Wright Stuff C

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jander14indoor
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Re: Wright Stuff C

Post by jander14indoor » January 10th, 2020, 3:00 pm

One caution, if your plane starts changing from climbing to diving as you increase torque, you really need to check for motor stick bending. If you have it, I think it needs to be addressed before you start making trim changes.

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Re: Wright Stuff C

Post by lechassin » January 11th, 2020, 8:53 am

Good point. We don't start flight trimming until we know all of a plane's basics are well-sorted. In the case of the motor stick, we place a fully wound motor onto the motor stick, hold the prop, and sight down the stick to be sure it's still straight. We do that during construction, using a motor torque we know exceeds any predicted launch torque (in our case, we've never launched above 0.5 in.oz, so we test the sticks at 0.6 in.oz). If the motor stick bows, we reject it. If the motor stick stays straight, we bevel it towards the ends in small amounts repeatedly until it juuuuust starts to bow. At that point we know we can't launch at maximum torque, but we never do anyways, and we know our motor stick is as light as possible while retaining a small margin of safety. In our case the motor stick with hub/hooks is around 1.8 grams.

This is part of an overall strategy of being sure the plane is reliable. We don't want tweaks to appear that we might miss under the stress of competition. That strategy includes the above, but also triangulated wing fences that keep the wings from unintentionally warping, tail booms that are supported during storage so we know they're straight, strong prop hubs so we know the props run true even after a hit, all glue joints and covering edges soaked in thin CA so we know they'll hold up to repeated hits, simple labelled shims that are easily moved, and trim settings that are all marked for easy and quick verification in the event of poor flight behavior (i.e.: after snagging a rafter).

Also, I posted this in the PMs in response to a question, might as well post it here too for all to see:

"Our wing location changes slightly depending on the weights of each particular plane's motor stick, prop, tail, etc... so we don't use that as a "spec".

Our wing incidence is about 4 mm going left, and 3 mm going right, which yields a CG 24mm from the leading edge to cruise flat. Stab is neutral, rudder is about 5mm either way but tweaked to control launch attitude.

Getting the tail 42 cm from the wing increases stability but it was hard to achieve and you may not get it that far. If you find that recovery from disturbances is not to your liking add 1mm of incidence right and/or left and tweak the CG forward (move the wing back) a few mm at a time until the cruise is flat."

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Re: Wright Stuff C

Post by nobodynobody » January 12th, 2020, 6:49 am

lechassin wrote:
January 10th, 2020, 6:21 am
I'm no expert but we've noticed some peculiarities to this year's design. We control most of the power stalling with the usual flaring prop, minimal decalage (that still recovers), and down thrust. But we also use the rudder to control the climb rate (whether diving or stalling). It makes our trim procedure somewhat unusual but quick and effective.

The key to this trick is to allow for at least some banking. It's OK if you are offsetting the wings or warping them to keep the plane from banking (that increases efficiency), but for the rudder trick to work, don't fully eliminate banking.

To trim our planes:
1) We set the rudder first to get the radius we want, using partially wound motors. We only worry about climbing or diving enough to do a lap and set the radius. It's important to do this first because you want to maximize the radius based on the venue (to minimize drag), and all other settings follow.
2) Next we set the CG to get a good flat cruise, using partially wound motors. Note that every single one of our designs this year has required about 1mm more decalage going left than right, so anticipate that. We start with about 4mm left and 3mm right and set the CG so the plane cruises flat. At that decalage, recovery from disturbances is adequate but you may need more decalage if your tail boom is short (our tail is light and it's 42cm from the wings). As stated above, put all of the decalage in the wing (incidence), so the stab stays flat. You get 1-2 degrees of down thrust without messing around with the prop hub. Down thrust reduces power stalling.
3) Next we adjust the climb rate using fully wound motors (note that we need to use flaring props, that took care of a lot of the power stalling). After the radius and cruise are nice both ways, we usually have at least one of two problems, both addressed with rudder adjustments:
a) If we launch and descend into the floor (usually going left), we reduce rudder about 1mm. That reduces banking, increasing lift, and solves the problem.
b) If we launch into a power stall (usually going right), we increase rudder 1mm, causing more side-slipping (not banking).That reduces lift and solves the problem.
This procedure can be used repeatedly as you increase torque to get more height.

