Flight B/C

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Re: Flight B/C

Post by bjt4888 »

jgrischow1 wrote: March 11th, 2023, 6:54 am
bjt4888 wrote: March 10th, 2023, 2:36 pm
jgrischow1 wrote: March 10th, 2023, 12:19 pm Any suggestions for fixing a rear stab (carbon fiber) that's warped? My kids tried to put weights on it and flatten it out overnight but that didn't do much.
Jg,

You can’t straighten warped carbon rods. However, you can tweak the flying surface (I assume it’s the stabilizer with the problem) to minimize the detrimental effect. For instance, if the warp is trailing edge down on the left side, this is not much of a problem if it’s only a degree or so of twist. A small amount of washin on the left side of the stab is occasionally used as a trim method. You may mean 0.5 degrees of additional decalage to compensate.

A picture of the warp would allow us to diagnose and give a better recommendation.

Brian T
https://drive.google.com/file/d/15lgztN ... share_link
https://drive.google.com/file/d/1rzL4hv ... share_link

Unfortunately it looks to be the opposite of what you hoped!
You can partially correct this warp by cracking the TE joint to the tailboom (I'm guessing that the picture shows the stab mounted to the tailboom) and slightly twisting the stabilizer to correct the warp as you reglue the joint. Hold the stabilizer up to "eyeball" the twist correction as you glue it. We have found the easiest way to twist is to squeeze the joint between two fingers and apply slight pressure one way or the other to change twist. The trick is to do this and still allow room for your glue tool to apply a drop without gluing fingers. I often do glue my fingers. If you do, twist finger back and forth to break your finger free (don't lift straight up or you'll just pull the joint apart or pull some covering off. Glue it with just a small dot of CA. Let this dry for about 1 min and then (as the joint won't be very strong yet) you can continue squeezing and twisting the joint to correct more and then add final gluing.

If you can get the stabilizer mostly flat, it looks like you will end up with slight TE droop on each tip of the stab. This is not a terrible situation, and the airplane can be flown with slight additional wing incidence (maybe 1-2 mm) or slight additional negative stabilizer incidence (maybe 1-1.5 degrees).

Then fly it and see how it goes.

Brian T
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Re: Flight B/C

Post by jgrischow1 »

bjt4888 wrote: March 11th, 2023, 7:23 am
jgrischow1 wrote: March 11th, 2023, 6:54 am
bjt4888 wrote: March 10th, 2023, 2:36 pm

Jg,

You can’t straighten warped carbon rods. However, you can tweak the flying surface (I assume it’s the stabilizer with the problem) to minimize the detrimental effect. For instance, if the warp is trailing edge down on the left side, this is not much of a problem if it’s only a degree or so of twist. A small amount of washin on the left side of the stab is occasionally used as a trim method. You may mean 0.5 degrees of additional decalage to compensate.

A picture of the warp would allow us to diagnose and give a better recommendation.

Brian T
https://drive.google.com/file/d/15lgztN ... share_link
https://drive.google.com/file/d/1rzL4hv ... share_link

Unfortunately it looks to be the opposite of what you hoped!
You can partially correct this warp by cracking the TE joint to the tailboom (I'm guessing that the picture shows the stab mounted to the tailboom) and slightly twisting the stabilizer to correct the warp as you reglue the joint. Hold the stabilizer up to "eyeball" the twist correction as you glue it. We have found the easiest way to twist is to squeeze the joint between two fingers and apply slight pressure one way or the other to change twist. The trick is to do this and still allow room for your glue tool to apply a drop without gluing fingers. I often do glue my fingers. If you do, twist finger back and forth to break your finger free (don't lift straight up or you'll just pull the joint apart or pull some covering off. Glue it with just a small dot of CA. Let this dry for about 1 min and then (as the joint won't be very strong yet) you can continue squeezing and twisting the joint to correct more and then add final gluing.

If you can get the stabilizer mostly flat, it looks like you will end up with slight TE droop on each tip of the stab. This is not a terrible situation, and the airplane can be flown with slight additional wing incidence (maybe 1-2 mm) or slight additional negative stabilizer incidence (maybe 1-1.5 degrees).

Then fly it and see how it goes.

Brian T
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Re: Flight B/C

Post by CSPark »

Throughout the season I've observed that some teams launch their plane 1ft off the ground and let it climb up. These teams tend to get a longer flight time, which is logical.

I would like to do this as well, but am having a hard time getting it to climb as soon as I let it go.

