Internal fillets

[ArthurSull]

Currently doing some internal fillets on my 4" Patriot.

I've just done the root edge-to-MMT fillets, but is it worth doing fillets on the inside of the BT where the fins go TTW too?

I remember seeing a diagram somewhere on here showing the effectiveness of the fillets in different areas, if anyone knows what I'm talking about that'd be great.

Ben

 

[sodmeister]

Well chum ,some may say yes ,some may say no ,but I always do on my builds,be they kits or scratch.

It never hurts to have the extra fillets in my opinion.

NOW THEN ******

I do think it VERY important to add internal fillets whilst working with PML Quantum tube ,as you need all the mechanical surface bonding you can achieve.

I have built a good many PML kits (just finished their 4" AMRAAM 4) and have not had any fins fail ,even the canard fins on my 2 Bullpuppys (although I do a modification on such fins ,including the AMRAAM)

I also have and fly the same kit you are building (4" Patriot) and it flys like a champ on H ,I ,J and Ks (although Ks take it pretty damn high LOL)

Here`s mine taking off on a CTI J394 Green , and into the winds she goes ,as we were launching on the brink of 30Km/h ....but a nice flight.

Hope that helps you out squire :wink:


Paul T

 

[ArthurSull]

Such a great photo!

Thanks for the info. I guess there's no harm in getting as much bonding in as possible. This is a heavy bird anyway and I'm not going for height so weight isn't restricting me too much.

They're not the best fillets (it's my first time doing internals and slow-cure epoxy) but I sanded it up fairly rough and washed everything with warm water and soap beforehand. Cert flight will be on a H, but I should be good to go too. Doesn't look like anything will break this thing!

 

[sodmeister]

Indeed chum ,she is a strong bird when built properly ,and a nice straight flier too.

Just a note.I like to wash down the parts with Isopropyl alcohol (70% is good) after washing with soap ,it will remove any residues and insures a great bond.

Not to worry about your fillets ,no one sees them ,just get that epoxy in there and on all the mating parts.

Happy building gov.

Paul T

 

[JohnCoker]

Yes to internal fillets, for sure. Also, 2-part polyurethane foam is an amazing adhesive for even more reinforcement.

John

 

[Peter Olivola]

West System 406 Colloidal Silica is a popular additive for fillets, but I've always preferred 407 Low Density filler to keep weight in the fin can to a minimum while providing sufficient strength. Keep in mind, almost any epoxy is going to be stronger than fin material or airframe tubing, even PML. There's nothing to be gained from bonding overkill and a lot to be gained keeping weight down.