Foamy sports jet - my own design

CarolineTyler

Legendary member
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

Fly harder!
Mentor
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

Legendary member
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

Master member
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

Site Moderator
Staff member
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

Legendary member
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

Legendary member
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".
 

Headbang

Master member
I have tossed around the same idea, but every time I do I land at a 1.2m ish wing span and dual 90mm edfs to get the wheels large enough to handle the grass fields without stripping the nose gear. I learned the hard way on the eflite phantom2 how hard things are on nose gear.
 

Piotrsko

Master member
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

Master member
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

Master member
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.