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Old Apr 09, 2011, 11:12 AM
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Amble, Northumberland, UK
Joined Nov 2008
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Aerofoil Section needed for 80" UAV

Hi,

I've been working with 54" and 73" flying wings for the past year for UAV use. AUW is 1.7 to 2.5 kg. However I need to spend less time building and more time flying and processing, so I'm getting FoamWings (Scotland) to build me an 80" with a central pod to take all the gear, with the aim of getting up towards the 3kg auw.

He's asked me what section I should go for, but I'm a bit stumped. Looked through Martin Hepperley and Profili, but still not sure.

I need a section for a sturdy result with a good lift. Operating speed 60 to 100 kph. Doesn't have to be aerobatic. Efficient if possible. What do you reckon? It will be covered in obechi veneer and a couple of coats of gf.

Tks
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Old Apr 09, 2011, 11:19 AM
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Indiana
Joined Jan 2003
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Originally Posted by nking View Post
Hi,

I've been working with 54" and 73" flying wings for the past year for UAV use. AUW is 1.7 to 2.5 kg. However I need to spend less time building and more time flying and processing, so I'm getting FoamWings (Scotland) to build me an 80" with a central pod to take all the gear, with the aim of getting up towards the 3kg auw.

He's asked me what section I should go for, but I'm a bit stumped. Looked through Martin Hepperley and Profili, but still not sure.

I need a section for a sturdy result with a good lift. Operating speed 60 to 100 kph. Doesn't have to be aerobatic. Efficient if possible. What do you reckon? It will be covered in obechi veneer and a couple of coats of gf.

Tks
I am a fan of the Bill Evans Simitar Airfoil, listed as ESA-40 or ESA40 on Profili.

Do a search in this group and you'll find my Simitar posting around page 8 or 9 of that thread I start building my own 85 inch Desperado 3000.

There is a short video of it flying under the Gas Videos.

Tight Turns,

Claude
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Old Apr 09, 2011, 03:46 PM
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Originally Posted by nking View Post
Hi,

I've been working with 54" and 73" flying wings for the past year for UAV use. AUW is 1.7 to 2.5 kg. However I need to spend less time building and more time flying and processing, so I'm getting FoamWings (Scotland) to build me an 80" with a central pod to take all the gear, with the aim of getting up towards the 3kg auw.

He's asked me what section I should go for, but I'm a bit stumped. Looked through Martin Hepperley and Profili, but still not sure.

I need a section for a sturdy result with a good lift. Operating speed 60 to 100 kph. Doesn't have to be aerobatic. Efficient if possible. What do you reckon? It will be covered in obechi veneer and a couple of coats of gf.
The ESA-40 would be OK for a plank although the lift to drag ratio could be improved upon. If you're building a swept 'wing there are much better choices. There are a lot of variables. The airfoil section you choose is part of an integrated system. Your speed and weight goals are easy for an 80" span. But if you want it to fly right, without too much post-production fiddling around, you should design it by the numbers. I posted a spreadsheet that can do most of them

--Norm
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Old Apr 10, 2011, 09:35 PM
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Amble, Northumberland, UK
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Thanks Claude and Norm.

Yes I am going swept flying wing, rather than plank. Unfortunately I'm a flyer, not a builder, and I'm getting confused with what the graphs all mean. And whilst I really would like to understand, I've got such a workload that I can't take time out to learn a new skill. I was hoping to say to the guy who is going to build for me "here is my current design - scale it up to 80" wingspan and send it back" But he asks what aerofoil section and I am stumped.

Reading around I'm seeing MH45 or MH60 as a good start. So far I've found best CG position on my UAV's through trial and error. It changes a bit anyway depending on what gear is packed inside. Is this a problem?

Cheers
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Old Apr 11, 2011, 01:38 AM
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The MH60 would be fine, Nigel. As a full size pilot I'm sure you understand weight and ballance. 'Wings are more sensitive to changes in weight than tailed aircraft. Basically the 'wing is designed for a specific weight AKA the design CL. Increasing the weight changes the CL at a given speed which will require either increased reflex or decreased static margin. Stability decreases as you move the CG aft just like a tailed airplane. Establish the aft CG limit in rough air and stay in front of that. If the nose swings around too much for good photography move the CG forward and increase the reflex. It would be a good idea to design a photo plane to have its CG pretty far forward in the first place because a long static margin (say 8 or even 10%) gives good pitch and directional stability

--Norm
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Old Apr 11, 2011, 06:32 AM
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Amble, Northumberland, UK
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The MH60 would be fine, Nigel. As a full size pilot I'm sure you understand weight and ballance. 'Wings are more sensitive to changes in weight than tailed aircraft. Basically the 'wing is designed for a specific weight AKA the design CL. Increasing the weight changes the CL at a given speed which will require either increased reflex or decreased static margin. Stability decreases as you move the CG aft just like a tailed airplane. Establish the aft CG limit in rough air and stay in front of that. If the nose swings around too much for good photography move the CG forward and increase the reflex. It would be a good idea to design a photo plane to have its CG pretty far forward in the first place because a long static margin (say 8 or even 10%) gives good pitch and directional stability

--Norm
Thanks Norm. Sure, I've found out about right CG placing the hard way. Because I bungee launch / zip start I've found that this shows up any errors quickly (and sometimes dramatically). I tend to start well forward and bring it back until its porpoising then push forward again. When en route it's managed by an Attopilot IMU which is a really good autopilot when it's correctly tuned. However, anything to assist stability is a bonus. I've also found a slightly higher wing loading (heavier) produces more stability, surprised me initially but makes more sense I think.

And thanks for the advice on MH60.

One question. Am I right that increasing the weight by, say 10%, will require the cg to be moved aft (a little) for the same speed if I want the reflex to stay the same?

Cheers
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Old Apr 11, 2011, 11:17 AM
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One question. Am I right that increasing the weight by, say 10%, will require the cg to be moved aft (a little) for the same speed if I want the reflex to stay the same?
Yes but the neutral point is dependent on the geometry of the airplane not the mass so the aft CG limit and static stability will be the same regardless of weight. Of course the moment (torque) about the neutral point increases proportionately to mass times static margin so it dose seem like a heavier plane is more stable but the % MAC is what counts

--Norm
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Old Apr 12, 2011, 02:36 AM
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Yes but the neutral point is dependent on the geometry of the airplane not the mass so the aft CG limit and static stability will be the same regardless of weight. Of course the moment (torque) about the neutral point increases proportionately to mass times static margin so it dose seem like a heavier plane is more stable but the % MAC is what counts

--Norm
I understand. Thank you so much for taking the time to explain it all Norm. You've really helped me make some better decisions and understand wings a little better.

Cheers
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