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Old Feb 28, 2012, 08:57 PM
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PiperCub49's Avatar
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Designing for scratch-built FPV wing...

Hey guys,

I will be ordering my first FPV system here soon, and I need a platform to fly it on. Based on all of the aircraft that I've seen, I've come here looking for a solid, stable, lightly loaded design to that will serve my FPV needs well.

I have noticed that the Ritewing Zephyr II is a popular platform. Because of it's flight characteristics, I have been thinking that I will use it as a base for my build. The biggest limitation that I have in making my own Zephyr is that I don't have a hotwire. That pushes me towards a KF airfoil. Here's some data that I have to work with:

Current design thoughts:
The more I look at airfoils, the more I confuse myself. According to this image:
I would think that I'd want an KFm-3 airfoil.

So, in the end, I guess I'm just asking for your opinion on my plans. I have so little experience with flying wings and large electric setups that I really need the help from those who have "been there, done that." Maybe my wingspan is off. Maybe my power system isn't viable. Maybe there is a better airfoil to use. Anything at all would help me tremendously.

Thank you,
Kody
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Old Feb 29, 2012, 09:41 PM
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Bumpity bump. Here's to hoping that someone has an opinion--anything to say at all...
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Old Mar 01, 2012, 12:26 AM
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I think im gonna try your plans. Im just gonna use pink homedepot foam.
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Old Mar 01, 2012, 12:48 AM
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the kfm4 will give you great stability at slow speeds on flying wings, and also its great at speed, my 48 inch divinity flys like its on rails
cant comment on the kfm3 have never built one, but have read alot saying they are good lifter heavy lift wings.
you can allways build the kfm3 and try it then add an extra step underneith to give you something like the kfm7.
try it and see.
RCT
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Old Mar 01, 2012, 02:11 PM
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Just out of curiosity concerning your plans, why is your motor mount so close to the CoG of the wing? Even the ZII doesn't have the motor that deep into the wing. Also, how many degrees of sweep does the nose have?
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Old Mar 01, 2012, 02:17 PM
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Plus one for the KFM4 - I have a KESL wing and its a great stable flyer. Heres another KFM4 wing that flies well. Check out the scratch built foamy forum for a few more

I perused your drawing in sketchup and imho your angles and dimensions seem pretty much spot on comparing them with mine

Regards

Frank
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Old Mar 01, 2012, 08:13 PM
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Quote:
Originally Posted by rcta15 View Post
the kfm4 will give you great stability at slow speeds on flying wings, and also its great at speed, my 48 inch divinity flys like its on rails
cant comment on the kfm3 have never built one, but have read alot saying they are good lifter heavy lift wings.
you can allways build the kfm3 and try it then add an extra step underneith to give you something like the kfm7.
try it and see.
RCT
RCT,

Thank you for the help. I'm thinking that the KFm3 might be a bit less stable than the KFm4 at high speeds because of the lack of a phillips-style LE, but of course this isn't suppose to be a speed plane, so I would be okay if this does prove true.

I really like having the ability to change it to a KFm7. That would get me closer to the KFm4, which has so much positive feedback.

Quote:
Originally Posted by hellabytes View Post
Just out of curiosity concerning your plans, why is your motor mount so close to the CoG of the wing? Even the ZII doesn't have the motor that deep into the wing. Also, how many degrees of sweep does the nose have?
Confession time. All I did to make that model was trace over the image here. I'll have to do some more looking and fix that mistake. Thanks for letting me know I was off on the drawing.

It is a 60* sweep.

EDIT: I have attached my modified plans and would appreciate your thoughts.

Quote:
Originally Posted by frank48 View Post
Plus one for the KFM4 - I have a KESL wing and its a great stable flyer. Heres another KFM4 wing that flies well. Check out the scratch built foamy forum for a few more

I perused your drawing in sketchup and imho your angles and dimensions seem pretty much spot on comparing them with mine

