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Author Topic: New sport ship...  (Read 560 times)
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Mugs914
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« on: September 19, 2017, 02:00:44 AM »

Greetings gents!

It has been a good long while since I have posted anything here on the forums, been lurking though.

Recently got back to the workbench after a somewhat extended hiatus due to the inevitable intervention of business and life matters. This is the result...

It was partially inspired by the old Graupner Cumulus and the Bell X-16, which was one of the initial designs for what ultimately became the U-2. The paint job came from the idea that the model might just represent some type of classified Air Force recce airplane from that era.

It spans 66", so it is on the small side, and is of all wood construction. The wing is a sparless design, the ribs and skins are 1/16" balsa with a 3/16 LE. The tail is 1/8 sheet.

The idea was to have a small, light sport type sailplane that could be hand launched, use a hi-start or tossed off of a slope on light lift days. To that end I tried to keep things reasonably light and the all up weight is just over nine ounces. There is space above the wing for ballast when conditions warrant.

Hoping to get in some initial trim tosses this week...

Thanks for looking!

Mike
Attached files Thumbnail(s):
New sport ship...
New sport ship...
New sport ship...
New sport ship...
New sport ship...
New sport ship...
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Konrad
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« Reply #1 on: September 19, 2017, 09:39:05 AM »

Will always have a soft spot for the Graupner Cumulus. I think she was the first mass marketed kit to do away with the banana shaped under-camber airfoil. This was the true start of R/C soaring, in which the ability to cover ground was found to be much more important than the dead air sink rate.

To that end what airfoil are you using? If it is your own drawn around a Florshein size 12.5 Roll Eyes , is it a flat bottom, semi-symmetrical, or an under-camber airfoil? Also what are your controls?

All the best,
Konrad
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Cut it twice and it's still too short!
Mugs914
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« Reply #2 on: September 20, 2017, 11:23:31 PM »

Hi Konrad,

I prefer to use my size 10 cowboy boot to design my airfoils, I usually prefer a pointier entry!  Grin

Seriously though, the airfoil on this one is a flat bottom, approximately 13% T/C with max thickness at about 35% of chord. All shoe-foil jokes aside, it does have a rather fine entry to help minimize drag. The wing is set at 2 deg. angle of incidence. I'm concerned that that might be a bit excessive, but time will tell.

The controls are rudder and elevator, but there is room in the wing for flap and aileron servos. Maybe on the next one (If it flies well enough warrant another!)

By the way, I really enjoyed your write-up on the Calypso. Made me want to go out and get one!

Mike
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Konrad
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« Reply #3 on: September 21, 2017, 09:34:07 AM »

Ah! The S-Kicker family of airfoils, they do motivate. Shocked  I’m sure you are aware that a sharp (relative term) leading edges really don’t work well at our Reynolds numbers. Yes, I know about the 0.015 leading edge of the F-104 Starfighter.

Yep, 2 degrees might be a bit excessive. I was surprised to learn that most "flat bottom", like the Clark Y, airfoils still produce lift down at negative 3 degree angle of attack!

Thank you for the nice comments about the Calypso write up. It isn’t my intention to sell whatever I’m writing about. Rather I post to try to help anyone (other than the marketing departments) that is thinking of getting or has the item, extract the most from their purchase. I hope it is clear that I hit the short coming of the product but also offer work arounds.

BTW, the Calypso with the mods (V1 tail incidence and flaps) really is a fine foamy. It might be a good ship to learn how to set up and use "Crow". Crow seems to be the bane of many a glider driver as they move up to higher performance gliders.

All the best,
Konrad
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dosco
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« Reply #4 on: September 28, 2017, 07:46:03 AM »

Mike:
Neat glider!

Regards-
Dave

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