Scioly.org

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).