Wright Stuff C

[jander14indoor]

commenting on Xiangyu's results.
Video, I find it a little hard to see what the plane is doing from that perspective, I recommend you take more from the side, I find it easier to see flight attitude that way.
Agree with Eric's comment on where you stand. Once you launch, back slowly away from the planes flight path, outside the circle. Less chance of the plane hitting you and as noted, you'd be surprised how much your body influences the local air movement. And back to the video, I personally find it easier to understand what the plane is doing from the side as opposed to being under it

General comment on mono vs bi-plane. Drag, yeah, at some point that becomes very important. With the faster planes this year, perhaps even more so.
I know you like the end posts to keep the wings tied together, but I'm not sure you really need them and I suspect they are a big source of drag. Consider sticking to the conventional solution of only two wing posts.
End fences. They do nicely taking the place of dihedral, but can be a surprisingly large source of drag if they aren't aligned correctly (think snowplow). You have the fences on both wings, consider dropping the lower ones, I suspect you don't need them.
Turn diameter. Turns are inefficient, we have to turn to stay in the gym, but larger turns are lower drag than smaller. Try to trim to the largest circle you can fly without significant risk of hitting the walls.

Jeff Anderson
Livonia, MI

[xiangyu]

Xiangyu,

As for possible improvements in flight duration under a 30 ft ceiling, there are many variables to test. Matching rubber to propeller, propeller design, propeller pitch and learning to wind close to 90% of breaking turns are a few of the most important. Actual projections of flight time I need to keep as private team information as you will understand.

Keep up the good work and keep up the research and testing.

Brian T

Of course. Good luck to you and your team!

[xiangyu]

commenting on Xiangyu's results.
Video, I find it a little hard to see what the plane is doing from that perspective, I recommend you take more from the side, I find it easier to see flight attitude that way.
Agree with Eric's comment on where you stand. Once you launch, back slowly away from the planes flight path, outside the circle. Less chance of the plane hitting you and as noted, you'd be surprised how much your body influences the local air movement. And back to the video, I personally find it easier to understand what the plane is doing from the side as opposed to being under it

Jeff Anderson
Livonia, MI

Yeah I discovered it's not very effective to film under the plane afterwards. I'll set up a tripod next time at the outer parameter of the circle and film it from there next time.

Thanks for the suggestion.

[lechassin]

Jeff, we aligned the fences with machine blocks and added lower fences after initial tests showed roll instability, hopefully our four small fences equals two larger ones. Our wings are very frail to spare as much weight as possible for the 18" motor stick, and we needed triangulated braces at the tips to keep the wings flat/square. The setup is really durable too, but yeah, we have two extra posts to drag through the air.

[lechassin]

I hope you'll all forgive this tedious post but I'd like to give details about our motor test and get some feedback:

We calibrated our torque meter using a formula we found online as well as actual measurements, and we were off by a factor of 2. We went with our measurements because our numbers were perfectly reproducible and perfectly proportional (twice the deflection doubled the number, etc...).

As for tests:

Our "32 inch motor": starting strand 66.625", weight unwashed and unlubed=2.75g (0.413 g/in density). Knot: full loop once, snug only to not damage the rubber, 1/2 loop over that pulled tight. Weight with O-rings/no lube=2.8g, with lube=2.9 g. Un-broken in relaxed length omitting O-rings=31.75". While pinching the un-knotted end the length was 32.25".

Break-in: 10x length=26.5 feet. Our rubber broke at the knot at 23 feet, and frankly I saw it coming There's absolutely no way the rubber was going to stretch to 26.5 feet, I hope to find out why.

We tied another knot, and to estimate what the motor would have been prior to break in, we tied a knot with scrap rubber and untied it to find it uses 1" of rubber, ergo we lost 1/2" of motor length by salvaging our test motor. 32.25"-0.5"=31.75" pinching the untied end. We stretched it 8x (not 7 for some reason ) to 20.5 feet for four minutes, after which the motor was 32.125" (3/8" increase). Relubed weight=2.85g (with O-rings).

