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Old Apr 08, 2012, 09:19 PM
YureZzZ is offline
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FPV only!
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Yeah, I meant 20mm each layer. So total thickness would be (in the thickest part) 60mm, which is pretty enough to hold all my FPV gear =)
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Old Apr 08, 2012, 09:41 PM
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Jack
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OK, I thought that might be it. So you want to build a KFm3 or KFm4 flying wing with a 1650mm (165cm or 65") wingspan and using 20mm (0.788") thick sheets of foam, right?

I think that might work, do you have any idea what the root chord would be on the wing? The distance from the tip of the nose to the back edge of the wing or prop slot?

Jack
Old Apr 08, 2012, 09:48 PM
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FPV only!
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You got it right.

I've used Kesl 32" plans scaled for my need.
Here is what I got:
wingspan: 162,5cm
root chord: 53,7cm
tip chord: 41,4cm

According to Dickeroo (cheers!) total thickness should be 9-12% which is 48mm-64mm, so I chose 60mm (3 layers of 20mm sheets).

I haven't calculate CG and wing loading, but I guess CG is going to be the same (in %) as Kesl and loading would be light - this bird is huge. (hmm maybe I shouldn't make it so big )
Old Apr 08, 2012, 09:59 PM
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Build straight - Fly twisty
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Nah! Big is Good.
Old Apr 08, 2012, 10:16 PM
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FPV only!
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Originally Posted by Whiskers View Post
Nah! Big is Good.
How about transportation? BTW, I've heard that bigger wingspan is less affected by the winds and gusts. Is that right?
Old Apr 08, 2012, 11:07 PM
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Build straight - Fly twisty
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I've heard that bigger wingspan is less affected by the winds and gusts. Is that right?
It's a complex area, but a given wind gust is greater for a small model than it is for a big one.
You can easily fly a real A-380 in turbulence that would ground your real Quicksilver.
Mind you, I see small birds and even smaller insects easily handling conditions that would ground all my planes.
Old Apr 09, 2012, 03:57 AM
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For a large lifting wing a KFm3 is likely the best option.. and that will give more self stability than the KFm4..and a better glide..
KFm4 is better for neutral aerobats
Bigger is more docile, so a big wing is better as it will fly smoother for the FPV ..
Wind is a problem here, its not the span that makes life easier but bigger models are usually heavier and more mass is less likely to be moved by gusts.. And as any wind tends to hit models more side on, its that profile is what takes more of the force
I find any light weights, going 7oz down are a real pain in wind.. thats why I tend to build more 10oz and up models..
Old Apr 09, 2012, 09:44 AM
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Jack
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Quote:
Originally Posted by YureZzZ View Post
You got it right.

I've used Kesl 32" plans scaled for my need.
Here is what I got:
wingspan: 162,5cm
root chord: 53,7cm
tip chord: 41,4cm

According to Dickeroo (cheers!) total thickness should be 9-12% which is 48mm-64mm, so I chose 60mm (3 layers of 20mm sheets).

I haven't calculate CG and wing loading, but I guess CG is going to be the same (in %) as Kesl and loading would be light - this bird is huge. (hmm maybe I shouldn't make it so big )
Sounds like you've got it all figured out about right. And I think davereap's advice is all right on the money too. As far as the CG, I always use the Flying Wing CG Calculator and it gets me right on the money for a starting CG.

The KFm airfoils tend to shift the CG to the rear just a little so I've found that using the 20% margin as a starting point works very well. The 15% will work too but will be a little bit more on the nose heavy/safe maiden flight side than is necessary.

Many try to locate all the heavier components as part of the design, I like to get the wing structure finished and then start arranging heavier parts in various locations to get the CG right. Then I use that to cut the battery pockets stuff.

For a FPV plane (I've never done one) I would probably include all the FPV related bits and pieces in the trial and error process too. But I would probably use dead weight in those locations to do the maiden flight and get things sorted out.

Good luck with it, looking forward to some reports and photos.

Jack
Old Apr 09, 2012, 09:52 AM
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Originally Posted by jackerbes View Post
As far as the CG, I always use the Flying Wing CG Calculator and it gets me right on the money for a starting CG.

The KFm airfoils tend to shift the CG to the rear just a little so I've found that using the 20% margin as a starting point works very well. The 15% will work too but will be a little bit more on the nose heavy/safe maiden flight side than is necessary.
Jack
This has been my experience, precisely.

Dave
Old Apr 09, 2012, 11:52 AM
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FPV only!
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Big thanks, guys! You've cleared my mind! Now I need to order that EPP sheets and get busy
Old Apr 09, 2012, 01:26 PM
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Tried to maiden my new wing this AM. Found a bad "brand new" HK 9 gram servo.

Replaced it with ANOTHER new one, and it was bad too!

Now just a BIT smarter, I tested the third and last one I had, and it TOO was bad!

Have used DOZENS of these w/o problem. Did I get a bad batch?

Could it be anything that I'm doing to them?

BTW, "bad" means that after moving the servo it does NOT return to the same position.

Steve
Old Apr 09, 2012, 02:08 PM
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Quote:
Originally Posted by Flyboy Steve View Post
Tried to maiden my new wing this AM. Found a bad "brand new" HK 9 gram servo.

Replaced it with ANOTHER new one, and it was bad too!

Now just a BIT smarter, I tested the third and last one I had, and it TOO was bad!

Have used DOZENS of these w/o problem. Did I get a bad batch?

Could it be anything that I'm doing to them?

BTW, "bad" means that after moving the servo it does NOT return to the same position.

Steve
Do you have a "servo cycler" that can run the servo back and forth for a minute or so, to "seat" the pot wiper?
Old Apr 09, 2012, 02:12 PM
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What confuses me is that the KF 'step' is what causes the air pressure difference to take the shape of the missing fixed airfoil back past the step. So, why the need for all the steps, shouldn't just one on the top or the bottom, or both do the job?

The KF1/2 can be vastly improved just by the shape of the leading edge.

So, what we need is access to a wind tunnel to see what all the variations actually do. Anyone know someone who works for Ferrari in there F1 program?
Old Apr 09, 2012, 02:15 PM
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Three in a row? I would start looking elsewhere for the problem. I've use loads of HK servos, never a problem.
Old Apr 09, 2012, 03:20 PM
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That's what I thought!

Any reason to try to spray some "contact cleaner" or something like that inside?


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