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Balsa,

We generally start testing by selecting a conservative CG based upon the neutral point and a slightly excessive decalage angle (difference between the wing and stabilizer incidence angles). We fly this setup, maybe slightly reducing wing incidence if stalling, with a variety of propellers (usually increasing pitch gradually) and a variety of rubber densities andmotor lengths. Once we have this trim setup flying well, we will start pushing the CG back till stalling (or,intense case of this year’s tandem, mushing and wandering) and then move the CG jus forward of this point or reduce the wing incidence, or try both adjustments separately on different flights.

We continue iterations of the above till changes stop increasing duration or till too unstable to survive air disturbances or ceiling hits.

Good luck and have fun at Nationals.

Brian T

bjt4888 wrote:Balsa,

We generally start testing by selecting a conservative CG based upon the neutral point and a slightly excessive decalage angle (difference between the wing and stabilizer incidence angles). We fly this setup, maybe slightly reducing wing incidence if stalling, with a variety of propellers (usually increasing pitch gradually) and a variety of rubber densities andmotor lengths. Once we have this trim setup flying well, we will start pushing the CG back till stalling (or,intense case of this year’s tandem, mushing and wandering) and then move the CG jus forward of this point or reduce the wing incidence, or try both adjustments separately on different flights.

We continue iterations of the above till changes stop increasing duration or till too unstable to survive air disturbances or ceiling hits.

Good luck and have fun at Nationals.

Brian T

Thanks, Brian for clarifying my questions with your own practices, I really appreciate it. I'll apply these in my upcoming, short but important flying sessions.

Though, I was wondering how you calculate the NP - do you have a special spreadsheet just to calculate it because I've seen some people use calculators to find the NP and SSM, but I can't seem to find one that works or don't know how to make one myself?

Balsa,

We use the Bernie Hunt NP/Design spreadsheet. Fern Rash also has published a good one. Both are available in the Yahoo Group “Indoor_Construction” in the Files section. Bernie’s sheet doesn’t calculate CG perfectly for heavy airplanes like we use for SO but we “trick” the spreadsheet by entering the ballast location different than actual in order to have the sheet calculate the CG correctly and thereby show the SSM correctly.

If you have detailed questions about use of the sheet, spend me a PM.

Brian T

Fred Rash, not Fern Rash.

bjt4888 wrote:Balsa,

We use the Bernie Hunt NP/Design spreadsheet. Fern Rash also has published a good one. Both are available in the Yahoo Group “Indoor_Construction” in the Files section. Bernie’s sheet doesn’t calculate CG perfectly for heavy airplanes like we use for SO but we “trick” the spreadsheet by entering the ballast location different than actual in order to have the sheet calculate the CG correctly and thereby show the SSM correctly.

If you have detailed questions about use of the sheet, spend me a PM.

Brian T

Thanks sm again Brian, I'll try to use them and gather some accurate data.

Hey, I’m not sure if anyone from Fossil Ridge is here. But they left a torque meter and winder on top of the thermostat right by the entrance.

DarthBuilder wrote:Hey, I’m not sure if anyone from Fossil Ridge is here. But they left a torque meter and winder on top of the thermostat right by the entrance.

There was practice today!?

NorCalplaya wrote:

DarthBuilder wrote:Hey, I’m not sure if anyone from Fossil Ridge is here. But they left a torque meter and winder on top of the thermostat right by the entrance.

There was practice today!?

no...?

congrats to coach chuck and his team for winning nats this year!!

1st: Albequerque HS with a 5:09
2nd: Bayard Rustin HS with a 4:25
3rd: Northville HS with a 3:50


From what I observed ^