540 Bearhawk Performance at Altitude?

[7acdriver]

Okay, so it's easy to find out what kind of performance people are getting out of their 540 Bearhawks off the ground and down low (everyone raves about it!), but what about up high? I'm thinking with a 540 and aux tanks it'd be easy to hook the O2 up to your face and climb into the mid to high teens where TAS is high and fuel burn low to cover some real distance if you wanted to. Not to mention avoiding weather, etc. Anybody flight test at these altitudes to see what sort of fuel burn/TAS/climb rate numbers the Bearhawk will do at 14K'-17K' or higher even? Wondering where it starts running out of steam!

[Mark Goldberg]

I was at 15,000 ft once with Bob Barrows flying my 540 powered BH. Above standard temps I am sure. And it still had some climb left. Mark

[Battson]

I regularly cruise at 13,000ft cross-country.

Performance does reduce obviously, but it's not sluggish by any means. Climbing at 500ft/min is still realistic. If you planned on regularly being higher than that, you might consider turbo-normalising.

At that height you're making less than 70% power, so I lean for maximum power. WOT, desired RPM, peak EGT mixture. I typically see about 130KTAS (100KIAS) without tailwinds, with very efficient fuel burn about 9 Gal/hr given the airspeed. With some tailwind component I regularly see upwards of 150KTAS, which is getting places.

There were reports floating around (Beartracks) of someone taking their plan to 23,000ft...

[jaredyates]

I have a spreadsheet that can model the performance of the Bearhawk with different engines, but it requires an input of the percent power that the engine is producing, and that decreases as you climb. When I input a sea-level engine HP of 235, a density altitude of 20,000 feet, and 40% power (just guessing on the percentage), it shows a climb rate of 444 feet per minute at 1700 pounds, and 6 feet per minute at 2500 pounds. I have to guess on the engine output at high altitudes, since I only have a chart for the 360. Also note that this data is based on that 235 hp engine turning my 76" prop, which is not going to be right. If someone wants to measure the bigger prop to get better numbers, let me know and I'll send directions. Or, consult the 2014 Q1 Beartracks issue for instructions on how to make your own spreadsheet.

[7acdriver]

Thanks everyone, good to know mid teens should be pretty easy.