Thankfully the effect of the final rudder adjustments on turn radius is negligible.
This has probably been discussed before, but how does the flare propeller work? At least to my understanding, it bends depending on how fast it's spinning, but I have a question about it. After watching the video on how to construct one, the spars connecting the blade to the hub are on the trailing edge of the blade. Wouldn't that mean it increases pitch at the beginning and therefore increases thrust? Would the spar on the leading edge of the blade be better since it will decrease pitch at higher spin rates? I am probably wrong because it obviously works for you. Also, how many winds can people fit onto rubber these days? I can only get about 2000 winds if I don't want it to snap frequently
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Re: Wright Stuff C

Post by CrayolaCrayon » January 12th, 2020, 6:54 am

nobodynobody wrote:
January 12th, 2020, 6:49 am

Also, how many winds can people fit onto rubber these days? I can only get about 2000 winds if I don't want it to snap frequently
Need a little more info than that;

-Thickness? (density would be better)
-Length?
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Re: Wright Stuff C

Post by nobodynobody » January 12th, 2020, 9:37 am

CrayolaCrayon wrote:
January 12th, 2020, 6:54 am
nobodynobody wrote:
January 12th, 2020, 6:49 am

Also, how many winds can people fit onto rubber these days? I can only get about 2000 winds if I don't want it to snap frequently
Need a little more info than that;

-Thickness? (density would be better)
-Length?
3g of .065" thick rubber
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Re: Wright Stuff C

Post by klastyioer » January 12th, 2020, 10:55 am

nobodynobody wrote:
January 12th, 2020, 9:37 am
CrayolaCrayon wrote:
January 12th, 2020, 6:54 am
nobodynobody wrote:
January 12th, 2020, 6:49 am

Also, how many winds can people fit onto rubber these days? I can only get about 2000 winds if I don't want it to snap frequently
Need a little more info than that;

-Thickness? (density would be better)
-Length?
3g of .065" thick rubber
3g sounds like quite a bit for only 2000 winds
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Re: Wright Stuff C

Post by lechassin » January 12th, 2020, 11:48 am

3 grams of 0.06+ rubber should be able to take 5000 and more turns depending on how close to breaking you're willing to go. Hopefully someone will chime in with a single good source for the best practices to use as a reference. We learned one bit at a time and we still can't get to 5000 for 0.0625" and 6000 for 0.060" without unpredictable breakage. I think others are doing better.

The flaring prop increases pitch at higher torque (launch). Higher pitch increases the speed of the air mass but moves that air less efficiently (more turbulence?). That lowers thrust and controls power stalling. As the motor runs out, the pitch decreases, so what little power remains can still move the air mass efficiently (albeit slower).

We spent out gym time today practicing for the 2nd invitational in 2 weeks, using the two planes with centered wings (banking allowed) that go 1'30"-1'45" both ways depending on HVAC, hits etc... Usually left is a few seconds shorter due to increased banking (prop torque). The planes are "identical" but the incidence shims are not, which I don't like, it speaks to some inconsistency in construction we can't see.

The biggest issue I can see for Luke that will make or break him is little errors that end up being costly. Forgetting to place the incidence shim properly and launching the wrong way into a wall seem to be the two most common mistakes, and I suspect the tendency will increase with the added stress of public scrutiny and competition. Next week we have no plans to increase performance, we need to spend the 3 hours just practicing.

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Re: Wright Stuff C

Post by klastyioer » January 12th, 2020, 12:13 pm

lechassin wrote:
January 12th, 2020, 11:48 am
3 grams of 0.06+ rubber should be able to take 5000 and more turns depending on how close to breaking you're willing to go. Hopefully someone will chime in with a single good source for the best practices to use as a reference. We learned one bit at a time and we still can't get to 5000 for 0.0625" and 6000 for 0.060" without unpredictable breakage. I think others are doing better.

The flaring prop increases pitch at higher torque (launch). Higher pitch increases the speed of the air mass but moves that air less efficiently (more turbulence?). That lowers thrust and controls power stalling. As the motor runs out, the pitch decreases, so what little power remains can still move the air mass efficiently (albeit slower).

We spent out gym time today practicing for the 2nd invitational in 2 weeks, using the two planes with centered wings (banking allowed) that go 1'30"-1'45" both ways depending on HVAC, hits etc... Usually left is a few seconds shorter due to increased banking (prop torque). The planes are "identical" but the incidence shims are not, which I don't like, it speaks to some inconsistency in construction we can't see.

The biggest issue I can see for Luke that will make or break him is little errors that end up being costly. Forgetting to place the incidence shim properly and launching the wrong way into a wall seem to be the two most common mistakes, and I suspect the tendency will increase with the added stress of public scrutiny and competition. Next week we have no plans to increase performance, we need to spend the 3 hours just practicing.
to add onto the first para, it also depends on winding technique :D
it's not about the medals; go out there and have fun. make progress, learn a few things and have one heck of a time; that's all that matters.