Also, whenever I wind it up 900+ turns, the plane, as soon as I let it go, zooms really fast and starts going incredibly nose high to the point where the plane is vertical. Then it falls 3ish ft before starting to fly pretty normally again (but this fall is not ideal). Reading the previous posts of this thread, I undertand that the rubber motor should generally have around 1200+ winds. How do I reach this amount without the plane traveling incredibly fast? When I wind it up with only 800 turns, it seems to do fine and is pretty stable (but has trouble climbing up and using the whole space).

Any other advice would be appreciated. I will try to provide photos and videos soon.

Thanks!
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Re: Flight B/C

Post by CypherKat »

https://drive.google.com/file/d/1BSGzer ... sp=sharing

https://drive.google.com/file/d/1uvC9tf ... sp=sharing

https://drive.google.com/file/d/1p-bK2U ... sp=sharing

hello! I am back after a round of test in my school gym.

For each of these flights we got the rubber to 100 winds, and dewinded 5 turns on the winder, we don't have a torque meter sadly so I cant speak for that. We used the same rubber on these which later snapped, but it came in on 1.90 g and around .63 g/in. we messed around on CG placement but I wanted some tips on hitting the 2:30 mark. States is this Thursday, so we'll try ot get one final testing in before comp.
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Re: Flight B/C

Post by bjt4888 »

CypherKat wrote: March 12th, 2023, 6:59 am https://drive.google.com/file/d/1BSGzer ... sp=sharing

https://drive.google.com/file/d/1uvC9tf ... sp=sharing

https://drive.google.com/file/d/1p-bK2U ... sp=sharing

hello! I am back after a round of test in my school gym.

For each of these flights we got the rubber to 100 winds, and dewinded 5 turns on the winder, we don't have a torque meter sadly so I cant speak for that. We used the same rubber on these which later snapped, but it came in on 1.90 g and around .63 g/in. we messed around on CG placement but I wanted some tips on hitting the 2:30 mark. States is this Thursday, so we'll try ot get one final testing in before comp.
Thanks
Cypher,

Your video is still loading and I can look at it in a little while. A 1.9 g motor of .063 g/in with two black rubber o-rings is a loop about 14.12 inches long and 105 winder turns is only 85% of breaking turns if you use good winding procedures (see video of me winding in one of my first posts).

Step one: make your motors at 1.98 grams instead of 1.9 grams and you will have 5/8” longer loop. This will let you get up to 110 turns at about 85% of breaking. If your propeller is spinning about 7 RPS, half of the10x15 additional turns (assume you have the typical 15:1 ratio winder) will probably become additional turns remaining and half will become flying turns leading to 10 seconds more flight time. Note in my video that I wind the motor to 1.4 in oz. too bad you don’t have a torque as all of the winding process is actually torque based and not focused on turns much. Also, as climb height is almost a linear relationship to launch torque. Knowing torque allows you to fly very close to the ceiling without touching (after lots of practice).

A longer motor might mean that a different (slightly higher) density is required. I could tell you more about this if you could tell me the turns remaining and the torque values of the current motor used in the flights.

Be sure to wind the motor off the airplane as I demonstrate in the video. If you don’t have a torque meter, at least mount a small wire hook to a board that can be clamped to a table (make sure your States will supply a table; all good Event Supervisors should do this).

I’ll comment on the videos after they load. What is the ceiling height for States?

Brian T
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Re: Flight B/C

Post by CypherKat »

bjt4888 wrote: March 12th, 2023, 7:35 am
CypherKat wrote: March 12th, 2023, 6:59 am https://drive.google.com/file/d/1BSGzer ... sp=sharing

https://drive.google.com/file/d/1uvC9tf ... sp=sharing

https://drive.google.com/file/d/1p-bK2U ... sp=sharing

hello! I am back after a round of test in my school gym.

For each of these flights we got the rubber to 100 winds, and dewinded 5 turns on the winder, we don't have a torque meter sadly so I cant speak for that. We used the same rubber on these which later snapped, but it came in on 1.90 g and around .63 g/in. we messed around on CG placement but I wanted some tips on hitting the 2:30 mark. States is this Thursday, so we'll try ot get one final testing in before comp.
Thanks
Cypher,

Your video is still loading and I can look at it in a little while. A 1.9 g motor of .063 g/in with two black rubber o-rings is a loop about 14.12 inches long and 105 winder turns is only 85% of breaking turns if you use good winding procedures (see video of me winding in one of my first posts).

