Wright Stuff B

coachchuckaahs
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Re: Wright Stuff B

Post by coachchuckaahs » April 16th, 2018, 10:53 am

Before cutting your LE, it will be important to observe the character of the "dive". If the inboard wing is tilting downward in the circle significantly, then you may need to add wash-in. If the plane simply goes down, look at your static stability, as well as your launch torque. A launch torque of 0.20 to 0.25, as Brian notes, is a good starting point, especially with a non-flaring prop. If your static stability is off, you can chase a LOT of adjustments (including wash-in) and still have the same symptoms. Get the plane working on low torque, then observe higher torque for further adjustments.

Unlike last year, we have ended up with very little wash-in on this year's plane. Of course, the amount needed may heavily depend on the plane's design and imperfections.

Depending on how your wing posts are mounted to the wing, you may be able to remove the wing post mount (cut it off), impose a slight tilt to the LE or TE, and re-glue the wing post. On some designs, this maybe easier than cutting and splicing the spar/LE/TE, but on other designs it may be harder. We have carbon LE, so this is the only approach we can use.

When any change is made, including wash-in, rudder, tail tilt, etc, be sure to re-trim the plane for smooth let down. Add incidence until stall just starts in letdown, then remove a mm or so. Almost any adjustment you can make to the airframe will require re-testing. We use 400-600 winds without any unwinds for our test rubber. this will climb a little, and then begin letwon where you observe for stalling.

Coach Chuck
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2016 C WS 8th place
2018 B WS 2nd place
2018 C Heli Champion
2019 B ELG 3rd place
2019 C WS Champion
AMA Results: 3 AAHS members qualify for US Jr Team in F1D, 4 new youth senior records

bjt4888
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Re: Wright Stuff B

Post by bjt4888 » April 16th, 2018, 12:38 pm

Yes, I'm in full agreement, static stability first, fly and observe, then determine if and how much washin might be needed.

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Re: Wright Stuff B

Post by waffletree » April 16th, 2018, 4:33 pm

Does anyone have a picture of or know the size of the wright stuff gym at PA states?
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jgrischow1
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Re: Wright Stuff B

Post by jgrischow1 » April 16th, 2018, 7:03 pm

coachchuckaahs wrote:The behavior sounds to me like too much torque or lack of stability. 50 unwinds may not be enough, depending on the prop you are using. We saw this behavior last year with the cut down Ikara non-flaring prop.

We are typically unwinding to about 0.2-0.25 oz-in this year. 50 unwinds on full rubber does not seem to be enough. We are using somewhat thinner rubber than that (maybe 0.056", or 0.372g/in), and that will wind somewhere around 3000 turns, and then unwind perhaps 200-250 turns. With your thicker rubber, its at even higher torque.

Just guessing, your rubber can probably take in the neighborhood of 2000 turns, and then back off at least 200 turns. Be sure to lube, and to stretch to about 7X nominal length. Wind about half at full stretch, then start walking in.

Can you describe the stability issues you had with the forward CG? By moving the wing forward, you reduce stability (moved CG back relative to the wing). SO maybe describe the stability issue you saw with the forward CG. Did you increase incidence until you got a stall on letdown, then decrease a little?

Your incidence would indicate a decent CG, unless you also have stab positive incidence. We are running 0 on the stab, about 9-10mm on the wing.

Coach Chuck
I'm sorry but I don't remember the details...when they tried to fly with that CG it just wouldn't climb...so one of my kids just moved the wing up until it started to climb normally.
bjt4888 wrote:Jgri,

Yes, most likely you need about 1/16" to 1/8" of left wing washin to prevent rolling to the floor during the initial high-power portion of the climb. Yes, partially cut through the left LE spar near the wing mid point and gently crack and hold about twice as much washing as you want and apply a drop of CA. Hold for about 90 seconds (if fresh CA) and the spar will partially return to where it was and you will have a starting point for washin.

Agree with Chuck that a detailed description of what you are observing when the CG is set to 1.875" forward of the wing TE.

