oriole

RE: CMP Hellcat
 

So if I understand your fix, I could drill a hole right through the Fuse before installation of the horizontal stab and add another dowel not unlike the one that's already there?


Hal, with your major mods to the horizontal stab installation did you have any trouble with flutter?

bigbird

RE: CMP Hellcat
 

I dont think HalH has had a chance to fly his yet.

RE: CMP Hellcat
 

Thanks John, I hope someone figures this out before I get that far...

RE: CMP Hellcat
 

Im having a heck of a time with the stock pushrods. Altho I did upgrade to a 4-40 size rod on each end of the wood pushrod, they just dont work right. There is way too much flexing going on in the back of the fuse as well as towards the servos. Even if I brace the back part with some supports, its just flexing too much for my liking. I have the HD servos as well as the HD servo arms with a OS 120 4 banger (I havent flown the plane yet), but it is worrying me that Im gonna have flutter or play in the system due to my pushrod setup.
Anybody got any solutions?
Thank ya!!
John

RE: CMP Hellcat
 

Hi,

I'm not sure if the CMP Hellcat is constructed similarly to their Zero which I am building, but I had concerns on how the separate elevator halves were to be installed. On the Zero, the horizontal stabs attach to the fuse very securely with two aluminum tubes which connect one half through the fuse and into the other stab half. However, the actual elevator halves are totally separate (not joined together) and attach to the H. stab with 3 CA hinges. The elevator control rods just "float" in a small hole drilled through each side of the fuse and are then glued into each elevator half. I was worried that this did not have any support other than the small fuselage hole to pivot on, and would put undue stress on the elevator hinges. So I glued a small balsa stick inside the fuse across from each of the elevator pivot holes and then used two torque rod type setups with the rods in short plastic tubes to support and pivot the entire elevator assembly. (Similar to how aileron torque rods would be installed in a wing.) I also decided to use separate servos and carbon fiber rods to control each elevator half, as opposed to the single servo and wooden dowel "Y" rod setup described in the manual. I'm sure I am adding some unwanted weight to the tail with the brace and torque rods, but I feel these changes are much improved over the existing setups. I'm still completing the retracts and engine install, so I can't comment on how well this helps the actual flight characteristics.
If the construction on their Hellcat is similar I would think that this type of modification would greatly improve the rigidity of the elevators. See attached pics of the original manual and my modifications.
Hope this helps.

Regards,

RE: CMP Hellcat
 

for those who ordered from Raidentech, how long did it take for the UPS tracking to change from "Billing Information Received" to "Origin Scan"? thanks!

RE: CMP Hellcat
 

WYDAH,

I really like your idea for setting up your elevator on your Zero. I just think that you should of used hardwood for the supports though. I am going to copy your setup for another airplane but not use balsa for the supports. The "torque rod" approach for the tail section is fantastic when there is enough room or you install an access hatch.


I love these forums for the ideas!

RE: CMP Hellcat
 

Hi,

One word of caution regarding my setup shown in the last pic. I ended up replacing the ball links that were attached to the elevator ends of my setup. I found that they wanted to make the horns on the elevator torque rods turn on the threads since they essentially push/pull on the side of the horn. Once the horn turned on the threads, it resulted in an offset in the elevator halves. (Not a good thing!) I ended up replacing them with standard clevis' which will not allow them to turn on the threads since the pin of the clevis prevents it from rotating. I left the ball links on the servo end, but have the regular clevis on the elevator end and it seems to work fine now with no tendency to rotate on the threaded torque rods.

I don't have a pic of the replaced ends, but they are just regular 4-40 clevis.

Johnny,
Your probably right regarding the hardwood support as opposed to the balsa I used. I know on the Zero with it's very short nose that it tends to result in a very tail heavy condition, so I wanted to limit the amount of weight I was adding to the tail section. I figure there is still enough strength in the balsa stick to adequately support the torque rods. It just gives them a surface to mount to and allow even push/pull on the rods.

Later.

RE: CMP Hellcat
 

Thanks.....that makes total sence.

RE: CMP Hellcat
 

bigbird,
Here is what I did: I inserted a 3/8" carbon tubing into the alu tube, which stiffend it up significantly. I then glassed over the roots of both stab halves where they are glued to the fuse. That strenghtened the whole tail section without adding a lot of weight. I know I will not have to worry about flutter.