Flight Consistency Problem

[MTV<=>Operator]

My team has been having problems with flight consistency and since our states competition is in a week, we need to find out what is causing this.
- In our school's gym, which has a 25 ft ceiling, we have been getting flights that range from 1:30 to 3:10 at best
- However, at our regional competition, the plane just circled around without lifting and got around a 12 second time
- The same thing happened at an invitational where the plane would not lift
- We tested the exact same regional configuration at our gym afterwards and it flew for 1:15
- We haven't changed the wing angles or the amount of torque we wind to for the past three weeks

Does anyone know what is causing this inconsistency and failure at competitions?
Any help is appreciated, thanks.

[bjt4888]

MTV,

If you could supply more info, we could provide very specific help. Here’s the info that would be helpful:

Wing and stab incidence angles or measurements
CG position
Weight of airplane
Airplane design (FF kit w/ no mods?)
Rudder offset
Stabilizer tilt
Wing offset
Wing and stabilizer washin
Thrustline offset
Propeller type and pitch angle
Rubber motor thickness, weight and length
Number of turns in best flights, max torque and launch torque

Poor climb can come from many settings. This info should help determine the source.

Brian T

[MTV<=>Operator]

MTV,

If you could supply more info, we could provide very specific help. Here’s the info that would be helpful:

Wing and stab incidence angles or measurements
CG position
Weight of airplane
Airplane design (FF kit w/ no mods?)
Rudder offset
Stabilizer tilt
Wing offset
Wing and stabilizer washin
Thrustline offset
Propeller type and pitch angle
Rubber motor thickness, weight and length
Number of turns in best flights, max torque and launch torque

Poor climb can come from many settings. This info should help determine the source.

Brian T

Thanks for your response. I can't provide exact values for many of these since I don't have the plane with me right now. However, the plane is a FF kit with FF propellers. The only things modified are wing and rudder angle (not really a modification). The CG is around 1/3 of the plane length from the front. Rubber thickness is 0.094 in. and weight with the o-rings is 2.5 g. We wind it to a reading of 1.5 on the FF torque meter and # of winds range from 133-138. The only thing that we have been changing is the rubber which snaps eventually. However, we make all of the motors the same length and thickness.

*Note: We wound it to a reading of only 1.3 on the torque meter at the regionals because the ceiling was lower than the ceiling of the gym we test in. Even so, the exact same configuration still lifted and flew in our gym.

[jajefan]

Thanks for your response. I can't provide exact values for many of these since I don't have the plane with me right now. However, the plane is a FF kit with FF propellers. The only things modified are wing and rudder angle (not really a modification) and weight. We placed a piece of clay on the CG which is around 1/3 of the plane length from the front. Rubber thickness is 0.094 in. and weight with the o-rings is 2.5 g. We wind it to a reading of 1.5 on the FF torque meter and winds range from 133-138. The only thing that we have been changing is the rubber which snaps eventually. However, we make all of the motors the same length and thickness.

*Note: We wound it to a reading of only 1.3 on the torque meter at the regionals because the ceiling was lower than the ceiling of the gym we test in. Even so, the exact same configuration still lifted and flew in our gym.

We've been winding to around .5 torque on our FF torque meter for a ceiling height of 30 feet. Seems like you've got a less-than-ideal wing incidence trim setup, as the plane should climb decently well when between .5-.6 in*oz torque. Check to see if your prop thrust bearing is actually parallel to the motor stick (we find that it is difficult to make parallel when building), as this may cause a significant amount of lost climb when at the beginning.

Additionally, when gyms have open doors (either at invitationals, regionals) with people coming in and out all the time to spectate, sign in, etc., then we find that we also have significantly reduced climb at the same torque output. We suspect it's due to these reasons that air drafts (minimal, if at all) are forming, as we find that we have a reduced climb rate at almost every competition we have gone to, especially when our flight circle is closer to the entrances of the gym. (This happened at the Solon and Mentor invitationals for sure, resulting in almost 1 minute decreases in flight times for participants on the unlucky side of the gym with the entrance).