Winding to 90% full turns measuring max torque (should be about .8 or .85 in oz) and backing off to a reasonable launch torque (initially .25 in oz) are critical steps to testing. Winding to 1,000 turns and backing off 50 is massively underwinding and then significantly short of the correct backoff turns (depending upon the length of the 1/16" motor). It is possible that the winding they are currently doing is resulting in a launch torque in the .35 to .45 in oz range ( based upon our test results) and, without left wing washing, this much torque can easily result in a banking turn to the floor.

How much left wing offset, stab tilt, tailboom offset and thrustline offset does your airplane have?

Brian T
1,000 winds wasn't our max...we were just doing different winds/torque to check if it was flying stably with the new settings. We usually start at about 300 winds and go up from there. My impression was winding a lot when you don't know if your plane will fly or not is not a good use of time. I will suggest to them about the torque stats you mentioned.

I will measure the stats you requested tomorrow.
bjt4888 wrote:Jgri,

One more note on cracking LE to add washin; make partial cut through at a shallow angle relative to the spar lengthwise direction. The resulting scarf joint will be pretty strong.

Brian T
OK, thanks.
coachchuckaahs wrote:Before cutting your LE, it will be important to observe the character of the "dive". If the inboard wing is tilting downward in the circle significantly, then you may need to add wash-in. If the plane simply goes down, look at your static stability, as well as your launch torque. A launch torque of 0.20 to 0.25, as Brian notes, is a good starting point, especially with a non-flaring prop. If your static stability is off, you can chase a LOT of adjustments (including wash-in) and still have the same symptoms. Get the plane working on low torque, then observe higher torque for further adjustments.

Unlike last year, we have ended up with very little wash-in on this year's plane. Of course, the amount needed may heavily depend on the plane's design and imperfections.

Depending on how your wing posts are mounted to the wing, you may be able to remove the wing post mount (cut it off), impose a slight tilt to the LE or TE, and re-glue the wing post. On some designs, this maybe easier than cutting and splicing the spar/LE/TE, but on other designs it may be harder. We have carbon LE, so this is the only approach we can use.

When any change is made, including wash-in, rudder, tail tilt, etc, be sure to re-trim the plane for smooth let down. Add incidence until stall just starts in letdown, then remove a mm or so. Almost any adjustment you can make to the airframe will require re-testing. We use 400-600 winds without any unwinds for our test rubber. this will climb a little, and then begin letwon where you observe for stalling.

Coach Chuck
Thanks for the tips.

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Re: Wright Stuff B

Post by jgrischow1 » April 17th, 2018, 3:18 pm

bjt4888 wrote:Jgri,

Yes, most likely you need about 1/16" to 1/8" of left wing washin to prevent rolling to the floor during the initial high-power portion of the climb. Yes, partially cut through the left LE spar near the wing mid point and gently crack and hold about twice as much washing as you want and apply a drop of CA. Hold for about 90 seconds (if fresh CA) and the spar will partially return to where it was and you will have a starting point for washin.

Agree with Chuck that a detailed description of what you are observing when the CG is set to 1.875" forward of the wing TE.

Winding to 90% full turns measuring max torque (should be about .8 or .85 in oz) and backing off to a reasonable launch torque (initially .25 in oz) are critical steps to testing. Winding to 1,000 turns and backing off 50 is massively underwinding and then significantly short of the correct backoff turns (depending upon the length of the 1/16" motor). It is possible that the winding they are currently doing is resulting in a launch torque in the .35 to .45 in oz range ( based upon our test results) and, without left wing washing, this much torque can easily result in a banking turn to the floor.

How much left wing offset, stab tilt, tailboom offset and thrustline offset does your airplane have?

Brian T
Not positive what left wing offset means. Both sides of the wing are the same length and are the same angle of dihedral. The wingposts are attached on the left side of the fuselage.

Not a whole lot of stab tilt that I can detect. However, before concluding that that (or the lack of wing offset) is why our plane isn't turning after a few turns, I must say that it was turning fine before. I do seem to recall our model last year (based on FFM from HS 2016) had a longer left side of wing and a decent amout of stab tilt, and this has neither, but I promise it turned fine the entire flight until recently. I think once we started having these issues one of my kiddos put a small amount of clay on the left wing to try to bank it more.

