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        Question 72" corsair .. @12 lbs

#1 screilly Jan 27, 2013 01:07 PM

72" corsair .. @12 lbs
 
I'm not sure of the brand the plane is but the Wingspan is 72" and weighs about 12lbs. I measured the wing root chord and the wing tip chord plus the swept distance. I actually entered all the data into a CG calculator that was part of another thread a while back.

http://adamone.rchomepage.com/cg_calc.htm



I can get a lot of different estimates by slight changes in the Static Margin % and the type of stabilizer efficiency. These are the specs that I entered.

Wing root: 14"
Tip chord: 10"
swept distance: 1"
1/2 wing span: 35.75"
________________________

Stabilizer root: 8
Stabilizer tip chord: 4.5
Stab sweep distance: 2.5
Stab half span: 13
Distance between both LE: 35
Stab efficiency: Std
________________________

Static margin: 7% .... because seems to be @ 1/2 way pt between 5% & 15%?

This gives me the following calculations:

MAC: 12.11
CG: 4.97

Does that seem right? Does anyone have a similar plane that could verify these calculations? I have talked to a few others way back in the past and they were saying 25% of the MAC .... That would be about 3.1" ( It does not sound like a winner here)? .... but depending on where you measure CG from, ... it may actually be a viable measurement. Keep in mind that the wing is swept so that measurement changes as you move from root chord to tip chord. Where is the correct location to establish the CG, ... At the "d" measurement: from the root chord to MAC .... which is 16.88" from the center of the Fuse ... out towards the wing tip, .... or right next to the fuselodge, ... or in the center of the wing right under the fuselodge itself?

I know thwere are a lot of different ways to get this and I appreciate your input.

#2 screilly Jan 29, 2013 06:58 AM

It seems that CG is measured from leading edge of the root wing chord and near the fuselodge area. The wing sweep does not start until after the gull angle of the wing design so anywhere before the wing changes angle would probably work?

Another question I have is about the stall speed? The calculator stats are saying around 28 mph. Is that a reasonable speed to assume? Does that suggest the landing speed is in the neighborhood of 28-30 mph? ... or more?

#3 Chad Veich Jan 29, 2013 11:49 AM

I scaled the Royal Corsair plans up to 72 inches span and the CG comes out to be 4.5 inches back from the leading edge at the wing root so the 4.97 number you arrived at is probably pretty close. I'm not sure what percentage of total area you are trying to arrive at but I generally shoot for around 27-28% for test flights on my new warbirds. Better to err on the side of nose heavy for test flying of course. Just keep in mind that whatever measurement you decide on it needs to be obtained with the fuel tank empty and the gear retracted, assuming you have retracts. Twelve pounds on a 72 inch span Corsair is very light and as long as it's built straight and true it should fly very well and slow down nicely for landing. I've never measured the true landing speeds of any of my airplanes so can't comment on the 28-30 mph stall speed other than to say it sounds plausible.

#4 screilly Jan 29, 2013 10:08 PM

It seems reasonable that 15 - 20 mph would get the tail up and if the plane were in an accellerated manner upwards to 30+ mph would sound like the ball park as far as typical to get it to begin a safe climb rate. Mybe 40 - 50 mph+ at a cruise rate?

Any thoughts on the OS 108 with the 16 x 12 prop?

#5 Chad Veich Jan 29, 2013 10:57 PM

Quote:

Originally Posted by screilly (Post 23975070)
It seems reasonable that 15 - 20 mph would get the tail up and if the plane were in an accellerated manner upwards to 30+ mph would sound like the ball park as far as typical to get it to begin a safe climb rate. Mybe 40 - 50 mph+ at a cruise rate?

Any thoughts on the OS 108 with the 16 x 12 prop?

That,s a lot of prop for the OS, IMHO. Best prop I found for my 1.08 powered warbirds was the APC 14X10.


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