Regards

Frank
Frank,

I was looking at the KESL. All of this support for the KF airfoils is really encouraging. I guess I feel that I am wasting lift or creating excessive drag by using a fully symmetrical airfoil on a plane that I won't be rolling or flying inverted with. I hope that the KFm3 will treat me as kindly as the KFm4 does that pilot in those videos!
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Old Mar 01, 2012, 10:32 PM
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For your first fpv plane I would suggest a trainer type plane. A wing is a really really bad first fpv plane.
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Old Mar 01, 2012, 11:24 PM
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For your first fpv plane I would suggest a trainer type plane. A wing is a really really bad first fpv plane.
Interesting. I'm curious as to why. If it's large enough with a light enough wing loading, I don't see why it can be flown similarly to a trainer. The wind might bump it around more than a trainer, but then again, one doesn't have to fly in the wind. I built a 16" Dead Simple Wing. It has a pretty high wing loading, but it is still one of the most docile and predictable plane I've ever built.
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Old Mar 02, 2012, 05:54 AM
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Quote:
Originally Posted by PiperCub49 View Post
Interesting. I'm curious as to why. If it's large enough with a light enough wing loading, I don't see why it can be flown similarly to a trainer. The wind might bump it around more than a trainer, but then again, one doesn't have to fly in the wind. I built a 16" Dead Simple Wing. It has a pretty high wing loading, but it is still one of the most docile and predictable plane I've ever built.
In my limited experience of flying a wing when the wind starts to blow its the one I fly. They handle windy conditions much better than a trainer type plane, maybe its because theres no fuselage to catch the wind
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Old Mar 02, 2012, 06:58 AM
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I only have The blucore wing to go by but I have built it in 34" up to 47" spans. The blucore is super simple to build, very easy to fly, with great flying characteristics. I let a fellow old timer fly one of my 34" wings, his comment was it flies better than a zagi, so you might look at this design.
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Old Mar 02, 2012, 11:57 AM
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Quote:
Originally Posted by PiperCub49 View Post
Interesting. I'm curious as to why. If it's large enough with a light enough wing loading, I don't see why it can be flown similarly to a trainer. The wind might bump it around more than a trainer, but then again, one doesn't have to fly in the wind. I built a 16" Dead Simple Wing. It has a pretty high wing loading, but it is still one of the most docile and predictable plane I've ever built.
Because trainers will auto correct where a wing will not.

I have both types of planes for fpv and trust me on this one. Wings are great and a lot of fun. But it's really nice to know that a trainer will fly itself for a bit if something goes wrong. Which it absolutely will for the first few flights. It's an entirely different type of flying so you have to relearn some basic skills.
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Old Mar 08, 2012, 06:59 AM
..in a Johnny Cash voice.
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Quote:
Originally Posted by ashdec87 View Post
Because trainers will auto correct where a wing will not.

I have both types of planes for fpv and trust me on this one. Wings are great and a lot of fun. But it's really nice to know that a trainer will fly itself for a bit if something goes wrong. Which it absolutely will for the first few flights. It's an entirely different type of flying so you have to relearn some basic skills.
This man speaks the truth! I fly FPV. Wing for wind, trainer for.....well... training.

You will lose your airplane..you will be happy when it glides itself to a safe landing on it's own...you will enjoy learning the systems....you will progress!

LOL, seriously. Fly/build what you like. I'm in on the kfm wing build for myself. Besides, you can't really go wrong, you're going to crash regardless so give' er.

PS- FPV at 25mph is still pretty crazy at first.
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Old Mar 08, 2012, 07:38 AM
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Thank you both. Part of me says, "You've gone this far. Don't back up now. You'll get it to fly." The other half of me knows that too many people come into the hobby with that attitude! I can build both platforms, and I think that's what I'll do. So if you think that it's necessary, I'll start with a trainer, learn on that, and move to the wing at some point. Sound like a smart plan of attack?
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Old Mar 09, 2012, 08:49 PM
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Hey Piper, was just thinking about your fpv dilemma not too long ago and i thought I'd point you in the direction of another thread that might peak your interest (if you're good at scaling upwards)

this post:
http://www.rcgroups.com/forums/showp...5&postcount=16

(you should be able to access the main thread from the link in the upper right of the page)

KFm4 might not be your best bet, but they're very very easy to slap together just for testing purposes. I'm still guessing it's the geometry that you're after. I'm actually poking for help in some other threads to see if my KFm7 approach is sound. More steps on the top = more lift = more gear. So far, my 38" rendition is working out pretty well with 14-16 minute flight times on a single 2200mah 3S, but I have no idea what will happen if i try to strap an additional half pound of fpv gear to it.
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