Test Runs: our launch torque to get to the rafters is +/-0.3 in/oz. Rubber stretched to 5x (size of the room), moving in slowly at about 60%, moving in and out more (briefly) to relieve sudden torque increases, last turns put in slowly:
Run #1: 4110 turns @ 0.6 in/oz backed off to 3900 turns @ 0.3 in/oz
Run #2: 4200 turns @ 0.6 in/oz backed off to 3960 turns @ 0.3 in/oz
Run #3 (relubed): 4500 turns @ 0.9 in/oz backed off to 4110 @ 0.3 in/oz
Run #4: 4350 turns, broke in the middle of the motor at 0.6 in/oz.

From my reading of this data we should fly on the second run and if we are willing to take a risk, we can put in 4500 initial turns, expecting to fly with almost 400 less. 4300 would be safer and launch turns wouldn't be much less. I could not find the Bob Parker formula so I do not know exactly what is predicted, but these tests do confirm that we were being conservative at 3750 turns.

Thoughts?

[klastyioer]

I just came back from the gym. Overall it was okay. When we got there the fans were on blowing pretty hard and we tried to fly the plane but it didn't work out great (the fan is one of those that's attached to the ceiling and blows straight down - We consistently got around 50s - a minute in that condition). We flew for about an hour in that condition and then decided to look for another place with less current. (My school has 2 gyms so...) The other gym was better and we did a couple of flights (See details below) but then sports practice started and we had to leave, but I think we're off to a good start and we'll test again next Sunday.

Details of flight in "the good gym";

Time: 1 minute 8 seconds
Wing incidence: 5 mm
Rubber width: 1/16 inch
Rubber Weight (without the 2 black rings): 2.54 g
Winds Forward: 3000
Winds Backwards: 345
Torque: 0.16
Winds Left after Flight = ~ 300 (not exactly sure since the plane hit one of my teammates and released a bunch of winds before we recovered it)
Main problem - Steep decline at last second (perhaps due to rubber running out?)
Gym Height - ~30 ft

See counter-clockwise video here (we didn't have time to try out turning clockwise): https://youtu.be/ISIuRUXOGik

Let me know if you see something that I should change. I think the main problem is that we ran out of winds causing the final steep dive so we will probably add another 300-600 winds next time.

Xiangyu

how did you already get the kits apparently everyones got back ordered??

[xiangyu]

how did you already get the kits apparently everyones got back ordered??

I'm not sure, but my coach ordered pretty early in the season and emailed Dave last week. Our kits are probably the first batch.

Xiangyu

[bjt4888]

Eric,

Your on the right track for max turns and max torque.

There are a number of threads in Hip Pocket that discuss motor winding, max turns and torque calculation, etc. Look in the sections for the lighter duration classes like F1D, EZB and even Penny Plane.

Brian T

[lechassin]

Alright, I found this formula here: https://www.hippocketaeronautics.com/hp ... opic=983.0

N=√L³/w . √d . (x-1)√x/√2π

L is length=32"
w is weight=2.75g
d is density=2.75g/32x0.0625x0.0625=22g/in³
x is breaking stretch ratio: 23 feet is 276", divided by 32"=8.625

Solving gives N=4572 turns, which is amazingly close! We got to 4500 turns just as the torque was starting to climb very fast, which IMO represents imminent breakage. The motor broke on the next run at low torque, which confirms that 4500 turns mortally wounded the rubber.

90% is 4115, so we'll shoot for 4100 and back off to launch torque for now. That's 137 cranks on our 30:1 winder.

If we had rubber capable of stretching 10x, N would be 5800, or 1700 more turns. IDK if that would translate to longer flights because I don't know if the torque of stretchier rubber is also weaker?

[DatSciolyBoi]

how did you already get the kits apparently everyones got back ordered??

I'm not sure, but my coach ordered pretty early in the season and emailed Dave last week. Our kits are probably the first batch.

Xiangyu

I ordered mine last month a built it this weekend.