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Stab Saddle Fillet?

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Old 03-20-2019, 04:56 AM
  #1  
hookedonrc
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Default Stab Saddle Fillet?

I am in the process of assembling and modifying the Top Flite Cessna 182. I am taking my time so as to build it to scale as closely as possible. I have the stab in place and it is securely epoxied, but the large hole that the stab fits in does not conform to the stab shape. This has left a very visible gab between the stab surface and the fuse on both top and bottom. I am trying to decide how to fill this space without making it look as if it is an afterthought. (even though it kind of is) The 182 is a white aircraft and is such that I have thought about using white silicone sealer in the stab smoothly applied to fill the gab. Regular balsa filler probably won't work because it would be off color and too brittle to keep from vibrating and cracking. I read a thread on here about using colored epoxy and I guess i could find some white pigment to mix with it for color match. Or even just using DAP since its white color is almost identical to the covering tint. And it would be flexible enough to withstand the vibration without cracking and falling out.

Any better tips would be welcome. I have done a search and most of the threads are about gaps in balsa before the covering has been applied.
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Old 03-20-2019, 07:11 AM
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Steve Collins
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White lightweight spackling compound from the hardware store.
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Old 03-20-2019, 08:31 AM
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I did think about that, but am concerned that it can be brittle and will crack and fall out.
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Old 03-20-2019, 08:56 AM
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I have a Great Planes Mustang ARF that I used RTV silicone as a fillet between the stab and fuse. The Monokote was dark silver and the RTV was Permatex Ultra Gray. I ran a careful bead and the end result looked very good. I think a bead of white RTV on yours would look good, and it will provide a strong yet very pliable reinforcement.
I also filleted between the vert stab and fuse and the ducting underneath. When you cut the right size opening in the nozzle provided with the tube, run the bead just slightly ahead, with the nozzle tilted back from the direction of travel, where it comes out of the tip so you end up with a slightly concave "fillet"
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Old 03-20-2019, 10:19 AM
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Originally Posted by Steve Collins View Post
White lightweight spackling compound from the hardware store.
Add me to that list.
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Old 03-20-2019, 01:21 PM
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I have done a little reading and the RTV sounds like what I need. It can also be used to make a gasket. I need one on the tail cone where there is a gap that needs one.

Thanks all.
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Old 03-21-2019, 05:37 AM
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I have used RTV in a similar situation for a fillet on fins for a large rocket. Its flexibility will allow the fillet to take stress and vibration well.
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Old 03-21-2019, 11:20 PM
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Joe Nagy
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Hi Don;

I would suggest a simple to make filler: slow cure epoxy, mixed thoroughly, then mix in balsa sanding dust to a consistancy of peanut butter; then don on a rubber glove, and smear on gently as needed, smoothing out with epoxy thinner. A little bit will go a long ways. I have used this method for about 50 years now, and kind'a learned it from the old Hobby Poxy ads and methods described by 'John Epoxy' actually the late Bev Smith. Sadly Hobby Poxy Products are no more, but thank goodness I stockpiled a stash, that should last me a long time. But current slow cure epoxys are around [ at least 30 minute or mor cure time] leaves you lots of time to mix thoroughly, and balsa dust is real easy to make....right old time builders'. Try my old timers' method, I think you will like it, best regards from Wickenburg, Arizona,

Joe Nagy.
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Old 03-22-2019, 04:27 AM
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Joe, if I were filling a gap in the balsa, I would be more likely to try your method or use the spackling process. In this case, there is covering on both pieces and I want to avoid removing and recovering. I am planning to use the RTV if I can find it in white to match the color already in place.
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Old 03-22-2019, 06:47 AM
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Steve Collins
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How about a white epoxy?

https://www.amazon.com/J-B-Weld-5017...ag=googhydr-20
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Old 03-22-2019, 03:32 PM
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Thanks Steve, I already have 2 tubes of white RTV silicone by JB Weld on their way. Rather than continue to go from store to store, I just used Amazon and it took 2 minutes. I am still in the assembly process for the 182, so the delay in delivery is not an issue.
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Old 03-23-2019, 01:48 PM
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RTV silicone works great lasts forever without breaking down.
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Old 03-24-2019, 03:06 AM
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Originally Posted by Steve Collins View Post
White lightweight spackling compound from the hardware store.
Another vote for spackling.
Epoxy adds too much weight. I wouldn't use epoxy to glue a tail together to begin with. And no! I have not had any tails fall off in 60 plus years of RC. Not from glue failure anyway.
RTV also adds more weight than the Spackle. But at least you have a cowl with plenty of room for lead to counter the tail. But if the stab is already firmly attached, RTV will do nothing for vibration.
Mixing balsa dust in epoxy can work but you can also mix it in the various wood (white) glues.

And regardless what you use, why can't you paint it to match the covering? I take it you've used one of the plastic heat shrink coverings on it.

Last edited by Appowner; 03-24-2019 at 03:10 AM.
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Old 03-24-2019, 04:07 AM
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I don't think the weight difference between epoxy, spackling, and the RTV silicone will make much difference on a 13 lb. plane. The gaps are small, and the fillets will be small and are for appearance only.
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Old 03-25-2019, 06:25 AM
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Get some slow setting epoxy and a bottle of microballoons. Mix up about 1/4 ounce of the epoxy then add a spoonful or two of microballoons until the mixture is about as thick as oatmeal. Trowel the mixture into the joint then wet your finger with a little water and swipe it to shape into a nice fillet. You can take multiple swipes but you have to clean your finger off each time then redip in water. When it dries the next day it is easily sanded. Most microballoons I have used are white so the fillet will be white as well. It is also pretty strong. NO way I would do it any other way. You can google microballoons and find them easily. Sig has them if no one else.

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Old 03-25-2019, 01:53 PM
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I've had some luck using light spackle and then soaking it with thin CA to harden. But, I prefer the epoxy method that carlgrover noted. Or doing the same with polyester resin, if one can find it any more.
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Old 03-25-2019, 04:00 PM
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Just got the white JB Weld RTV silicone, cut the tip to the approximate size of the gap and squeezed into the gap. Then I used my finger to smooth it along the gap and it came out absolutely perfect. And, the white matched the white of the covering. If it holds up and does not crack I will use it again. Thanks for all the input everyone.
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