Flight Consistency Problem

falcon1236912
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Re: Flight Consistency Problem

Post by falcon1236912 » March 9th, 2019, 7:21 am

jajefan wrote:
MTV<=>Operator wrote:
jajefan wrote: 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.
bjt4888 wrote: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).
when doing backoff turns fo you use the winder to wind to 85% max and then unwind to the correct torque using the winder, or is the rubber placed on the plane before hand an then you unwind the propeller to the correct torque?

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Re: Flight Consistency Problem

Post by coachchuckaahs » March 9th, 2019, 8:03 am

You need to monitor torque during backoff, so do it in the torque meter. While backing off, maintain the rubber length to match your hook to hook length. Changing length will change the torque measurement.

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jajefan
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Re: Flight Consistency Problem

Post by jajefan » March 9th, 2019, 1:33 pm

Just fyi, the thing with the doors opening/audience watching causing air drafts is pretty much true -

we got a 2:25 after reaching 35 foot altitude at our regional today

we got a 3:08 after reaching 30 foot altitude in our gym during practice

exact same trim setups (increased incidence a little to take advantage of higher regional ceiling), rubber might've become weaker but it shouldn't have been enough to drop us 40 seconds

Saw another team got 1:35 after their whole team came in to watch - that team usually gets 2:30's, their plane only climbed to 1/3 the ceiling height, he looked really sad after so we assumed it could've been a lot better.
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Re: Flight Consistency Problem

Post by bjt4888 » March 9th, 2019, 2:10 pm

Too bad about a Regionals with blowers on. We are lucky to have very cooperative facilities staff at my schools. They take pride in turning the blowers off and contributing to the students success. For two of my five schools, the maintenance staff have to climb onto the roof to shut off (in Michigan with sub-zero windchill). The other three schools can program the shutoff and restart into the facility management software.

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