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Re: Wright Stuff C

Post by nobodynobody » January 12th, 2020, 1:12 pm

klastyioer wrote:
January 12th, 2020, 12:13 pm
lechassin wrote:
January 12th, 2020, 11:48 am
3 grams of 0.06+ rubber should be able to take 5000 and more turns depending on how close to breaking you're willing to go. Hopefully someone will chime in with a single good source for the best practices to use as a reference. We learned one bit at a time and we still can't get to 5000 for 0.0625" and 6000 for 0.060" without unpredictable breakage. I think others are doing better.

The flaring prop increases pitch at higher torque (launch). Higher pitch increases the speed of the air mass but moves that air less efficiently (more turbulence?). That lowers thrust and controls power stalling. As the motor runs out, the pitch decreases, so what little power remains can still move the air mass efficiently (albeit slower).

We spent out gym time today practicing for the 2nd invitational in 2 weeks, using the two planes with centered wings (banking allowed) that go 1'30"-1'45" both ways depending on HVAC, hits etc... Usually left is a few seconds shorter due to increased banking (prop torque). The planes are "identical" but the incidence shims are not, which I don't like, it speaks to some inconsistency in construction we can't see.

The biggest issue I can see for Luke that will make or break him is little errors that end up being costly. Forgetting to place the incidence shim properly and launching the wrong way into a wall seem to be the two most common mistakes, and I suspect the tendency will increase with the added stress of public scrutiny and competition. Next week we have no plans to increase performance, we need to spend the 3 hours just practicing.
to add onto the first para, it also depends on winding technique :D
To wind, I typically stretch it to about 3 times its length, wind to about 75% of the full torque then walk into the length of the plane while winding. I finish up winding slowly and dewind ~ 100 turns. Stretching longer than 3x its length feels like it will snap (3g of .065"). Is there anything I could do to improve that? My rubber usually snaps every 7 flights or so, what about you guys?

Edit: how often do you switch out rubber? Will using old rubber change the results while testing? Will using used rubber during a competition screw up the plane?
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Re: Wright Stuff C

Post by CookiePie1 » January 12th, 2020, 1:45 pm

nobodynobody wrote:
January 12th, 2020, 1:12 pm
klastyioer wrote:
January 12th, 2020, 12:13 pm
lechassin wrote:
January 12th, 2020, 11:48 am
3 grams of 0.06+ rubber should be able to take 5000 and more turns depending on how close to breaking you're willing to go. Hopefully someone will chime in with a single good source for the best practices to use as a reference. We learned one bit at a time and we still can't get to 5000 for 0.0625" and 6000 for 0.060" without unpredictable breakage. I think others are doing better.

The flaring prop increases pitch at higher torque (launch). Higher pitch increases the speed of the air mass but moves that air less efficiently (more turbulence?). That lowers thrust and controls power stalling. As the motor runs out, the pitch decreases, so what little power remains can still move the air mass efficiently (albeit slower).

We spent out gym time today practicing for the 2nd invitational in 2 weeks, using the two planes with centered wings (banking allowed) that go 1'30"-1'45" both ways depending on HVAC, hits etc... Usually left is a few seconds shorter due to increased banking (prop torque). The planes are "identical" but the incidence shims are not, which I don't like, it speaks to some inconsistency in construction we can't see.

The biggest issue I can see for Luke that will make or break him is little errors that end up being costly. Forgetting to place the incidence shim properly and launching the wrong way into a wall seem to be the two most common mistakes, and I suspect the tendency will increase with the added stress of public scrutiny and competition. Next week we have no plans to increase performance, we need to spend the 3 hours just practicing.
to add onto the first para, it also depends on winding technique :D
To wind, I typically stretch it to about 3 times its length, wind to about 75% of the full torque then walk into the length of the plane while winding. I finish up winding slowly and dewind ~ 100 turns. Stretching longer than 3x its length feels like it will snap (3g of .065"). Is there anything I could do to improve that? My rubber usually snaps every 7 flights or so, what about you guys?

Edit: how often do you switch out rubber? Will using old rubber change the results while testing? Will using used rubber during a competition screw up the plane?
we've been stretching to 4x length and winding up to our target torque and slowly walking in to keep the torque at that level. We haven't been dewinding because we don't know what the max torque is lol. how do you find that?
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