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Old Dec 05, 2012, 09:56 AM
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Blacksburg, VA 24060 USA
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But with a wide angle view, you don't have to get the airplane up at a ridiculous height in order to get shots like "aerial image."

Jim R....
...who has scared himself for flying to speck height...
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Old Dec 05, 2012, 06:01 PM
Lift is cheap - Drag sucks
Tom Harper's Avatar
Socorro, NM
Joined Jul 2004
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Development

Covered the mount with silkspan. I'll let it set up another night and then sand it.

The photos show some trash on the port window so I removed it and found a coating of fine sawdust and several balsa chips. I thought I had taped the lens port but appearently not enough. So, replaced the window and sealed the lens port with tape. It will only be removed as the camera is put in place immediately before launch.

Scheduled to fly again Saturday.

Tom
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Old Dec 06, 2012, 09:15 AM
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Blacksburg, VA 24060 USA
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If you will be flying in dry conditions, beware that, when you pull the tape off the window, static electricity might attract more grunge.

Jim R.
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Old Dec 06, 2012, 10:03 AM
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Originally Posted by JRuggiero View Post
If you will be flying in dry conditions, beware that, when you pull the tape off the window, static electricity might attract more grunge.

Jim R.
If that were true why do all the grunge bands come from Seattle? Sorry, couldn't resist.
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Old Dec 06, 2012, 11:05 AM
Lift is cheap - Drag sucks
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Socorro, NM
Joined Jul 2004
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Norm!

Good to hear from you. How are you doing?

Tom
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Old Dec 06, 2012, 11:19 AM
Lift is cheap - Drag sucks
Tom Harper's Avatar
Socorro, NM
Joined Jul 2004
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Development - CG

I've been concerned about the impact of all the mods on the CG. Found the attached drawing that Norm did a couple of years ago and measured the current CG against it.

The CG is 7 inches behind the reference line of the drawing. That's just ahead of the E-point. Changing from two Lipos to one moves it back to about 7.25 inches. I believe I'll leave it there.

Norm, comments?

Tom
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Old Dec 06, 2012, 11:30 AM
Lift is cheap - Drag sucks
Tom Harper's Avatar
Socorro, NM
Joined Jul 2004
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JR,

Excellent point.

The tape I referred to covers the hole in the camera mount where the lens looks through.

The problem surface is the clear stuff on the bottom of the wing. I have to clean it just before launch but you can see it attract lint and dust as you clean it. Probably the best approach is to use the cloth that comes with the camera and wipe the surface very slowly.

Tom
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Old Dec 06, 2012, 06:43 PM
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Originally Posted by Tom Harper View Post
I've been concerned about the impact of all the mods on the CG. Found the attached drawing that Norm did a couple of years ago and measured the current CG against it.

The CG is 7 inches behind the reference line of the drawing. That's just ahead of the E-point. Changing from two Lipos to one moves it back to about 7.25 inches. I believe I'll leave it there.

Norm, comments?

Tom
That CG range looks fine, Tom. Theoretically it will be most efficient nearer the E-point but the 1/4" difference will probably be so small that you won't notice it. It's mostly an induced drag difference anyway so it would only show up in slow flight. Both pitch and directional stability go up with forward CG though. Are your elevons neutral in cruise?

--Norm
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Old Dec 06, 2012, 06:50 PM
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Norm!

Good to hear from you. How are you doing?

Tom
Been more busy than I'd like. Reading my internet stuff but not participating as much because of real world responsibilities.
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Old Dec 06, 2012, 07:25 PM
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Quote:
Originally Posted by JRuggiero View Post
But with a wide angle view, you don't have to get the airplane up at a ridiculous height in order to get shots like "aerial image."

Jim R....
...who has scared himself for flying to speck height...
.
With a good wings level pass, it's possible to get enough images to stitch together for a panorama.
Here's two stitched together from the GoPro...
With that ultra-wide angle lens, any looking up or looking down distorts the horizon too much to get a decent sequence of stitchable images.
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Old Dec 06, 2012, 08:04 PM
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Those ultra-wide lenses are only decent for level images... any looking up or down gives a very distorted image.
110 degree field of view is nice though.
Pictures are nice but your lawn looks like it needs a bit of water --
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Old Dec 06, 2012, 08:19 PM
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I don't water my lawn any more.. had the whole thing concreted, no yard work at all!
That desert is really bright in the summer time.
I was using the Futaba autopilot to put a fun-fly plane into an auto-hover mode, ala Don Incoll in Australia... The Futaba looks for the difference between the dark ground and the lighter sky.. but the desert tends to brighter than the sky, so the plane wanted to hover nose down... Works poorly...
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Old Dec 08, 2012, 07:02 PM
Lift is cheap - Drag sucks
Tom Harper's Avatar
Socorro, NM
Joined Jul 2004
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Development

Nice 5.2 km flight today. Got some more data:

Max airspeed - 107 kmh
Stall speed - 45 kmh
7 Amps cruise current (60kmh)
76 Watts cruise power (60 kmh)

It takes about 500 mah for take off and landing, so the range on a single 1600mah lipo is 12 km at 60 kmh. I used two cells today for safety.

The aerial photos are useful for data but are not 'good'. On autopilot the model is oscillating 20 degrees or more in roll causing some blur. I have to change the linkage gain and work on the autopilot constants.

We were losing power due to vibration in the temporary motor mount and the damaged motor. Eliminating the oscillations and removing one lipo may get cruise current down to 6 or even 5 Amps.

Tom
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Old Dec 08, 2012, 08:53 PM
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Roll oscillation is usually caused by excessive dihedral effect, specifically the skid roll moment. Since your cruise CL is pretty low the dihedral effect due to sweep should also be low. That leaves the dihedral effect of the tip fins.

I'm just guessing here but it sounds like you're skidding and the tip fins are turning the cross wind into rolling motions.

You can reduce the skids by moving the CG up to Sine^2.5 but at the cost of some extra induced drag.

There are two ways you can change the geometry of the tip fins to reduce the skid/roll moment:

1: Area above the wing adds to the dihedral effect and area below the wing subtracts from the dihedral effect so if the area of the tip fins is equal above and below the wing the contribution to the skid/roll moment should be neutral. Of course this would mean having a large fin hanging down below the wing which will get knocked off a lot.

2: The other way is a trick that Burt Rutan used on the Long-EZ and pictured on this thread.

--Norm
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Old Dec 08, 2012, 11:02 PM
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Fin below the tips would dig the prop into the ground... prolly have to add a small nose ventral fin along with the lowered tip fins.
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