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Scaled up Somethin' Extra

Old 09-22-2004, 10:52 AM
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Default Scaled up Somethin' Extra

I need some input. As some of you are aware, I scaled up the Somethin' Extra to a 77" span bird. She ended up a bit heavy, just under 17 lbs. That is still around 24oz's/sq ft. She fly's nicely with an O.S. 1.60. I balanced her at 28% and have since taken 7 oz. out of the nose. She still feels sluggish to me, on the elevator. She requires no elevator trim for flight. When I roll inverted, she requires almost full down elevator on low rates(I would guess this to be about 15 degree's down elevator), to fly level. When I cut the throttle, she will fly extremely slow, but almost in a harrier position. She still is very stable though. My instinct tells me to take more lead out of the nose, but her nose high, slow flight characteristics tell me she is already getting tail heavy. The wing and engine are all at 0 degree's relative to the tail.

I would appreciate some feedback on your thoughts before I take anymore lead out.

Andy

I posted this in the Aerodynamics section also but didn't get much feedback. I placed it here in hopes of gettign more.
Old 09-22-2004, 10:54 AM
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Default RE: Scaled up Somethin' Extra

Here she is before taking 7 oz. out. Notice the nose high attitude already? She is flying here around 20-30 mph. With the extra weight out, it is very noticeable. She will fly in the 15 mph range, I would guess.


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Old 09-22-2004, 11:05 AM
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Default RE: Scaled up Somethin' Extra

Not sure why the picture didn't come up, I'll try again.
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Old 09-22-2004, 12:54 PM
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Default RE: Scaled up Somethin' Extra

If the incedences are pretty much 0-0-0 and it needs down elevator for level inverted then it is still nose heavy. I have several planes that I fly from nose heavy to very tail heavy. If it gets a little tail heavy it isn't like is suddenly going to be unflyable. In the pic you posted, were you holding up elevator to maintain that attitude? If not, I'd check your incedences as the fuse may not be straight with the wing and will always look tail low in level flight.
Later,,,Matt
Old 09-22-2004, 02:53 PM
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Default RE: Scaled up Somethin' Extra

Thanks Matt!

In the picture, I was feeding up elevator, but it wasn't responding. She reaches a point where all the sudden she rises quickly. That is what I meant by the elevator acting sluggish. The quick agility of the .40 isn't there. I know this is a much bigger plane, but there doesn't seem to be any proportionality in its agility. That is what makes me think she is nose heavy. The only reason I am afraid to take more lead out is that in a slow fly bye or landing, the nose is at 15 degree's or so. I am afraid that will continue to increase as the lead comes out, until she stalls easily. I guess I just need to hear from others that my thinking on the sluggishness and inverted flight is right.

Thanks again, Matt!

Bye the way, the incedences have been checked at 0-0-0.
Old 09-22-2004, 04:11 PM
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Default RE: Scaled up Somethin' Extra

Landing some of these bigger planes is where I have a lot of trouble. They don't seem to want to sink in like the 40 and 60 sizes. I have lost two 1/4 scales stalling them in on landing. It's like they don't want to quit flying and it gives a false sense of security. You may be on the edge with yours as well. I have found that these bigger planes have to be flown in to touchdown. Low speed and pulling on the elevator like that is a stall begging to happen and with a 160 at 17 lbs, it won't save it quick enough.
Good luck,,,Matt
Old 09-22-2004, 07:53 PM
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Default RE: Scaled up Somethin' Extra

I saw a scaled up Somethin Extra fly at my local field. It was in the air so I suppose thats flying, but it seemed to handle horribly. It was around 8' wing span with a G38 or G45 gasser. I think the builder just scaled up the plans to the size he wanted and built it that way, the wing chord was like....THICK!!! Much thicker than any of the typical Hanger 9 1/3 scale planes.

I'm sure others with more aerodynamics knowledge can chime in, but I don't think that you can just blow up the airfoil on the copier and expect it to fly the same. The scaled up plane is now operating in another Reynolds number range and a more appropriate airfoil should've been used.

Just some observations as you didn't mention anything regarding this.
Old 09-23-2004, 07:18 AM
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Default RE: Scaled up Somethin' Extra

Thanks for the input guy's! I did look into the reynolds numbers a bit and concluded that with the way the numbers are generated, going bigger was going to change them regardless. If anyone wants to give more input on that, I am definately open to it. On that note, however, I have made up my mind that if I shoot for building this plane at under 12 lbs, I will reduce the thickness a little. As I have said before, this bird fly's extremely well, too well. I am afraid it is deceiving me. If it is, I could be on the edge of stall right now and wouldn't know it until I burn an ounce or two of fuel too much. It it actually fun having the plane go into a natural harrier, but it is scarry at the same time. I have taken this plane up high and tried to stall the wing and she won't stall. I fly it slowly, using ailerons to stear it around, and it just keeps going.
Old 09-23-2004, 09:11 AM
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Default RE: Scaled up Somethin' Extra

I scaled up a Magic (80inch) got the weight to 13lbs flys great. The thought I was having is to check the angles on the flaperons, on the larger planes they act more like an elevator than flaps. You may be able to play with the angle and get the results you are looking for.

Verfur
Old 09-23-2004, 12:55 PM
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Default RE: Scaled up Somethin' Extra

Ineffective elevator is generally a sign of cg being to far forward, should be at 30-35%. SE has a positive incidence in the wing, doesn't like 0,0.

Mike
Old 09-24-2004, 06:07 AM
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Default RE: Scaled up Somethin' Extra

Hey Mike:

Do you know how many degree's positive the incidence is supposed to be? My .40 size SE is at 0,0,0.
Old 09-24-2004, 11:06 AM
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Default RE: Scaled up Somethin' Extra

Stock SE has about 2 degrees of wash in built into the wing. The root incidence is 0. I tried mine at -1 and -2 at the root and went back to the original setting.

Mike
Old 09-24-2004, 11:48 AM
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Default RE: Scaled up Somethin' Extra

Thanks Mike! I only measured mine at the root, so that would explain my reading. It also would explain some of the differences in flight between the .40 and the 1.60.
Old 09-24-2004, 04:52 PM
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Default RE: Scaled up Somethin' Extra

I wish they made a 60 or 90 size SE... I'd probably buy 2.
Old 09-27-2004, 07:37 AM
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Default RE: Scaled up Somethin' Extra

I honestly thought they would. I had hoped that when I contacted them about my project, that they would be inclined to come out with other sizes. With the $200.00 price tag on the .40 size, I would hate to see the price on a larger one.[X(]
ORIGINAL: ben beyer

I wish they made a 60 or 90 size SE... I'd probably buy 2.
Old 10-01-2004, 10:16 AM
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Default RE: Scaled up Somethin' Extra

The quick agility of the .40 isn't there. I know this is a much bigger plane, but there doesn't seem to be any proportionality in its agility.
performance isn't proportional, if you just scaled up the plans and built it, there are certain elements of the design that are designed into it for a 40 size plane. control surface and stabilzer areas and such, won't be mixed well for the performance of the .40. its like taking a Learjet enlarging it to the size of an md-80 and expectig it to fly with some bigger engines.
Old 10-26-2004, 05:10 PM
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Default RE: Scaled up Somethin' Extra

I just happened to discover this thread, and for those looking for a bigger SE, you might want to check out www.ak-models.com and their 3D Freedom. If anyone's interested, I think I can find a link to a really old thread that shows several 3D Freedoms and some mods.
For what it's worth, I just finished one this spring, and it flies great, rock solid either upright or inverted.
Hope this helps.

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