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Old Oct 17, 2003, 04:35 PM
sethorus
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Enlarging Plans Based on Engine Size (A7 Corsair II propped)

I would like to figure what percentage I need to modify plans based on engine size. I have recently ordered the Rich U. plans for the prop driven A7 Corsair II. Everything I've read about this plane says its underpowered, it was designed for a .25 but people said it was adequately powered with 28s and 32s. I would like to enlarge the plans so the plane will accept an OS 46FX I have lying around and have plenty of power for the chosen enlargement. I don't want to try and cram this engine into its existing frame. Any advice, calculations or suggestions would be helpful.
Thanks,
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Old Oct 19, 2003, 03:11 PM
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Dick Huang's Avatar
Dallas,TX, USA
Joined Mar 1999
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sethorus,
You need to provide the current model's gross weight,wing span, and wing area before any meaningful recommendations to increase size can be made.
MY data shows that a 0.25 glow engine should provide about 0.475 hp and the .46 should provide 0.875 hp.With power and size data the enlargement can be estimated.

Dick Huang
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Old Oct 19, 2003, 09:42 PM
HAWK3Y3
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United States, VA, Hopewell
Joined Jun 2002
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SETHORUS,

I have also toyed with the idea a enlarging the plans. I built the House of Balsa A7 Corsair II. It is hot. I flew mine with a .25. Needed a lot of space to set up for the landing. I ended up adding flaps which helped greatly. It did not like to slow down. Tip stalled on final which lead to the modification of the wing.

I have talked with a few people who would be interested in building a 40 sized A7. No one knew the correct size to enlarge. If you can find the info, I will build on with you.
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Old Oct 20, 2003, 09:22 AM
sethorus
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Hawk, What mods to the wing do you recommend other than adding flaps or flaperon? Someone on another post enlarged theirs 30 percent to accept a .46 and also made the leading edge straight. I was thinking maybe 50 percent to use a .61. If bigger flies better than maybe this would help with some of its design shortcomings. Any other mods from anyone would be appreciated.
Thanks,

Seth.
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Old Oct 20, 2003, 03:31 PM
sethorus
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Dick, Here are the stock specs from Rich Uravitches site

Wingspan..........35.5"
Length..............36.7"
Weight.............3.2 - 4.2 lbs
Wing Area.......328 SQ. IN.
Power Req'd.....25 - .32 2c
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Old Oct 20, 2003, 05:02 PM
HAWK3Y3
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United States, VA, Hopewell
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The only modification was the addition of flaps. I also saw the post you are refering to. Interesting. A 30% enlargement sounds interesting. Nice to know that someone has one that flew. I may crunch numbers and look into it.
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Old Oct 21, 2003, 04:44 PM
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Dick Huang's Avatar
Dallas,TX, USA
Joined Mar 1999
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Quote:
Originally posted by sethorus
Dick, Here are the stock specs from Rich Uravitches site

Wingspan..........35.5"
Length..............36.7"
Weight.............3.2 - 4.2 lbs
Wing Area.......328 SQ. IN.
Power Req'd.....25 - .32 2c
sethorus,
I recommend a 12 to 13% increase in size to accomadate the
OS 46FX:
The new dimensions
Wingspan..........40"
Length..............41.4"
Weight.............5.3 lbs
Wing Area.......416 SQ. IN.
an equal power loading of 6 lbs/hp was used. This gave a new weight from 3.7lbs(.32=.608 hp) to 5.3 lbs(.46=.874hp). From previous experence about 40% of total weight is the airframe; this was scaled by K*(wing area)^1.5 to determine a new wing area.

The math has been omitted.

Dick Huang
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Old Oct 22, 2003, 09:09 AM
sethorus
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Dick, Thanks for the Info. As this will be my first scratch build kit does anyone have a good resource, book or link, on the subject. I have built many balsa 'kit' planes but am sure there are some new skills and equipment I'll have to obtain.
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Old Oct 22, 2003, 10:53 PM
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Oklahoma City
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a quick and dirty way to determin the weight change when scaling is the cube the scale factor. So if you make the plane twice as big it will be 8 times the weight. And if you make it half the size it will weigh 1/8th as much. One thing to be carefull of though is if you scale it by too much the engineering on the strength changes such that if you are scaling it up by a lot you need to make the structure a little big beefer and if you scale down by a lot you can trime down the structure a little and still be fine.

That is all based on G load stress and not aerodynamic stress so take it for what it's worth.
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