Jim D

My Feedback: (8)

Although I'm pleased with the flight characteristics of my H9 Cap232 (1/4), the wing makes me uneasy. It's heavy and just doesn't seem to sturdy. I've also noticed quite a difference in the left and right wing halves close to the root (looks like a miscut rib or two was used).

I'd like to cut me a foam wing. Question is, What airfoil is used on this model (or other similiar sized Cap232 models). Anybody got some insight on this?

stomper

My Feedback: (20)

Hey Jim

If it were me I'd build an extra 300 wing for that h9 cap. The Midwest 80" Cap is using an extra wing and the flying difference beteen the two is like night and day!!



I would like to hear what you come with.
Good luck
Doug

Ted_Sander

Don't know how bad the winters are in TN, but here in Minnesota we have the advantage of a really, really long building season...so you could do as I did to various other planes - run the wing through a band saw to get cross sections, and use those as templates for your foam wing.....I even then throw them into my scanner for CAD reporduction/cleanup/scaling....

Hmmm - and isn't the CAP232 supposed to have the Extra wing anyway? I thought that was the primary upgrade from the CAP231???

stomper

My Feedback: (20)

Hey Ted


Hmmm> You are so right! Just what was I thinking?

Doug

DKjens

My Feedback: (50)

When you guys are talking Cap232 and Extra300 wing profiles, you are just talking 1/4 scale profiles right? The profiles used on the full size planes are so different from what's used on the models. Can you tell me what the difference between the profile on the Cap231(EX) and the Cap232/Extra300 is(are). I have a 30%Cap231EX ARC that I am about to start, and I'd like to know what the difference is. Thanks.
DKjens

Tapio

H-9 used the Eppler 169 on their new Sukhoi, A quick search will give u outline & co-ordinates. I dont know if they transitioned to a diff tip foil though. Often they thin it out.

SA Flyer

My Feedback: (3)

So, what airfoil is the CAP/Extra using?
I have been coming back every day to see who would answer that question. The answer would be interesting.
SA Flyer

rmh

The airfoil-is pretty stand model profile -and I never bothered to plot it -but the new "eppler"169 -is like the foils I have used for years - basically a nice rounded transition from LE to high point - then a pretty straight shot to the TE.
On ouraerobatic models - one of the least important things--is the airfoil--that is to say, the thickness changes stall angle -but aside from that - the fine points of full size airfoils is lost on these models.
If you want to make a real difference -on our models - change the wing loading -
Having done identical sized/ planform wings -in differing airfoils - many times - I find that the wing loading is first ,second and third in order of importance - the planform of the wing is next and last -the airfoil.
Going from a 20% to a 10% airfoil does show some differences --but minor shifts in curves -high point le sharpness are pretty much lost in the shuffle.

Ollie

Dick Hanson has hit the nail squarely on the head. There is only one airfoil characteristic that has high priority for an aerobatic model and that is: it should be symmetrical. The lighter the model, the less lift the wing has to produce, the less thrust the prop has to deliver in vertical line maneuvers and the less control throws and forces are necessary to maneuver. All other characteristics are quite unimportant compared to light weight. The aerobatic model does not have to be low drag. In fact drag can be an advantage in limiting acceleration along down line maneuvers. The stall characteristic of the airfoil can affect the ease of entry and exit form stalled maneuvers like spins and snap rolls but there are other things than the airfoil that can determine stalled maneuvers.

Airfoil technology is a high priority for speed, duration, range and economy but not for aerobatics.

Tapio

Jim D you might also want to try increasing the tip chord a bit or maybe even the span. Extra area and lower Rn on the tip. I think at your size models still like wings closer to constant chord, look at the latest rash of 3D models.

Tapio

If a Eppler 169 was used for the root what would you guys recommend for a tip foil on a tapered aerobatic wing. I'm just not happy with any of the kits out there so I will scratch my own this winter. I imagine the same thing is true of stab foils then too? Not too critical ?

rmh

A 10% tip - -make it similar to root in high point and blend -
From high point back- a STRAIGHT line - curves are just harder to sand and add Zip.
Actually the full scale Caps etc., are straight lines from high point to TE.
As for stabs?
10%.
and - the shape -as long as the stab is absolutely rigid - do what ever you like -
One of the best -is simple a diamond airfoil -really.
for purty - make the transition gradual to the -or just before the hinge line.
All of the old crappola about " airfoil stabs vs flat is a bunch of hooey-- except that the flat stuff flexes easily - requires wires etc..
The real trick - make it STIFF.
and as light as possible

Tapio

Yeah I think your right about the foils on stabs but for bigger models I like to use them. I like the idea of the diamond foil, as I'm also working on a 35% Swick Taylorcraft but could'nt figure out how to make plug in stabs, but the diamond would give lots of thickness for a joiner, and stiffness to boot. For the main wing I was planning on using a S 8037 like on my little P-47.

Jim D

My Feedback: (8)

Wow, after laying dormant for over a month, this thread has picked up steam. Thanks for the info.

BTW Dick, aside from the questionable integrity of the wing another reason I wish to replace it is weight. It is HEAVY (probably full of hot glue or the likes) and therefore, the wing replacement will also effect wing loading, which is very important as you pointed out.

It's crazy, but the 80 inch, constant chord foam wing I built for my Stinger 120 actually weighs less than the 73 inch double taper wing on my Cap. Go figure.

Ted_Sander

Jim - you're right about the H9 CAP, mine's overweight also. While a built up wing can be lighter, it's also easier for it to get away from you. Foam wings are more consistent. My last aerobatic plane came in at 7.5 lbs with 1000 sq in, a YS .61, foam plug-in wing. No honeycombing or nothin' fancy. Just was careful about glue and the finish. I'm gonna try hard to hit 11 lbs on my next scratch built, an Edge with 80" wing, 2.4 gas. I've also found that with aerobatics (as Dick noted) the kind of symmetrical airfoil doesn't matter much - but I do prefer a little thicker/blunter for the drag/speed control it can give.
Replacing my H9 stab with an airfoiled one didn't produce substantial changes, except that it gave me much more response to elevator. Almost too much - had to dial down the throws significantly for smooth normal flying. But it looks better! That's the good part about doing it yourself - you can tweak it the way you want it!

rmh

FWIW- a foam wing -1lb foam- 6-7 lb wood --12-10 % airfoil - plug in -each panel 36"long-chord root 21 -tip 11"
no spars NO plywood - all done inc full size servo- covered ready to fly--weight can be - easily - 18 oz to 19 oz per panel.
Done it -over and over ---no cutouts except lightening holes in ailerons -to reduce off center mass.
Total lightening -5 grams per aileron

Tapio

Just went in the garage and weighed my 300 wings at 16oz with 4721 servo. Built up wing but this is with a tapered blade spar so essentially the joiner is included with this weight. 10.5" tip, 19" root chords and 35" long. Its based on the outline of the MW 300.
I wish I knew where to get a good cowl and canopy, and outline for a 100" aerobat to scratch build.
If you guys skin with epoxy resin here is a technique that I find works great for putting on just enough glue. Take wax paper 2" oversize of each wing panel (4) for a complete wing. I then spread my epoxy on the wax paper with a notched card. it flows really well. Then carefully place the paper on the skin and lightly press the resin onto it, peel the paper off. About half the resin stays on the wax paper. Clamp or bag well and there you have it.