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Re: Wright Stuff C

Posted: January 29th, 2019, 5:36 am
by terence.tan
For more lift how should my front and back wing be angled relative to the fuselage?

Re: Wright Stuff C

Posted: January 29th, 2019, 6:01 am
by bjt4888
Albatross tree,

Actually, a motor stick length is not related to motor length. You can put a long motor on a short motor stick. For example, the AMA class called Limited Penny Plane requires in the rules a maximum motor stick of 12” and successful fliers often use 20” to 24” motors.

It is true that a longer motor will take more turns. As to how much this increases duration, the answer is “it depends” (on rubber thickness, airplane trim, propeller type and pitch, etc.). The best way to determine the best rubber length and thickness is to test many variations.

Brian T

Re: Wright Stuff C

Posted: January 29th, 2019, 6:04 am
by bjt4888
Terence.tan,

What are you trying to accomplish with “more lift”? Describe the issue you are encountering; give us the details of your airplane design, trim settings, propeller and pitch, rubber and winding specs and we can give very specific help.

Brian T

Re: Wright Stuff C

Posted: January 29th, 2019, 6:23 am
by AlbatrossTree
Albatross tree,

Actually, a motor stick length is not related to motor length. You can put a long motor on a short motor stick. For example, the AMA class called Limited Penny Plane requires in the rules a maximum motor stick of 12” and successful fliers often use 20” to 24” motors.

It is true that a longer motor will take more turns. As to how much this increases duration, the answer is “it depends” (on rubber thickness, airplane trim, propeller type and pitch, etc.). The best way to determine the best rubber length and thickness is to test many variations.

Brian T
Thank you for the help. Bit confused as to why the FF kit suggests extending the motor stick for nonbeginners if motor stick length isn't a big constraining factor...

Re: Wright Stuff C

Posted: January 29th, 2019, 6:33 am
by OpticsNerd
Albatross tree,

Actually, a motor stick length is not related to motor length. You can put a long motor on a short motor stick. For example, the AMA class called Limited Penny Plane requires in the rules a maximum motor stick of 12” and successful fliers often use 20” to 24” motors.

It is true that a longer motor will take more turns. As to how much this increases duration, the answer is “it depends” (on rubber thickness, airplane trim, propeller type and pitch, etc.). The best way to determine the best rubber length and thickness is to test many variations.

Brian T
Thank you for the help. Bit confused as to why the FF kit suggests extending the motor stick for nonbeginners if motor stick length isn't a big constraining factor...
Extending the motor stick allows the plane to have slightly higher torque later in the flight.

Re: Wright Stuff C

Posted: January 29th, 2019, 9:13 am
by bjt4888
All,

The rest of the story; although a long motor can be mounted on a short motor stick, it is easier to mount a long motor on a long motor stick. Easier because it is not necessary to use sleeves (small pieces of tubing that the motor slips into) on the motor next to the rear hook and front hook. Sleeves prevent the motor from creating bunches of knots up against the front or rear hooks. Bunches of knots interfere with the smooth unwinding of the motor and also cause a shift in the center of gravity leading to diving or stalling.

So, what is a good match of motor stick to rubber motor length? Generally, motors longer than 1.5 times the hook to hook distance start to have bunching or knot chain (sticking out and rubbing on the stick) problems. So, if you plan to use an 18” motor, or so, a 12” stick, or more, is a good idea, etc.

The other benefit of a longer motor stick is overall fuselage length that lengthens the tail moment arm (basically, the distance from the wing TE to the stab LE). A longer tail moment arm allows a more rearward CG location which generally allows a lower decalage angle which generally reduces drag, improving the lift/drag relationship of the flying surfaces (more efficient).

The above is complicated by this year’s rules allowing what is essentially a tandem (wing and stab almost the same size). The best way to sort out the complications of the tandem configuration is to test and test and test.