Step one: make your motors at 1.98 grams instead of 1.9 grams and you will have 5/8” longer loop. This will let you get up to 110 turns at about 85% of breaking. If your propeller is spinning about 7 RPS, half of the10x15 additional turns (assume you have the typical 15:1 ratio winder) will probably become additional turns remaining and half will become flying turns leading to 10 seconds more flight time. Note in my video that I wind the motor to 1.4 in oz. too bad you don’t have a torque as all of the winding process is actually torque based and not focused on turns much. Also, as climb height is almost a linear relationship to launch torque. Knowing torque allows you to fly very close to the ceiling without touching (after lots of practice).

A longer motor might mean that a different (slightly higher) density is required. I could tell you more about this if you could tell me the turns remaining and the torque values of the current motor used in the flights.

Be sure to wind the motor off the airplane as I demonstrate in the video. If you don’t have a torque meter, at least mount a small wire hook to a board that can be clamped to a table (make sure your States will supply a table; all good Event Supervisors should do this).

I’ll comment on the videos after they load. What is the ceiling height for States?

Brian T

We counted turns remaining by unwinding the rubber and it lies consistently around 300 winds (20 turns on 15:1 winder). We wind the rubber by holding one black o-ring as far as we can stratch and the other attached to the winder. Ceiling height hasn't been released but from memory I think it's about 25 (I'm lowballing it but there are also rafters). We'll be measuring and making new rubber bands and winding and unwiding them so we can use it best at comp. I didn't send a really short flight because it clipped the ceilling where we testing, but that was on 105 winder turns and 5 dewinds.

should also mention that the air conditioning was on in the gym so it did push the plane down.

What would you suggest we do for dewinds given we don't havea tprque meter?
Last edited by CypherKat on March 12th, 2023, 11:25 am, edited 1 time in total.
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Re: Flight B/C

Post by pumptato-cat »

So, I did some testing today. I'm getting a small circle diameter and an unstable descent, AGAIN, and almost all the ballast is on the nose(I think that adds up to around 1.4g). No matter what I do, it's still wobbly.
I decided to try some glide tests, and the results are not very encouraging.... on the exact same setting of shim, washin, incidence, and ballast, I got 4 different results with 4 different glides, back to back, with the exact same airflow. One went almost perfectly straight with a floaty descent, the other dived straight into a nasty right turn, and then the last two turned VERY sharply to the left. Almost a full left turn with a right angle and all. Nothing changed except the behavior of the glide. All settings were 100% the same, as far as I could tell.
Any ideas on what might be the issue? I thought it might have been the shim moving like Coach Chuck and Coach Brian said, but I checked it very thoroughly(marked with a pencil and everything) every time, along with the wing saddle. Neither seem to be moving, so I'm convinced that it's another problem...
(i can provide videos when I get home, if that helps)
EDIT: WAIT. The stab joint's loose. Not sure when this happened but it might be the cause of all this trouble. I recall checking that joint and it seeming fine, though. Odd.
Last edited by pumptato-cat on March 12th, 2023, 1:05 pm, edited 1 time in total.
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Re: Flight B/C

Post by bjt4888 »

CypherKat wrote: March 12th, 2023, 11:17 am
bjt4888 wrote: March 12th, 2023, 7:35 am
CypherKat wrote: March 12th, 2023, 6:59 am https://drive.google.com/file/d/1BSGzer ... sp=sharing

https://drive.google.com/file/d/1uvC9tf ... sp=sharing

https://drive.google.com/file/d/1p-bK2U ... sp=sharing

hello! I am back after a round of test in my school gym.

For each of these flights we got the rubber to 100 winds, and dewinded 5 turns on the winder, we don't have a torque meter sadly so I cant speak for that. We used the same rubber on these which later snapped, but it came in on 1.90 g and around .63 g/in. we messed around on CG placement but I wanted some tips on hitting the 2:30 mark. States is this Thursday, so we'll try ot get one final testing in before comp.
Thanks
Cypher,

Your video is still loading and I can look at it in a little while. A 1.9 g motor of .063 g/in with two black rubber o-rings is a loop about 14.12 inches long and 105 winder turns is only 85% of breaking turns if you use good winding procedures (see video of me winding in one of my first posts).

Step one: make your motors at 1.98 grams instead of 1.9 grams and you will have 5/8” longer loop. This will let you get up to 110 turns at about 85% of breaking. If your propeller is spinning about 7 RPS, half of the10x15 additional turns (assume you have the typical 15:1 ratio winder) will probably become additional turns remaining and half will become flying turns leading to 10 seconds more flight time. Note in my video that I wind the motor to 1.4 in oz. too bad you don’t have a torque as all of the winding process is actually torque based and not focused on turns much. Also, as climb height is almost a linear relationship to launch torque. Knowing torque allows you to fly very close to the ceiling without touching (after lots of practice).

