Wright Stuff C

[coachchuckaahs]

Wouldn't the shim prevent nosediving as well as a reduction in the circle radius? For example for a left (clockwise) turn the shim should be positioned such that the right side of the wing has a higher angle of attack, which prevents spiraling inwards.

The wash-in should be on the inboard wing. I believe the FFM kit uses shims to accomplish this.

A "Left: turn would be counter-clockwise (viewed from above), and would require left wing wash in.

Coach Chuck

[vehicleguy]

What do you mean by more load on the prop, just more weight?

[coachchuckaahs]

What do you mean by more load on the prop, just more weight?

More pitch, more prop area, different planform. Anything to load up the rubber in torsion, or slow down the prop.

Prop load and rubber width work together. Keeping same rubber but loading up prop may help your time, but it just optimizes with that rubber. It may be thinner rubber with same prop shows greater gain. Need to map out the response space with both variables to find a better optimum.

Coach Chuck

[xiangyu]

I just did a quick test with my plane, seems like new prop isn't that good as juat a regular cut down prop. (Could be that it's not fully optimized as well). Just got 1:45 to the right with cut down prop and only 1:37 with new prop) I kept everything the same, and took off a bit weight when I put on the prop as it is slightly heavier than regular Ikara.

Gonna test a bit more, will let y'all know what I find.

Xiangyu

[coachchuckaahs]

I just did a quick test with my plane, seems like new prop isn't that good as juat a regular cut down prop. (Could be that it's not fully optimized as well). Just got 1:45 to the right with cut down prop and only 1:37 with new prop) I kept everything the same, and took off a bit weight when I put on the prop as it is slightly heavier than regular Ikara.

Gonna test a bit more, will let y'all know what I find.

Xiangyu

Keeping everything the same would not probably work. every prop will need rubber optimization. No reason to expect this new, different prop would optimize at same point of rubber.

Coach Chuck

[calgoddard]

Without the benefit of any testing, to me the newly introduced 8 cm diameter Ikara prop would seem likely to be more efficient than the indoor 15 cm (six-inch) Ikara prop cut down to 8 cm in diameter. The P/D and blade plan form of the former prop were probably specifically designed for a WS 2020 model whereas the latter prop was designed for operation at its original 6-inch diameter, probably on the Ikara Butterfly stick model. Significantly cutting down the diameter of the indoor 6-inch Ikara prop distorts its shape from optimum. The P/D of the cut-down indoor 6-inch Ikara may be too high for optimal thrust generation on an indoor stick duration model airplane like a WS 2020 model. I agree with coach Chuck that a prop with a P/D between 1.5 and 2.0 would probably be optimal for a WS 2020 model.

Visually comparing the two props at www.wind-it-up.com, the new 8 cm Ikara prop has a wide blade plan form that would beneficially allow a lower RPM on a WS 2020 model. Aerodynamic drag increases exponentially with air speed and the tips of the new 8 cm Ikara blade would be traveling slower than the tips of a cut-down 6-inch indoor Ikara prop when each is generating enough thrust to keep a WS 2020 airplane aloft. Of course, the stop watch will ultimately determine which prop is best. However, I definitely agree with coach Chuck that testing the two different props with the same rubber motor on the same airplane will not tell you which prop is more efficient for a given WS 2020 airplane. You need to optimize the rubber (and winding) for each different prop.

For those who cannot purchase the new 8 cm Ikara prop, you can re-make the 6-inch indoor Ikara prop so that it has an 8 cm diameter and so that it has an adjustable pitch. The spars can be cut to an appropriate length and snugly inserted into opposite ends of a tubular prop hub with an appropriate inner diameter (ID). Each blade can be rotated about the axis of its spar and set to an appropriate pitch at a given point along the radius using a pitch gauge or a simple jig, and then glued in position.

[lechassin]

It would unfair to all of those who helped us this year to fade away without an update on our experience at regionals: https://www.youtube.com/watch?v=4cKY4swSvU8

This flight placed Luke 3rd. Even if he'd gotten 1st, the extra 2 points would not have been enough to get the team to State (they needed 7 more points), so what follows thankfully did not cost the team anything, but it is a cautionary tale to learn from one's mistakes, yet also not get too bogged down in them during a stressful time.

The experience was essentially identical to his 1st invitational. An unexpected obstacle (in this case the net) should have prompted a downward adjustment of the launch torque, and acceptance of a lower flight time. Instead, going left, he did test flights using excessive rudder deflection to increase banking under high torque at launch, and therefore limit the climb. This resulted in 1'50" at less than 20 feet height, avoiding the net.

Undaunted, (as is his nature), he kept that setup and paid the same price he paid at last Fall's invitational: a slow descent after a left launch into the floor.

There's more: thinking he might have gotten close enough to a full lap, and therefore might still get the bonus, he did not switch to the backup plane. He did worry that the descent was caused by an unknown tweak, so he called a trim flight to the right during the 8 minute window. The trim flight was 1'50", and you can guess the rest: that left precious few seconds to rewind the motor hastily to launch torque (no dewinding), and produce the flight in the video. He didn't think to wind another motor during the trim flight and have a team mate retrieve the plane for him (stress). 1'30" is pretty good for launching at 0.2 in.oz without dewinding, but it also betrays how aggressive the setup was in terms of rudder, decalage, and CG. Luke's decision making tree was flawed, but I will give him ample credit for making something of it regardless.

Take what lessons you will from this and our other experiences (in and out of the gym...), thanks again for all the help, and best wishes to all for the rest of the season.

[bjt4888]

Eric,

Thanks for the update and too bad about not going to States.

Great job to you and Luke this year.

Luke doesn’t need to feel alone with the experience of flight issues in competition. I had eight teams participating in an Invitational an only three got through the procedure without issues. The others still posted pretty good scores relative to the rest of the teams, but there’s room for improvement. Luckily, we have three weeks yet till Regionals to practice procedures.

Brian T

[bjt4888]

Invitational was yesterday.

[buildergirl]

Hi! I've never posted in this forum but regularly read it and have definitely learned a lot in the process, so thank you.

We currently have 2 Freedom Flight monoplanes that work decent under the right torque (torque of 0.25 oz gets around 1:30 in 24 ft), however with higher torque we experience a lot of the problems described earlier in the forum including power stalling and diving into the ground. I read about the wing wash-in and I know there is a shim included in the kit to help with that, but I feel like I'm not alone when I say I have no idea how to use and connect it to the plane. The instructions on that part are a little unclear and many of the teams I've talked to don't really understand it as well, so have omitted it. However, I think it is time to figure out how to use the shim as our state is in 90 ft and our planes need to be able to handle the torque. If anyone has a visual on how to use the shim it would be greatly appreciated, or an alternate way to fix the high torque problem.

Also, I was wondering what our first change should be when trimming (incidence or cg?). I usually leave the incidence the same and just move the wings backwards or forwards to adjust the cg, however I don't know in what situation you would change each one to optimize the trim. Speaking of which, how do you know when the trim is optimized (whats should the climb, cruise, and descent look/time like?). Sorry for so many questions, many of which have probably already been answered, but I would really appreciate the help!