Plane descending too fast

[Bitconnect]

It definitely was the pitch. I increased the pitch of the prop to 40 degrees, reduced wing incidence to 3/32, made my stab LE 1/16 higher than stab TE, and the plane is descending slowly now. Launching at .4 inch-oz no longer shoots the plane into the ceiling, rather it climbs 3/4 the way up.

[klastyioer]

It definitely was the pitch. I increased the pitch of the prop to 40 degrees, reduced wing incidence to 3/32, made my stab LE 1/16 higher than stab TE, and the plane is descending slowly now. Launching at .4 inch-oz no longer shoots the plane into the ceiling, rather it climbs 3/4 the way up.

is that good or bad for u idk what ur goal is

[bjt4888]

Bitconnect,

Good job. Next step (probably you’re already doing this), wind to higher max turns and torque; probably keep the backoff and launch torque the same as your not all the way to the ceiling yet. Winding to a higher percentage of breaking torque will extend the flat portion of the unwinding torque curve. Try it on the torque meter without loading the motor on the airplane (wind and wind and record data points every 50 unwind turns).

Brian T

[bjt4888]

...wind and unwind...

[Bitconnect]

I was close to deadsticking so I intend to test with a longer motor and figure out how much to back off from max winds.

[bjt4888]

Bitconnect,

Good plan. Every additional inch of 3/32” rubber will take another 130 turns (approx). As the best setup Ikara propeller with the modifications you describe will spin at around 6.5 revolutions per second, 130 turns that another inch of rubber allows will likely increase duration nicely (if wound to 90% breaking turns and backed off appropriately for your ceiling height, you’ll find that about 50% of these additional turns convert do seconds on the stopwatch).

Keep testing additional pitch too.

Brian T.

[jander14indoor]

Longer motor means more mass, you'll probably need a slightly higher launch torque to get to the ceiling. May find you need a slightly thicker motor to increase cruise torque to offset the mass.
However, don't try to do everything at once, step by step, just things to watch for.
But I strongly suspect there is more time with more motor available.

Jeff Anderson
Livonia, MI

[Bitconnect]

I recently got some 1/8" to test with too, but I don't think I will have issues with 3/32" not giving enough torque. I'm not winding to max right now and have been backing off to .4 in-oz from .75 in-oz just for safety. I'll continue to increase the pitch slightly thought to see if there are further improvements.

[Polar]

So I've seen a lot of people mentioning backing off when winding. What is the purpose of this exactly? Is it to help prevent the rubber from snapping?

[jander14indoor]

To manage altitude gain (done by controlling launch torque) while maximizing turns (to maximize flight time).
Here's an experiment I recommend every year. You'll need a torque meter.
Make 3-4 identical 4 inch loops (convenient length, doesn't consume a lot of rubber, results scale).
Take the first and stretch wind till breaking. Take data on torque vs turns regularly, say every 10 or 20 turns. Graph it. You now know the breaking point of that thickness rubber for that batch of rubber.
Now, take a second motor and wind till 90% of breaking and unwind. Taking data on torque and turns in both directions. Graph it. Turns on X, torque on Y.
Do same for a third motor (this is science, you need to show repeatability). Oh, and of course you can re wind and take data on second wind, third, etc. Keep track of all that.
Now, examine the curves. You'll find for the first wind UP, the curves mostly (experimental variability) lay on top of each other. BUT, the UNWIND is way lower than the wind curve. Technical term for this is hysteresis, basically you never get back what you put into a storage system. You FLY on the unwind curve.
So, say you need 0.4 in-oz torque to get to a 25 ft ceiling. Examine your curves. If you wind up to 0.4 in-oz and launch you'll have x turns. But if you wind past 0.4 to say 0.6 and wind back to 0.4 you have x+something turns. More fuel (turns), longer flight.

Oh, how to scale to different length motors, same thickness. Just ratio the length of the loop. If it took 1000 turns to get a 4 inch motor to torque X, it will take 2000 turns to get an 8 inch motor to the same torque X. 3000 turns for a 12 inch motor to torque X, and so on.

Thickness can be scaled also, it affects the height of the curve, but not in so nice and linear a fashion and I don't have that formula memorized, sorry.

Jeff Anderson
Livonia, MI