A longer motor might mean that a different (slightly higher) density is required. I could tell you more about this if you could tell me the turns remaining and the torque values of the current motor used in the flights.

Be sure to wind the motor off the airplane as I demonstrate in the video. If you don’t have a torque meter, at least mount a small wire hook to a board that can be clamped to a table (make sure your States will supply a table; all good Event Supervisors should do this).

I’ll comment on the videos after they load. What is the ceiling height for States?

Brian T

We counted turns remaining by unwinding the rubber and it lies consistently around 300 winds (20 turns on 15:1 winder). We wind the rubber by holding one black o-ring as far as we can stratch and the other attached to the winder. Ceiling height hasn't been released but from memory I think it's about 25 (I'm lowballing it but there are also rafters). We'll be measuring and making new rubber bands and winding and unwiding them so we can use it best at comp. I didn't send a really short flight because it clipped the ceilling where we testing, but that was on 105 winder turns and 5 dewinds.

should also mention that the air conditioning was on in the gym so it did push the plane down.

What would you suggest we do for dewinds given we don't havea tprque meter?
Cypher,

The flights look pretty good. It's nearly impossible to optimize flight character and winding with the blowers on, so don't feel bad about the times your getting. If you were flying in calm air, I'd say that 300 turns remaining sounds like a lot and this would indicate a need for slightly higher density (thicker) motors. However, since the airplane is being forced down by the blowers and is being disrupted occasionally by blowers, you could just be landing with a lot of turns remaining for these reasons. So, I'd focus on getting more turns on the motor and making 1.98 gram motors and not too much on retrimming or using different backoff turn strategies. Your airplane is climbing really fast, but this might be a good strategy in bad air.

You might already be doing better than 2:30 if the air was calm. Also, if the air is calm, you might have to backoff more like 8-10 winder turns (of your 15:1 winder) to keep the airplane from hitting the ceiling too quickly. In good air, our airplanes reach the top of their climb at about 1:05 - 1:15 and we're backing off 10-20 winder turns (our airplane design is different and uses thicker rubber and a flaring propeller though; it's very different).

Good job though to fly so well in rough air.

Brian T
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Re: Flight B/C

Post by bjt4888 »

pumptato-cat wrote: March 12th, 2023, 12:55 pm So, I did some testing today. I'm getting a small circle diameter and an unstable descent, AGAIN, and almost all the ballast is on the nose(I think that adds up to around 1.4g). No matter what I do, it's still wobbly.
I decided to try some glide tests, and the results are not very encouraging.... on the exact same setting of shim, washin, incidence, and ballast, I got 4 different results with 4 different glides, back to back, with the exact same airflow. One went almost perfectly straight with a floaty descent, the other dived straight into a nasty right turn, and then the last two turned VERY sharply to the left. Almost a full left turn with a right angle and all. Nothing changed except the behavior of the glide. All settings were 100% the same, as far as I could tell.
Any ideas on what might be the issue? I thought it might have been the shim moving like Coach Chuck and Coach Brian said, but I checked it very thoroughly(marked with a pencil and everything) every time, along with the wing saddle. Neither seem to be moving, so I'm convinced that it's another problem...
(i can provide videos when I get home, if that helps)
EDIT: WAIT. The stab joint's loose. Not sure when this happened but it might be the cause of all this trouble. I recall checking that joint and it seeming fine, though. Odd.
Cat,

Yes a loose stabilizer joint could be the cause all of the issues you've been having.

Brian T
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Re: Flight B/C

Post by pumptato-cat »

UPDATE: I didn't get any good videos but I'll send a couple I guess? They were of the broken stabilizer flights, though, and are still processing.
After I glued the stabilizer joint in, I flew and got a decent glide test(Still a rather strong left turn. Oh well). Bjt488, I think you're definitely right about the stabilizer joint causing problems. And then... The problems started again.
I felt something rattling and looked at every joint, and discovered that both wing post joints had failed 😭 I'm not sure why. The balsa tore straight off the side of the stick, and I don't understand what happened... That's three glue joints broken and I'm not that bad at gluing..
The odd part is that I went so long without seeing the break in the joint. I don't know when it broke, but the fillet of glue between the wood and the CF was intact, so I must've not seen the break. Very strange.
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