8KCAB Metal belly on Decathlon

[rjgritter]

Hi all,

Has anyone successfully installed a metal belly on a Decathlon? As I understand it, the kit is not officially approved for the 8KCAB, though it should physically work fine.

The trick is in getting it approved - my FSDO says the only viable route is to find someone who has already had it approved and use their approval as basis for mine.

Can anyone help out?

Thanks!

RJ

 

[Bartman]

RJ,

First of all, nice to see you back visiting the site and holy hell are you getting good at flying that 150 CS Decathlon!!!

Regarding the belly skins, have you spoken to Dale at the factory about another Decathlon with the metal belly? Maybe someone here has the info you need but I'd bet Dale has a pretty good idea if it's been done yet.

Bart

 

[Bob Turner]

Um - why? Unless you are crop dusting or bush flying, the fabric is lighter and better. Opinion. I fly a Cub with metal belly - 400# useful load. Too many heavy mods.

 

[Big Ed]

RJ,

First of all, nice to see you back visiting the site and holy hell are you getting good at flying that 150 CS Decathlon!!!

Regarding the belly skins, have you spoken to Dale at the factory about another Decathlon with the metal belly? Maybe someone here has the info you need but I'd bet Dale has a pretty good idea if it's been done yet.

Bart

Dale posted on the FB group that the metal belly is not an option for Decathlons. He did not explicitly say it has never been done, but that is somewhat implied.

 

[rjgritter]

Um - why? Unless you are crop dusting or bush flying, the fabric is lighter and better. Opinion. I fly a Cub with metal belly - 400# useful load. Too many heavy mods.

Flying airshow aerobatics and using smoke oil, the fabric belly needs extensive repairs almost annually. It's not well-enough supported to survive the turbult flow in that area. It's an unfortunate reality.

 

[Bartman]

RJ,

Could it be legally double covered like high performance biplane wings or put double tapes, 3" over the 2" or vice versa, to reinforce the area?

 

[Bob Turner]

I have seen those problems. There are cross members that can come loose, and then the fabric fails. Then, when gluing a patch, the original fabric is so oil soaked nothing will stick.

What we did was reinforce the formers, then stitch the patch on under the surface tape. The tapes will still pull loose, but it then becomes a simple repair.

I suppose for airshow work the increased weight will not be a factor. You could just do the area under the cockpit? Probably in "field approval" territory.

 

[Big Ed]

Flying airshow aerobatics and using smoke oil, the fabric belly needs extensive repairs almost annually. It's not well-enough supported to survive the turbult flow in that area. It's an unfortunate reality.

Both of my Decathlons had oil soaked belly fabric, and that was just from regular Sportsman acro. I agree, a potential weak point of the design.

If you cannot break the code on FAA approval of a metal belly, there might be some interim fixes to improve durability that could be justified as minor alterations. First and most obvious would be heavyweight fabric, extra tape, and extra coats of paint on the belly.

Beyond that, you might consider reinforcements to the area such as aluminum cross members spanning the stringers and longerons. There are already cross members on the stringer brackets at the end of the control tube and the bracket immediately aft of that. A similar piece under the battery box area might help.

Dale Gauger and Jerry Melhalf Jr would be the best sources of insight.

 

[Bartman]

@rjgritter

a couple of ideas that might be better than the expense and weight of a metal belly.

have you considered doing a vinyl wrap over the belly fabric to give it additional strength and to make it more resistant to the oil and easier to clean?

also, if the belly fabric can't be protected, maybe re-do the fuselage fabric but instead of doing the belly first, do it last and use dope so the longeron tapes and belly fabric can be removed without stripping the rest of the fuselage? Use of dope would allow you to use MEK to melt the longeron tapes off along with the belly fabric. you could leave the side fabric on and just redo the belly. just a thought.

it would suck to add weight and to have to spend a lot of money because of the problems caused by smoke oil.

 

[Bartman]

if anyone isn't familiar with RJ, here he is in his 150 hp constant speed prop Decathlon earlier this year

 

[rsrguy3]

Before going to an aluminum belly pan I'd remove the belly fabric, and ensure the vertical fabric is properly secured to the lower longerons. Then I'd use oratex as a patch, if I l remember correctly Lars said it's approved over all covering systems as patch \ repair. The stuff is way stronger than anything else.
Here's the trick though, it won't clean any better than polytone. You'll need to put a high gloss urethane on it. I use aerothane. Oratex takes urethane better than any other fabric system substrate, it is absolutely gorgeous, and will clean up with less effort.
Oratex weighs less than the other systems so a coat of urethane wouldn't push the finished weight beyond what's on it now.
Here's an aircam we just finished with painted oratex control surfaces.

 

[rsrguy3]

As a ps to that last post. After the urethane I'd shoot some cerakote or other high end ceramic coating on it to further aid cleaning. All of my personal a\c from here on out are getting black or dark gray bellies, white always ends up dingy and brown, it never comes clean ..... GROSS!