Tail boom offset seems to be a few degrees max. Hard to measure.

Pardon my ignorance, but does thrustline offset mean relationship of prop axis to fuselage? If so, 3 degrees is what the kids say they did.

Sorry I'm not more helpful in describing our issues or providing stats. Sometimes I feel like a patient who can't describe his symptoms to the doctor.

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Re: Wright Stuff B

Post by jgrischow1 » April 19th, 2018, 5:35 pm

bjt4888 wrote:Jgri,

Yes, most likely you need about 1/16" to 1/8" of left wing washin to prevent rolling to the floor during the initial high-power portion of the climb. Yes, partially cut through the left LE spar near the wing mid point and gently crack and hold about twice as much washing as you want and apply a drop of CA. Hold for about 90 seconds (if fresh CA) and the spar will partially return to where it was and you will have a starting point for washin.

Agree with Chuck that a detailed description of what you are observing when the CG is set to 1.875" forward of the wing TE.

Winding to 90% full turns measuring max torque (should be about .8 or .85 in oz) and backing off to a reasonable launch torque (initially .25 in oz) are critical steps to testing. Winding to 1,000 turns and backing off 50 is massively underwinding and then significantly short of the correct backoff turns (depending upon the length of the 1/16" motor). It is possible that the winding they are currently doing is resulting in a launch torque in the .35 to .45 in oz range ( based upon our test results) and, without left wing washing, this much torque can easily result in a banking turn to the floor.

How much left wing offset, stab tilt, tailboom offset and thrustline offset does your airplane have?

Brian T
I think what may have happened is when my kiddos hacked off the tailboom and reglued it the angle of the tailboom to the fuse changed. One of my kids today removed the horizontal stab and reglued it with the left side about 3/8 in higher than the right and it now circles OK.

Of course, now we have a new problem: it flies OK, but it kind of goes up and down slightly like it mini stalls then immediately corrects itself and keeps going and mini stalls again etc. Haven't had this before. Is this an angle of incidence issue or CG or something else?

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Re: Wright Stuff B

Post by waffletree » April 19th, 2018, 5:42 pm

jgrischow1 wrote:
bjt4888 wrote:Jgri,

Yes, most likely you need about 1/16" to 1/8" of left wing washin to prevent rolling to the floor during the initial high-power portion of the climb. Yes, partially cut through the left LE spar near the wing mid point and gently crack and hold about twice as much washing as you want and apply a drop of CA. Hold for about 90 seconds (if fresh CA) and the spar will partially return to where it was and you will have a starting point for washin.

Agree with Chuck that a detailed description of what you are observing when the CG is set to 1.875" forward of the wing TE.

Winding to 90% full turns measuring max torque (should be about .8 or .85 in oz) and backing off to a reasonable launch torque (initially .25 in oz) are critical steps to testing. Winding to 1,000 turns and backing off 50 is massively underwinding and then significantly short of the correct backoff turns (depending upon the length of the 1/16" motor). It is possible that the winding they are currently doing is resulting in a launch torque in the .35 to .45 in oz range ( based upon our test results) and, without left wing washing, this much torque can easily result in a banking turn to the floor.

How much left wing offset, stab tilt, tailboom offset and thrustline offset does your airplane have?

Brian T
I think what may have happened is when my kiddos hacked off the tailboom and reglued it the angle of the tailboom to the fuse changed. One of my kids today removed the horizontal stab and reglued it with the left side about 3/8 in higher than the right and it now circles OK.

Of course, now we have a new problem: it flies OK, but it kind of goes up and down slightly like it mini stalls then immediately corrects itself and keeps going and mini stalls again etc. Haven't had this before. Is this an angle of incidence issue or CG or something else?
I'm not as experienced in this event as some of the others on here, but my team has had these problems before. From my experiences, the stalling comes from the wing not being balanced, and the front of the plane is probably heavier. If you move the wing back a tiny bit, about a centimeter at a time, fly it, and adjust it as needing.
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Re: Wright Stuff B

Post by jgrischow1 » April 26th, 2018, 3:11 pm

So our plane's issue with rolling in and diving after a half circle or so may have something to do with what I noticed today: Our plane's left front spar dips a bit as you go out away from the fuselage. I think it's experience too much breakage, as neither my kids nor I could detect any new breaks. One of my kids moved the wing support further up the wing post and re-glued, but the support only goes out on the spar a small amount, and I'm not sure it's lifting the outer edge of the spar enough. A typical flight behavior we saw today is use .065 rubber, wind 2000 back off 300. Plane dives and rolls. Pick it up, re-launch with no adjustments, and it flies for 1 min 12 seconds.

