Circular

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Re: Circular

Post by 28builder » November 28th, 2014, 7:27 am

oops previous pot wasnt finished. meant to say appreciated!! when you say the stabalizer tilted to the right. are you looking at the plane front to back or back to front? if i were looking at the plane from the back would the stab be slightly lower on the right side? thanks again first time fliers and the plane go straight currently

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Re: Circular

Post by jander14indoor » November 28th, 2014, 10:52 am

You have it, from back, stab lower on right side than left. With wings level, about 1/2 inch difference is a good starting point.

Jeff Anderson
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Re: Circular

Post by someusername » November 30th, 2014, 8:45 am

I had a question not really on how to make the plane circle to the left, but more-so why it circles. I understand that the left part of the wings trailing edge is lower than the left sides leading edge, but in my mind that just makes the left side have more lift and make it want to circle right. Would that change in the leading and trailing edge cause more drag and slow the side down more? Also on the horizontal stabilizer the left side is higher than the right, but again that just doesn't makes sense in my head of why that makes it turn to the left.
simplicity is key...sometimes

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Re: Circular

Post by artysophia » November 30th, 2014, 7:10 pm

Uhm so I also have a question. Looking from behind the trailing edge of the wing, is the back wing post supposed to be angled towards the left or right?

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Re: Circular

Post by jander14indoor » November 30th, 2014, 7:55 pm

Note, this is getting into advanced discussion, you should probably skip this unless you are already flying > 1 min and able to get to the ceiling in a typical school gym.

OK, why do we turn left. Heck why do we turn at all. The later is easy, with these things capable of flying for 3+ minutes, you can't fly in most sites in a straight line.

Now, why left.

It starts with that big, slow turning prop. It takes a lot of torque which has to be reacted somehow. Newton equal and opposite can't be ignored. The prop conventionally spins clockwise (when viewed from the back). That means the plane tries to spin the opposite way, rolling left, forcing a left turn. Thus the need for the wing to be longer on the left and have a higher angle of lift just to bring the wings back to level (mostly at least) for maximum lift. It also stops the plane from just continuing to roll left and into the ground. Which it will do if you let it. And yes that adds drag on the left side, slowing it down, also forcing a left turn.

You can force an indoor plane to turn right, but the lift on the left side as to be lots higher to actually get a right bank and you have to add a LOT of right rudder to offset that left wing drag. Overall a MUCH draggier trim state and shorter flight.

Now the rest of the trim is just to keep the turn a constant size over the full speed range these planes fly at.
The prop is actually set with its access down and left to offset the excess lift at high torque (max winds) and off set the excess left wing lift (which increases left turn radius, sometimes to point of right turn) at higher speeds with left thrust.
The tilt of the stab to the right causes a left turn because of force vectors. To all intents and purposes the lift from a flat wing or stab is perpendicular to the surface left to right. If the surface is tilted right that force vector points up AND right. That right component pushes the rear of the plane right, pivoting the nose to the left. Another left turn. This force becomes dominant at slower speeds.
The vertical stab is typically set for a left turn too. But set properly it doesn't so much control turn, but just minimize drag in a plane that's turning anyway.

The goal for all those adjustments is to get a plane to fly with lowest drag on a relatively constant radius circle (so you can predict where it will be flying in these relatively small flying sites) in spite of the wide range of speed conditions these planes fly over (not as wide as gliders, but still pretty wide).

Hope that makes sense, if not, feel free to keep asking questions.

Jeff Anderson
Livonia, MI

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Re: Circular

Post by someusername » December 1st, 2014, 3:26 pm

Thank you very much. That answered all my questions and then some, Should help to get a little more time into my flights without increasing the number of winds.
simplicity is key...sometimes

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Re: Circular

Post by artysophia » January 15th, 2015, 7:24 pm

How small is considered too small a circle in terms of circular flight? My plane is flying in relatively small circles. Also, I can't get it to climb. I was testing out a plane built from the freedom flight model kit

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Re: Circular

Post by jander14indoor » January 15th, 2015, 7:43 pm

Smaller will always hurt time over larger, MUCH more drag so more power required to climb and MUCH shorter duration.

One year my daughter and her partner spent a lot of time trimming and had a very good flying plane. The design they used allowed easy adjustment of tail tilt to control circle and they knew to set it for larger circles. Well, come the state tournament they practiced carefully and had the plane trimmed for a potentially tournament winning flight. Come time to launch, the bumped the tail tilt dropping from a 40 ft circle to something less than 10. Time went from two plus minutes to less than 30 second.

I cried. Saw it happening and couldn't (wouldn't) do anything. Almost bit through my tongue. While I taught them everything I knew in practice, they built their own planes and at contests I stood as far away as I could and zipped it.

Never coached that design feature again.

Learn to adjust the circle at the contest, not too hard. Use as much of the room as you are comfortable with. More if no air moving, say 75 % of the narrowest dimension. Less if lots of air, say 50%.

So, open the circle and you should climb better. Also, check the left wing wash in, make sure the plane is flying close to level. Both will help climb and times a surprising amount.

Jeff Anderson
Livonia, MI

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Re: Circular

Post by Chris_L » January 15th, 2015, 8:59 pm

Getting it to climb better might be a combination of multiple things.
1. Change the pitch on your propeller, more angle for better climb.
2. Try adjusting your leading and trailing edges maybe but the leading edge 1/16" or less up.
3. Winding, try using a heavier rubber and winding it more, you could very well be under-wound for the plane.
However, these are not panaceas and you should try and test and keep testing.
"A wise man can learn more from a foolish question than a fool can learn from a wise answer." -Bruce Lee

When asked what his IQ was, Stephen Hawking said "I have no idea. People who boast about their IQ are losers"

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Re: Circular

Post by bjt4888 » January 16th, 2015, 9:44 am

artysophia,
Congrats on constructing a great airplane! If you could please supply more data, I could answer your question. For example: what thickness and length is your rubber motor, how many turns are you putting in it (what are you lubricating it with), are you backing off any turns on the rubber motor, are you using a torque meter (very important), if so what is the measured maximum and launch torque, what is the wing incidence setting (ex. leading edge 3/32" higher than trailing edge, which would be per plan and which would be 1.73 degrees positive), is the stabilizer incidence as suggested in the kit plan and instructions (positive 0.65 degrees with the tailboom bottom edge in line with the motor stick bottom edge)(these incidence settings will result in a decalage angle of 1.08 degrees), is the center of gravity with the motor installed per the plan at 2.75" behind the wing trailing edge and is the stabilizer tilt per the plan at left tip 3/8" higher than the stabilizer center, and is the left wing washin per the plan at 3/32" (leading edge higher than the trailing edge) and are all other flying surfaces unwarped?
The three high schools that I am coaching have constructed eleven of these Freedom Flight airplanes so far and all are achieving over three minutes duration in gyms that have about 25 - 27 ft ceiling heights (best flight to date with the stock propeller 3:16). If you can supply the above data, I can give you specific ideas of what to try next.

Brian T.
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NFFS for a very long time too

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