Very good questions. You all are heading in the direction now of the Clay Mathematics Institute Millennium Problem for smooth solution of the Euler Equations (just kidding, but look it up; $1,000,000 prize up for grabs).

Brian T

Re: Wright Stuff C

Posted: January 29th, 2019, 7:24 pm
by terence.tan
Terence.tan,

What are you trying to accomplish with “more lift”? Describe the issue you are encountering; give us the details of your airplane design, trim settings, propeller and pitch, rubber and winding specs and we can give very specific help.

Brian T
Our rubber thickness .109. The distance between the propeller and metal hook is 40cm while our rubber motor is 50cm. Our plane without the rubber is around 9 grams. and we do around 1350 winds. Our plane would go up around 2-3 feet. I am unsure about how to angle the front and back wing.

Re: Wright Stuff C

Posted: January 30th, 2019, 2:49 am
by klastyioer
Terence.tan,

What are you trying to accomplish with “more lift”? Describe the issue you are encountering; give us the details of your airplane design, trim settings, propeller and pitch, rubber and winding specs and we can give very specific help.

Brian T
Our rubber thickness .109. The distance between the propeller and metal hook is 40cm while our rubber motor is 50cm. Our plane without the rubber is around 9 grams. and we do around 1350 winds. Our plane would go up around 2-3 feet. I am unsure about how to angle the front and back wing.
yea increase the front being post angle and decrease the back wing post angle if necessary . what's the torque on that motor when you wind to that?

Re: Wright Stuff C

Posted: January 30th, 2019, 4:38 am
by bjt4888
Terence.tan,

Good job supplying initial specs. Typical decalage angle (difference between wing surface angle and stabilizer surface angle as measured from a reference point like the top of the fuselage stick) for this year’s rules is between 2.5 and 5 degrees, depending upon other specs of your design.

If your stabilized is perfectly flat (leading edge and trailing edge same distance from the extended reference point that is the top of the fuselage stick) and the wing leading edge is 1/8” higher than the trailing edge, this is about 2.6 degrees of decalage. Use a long straight edge to extend the fuselage top edge for measurement. This might take two people to do. And, of course, 1/4” would be 5.1 degrees.

Climb rate is more affected by propeller pitch and type and launch torque and rubber thickness than decalage angle. What is your rubber length, max torque, backoff turns, launch torque, propeller diameter, propeller pitch and propeller type. Overweight will also affect the flight character quite a bit.

Good job reaching out to research your project.

Brian T

Re: Wright Stuff C

Posted: January 31st, 2019, 6:15 pm
by sciencegirl03
Terence.tan,

What are you trying to accomplish with “more lift”? Describe the issue you are encountering; give us the details of your airplane design, trim settings, propeller and pitch, rubber and winding specs and we can give very specific help.

Brian T
Our rubber thickness .109. The distance between the propeller and metal hook is 40cm while our rubber motor is 50cm. Our plane without the rubber is around 9 grams. and we do around 1350 winds. Our plane would go up around 2-3 feet. I am unsure about how to angle the front and back wing.
There are a couple of factors that may help you rise more.

1. In terms of angling your front and back wings relative to each other, your front wing should be higher than the back one. The leading edge of the front wing should be higher than the trailing edge, and you should play around with that angle until you find the perfect spot. The back wing's leading and trailing edges should be relatively horizontal. You may have to lower the entire back wing if your plane still doesn't rise.
2. Try more winds. I feel like you can definitely get more winds in your rubber band. Try winding a rubber band until it breaks and then consistently winding to 70% of that value. Try this at first, but you'll eventually have to unwind a little bit to release excess torque.
3. If the nose of your plane tends to drop as soon as you release, the front of your plane may be too heavy (aka the center of gravity is too far forward). To fix this, you'll need to move the entire wing FORWARD.

There are other ways to generate more lift regarding the propeller pitch, etc, but this much should get you to 20+ feet.
Hope it all works!