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Foamy sports jet - my own design

CarolineTyler

Well-known member
#1
I fancy a fast foam sports jet and love the look of the H-King Flycat.
The power of the 70mm 6S EDF I have in the X-29 I think will be ample. This will have electric retracts too.
First the wings - I'm looking to have approximately a metre wingspan and have made this card template.
IMG_20191020_201458355.jpg
Where shall I put the spar? 1/4 or 1/3rd of the chord of the wing. I'm leaning towards 1/3.
 

The Hangar

Well-known member
#2
I fancy a fast foam sports jet and love the look of the H-King Flycat.
The power of the 70mm 6S EDF I have in the X-29 I think will be ample. This will have electric retracts too.
First the wings - I'm looking to have approximately a metre wingspan and have made this card template.
View attachment 145918
Where shall I put the spar? 1/4 or 1/3rd of the chord of the wing. I'm leaning towards 1/3.
1/3 seems good to me. I’ll definitely be watching this - 6s edf jet with retracts out of foam board!
 

Vimana89

Well-known member
#7
Awesome project! This one sounds like a lot of fun. I wasn't familiar with the Flycat, but I looked it up and besides small differences mostly in the fuselage and nose, it has a layout like a de Havilland Sea Vixen. Nice looking plane, should be a great basis for your EDF foamie. I'm definitely looking forward to seeing how this turns out.
 

PoorManRC

Well-known member
#8
Holy CRAP @CarolineTyler !!!! 😲😎👋👋👋👋
DESIGNING JETS?? Well, that's a bit Next Level, isn't it? 😮
You've definitely piqued my curiosity dear. I'll be watching with excitement!

I'm actually glad for this. My Glue Gun BLEW UP, giving me 2nd degree burns on my Hand!! 🔥🔥🌋😯🔥

I'm OUT of Foam Board, CA Glue, need 2 Motors, 4 Servos (one 12g), and a 40-50A ESC...
And of course a new Hot Glue Gun....
And NO MEANS to get any of it! 😖😤😭😢

So I've got time on my hands and will welcome what will be an interesting and creative Build! 😉
 

Merv

Well-known member
#12
Where shall I put the spar? 1/4 or 1/3rd of the chord of the wing. I'm leaning towards 1/3.
I like the spar to be located on the CG. The location of CG is a matter of personal choice, some prefer mild @ 25%, I prefer wild, CG @ 30% of the MAC
The thickness is close to 11.7% of wing chord.
I've done some experiments with wing thickness and have not noticed any significant speed advantage to thickness less than 15%. If a 15% wing would let you cover the wheal, it may be faster. A 15% wing will handle slow speeds much better than a 12% wing.
 
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CarolineTyler

Well-known member
#13
I like the spar to be located on the CG. The location of CG is a matter of personal choice, some prefer mild @ 25%, I prefer wild, CG @ 30% of the MAC
I've done some experiments with wing thickness and have not noticed any significant speed advantage to thickness less than 15%. If a 15% wing would let you cover the wheal, it may be faster. A 15% wing will handle slow speeds much better than a 12% wing.
I was following the Clark-Y spec of 11.7%. this is just a test at present, I work better when I have something to look at in 3D :)
 

CarolineTyler

Well-known member
#15
As I understand it Clark Y is not a super slippery aerofoil so if you are going for speed, maybe there are better sections - FT article
Yes, However I'm also trying to make this fairly easy to build and a mostly flat bottom airfoil is simple to make in foamboard.
Notice the wing has a sharper front fold than a usual FT wing.
I have been eyeing up hotwire cutting of wings but decided for this first design to keep it "in my ballpark".
 

Piotrsko

Well-known member
#17
With DTFB, most all you can do is sharpen the LE, and keep it thin. Almost doesn't matter the profile. Something "laminar" requires up to 3 spars to keep the shape and it won't be laminar.

But at 12%, you COULD do a pointy semi symmetrical by creasing the lower skin just in front of the spar and massage the upper skin back just a bit.
 

PoorManRC

Well-known member
#19
With DTFB, most all you can do is sharpen the LE, and keep it thin. Almost doesn't matter the profile. Something "laminar" requires up to 3 spars to keep the shape and it won't be laminar.

But at 12%, you COULD do a pointy semi symmetrical by creasing the lower skin just in front of the spar and massage the upper skin back just a bit.
I like this idea! You can keep the same chord, same root thickness, yet still have a sharper LE.

Oh..... and love the idea of some lights! 😉
 

Piotrsko

Well-known member
#20
Y'all do realize that making the leading edge really sharp causes really unpredictable and nasty plane munching stalls? Ref: German NATO pilots and F-104

Fortunately, there are 2 cures: Don't stall (duh) Horizontal stabilizer has to approach about 15% of wing area to over power the "flick" tendencies at stall.