Wright Stuff B

[hogger]

One more time to be sure I understand this partial motor practice thing. Real gym is twice as high, make a fake 1/2 motor with a stick, then use 1/2 rubber motor, 1/2 the winds (theoretically same torque as if you use full motor and full winds), then try to trim to fly to maximum time. Then in theory, the maximum time aloft should be twice as much when you are actually at the real gym vs practice gym? Maybe this last part is not actually true. If not, what kind of time can we expect to get, so that we can get a sense of how to compare our time vs the estimated achievable time quoted here (around 3 minutes).

Finally, if you follow this procedure and properly trim your plane, you no longer need to worry about adjusting prop pitch or rubber width at the real gym because in theory they both scale and should match within a small margin of error. Maybe, you just need to slightly modify the initial torque by slightly changing the number of turns of the motor winding. Am I on the right track here?

[jander14indoor]

You more or less have it. Like most small scale tests, not everything works quite as easily as you describe, but as a first approximation you've got it.

Some examples for error in this technique.
The idea of winding to full torque is to see if the plane misbehaves in this condition. But of course it is at high torque for a shorter time, so in full motor flights a minor problem on half motor launch may grow to a major one.
A hidden assumption is you fly no touch (no ceiling bumps). Ceiling bumps are very unpredictable, sometimes you get good ones, sometimes not. Hard to replicate from half motors to full.

So, yes, half motors in a low site provide a lot of the development needed to fly in a larger site. I'd still take advantage of practice time in the higher site to make sure you don't have any surprises.

Jeff Anderson
Livonia, MI

[WrightStuffMonster]

I have about 200 pictures documenting the build to choose from and I started a write up. My intention is to update the wiki with a step by step building process which might be helpful to a few and I am going to try to post some videos of trimming which people may find more useful. Now I just need to find some time... Probably wont be all that useful this year as its kinda late but WS is going to come back.

[Pleiades]

..If our state competition is held at the usual gym, the ceiling height there will be almost twice as high as our home gym..

do you by any chance know the height of the gym?

how important is it to practice before the event in the actual gym? I wont be able to make the practice flight block because i'm in another event and i trust very few people with my plane [sad, isnt it?] Those that i do trust have events at that time as well. If i can find a gym with similar height, would i be able to skip the practice flight at the cometition?

[andrewwski]

I always just practiced in my school gym...it's a tad lower than the one we used at competition but pretty close.

I would make a few very conservative test flights before competition. Low winds. Enough to make sure that nothing was misadjusted during transport, but just a short flight so that it wouldn't get damaged.

[hogger]

do you by any chance know the height of the gym?

I think I'm not at liberty to discuss....

Just kidding. There are 2 gyms at Assumption. The most likely place will be at the new gym which from my memory, it is about 40 feet high give or take a couple of feet. Our home gym is about 25 ft high.

[GitItWright]

A) So, has anyone found that their motorstick is bowing under the high torque loads at launch?

It is indicated by-

1) Airplane rolls slightly to the left while entering a shallow dive.
2) Airplane flies fast, does climb and simply orbits until power bleeds off.
3) Airplane does not climb for half the flight then slows down, climbs slightly then stalls.

Assuming some teams will have this problem (many already do!), how about some suggestions....

As for B) What kind of flight times are teams getting consistently so far?

C) What Ikara or other style props are working this year?

Inquiring minds want to know-

[WrightStuffMonster]

I have had motor sticks bowing before under launch torque before. If i did not want to make another motorstick out of stronger wood, and had weight to spare, I would usually just glue a strip of 1/16 medium density balsa across the top of the motorstick. That is probably the easiest fix. I like the 8 and 7/8th inch Ikera prop for this years rules personally but I think that the 12" bulldog version could probably be made to work just as well or better. I have never had much luck with the 9.5 inch Ikera prop but I know a couple of fliers who are better than me that used it with good results. The 8 7/8th inch version is your best bet if you dont want to re-pitch any props.

If your plane is rolling to the left at the beginning and then dives and then wont climb and then stalls at the end it could also mean that you dont have enough wingin in your left wing panel. In fact, for the symptoms you describe I would almost say that not enough washin is probably a bigger problem then a bowing motorstick. I would suggest that you look into both.

[jander14indoor]

A) So, has anyone found that their motorstick is bowing under the high torque loads at launch?

Common problem with Wright Stuff planes from my observation as an event supervisor. But I have to agree with WrightStuffMonster about either lack of washin on your left wing or unevenly flexing wing spars giving same effect.

OK, stiffer motor sticks.

In addition to previous suggestion about slabbing a stick on top here's a few other approaches to fixing an existing stick:
- Smear a thin layer of balsa cement on top and bottom of the stick, helps more than you expect, but does add weight.
- Glue on some kevlar threads (its a plastic, should meet rules), top and bottom, they'll need to be stretched a little. Again, adds weight. Carbon or glass fiber would also work, but probably don't meet rules. Tissue might work too, again, stretch it a little and laminate down with balsa cement.
- Shorten the motor stick. There is no reason rubber length and hook to hook length have to match. Properly flown the motor will never unwind fully (though you want it close) so it will be tight for hook spacing much shorter than unwound motor length. This approach SAVES weight.

Better still is to make a new stiffer motor stick.
Most motor sticks are to floppy because someone choose a hard high density balsa for 'strength' and used a small cross section to minimize weight. BZZZZT, ERROR, wrong approach. You don't need strength, you need stiffness. For that you need your material as far away from the neutral axis (centerline of a sort) as possible. Thus hollow tube structures when weight is important. Think bike frame.
The ELEGANT solution is to make a hollow motor stick. Also the hard solution and a bit of overkill. Several spots on the web show ways to do this.
The expedient, easy, and very effective solution is to use much lighter balsa, significantly increase its cross section, and shorten the motor stick. Select the lowest density balsa you have and size to same weight as your hard floppy one. As a reference, my motor sticks are in the 1.8 to 2.2 gm range, leaning toward the higher side, saving weight elsewhere to hit 7.0 gm. You'll be amazed how much stiffer this is than a long, hard, skinny motor stick.

Note, there are situations where flexy motor sticks are useful, mainly very low ceiling flying. But in general for Wright Stuff, stiffer is better.

Jeff Anderson
Livonia, MI

[dinodude]

We've had similar problems when we wind over 1000 turns with 3/32" rubber. The plane flies quickly, banks too much left and can't climb--actually dives down and hits the floor. We think this is purely too much torque, and we've tried to fix with wash-in on the left wing and twist on the horizontal stab...not much success. Also, the left wing is larger than the right. We're getting the left wing wash-in (and right wing wash-out) by gluing the leading edge wing post slightly offset (about 1/16th to the right of vertical at the bottom). This seems to produce some wing twist, but the tissue tube doesn't hold the angle as we'd like and we lose some of the twist. Is the best way to get washin/out? Any tips to making it more effective? Of course, we'll go back and check to see if we're getting much motor stick flex--using 1/4" x 1/8" balsa, about 12" long.

For what its worth, we've ordered .08" and .085" rubber to experiment with lower torque motors. Could also adjust prop pitch, but we'd like to avoid that if we could. As always, the collective wisdom of the forum is greatly appreciated!