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Old Jul 11, 2011, 10:03 PM
B for Bruce
BMatthews's Avatar
The 'Wack, BC, Canada
Joined Oct 2002
11,422 Posts
HOLD THE PRESSES! ! ! !

Your prop is still in front of the window for any forward facing camera? Then what is the point of going assymetrical?
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Old Jul 12, 2011, 08:12 AM
Lift is cheap - Drag sucks
Tom Harper's Avatar
Socorro, NM
Joined Jul 2004
3,619 Posts
No, the prop tip extends just to the inside edge of the camera pod. The center line of the camera lens is 2 inches beyond that.

Tom
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Old Jul 16, 2011, 04:00 PM
Lift is cheap - Drag sucks
Tom Harper's Avatar
Socorro, NM
Joined Jul 2004
3,619 Posts
Current Sketch

Changed the pod to the same section as the wing and terminated it at the trailing edge:

B=82"
C=10.5"
S=6 sq ft
AR=7.8:1
AUW 80 ounces
WL=13.34 oz/sq ft

The motor mount will accomodate three different motors:

Microdan 2510
Hacker A30 12M
Power Up 3548-09

The model is a bit heavy so I want some options.

Tom
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Last edited by Tom Harper; Jul 16, 2011 at 05:04 PM.
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Old Jul 17, 2011, 03:59 PM
B for Bruce
BMatthews's Avatar
The 'Wack, BC, Canada
Joined Oct 2002
11,422 Posts
You're not being all that brave with this. Where's the high aspect ratio biplane wing on one side with the high sweep angle delta wing on the other?

I suspect you're setting yourself up for some nose weight issues with the design as shown. The tail surfaces and moment arms are pretty big for the wing and the nose moments aren't all that long. I foresee mucho lead in the nose to get things to balance decently. And your tail surfaces are far larger than needed. The vertical in particular looks like it'll result in the model being nasty for spiral stability. It's large enough that it'll likely make the model want to steepen into any turns.
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Old Jul 17, 2011, 04:23 PM
Herk
HerkS's Avatar
Virginia USA
Joined Jun 2007
1,647 Posts
Obviously - you can design and build an asymmetrical model that will fly fine. The camera could be in the nose of the fuselage or in the pod with the powerplant in the other.

Lateral balance is essential. Otherwise you should have a lot of latitude.

Thrust offset can be managed by trim or by thrust line offset (or both.) It might be slightly more effective if the fin and rudder were directly downstream of the motor-prop.

If you are going to use a folding prop, remember that it needs room to fold without being captured by the wing leading edge. If you are not using a folding prop, consider three or four blades to absorb the power. That would allow a smaller diameter and thus less offset.
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Old Jul 17, 2011, 04:29 PM
Lift is cheap - Drag sucks
Tom Harper's Avatar
Socorro, NM
Joined Jul 2004
3,619 Posts
Bruce,

The rudder is arbitrary in the sketch. I'll work on it later.

On my spreadsheet the CG prediction gives some positive margin.

This is essentially the B&V layout. As I mentioned above that airplane is not as asymmetrical as it appears. The configuration is really rather conservative.

This design is to meet the requirements of our next AP grant, so I'm not going out on a limb.

However, I started with an asymmetrical flying wing with forward sweep. Maybe later.

Tom
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Old Jul 17, 2011, 04:32 PM
Lift is cheap - Drag sucks
Tom Harper's Avatar
Socorro, NM
Joined Jul 2004
3,619 Posts
Herk,

Thanks.

I will use a folder with enough nose moment to close against the fuselage.

I couldn't get the CG right with the motor in the pod, so I switched.

Tom
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Old Jul 18, 2011, 03:02 PM
Don't take your guns to town
vespa's Avatar
Thousand Oaks, CA
Joined Mar 2004
2,607 Posts
Tom, I suggest a symmetrical airfoil for your camera pod, rounded into a torpedo shape. Maximum efficiency is obtained when the tail, pods, fuselage, etc. just stay out of the way and let the wing carry 100% of the weight.
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Old Jul 18, 2011, 03:12 PM
Registered User
Joined Oct 2004
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I wonder. If camera and battery have roughly the same weight, couldn't the plane just use two pods on the sides of a thin fuselage?
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Old Jul 18, 2011, 04:50 PM
Lift is cheap - Drag sucks
Tom Harper's Avatar
Socorro, NM
Joined Jul 2004
3,619 Posts
Vespa,

I used a Symmetrical section on the last pod design and Norm asked why I didn't use the wing section. That's what I get for tossing this out to a committee.

Actually the NM57 section conforms better to the camera.

Thanks,

Tom
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Old Jul 18, 2011, 04:52 PM
Lift is cheap - Drag sucks
Tom Harper's Avatar
Socorro, NM
Joined Jul 2004
3,619 Posts
Brandano,

The battery is about twice the camera weight and the camera is about 4 times as wide as the battery.

It does seem that a fuselage and single pod is the simplest solution.

Tom
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Old Jul 18, 2011, 05:41 PM
Don't take your guns to town
vespa's Avatar
Thousand Oaks, CA
Joined Mar 2004
2,607 Posts
Yeah, you never want cambered airfoils on anything other than the wing. Not only will that shape produce a lot of drag and almost zero lift, it will also produce huge vortices that will disrupt flow on the wing, causing even more drag and lost lift. There are a few cases of lifting fuselages on successful designs but it's very difficult to do and always results in lower performance. It's only done for cases where the fuselage must already be in some shape such that a cambered airfoil is the least drag option.
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Old Jul 18, 2011, 09:59 PM
Lift is cheap - Drag sucks
Tom Harper's Avatar
Socorro, NM
Joined Jul 2004
3,619 Posts
Sized the surfaces

A symmetrical pod would not conform to the downwash at the TE. The aspect ratio is calculated for the entire wing so the pod should not cause significant induced drag.

I sized the surfaces using the equations in the rudder size thread. They look small, but that's how they calculate.

Tom
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Old Jul 19, 2011, 12:02 AM
internet gadfly
nmasters's Avatar
Colorado
Joined Aug 2006
2,171 Posts
Quote:
Originally Posted by Tom Harper View Post
Vespa,

I used a Symmetrical section on the last pod design and Norm asked why I didn't use the wing section. That's what I get for tossing this out to a committee.

Actually the NM57 section conforms better to the camera.
As I recall I recommended a cambered section for your conduit AP plane because the downward pointing camera fit better into a pod with a flat bottom
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Old Jul 19, 2011, 12:16 AM
internet gadfly
nmasters's Avatar
Colorado
Joined Aug 2006
2,171 Posts
Quote:
Originally Posted by vespa View Post
Tom, I suggest a symmetrical airfoil for your camera pod, rounded into a torpedo shape. Maximum efficiency is obtained when the tail, pods, fuselage, etc. just stay out of the way and let the wing carry 100% of the weight.
Yeah but those other things don't stay out of the way. Unless you leave them on the drawing board which Tom has done at least once that I know of. The minimum drag of the fuselage or a pod attached to the wing is achieved when the mean line of that pod is aligned with the free stream. Since the airflow around a wing is curved by the pressure field an axisymmetric pod is never optimum. All modern high performance sailplanes have cambered fuselages and the Piagio Avanti has one. Usually utility airplanes have their non-lifting structures designed by some other criteria such as cargo shape or production cost.

--Norm
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