Think it will balance?
05-04-2010, 10:02 PM
#1
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Think it will balance?
It's a pretty big plane, 55" span, Norvel .074s are shown in the drawing. I can extend them out from the LE a bit, and if that don't do it she's getting AME .15's! The guts will be as far into the D-box as possible, same for servos-might put them further out in the wing panels to take advantage of the forward sweep.
I kinda don't want it to balance with the .074's
But if it didn't, I'd be wishing I had built it stronger/different.
I kinda don't want it to balance with the .074's
But if it didn't, I'd be wishing I had built it stronger/different.
05-04-2010, 11:04 PM
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RE: Think it will balance?
Dave;
It should be pretty easy to figure out. The sum of the moments should equal 0...
So figure out where the CG should be (25-30% would be good)...weight the motor and times it by the distance to the middle ...and weigh the tail and times it by the distance...(you can approximate the weight)...same for any other structures such as the wing and the fuselage (guess at where each component will balance) ...add all the moments up and viola if it is positive it is nose heavy...negative...er tail heavy...zero would be right on.
Or...you could just build it and if it is tail heavy make the nose longer or put bigger engines on it...(heck sounds like you want the bigger engines anyway)...lol
I vote tail heavy...the forward swept wing will move the cg position forward and the engines are pretty far back...but I build my tails pretty heavy.
Steve
It should be pretty easy to figure out. The sum of the moments should equal 0...
So figure out where the CG should be (25-30% would be good)...weight the motor and times it by the distance to the middle ...and weigh the tail and times it by the distance...(you can approximate the weight)...same for any other structures such as the wing and the fuselage (guess at where each component will balance) ...add all the moments up and viola if it is positive it is nose heavy...negative...er tail heavy...zero would be right on.
Or...you could just build it and if it is tail heavy make the nose longer or put bigger engines on it...(heck sounds like you want the bigger engines anyway)...lol
I vote tail heavy...the forward swept wing will move the cg position forward and the engines are pretty far back...but I build my tails pretty heavy.
Steve
05-05-2010, 01:19 AM
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RE: Think it will balance?
Dave, I think that if you angled the tail booms to come to a point at the tail, I could definitely see a resemblance to one of those old timey rubber pusher models. I’d say put on left-handed props, the fin at the other end, make it a pusher and it ought to balance OK. Pushers need some weight on the canard.
al
al
05-05-2010, 02:41 PM
#5
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Thread Starter
RE: Think it will balance?
ORIGINAL: Doc.316
Dave;
It should be pretty easy to figure out. The sum of the moments should equal 0...
So figure out where the CG should be (25-30% would be good)...weight the motor and times it by the distance to the middle ...and weigh the tail and times it by the distance...(you can approximate the weight)...same for any other structures such as the wing and the fuselage (guess at where each component will balance) ...add all the moments up and viola if it is positive it is nose heavy...negative...er tail heavy...zero would be right on.
Or...you could just build it and if it is tail heavy make the nose longer or put bigger engines on it...(heck sounds like you want the bigger engines anyway)...lol
I vote tail heavy...the forward swept wing will move the cg position forward and the engines are pretty far back...but I build my tails pretty heavy.
Steve
Dave;
It should be pretty easy to figure out. The sum of the moments should equal 0...
So figure out where the CG should be (25-30% would be good)...weight the motor and times it by the distance to the middle ...and weigh the tail and times it by the distance...(you can approximate the weight)...same for any other structures such as the wing and the fuselage (guess at where each component will balance) ...add all the moments up and viola if it is positive it is nose heavy...negative...er tail heavy...zero would be right on.
Or...you could just build it and if it is tail heavy make the nose longer or put bigger engines on it...(heck sounds like you want the bigger engines anyway)...lol
I vote tail heavy...the forward swept wing will move the cg position forward and the engines are pretty far back...but I build my tails pretty heavy.
Steve
Really didn't want to, but I might have to put mini-nacelles on the front.
05-05-2010, 02:42 PM
#6
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RE: Think it will balance?
ORIGINAL: Big Al-RCU
Dave, I think that if you angled the tail booms to come to a point at the tail, I could definitely see a resemblance to one of those old timey rubber pusher models. I’d say put on left-handed props, the fin at the other end, make it a pusher and it ought to balance OK. Pushers need some weight on the canard.
al
Dave, I think that if you angled the tail booms to come to a point at the tail, I could definitely see a resemblance to one of those old timey rubber pusher models. I’d say put on left-handed props, the fin at the other end, make it a pusher and it ought to balance OK. Pushers need some weight on the canard.
al
LoL, pure genius! I looked at while drawing and thought it looked like some kind of rubber powered canard, but it never occurred to me to make it a pusher canard!
05-05-2010, 09:51 PM
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RE: Think it will balance?
If the outer panels had a straight line trailing edge instead of being swept forward I'd say you'd be OK if you can keep the tail end light. But as shown I'd bump the engines out by a good 1/2 chord length.
05-06-2010, 08:55 AM
#8
RE: Think it will balance?
The forward sweep looks cool, but yes, it's going to make it hard to balance. You will need to move the engines forward.
If you shortened the tail booms to save weight in the rear, be aware that it would require a MORE FORWARD center of gravity. People sometimes think they can improve a tail heavy condition by reducing the stab or shortening the tail, but it tends to be self-defeating, within reasonable limits. If you reduce the stabilizing power you have to have a more forward CG.
Just eyeballing it, you've got pretty big tail volume, and your balance point might work as far back as about 40%. But the forward sweep still puts it pretty close to the motors.
Jim
If you shortened the tail booms to save weight in the rear, be aware that it would require a MORE FORWARD center of gravity. People sometimes think they can improve a tail heavy condition by reducing the stab or shortening the tail, but it tends to be self-defeating, within reasonable limits. If you reduce the stabilizing power you have to have a more forward CG.
Just eyeballing it, you've got pretty big tail volume, and your balance point might work as far back as about 40%. But the forward sweep still puts it pretty close to the motors.
Jim
05-06-2010, 03:59 PM
#9
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RE: Think it will balance?
The tail area isn't set in stone, I just drew something on there that was close. I'm still debating on how to size it because the last time I sized a tail at 23% of wing area it was too small and I didn't like the way the plane flew. The problem with going too big on a plane with no real side area is that at high angles of attack/low airspeed it will fly like a pancake and yaw around a lot. My Aerocraft Snapper was like this circa 1994, and I was hoping to design in some improvement. The tail moment may actually be longer for this reason alone.
Starting to look like I need little nacelles.[
]
Starting to look like I need little nacelles.[
]
