Tony Gag Jr.

My Feedback: (124)

I have a question for all the experts out there. I am putting together a H9 Hellcat and I have read that some people are having a problem with the horizontal stab trailing edge being weak and failing during flight. Here is my attempt at a fix to that problem and I want to see if you guys think it is sufficient. The first two pics are the stock h-stab, the trailing edge is a hardwood, maybe basswood and there is a doubler that I think is hard balsa. The last two pics are my fix. I was planning on gluing 4 pieces of 1/4" plywood(I just put in 1 piece of plywood so far for the picture) to the doubler between each rib. Please let me know what you think. Fred, if you read this, your opinion will be VERY much appreciated!!!

Here is link with a picture of a h-stab that failed on the Hellcat:
http://www.rcuniverse.com/forum/m_43...hellcat/tm.htm


Thanks,
Tony Gagliardi Jr.

alanc

all you are doing here is creating a definite sheer point, all that is needed, is a triangular corner gusset, from material fractionaly thinner than the stab material, ensure that the grain flows at 45 degrees, MOST important this, also, it would do no harm to fit gussets in the corners of the leading edge, where the break occurred, i suspect the break started at the TE, and the LE suffered as a result, glue the gusset in with what we call aliphatic resin, or white PVA glue, NOT cyno,
hope this helps.

Tony Gag Jr.

My Feedback: (124)

Alan,
Thanks for the help. Your idea is actually the same idea that CorsairJock used on his h-stab. His fix is pictured on the link that I posted. Maybe I will just go that route instead of my fix. The grain of the gussets should be 45 degrees to what? Also, what is the reason for not using CA?

Thanks,
Tony

Check6

My Feedback: (427)

Hi Tony,
I have to agree with Alan, just putting the ply piece there is changing where the next stress crack would appear. I would do one of two things besides the gussets. I would sheet top and bottom of stab, problem solved or glue in a 1/32 piece of ply or carbon fiber the length of the trailing edge to stiffen up things. My 81 in. Dynaflite Spitfire had the same open area stab and I elected to sheet it with 1/16 in. balsa top and bottom. Stab was rock solid. Do you remember that Spit??
Later,
Fred

Tony Gag Jr.

My Feedback: (124)

Fred,
Yes I do remember that Spit, it had the OS 1.08 in it and flew great. If I decide to glue in the 1/32 ply or carbon fiber, does that go between all the ribs or on the top and bottom of the trailing edge? Sheeting is probably the easiest and best thing to do but the only problem is since this is an ARF the h-stab has to slide in the opening and if I add the sheeting I am not sure it would fit.

Thanks,
Tony Jr.

proptop

My Feedback: (8)

After reading of stab problems, I used 1/32 ply and sheeted the entire underside of the stab on my H9 P-40...did it after stab installation in the fuselage. (used Titebond 2 )

Check6

My Feedback: (427)

Hi Tony,
You could sheet the entire stab first then relieve the stab opening with a razor saw 1/16 of an inch on the top and bottom of your fuse. You also can install the stab first and sheet up to the fuse. It looks like you have substantial balsa in the middle of the stab. If you want to use the 1/32 ply and carbon fiber cut a piece the width of the face of the trailing edge and the entire length of the stab . Glue it to the face of the trailing edge not on top or bottom. This will make the trailing edge like a laminated beam, very strong with little weight. Let me know how you make out.
Fred

alanc

fix is up to you, BUT, fit sheet, more nose weight, and surgery to open out the fuzz slot, risking getting the incidence angles cocked up, also getting at least a 1/8th additional thickness of taiplane, and you will have to fit sheet top and bottom, or the stress point will still be there, fitting carbon along the TE is a bit OTT, as the failure area is at the root, not the entire stab lenght,

just seen your message think of a 90 degree angle, draw across the corner of the angle at 45 degrees, this is the direction the grain needs to go, fit it with the grain vertical, or horizontal, and the gusset WILL fail, cyno i not used because it is a brittle glue, PVA will soak into the structure, and become part of the structure

alanc

please do not sheet up to the fuzz sides, this will create a shear point that could fail, the sheet will brace itself against the fuzz sides, top and bottom, in pos and neg G manouveres, this bracing will flex the fuzz, and could lead to failure, either sheet it complete, or not at all, even thin veneer, or 1/64 ply could be used, this would give torsional stess to both sideds, and minmal weight gain, IF you are tight with the adhesive,