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.

 

[The Fopster]

Well it flies! I did a short maiden this afternoon in very blustery conditions and all went pretty well. Plenty of power on 4s, which bodes well as it will be on 6s when it's finished. Not surprising as it has a 1.7m wing with lots of wing area, and as it stands part finished it barely weighs 2kg RTF. That's a glider-like wing loading.
CG felt good, but it climbed on throttle so I'll reduce the angle of attack of the wing a little (easy to do as the fuselage is only the central core at present...).
Flight was cut short as the prop loosened - clearly I'm not used to how tightly you need to torque up a 15" prop! There was a little damage to one wing leading edge - easily fixed.
So - seems it will be worth my while building the fuselage exterior!

 

[The Fopster]

Time for an update on the big Bearcat project. I had a trip to the field this morning and the weather was fine for a maiden. A quick taxi test on the takeoff dolly showed power on 4s was more than enough, so full throttle and full up elevator and away she went!


Flight performance was as I’d hoped - the light weight and large size made for slow and realistic manoeuvres. Rolls are very slow, but elevator response is more than adequate and she is very stable and easy to fly.

I flew two flights. The second was for 6 minutes with some rolls etc. and on landing the two 2200mAh 4s batteries (connected in parallel) were still at 54%, so eight minutes should be very comfortable!

Next flights will push the envelope a little to test inverted, loops etc. Really pleased with how she looks in the air. The slow flight looks very realistic - given the 1.7m wingspan and only 2.5kg weight ready to fly that was what I’d hoped for. That seems like a very low weight for something this big, so mission accomplished on that score.

I’ve obviously got some finishing to do now. The plan is to sand the airframe and fill the worst gaps before fibreglass (for extra strength) and paint to finish. It will be very rough up close, but I think it will look great from a distance in the air!

 

[The Fopster]

The Bearcat is getting closer to being “finished”. The fuselage is fibreglassed (with water based varnish) and has a first coat of paint. I’m already flying it to get used to it - not without incident! Some issues with the takeoff dolly lead to a punctured lower wing skin (after a nose-over) but it was an easy fix, and once I’ve got to the shops to buy some more glass cloth the wings will be more robust (photos of the damage and the repair below).

However - once off the trolley it flies really well. I’ve increased the size of the ailerons by about 30% over scale as rolls were soooooo slow. But it flies slowly, smoothly and has plenty of power.

My clubmate Scott filmed some chase footage with his drone this afternoon so here is some air to air filming to show it in flight!

 

[bisco]

it looks great, what a nice smooth roll

 

[The Fopster]

I’ve been flying the unfinished Bearcat quite a bit, so progress has been slow. However - some more things slowly getting ticked off the list. Paint is 80% complete after covering - a mix of fibreglass and brown paper. I’ve 3d printed a dummy engine and finally sorted out how to fix the belly cover in place. Getting closer…

 

[The Fopster]

Markings (hand cut vinyl) and paint progressing on the Bearcat. First attempt at a clear canopy was not a success - I can’t find a coke bottle big enough! So as a stopgap I’ve made a Flitetest style foam one which I will paint. It’ll look fine in the air…

 

[The Fopster]

Well here it is with the temporary canopy in place. I’m really pleased with how it turned out. It does have that “starved horse” look because of how I did the fuselage skin in segments across instead of strips along the fuse. It’s totally lacking in scale detail, and up close there are plenty of really rough bits. But - it was quick and cheap to build, it is very light for its size, it flies really well and it looks great from a few paces away. Mission accomplished!
I’ve got some paint to tidy up, but first I’ll fly it for a while then maybe do a few improvements - clear canopy and retracts are both on the list…

 

[Draftman1]

Very cool

 

[bisco]

wow!

 

[Mr NCT]

Love your badgers!

 

[The Fopster]

Love your badgers!

A Christmas gift. Santa was very generous!

 

[FlyerInStyle]

Well here it is with the temporary canopy in place. I’m really pleased with how it turned out. It does have that “starved horse” look because of how I did the fuselage skin in segments across instead of strips along the fuse. It’s totally lacking in scale detail, and up close there are plenty of really rough bits. But - it was quick and cheap to build, it is very light for its size, it flies really well and it looks great from a few paces away. Mission accomplished!
I’ve got some paint to tidy up, but first I’ll fly it for a while then maybe do a few improvements - clear canopy and retracts are both on the list…

View attachment 244942 View attachment 244943 View attachment 244944

How do you transport it? Does it come apart?

 

[The Fopster]

How do you transport it? Does it come apart?

It does. The wings are bolted on, and themselves can be removed from a central wing joining spar. Fits in my small car - just!