location, location, location...

[apkp777]

Originally Posted by 1Oldguy

Is the cabin for sale and are the roads plowed in the winter?

Several years back this area got a record snowfall of something like 150 feet..you'll need a bigger shovel.

[Kevin Horton]

Originally Posted by schristo@mac.com

after completing a high speed cruise test run with all of the gear fairings finally completed (215 mph at 8,000 feet and 75%), i noticed something unusual on a remote peak...

Neat photos.

If the IO-390 percent power vs rpm, MP and altitude is similar to that of the IO-360-A series engines, 2600 and 23" at 8000 is about 81% power (assuming standard temperature), if the IO-360-A series power chart is to be believed. If you want 75%, that would be more like 2450 rpm and 23" at 8000 ft.

Note: some folks will tell you that 2700 rpm and full throttle should give 75% power at 8000 ft. That might be true if the air box was less efficient, and the TAS was lower so there was not so much ram pressure rise. But, RVs, with their well designed air boxes and high TAS realize higher MP than many other aircraft.

[hevansrv7a]

Originally Posted by Kevin Horton

Neat photos.

If the IO-390 percent power vs rpm, MP and altitude is similar to that of the IO-360-A series engines, 2600 and 23" at 8000 is about 81% power (assuming standard temperature), if the IO-360-A series power chart is to be believed. If you want 75%, that would be more like 2450 rpm and 23" at 8000 ft.

Note: some folks will tell you that 2700 rpm and full throttle should give 75% power at 8000 ft. That might be true if the air box was less efficient, and the TAS was lower so there was not so much ram pressure rise. But, RVs, with their well designed air boxes and high TAS realize higher MP than many other aircraft.

I completely agree with Kevin that WOT at 8000 DA is more than 75% on an RV and that there is observable MP boost at typical RV high speeds. I usually see >1" over ambient.

However, 81% of 210 is 170.1 and at best-power SFC, that should be about 14.175 gph (using 6#/gal). To get 170.1 from 13.4 gph would require a best-power SFC of .4727.

Kevin, what's the right approach to this?

[Kevin Horton]

Originally Posted by hevansrv7a

I completely agree with Kevin that WOT at 8000 DA is more than 75% on an RV and that there is observable MP boost at typical RV high speeds. I usually see >1" over ambient.

However, 81% of 210 is 170.1 and at best-power SFC, that should be about 14.175 gph (using 6#/gal). To get 170.1 from 13.4 gph would require a best-power SFC of .4727.

Kevin, what's the right approach to this?

There is no magic single SFC value for the mixture for best power condition. I've got a Lycoming document that shows a method to calculate power from fuel flow data. The data in this document shows that there is a range of fuel flows around the best power condition where the power is essentially constant. For an IO-360-A engine at 2600 rpm and 81% power at mixture for best power, they show the fuel flow could be between 12.55 and 13.6 USG/hr with no change in power, or an SFC of anywhere between 0.476 and 0.507.

Note: the range of SFCs at best power varies somewhat with compression ratio, rpm. and power.

[RV7AV8R]

Originally Posted by Carl J. Niedermeyer

Looks like the lookout on Three Fingers, East of Arlington, WA.

Right and just south of Darington. I see I was wrong, it was built in 1970 by the forest service but now maintained by the climbing club. Pretty cool to fly over!

[Jaypratt]

Steve,

Could you tell if it was a tent? or more perment?

Is a 390 an angle valve, haven't seen one of those yet.

Thanks

[Jamie]

This is NOT me, but I did stumble across this video on youtube of an RV flying by that same structure. He notes that on the second pass someone actually came outside.

http://www.youtube.com/watch?v=_ZpDYdWr_E8

[N8RV]

You guys are making my head spin ...

... the engine performance data stuff, not the cool cabin pic.

[drycreek]

I would imagine there would be some serious wind chill during the winter.

[hevansrv7a]

Humbly accepting that Kevin is always right (), I calculate that if the drag numbers are similar to mine (corrected for the nose wheel), then the prop efficiency is only 79.6%.

This is a big difference, but it's all in what you use for BHP. SChristo used 75% but Kevin is saying 81% is closer to accurate.

If I use Kevin's view of BHP at 8000', then the Ellipse-6 that I posted about recently would not be 78.3%. Rather, it would be around 77.4%.

Using my BHP method, same as for the 6, this -7 is at 81.7%, a relative difference of 4%.

Using Kevin's BHP method for both airplanes gives a similar percentage difference.

Granted, I'm making educated guesses about drag in both cases, but the two engine power estimates are based on equal concepts in each case while the cases use differing methods of estimating BHP.

Prop efficiency in this context is THP/BHP. Since THP is drag times speed, the drag estimate is the weak point in this comparison.

My drag estimate on the RV7/7A is not as solid as the CAFE 6A data. But, if you think the drag comparisons are reasonable - as I do - then the WW 200RV prop is more efficient. At only 4% difference, this is useful data but not conclusive.