[bjt4888]

One more useful data point. If you could report typical number of backoff turns. Agree that bad air affect duration quite a bit sometimes. Shouldn’t change duration as much as you are describing though. .094” rubber, when paired with a moderate pitch propeller, should produce good results.

[MTV<=>Operator]

We've been winding to around .5 torque on our FF torque meter for a ceiling height of 30 feet. Seems like you've got a less-than-ideal wing incidence trim setup, as the plane should climb decently well when between .5-.6 in*oz torque. Check to see if your prop thrust bearing is actually parallel to the motor stick (we find that it is difficult to make parallel when building), as this may cause a significant amount of lost climb when at the beginning.

Additionally, when gyms have open doors (either at invitationals, regionals) with people coming in and out all the time to spectate, sign in, etc., then we find that we also have significantly reduced climb at the same torque output. We suspect it's due to these reasons that air drafts (minimal, if at all) are forming, as we find that we have a reduced climb rate at almost every competition we have gone to, especially when our flight circle is closer to the entrances of the gym. (This happened at the Solon and Mentor invitationals for sure, resulting in almost 1 minute decreases in flight times for participants on the unlucky side of the gym with the entrance).

Thanks for your help. What size rubber are you using? We are going to try building another plane and fix the wing incidence trim.

One more useful data point. If you could report typical number of backoff turns. Agree that bad air affect duration quite a bit sometimes. Shouldn’t change duration as much as you are describing though. .094” rubber, when paired with a moderate pitch propeller, should produce good results.

Sorry, but what are backoff turns? I haven't heard this terminology used before.

[bjt4888]

You may want to read this thread on Winding from the 2015 Scioly.org wiki:

viewtopic.php?f=191&t=6247

Brian T

[jajefan]

We've been winding to around .5 torque on our FF torque meter for a ceiling height of 30 feet. Seems like you've got a less-than-ideal wing incidence trim setup, as the plane should climb decently well when between .5-.6 in*oz torque. Check to see if your prop thrust bearing is actually parallel to the motor stick (we find that it is difficult to make parallel when building), as this may cause a significant amount of lost climb when at the beginning.

Additionally, when gyms have open doors (either at invitationals, regionals) with people coming in and out all the time to spectate, sign in, etc., then we find that we also have significantly reduced climb at the same torque output. We suspect it's due to these reasons that air drafts (minimal, if at all) are forming, as we find that we have a reduced climb rate at almost every competition we have gone to, especially when our flight circle is closer to the entrances of the gym. (This happened at the Solon and Mentor invitationals for sure, resulting in almost 1 minute decreases in flight times for participants on the unlucky side of the gym with the entrance).

Thanks for your help. What size rubber are you using? We are going to try building another plane and fix the wing incidence trim.

One more useful data point. If you could report typical number of backoff turns. Agree that bad air affect duration quite a bit sometimes. Shouldn’t change duration as much as you are describing though. .094” rubber, when paired with a moderate pitch propeller, should produce good results.

Sorry, but what are backoff turns? I haven't heard this terminology used before.

We've generally stuck with .087 and .094 width rubbers depending on the plane we are using, though .087 has been getting longer times for us. We're still trying to find the optimum rubber loop length for our current plane though. However, we find that variation in the density is quite high and so I take anything I cut with a grain of salt, as I've seen two almost identical motors have three different climb rates (one motor consistent, the other with high variability between not climbing on break-in and then climbing more than we'd thought for our given torque after break-in).

Backoff turns are used to find the optimum launch torque while also packing more winds into the rubber than if you had not backed off to get the optimum launch torque (since rubber torque curves lose torque faster on the dewind than the initial winding process - see bjt's 2015 post on winding up above).

[newflight]

How do you 'Check to see if your prop thrust bearing is actually parallel to the motor stick', I was trying to do that, however, I had a difficult time to exactly measure it

[CrayolaCrayon]

How do you 'Check to see if your prop thrust bearing is actually parallel to the motor stick', I was trying to do that, however, I had a difficult time to exactly measure it

Lightly pull on the hook, or apply pressure to the prop lightly, and see if it angles down, up or remains parallel.