Some possible solutions:

-gently stroke the spar before each flight and try to bend upwards
-make a new support that is longer and can lift the wing up more
-build a new wing (State is Saturday, not ideal)

Any suggestions?

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Re: Wright Stuff B

Post by coachchuckaahs » April 26th, 2018, 3:32 pm

4. Increase SSM a little
5. Reduce launch torque a little (you have not reported launch torque)

I still think the majority of your issue is related to these two items. Of course, without video hard to be sure, but your reported CG is quite far back for this year's model, and in my experience so far, increasing torque with a small SSM results in dive. When you move the CG forward, you must increase incidence until stall begins in letdown, and then decrease just a little. It appeared that you moved the CG forward but never increased incidence or decalage to compensate. Don't be surprised if this year's model requires as much as 1cm of incidence.

Your observations of the warp in the wing, not previously seen, could make this even worse. You may have 1cm incidence at the center and half of that at the tip. You also may have a stab incidence or warp issue, which could impact decalage and mask the correct incidence.

It sounds like you need to go to the basics of trimming, step by step, starting with a thorough inspection of the plane and straitening of bent surfaces. CG and incidence adjusted at each step with low torque (50-60 winds) launch and observe letdown, get it right before moving to next steps.

Chuck
Coach, Albuquerque Area Home Schoolers Flying Events
Nationals Results:
2016 C WS 8th place
2018 B WS 2nd place
2018 C Heli Champion
2019 B ELG 3rd place
2019 C WS Champion
AMA Results: 3 AAHS members qualify for US Jr Team in F1D, 4 new youth senior records

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Re: Wright Stuff B

Post by jgrischow1 » April 26th, 2018, 5:59 pm

coachchuckaahs wrote:4. Increase SSM a little
5. Reduce launch torque a little (you have not reported launch torque)

I still think the majority of your issue is related to these two items. Of course, without video hard to be sure, but your reported CG is quite far back for this year's model, and in my experience so far, increasing torque with a small SSM results in dive. When you move the CG forward, you must increase incidence until stall begins in letdown, and then decrease just a little. It appeared that you moved the CG forward but never increased incidence or decalage to compensate. Don't be surprised if this year's model requires as much as 1cm of incidence.

Your observations of the warp in the wing, not previously seen, could make this even worse. You may have 1cm incidence at the center and half of that at the tip. You also may have a stab incidence or warp issue, which could impact decalage and mask the correct incidence.

It sounds like you need to go to the basics of trimming, step by step, starting with a thorough inspection of the plane and straitening of bent surfaces. CG and incidence adjusted at each step with low torque (50-60 winds) launch and observe letdown, get it right before moving to next steps.

Chuck
Thanks, Chuck, for your quick reply. As far as the CG goes, as I said awhile ago, when my kids altered their plane to Brian's specs, it wouldn't fly. Moving the wing up seemed to help. However, maybe they weren't trying enough other things, and the plane has been changed since then, so we will try again.

However, we also had to redo the wing covering, and either that or spraying more glue added more weight, so we had to remove some form the clay ballast on the nose. So, I think it will be even harder to get the CG as far forward as you recommend. But, we will try.

As far as torque goes, we usually launch at .15-.3. Our torque meter has broke several times though (read: my kids broke it) and the indicator wire has never been perfectly straight up and down at 12 noon, so we are estimating some what. We aren't getting close to the ceiling though at that torque, and ours is 24 ft ish, so I don't know how they will be able to climb higher for State, which has a 48 ft ceiling.

I will try to take a video tomorrow.

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