Experimental build - 1.7m F8F Grumman Bearcat

[The Fopster]

Just starting an experimental build of a Grumman F8F Bearcat. If it gets finished it will be 1.7m span and very approximate in terms of scale detail. The payback will be that it should be a very quick and cheap build.
Material will be a mix of Hobbycraft foamboard (heavy UK stuff) and B&Q home insulation foam sheets. Plans are being done extrapolating from a 24in span balsa control line design, blown up to 270%.
Tomorrow I’ll try building one wing and see if the design works. If it doesn’t I may park the idea.
Here goes nothing!

 

[Tench745]

Just starting an experimental build of a Grumman F8F Bearcat. If it gets finished it will be 1.7m span and very approximate in terms of scale detail. The payback will be that it should be a very quick and cheap build.
Material will be a mix of Hobbycraft foamboard (heavy UK stuff) and B&Q home insulation foam sheets. Plans are being done extrapolating from a 24in span balsa control line design, blown up to 270%.
Tomorrow I’ll try building one wing and see if the design works. If it doesn’t I may park the idea.
Here goes nothing!

You may want to add extra ribs between the ones on the plans. Some quick guess math says yours will be about 5.5" apart and depending on your choice of material for the wing skins, that's a relatively large unsupported area of wing skin.

 

[The Fopster]

You may want to add extra ribs between the ones on the plans. Some quick guess math says yours will be about 5.5" apart and depending on your choice of material for the wing skins, that's a relatively large unsupported area of wing skin.

Agree - my plan is to put spanwise foam strips tween the ribs as they will be mainly straight lines so quicker to cut. May not work - we will see!

 

[Tench745]

Agree - my plan is to put spanwise foam strips tween the ribs as they will be mainly straight lines so quicker to cut. May not work - we will see!

That should work just fine, especially if you've got the existing ribs. Think of them like multiple spars and/or stringers. If you rough cut the stringers to fill in between the ribs, you can use a sanding bar with some 180 grit paper to quickly shape them to perfectly match the ribs.

 

[The Fopster]

First wing is underway. Foamboard box spar is full depth, 9mm foam ribs and 6mm foam skin. Hot glue for the spar, foaming gorilla glue for the rest. As it stands it’s 160g with lower skin and wing tip still to be added. Feels VERY rigid for that weight. Quite excited about this one….

 

[Jonny Gum]

Very interesting construction, I'm excited to follow this.

 

[The Fopster]

Lots more progress on the big Bearcat. The wings are complete, and I'm really pleased with the stiffness combined with low weight - very promising!

Next challenge was how to fix the wings to the fuselage. I've gone with two locating pins that go directly through the spar and locate in a cross member in the fuselage, with two wing bolts towards the rear. It feels pretty solid and should easily cope with normal flight loads - crash loads are, of course, a different mater entirely...

I also made up the foam board empennage so I can finally put the bits together to get a feel for the size of the thing - it's a decent size! I also realised that I don't need to build the fuselage to carry out the maiden. I can fly with just the box structure internal fuselage structure to assess the flight behaviour and make any major changes if I've got thrust angle, wing incidence etc. badly wrong, and once I know it should fly OK I can skin the fuselage.

Might try and get ready for a maiden this weekend.