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Old Mar 03, 2002, 02:10 PM
jah
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EDF50 SU25 Frogfoot

Making another attempt at making a GWS EDF50 powered plane. This time choose the SU25 Frogfoot as a subject. Its wing looked pretty close to the wing off a little lear from Walmart. This was a failed attempted to use the EDF50 for power. See these threads for details:
http://216.40.226.212/~admin2/forums...highlight=lear
http://216.40.226.212/~admin2/forums...highlight=lear

At any rate, have a question about ducting. I made the intakes larger than the exhausts. Additionally the interior is pretty rough, so my questions are:

Would photo paper exhaust ducting increase the thrust?
Would photo paper intake ducting increase the thrust?

At this point the intake looks larger than the fan, and there is a large cavity that is bigger than the fan on the intake side. The exhaust side has a cavity a little larger than the fan, but splits into two smaller, restricted exhaust ports. I would guess the intake side has over 2.5 sq inches, and the exhaust side about 1.75 sq inches. (NOTE: this is me just eyeballing it)

I think I am going to photo paper the exhaust side, and leave the intake alone. Let me know what you think.]

Thanks
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Old Mar 03, 2002, 02:11 PM
jah
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more pics

More pics
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Old Mar 03, 2002, 02:12 PM
jah
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Yet more pics
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Old Mar 03, 2002, 02:13 PM
jah
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Yes, more pics
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Old Mar 03, 2002, 03:35 PM
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NICE, what did you use to make the rudder out of? yes foam i know, but was it off of a wally world special?
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Old Mar 03, 2002, 04:08 PM
jah
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Yeah the tail is from an over-rampageous effort to convert a WalMart big glider (vs the little biz jet) into a Klingon Battle cruiser!

I put everything on a scale (R4P tx, 2 pico servos, 2amp ESC, EDF50, 6X110mah battery, and all the "airframe" and its under 200 grams right now. Expect to sand some more, then with glue, and tape be just over 200 grams. Hopefully the fan won't be too hamstrung with the ducting!
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Old Mar 03, 2002, 05:30 PM
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Nice choice! I was thinking of the Su-25 as a contest entry for two MF-480's ,love that wing planform!, but decided on the Bigger FA-18F Superhornet for two Kyosho Fans.

A little constructive critisizm...you would do very well to carve alot more foam out of this bird... My A-10 is made this way and I could
have thinned it out alot more.

Bruce
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Old Mar 03, 2002, 08:46 PM
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Keep the exhaust area at least as large as the swept fan area (area of face of fan minus hub) and both inlet ducting and exhast ducting as smooth as possible or you'll lose a fair bit of power :/ Nice looking so far
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Old Mar 04, 2002, 04:23 AM
jah
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Thanks guys, I already opened up both sides of the ducting, and started glueing in the photopaper to smooth things out.

Again thanks for all the input.
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Old Mar 16, 2002, 06:25 PM
jah
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PROGRESS

I have completed some more of the SU25. Whats left is permanently mounting the wings, shaping a removeable cover to go between the wings, linkages for the rudder/elevator, and painting it. Here are some specs:

Everything except the battery and paint it weighs 150grams (5 1/4oz). With a 6 cell 150mah it ways 196 grams (6 7/8oz), with 7X150mah its at 204 grams (7 1/4oz).

I ran it up and noted the following (the batteries have been sitting over a week, so I expect better performance hot off the charger):
With 6 cells I had approximately 30 grams of thrust (19mph efllux)
With 7 cells I had about 40 grams (25mph efflux)

By my caculations it has just over 70sq" of wing area.

Hopefully this one will actually fly!
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Old Mar 16, 2002, 06:29 PM
jah
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One more pic.
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Old Mar 17, 2002, 08:03 AM
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jah,great looking plane,but it looks like you need more horizontal stabilizer area. It looks like you have a template cut out thats bigger.
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Old Mar 17, 2002, 10:14 AM
jah
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Painted, ready to go

Here are some more pics:

Dblum, the template in the background is what I used to cut the elevator/stablizer. The fuselage just swallows it up, and I am kinda of worried. If it does fly, but has a problem in pitch, then I will retrofit bigger tail feathers. Right now I am worrying more about my CG. Will post a pic of the wing dimensions in a few, so maybe somebody can double check me.

Well thanks for the input, and here are the pics (the paint added 10 grams, so weight, minus the batteries, but otherwise ready to fly is now 160 grams.
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Old Mar 17, 2002, 10:15 AM
jah
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another pic

Yet more pics:
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Old Mar 17, 2002, 10:21 AM
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You'll want to add at least 10% to scale stab area for stability.
The edf is putting out 40 grams thrust which is approx. 1 1/2 oz.
From my experience, 1/4 Thrust to weight is barely flyable, 1/2 TTW will fly, 3/4 TTW will fly well and everything over that is gravy.Your at 7 1/4 oz without finishing. I think you need to somehow get the AUW down. And at 70 sq. in. wing area it will have to be a screamer to stay in the air. Just my thoughts.
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