Circular

someusername
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Re: Circular

Post by someusername »

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
artysophia
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Re: Circular

Post by artysophia »

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
jander14indoor
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Re: Circular

Post by jander14indoor »

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 »

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

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Re: Circular

Post by bjt4888 »

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.
AMA since 1972 (off and on)
NFFS for a very long time too
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Re: Circular

Post by torqueburner »

jander14indoor wrote: . . .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.

. . .Hope that makes sense, if not, feel free to keep asking questions.
When we originally read this, it matched up perfectly with our experience, and we had no trouble with our planes flying well, in a circle of approximately constant radius. But during this morning's flying session we had an experience that has us scratching our heads.

The plane in question has twin stabilizer end plates at an angle of about 15 degrees from vertical. The stab is angled and the tailboom is set at an angle consistent with a left turn. The thrust line is angled to the left. Originally, we had the tailboom angled too much, and the plane flew in a circle with a diameter of only about 15 feet. Too tight, but it flew well enough to do 2:45 in a venue with about 25 feet of flyable height. This plane was also flying the bonus wing with a 7 cm chord. Not too bad, but we wanted to enlarge the circle, so we decreased the tailboom angle.

The first few flights were made with a prop pitched to P/D = 1.5. This went pretty well, with a nice circle of about 30-35 feet, though we did notice that it took a little while for the plane to start circling properly. This was easy to compensate for by shifting the launch position to a different part of the gym.

Next, we wanted to try a prop with a higher pitch - P/D = 1.7. Now the plane really didn't want to turn; it headed for the side wall, not quite a straight line, but pretty close. We retrieved it from its landing spot and relaunched, and then it circled to the left, , about diameter about 30-35 feet.

So it appears that the plane doesn't want to turn when the torque is at its greatest, and the plane is flying fastest. Do I remember hearing that the rudder is more effective at higher speeds? If so, do the above observations suggest that we increase the tailboom angle a bit? We are planning to try this, of course, but we have the usual problem that gym access is severely limited, as we are not basketball players, or the like:( So if we can get an idea of what else to try, it might help us to save some time.
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Re: Circular

Post by bjt4888 »

torqueburner,
One possibility would be that the motor you are using cannot operate the higher pitch propeller well enough to create the airspeed necessary for the tailboom offset or the stabilizer tilt to create adequate turn. We had this exact result as propeller pitch was increased or when substituting a "softer" flaring propeller or when substituting a broader bladed propeller. One possible solution would be to try a slightly thicker rubber motor. Our experience doing exactly this was the thicker motor (we substituted an 0.94" motor for a 0.90" motor) tightened the turn up nicely and flew the airplane through an excellent climb/cruise/letdown pattern. That being said, my students are getting their best duration with a slightly narrower bladed propeller with slightly less pitch (about 13.5" pitch) that has good flaring capability and with 0.087" motors. Best duration using this combination has been 3:16 in a gym with 27 ft. flyable height. Best duration with the broader bladed balsa "Bucket" propeller (also about 13.5" pitch and weighing 1.2 grams) is 3:10 at a flying height of 21 ft (different site). This propeller shows a lot of promise, but so far the students have not had the time to continue testing it. Unfortunately, the students need to set their airplanes to fly in about a 20 - 25 ft circle as the regional site they are preparing to fly in is the size of a single basketball court with goals projecting into the court on three sides. This smallish flying circle probably affects duration a bit.

Good luck and good flying,

Brian T.
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Re: Circular

Post by jander14indoor »

First, whenever you notices sudden changes in a plane that has otherwise been flying OK, check for something broken. Can be very subtle sometimes and not always the cause, but check.

Turn radius with a higher pitch, surprises me that your turn opens up. Normally more torque rolls the left wing down decreasing turn radius. Perhaps the pitch was so high the prop stalled and you were not rolling as much as before? Are you sure the prop axis is angled left? Again, higher pitch prop, more thrust, generally tightens turn.

Reading carefully I'd really check the prop axis. Consider more tail boom angle and stab tilt, one at a time.

Jeff Anderson
Livonia, MI
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Re: Circular

Post by torqueburner »

bjt4888 wrote: One possibility would be that the motor you are using cannot operate the higher pitch propeller well enough to create the airspeed necessary for the tailboom offset or the stabilizer tilt to create adequate turn.

jander14indoor wrote:First, whenever you notices sudden changes in a plane that has otherwise been flying OK, check for something broken. Can be very subtle sometimes and not always the cause, but check.

Turn radius with a higher pitch, surprises me that your turn opens up. Normally more torque rolls the left wing down decreasing turn radius. Perhaps the pitch was so high the prop stalled and you were not rolling as much as before? Are you sure the prop axis is angled left? Again, higher pitch prop, more thrust, generally tightens turn.

Reading carefully I'd really check the prop axis. Consider more tail boom angle and stab tilt, one at a time.

Jeff Anderson
Livonia, MI
Thanks, Brian and Jeff. Since this happened right after decreasing the tail boom angle, that is probably the first thing we'll try, after double checking the thrust axis. It was angled to the left, but perhaps it has loosened up and shifted.

Dave D.
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Re: Circular

Post by torqueburner »

jander14indoor wrote:First, whenever you notice sudden changes in a plane that has otherwise been flying OK, check for something broken. . . . Reading carefully I'd really check the prop axis. Consider more tail boom angle and stab tilt, one at a time.

Jeff Anderson
Livonia, MI
Well, some bad weather forced an early dismissal, but we were able to sneak down to the gym for a few flights. We discovered that the thrust bearing had indeed loosened. We fixed that. Back in business! So as Jeff said, the lesson here is to check the plane for something broken if anything changes suddenly.

Dave D.
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