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location, location, location...

schristo@mac.com

[email protected]

Well Known Member
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...

screenshot20101017at742.jpg


screenshot20101017at742.jpg


screenshot20101017at743.jpg
 
Great pics, but some questions..

Some questions, please..
1. Was the speed GPS verified?
2. Is the nominal HP 210?
3. Is the 75% an assumption or what the EIS/EFIS says?

Thanks!
 
speed runs...

during fairing fitting i have made several separate high speed cruise runs, all conducted with multiple legs recording both TAS and GPS groundspeed, stabilized at a density altitude of 8,000 feet using the autopilot...

TAS and GPS averages have all been within one or two mph on each run. %power is as shown on the EIFS but generally is from full throttle giving about 23 inches and 2600 rpm.

gear intersection fairings look to have added 2-3 mph at the very most. the first run prior to fitting them showed and average of 212, lowers brought that to just under 214, the uppers bring it just up to 215... it really gobbles fuel at these speeds though; 13.4 gph when pushing the cruise speed limits! dialed back a bit i see 200 mph at 9.5

the engine is a standard lycoming IO-390 sea level rated at 210 hp at 2700.
 
thats a really interesting structure. can you tell where it is location wise? i don't imagine anything less than rock walls would last very long with winter storms inthe cascades and lightening damage. You often find rock walled huts on summits, but i've never seen anything that big. i wonder if it is a temporary structure for some sort of scientific study?

is the land designated wilderness?
 
Some people don't like company

Some people don't like company and will go to great lengths to avoid it.

IMG_1127.jpg


Bob Axsom
 
Stephan, This is near Darington right? If so it was a overnight cabin build by a climbing club in the 1930s.
 
I could not resist a few calculations!

[email protected] said:
during fairing fitting i have made several separate high speed cruise runs, all conducted with multiple legs recording both TAS and GPS groundspeed, stabilized at a density altitude of 8,000 feet using the autopilot...

TAS and GPS averages have all been within one or two mph on each run. %power is as shown on the EIFS but generally is from full throttle giving about 23 inches and 2600 rpm.

gear intersection fairings look to have added 2-3 mph at the very most. the first run prior to fitting them showed and average of 212, lowers brought that to just under 214, the uppers bring it just up to 215... it really gobbles fuel at these speeds though; 13.4 gph when pushing the cruise speed limits! dialed back a bit i see 200 mph at 9.5

the engine is a standard lycoming IO-390 sea level rated at 210 hp at 2700.
Click to expand...

Let's start with power. I calculate you are getting (23 x 2600) roughly 74% at those numbers = 155.5 BHP. If I'm right about that, then your best power SFC is .516. Conversely, if your SFC is the normal .500, then your BHP is 160.9 = 76.6%. I won't go into detail here, but based on my airplane, the 155.5 is more likely to be correct. This balances to your fuel burn at .516 SFC.

Now that we have that, we have the minimum drag, too (skipping the details, I used my spreadsheet, linked below). Your minimum drag should be a little less than mine (7 vs 7A) plus or minus individual airplane issues. I used 146.4 pounds at 110.5 mph for your airplane. Close, but probably not perfect. It matches my 150# corrected for the difference in nose wheel using Van's delta. I've ignored weight here, but my specs and yours appear to be a solo weight so the differences are small.

Taking an academic chance, if we use those numbers for a guesstimate, your Thrust HP at 215 at 8000 is 135.42 and that makes your WW 200RV prop 87.1% efficient. Considering that the prop was designed to be about 90% efficient at 8000 and 150 HP, but for an RV8 going 220, this is very close to design specs. Even if your BHP is the higher figure, your efficiency is 84.2%. If I use your 75%, it is 86% efficient.

Thanks for the data!
 
[email protected] said:
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...
Click to expand...
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.
 
Kevin's numbers

Kevin Horton said:
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.
Click to expand...
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?
 
hevansrv7a said:
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?
Click to expand...

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.
 
tent?

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
 
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You guys are making my head spin ...

... the engine performance data stuff, not the cool cabin pic. ;)
 
A great view but...

I would imagine there would be some serious wind chill during the winter. :eek:
 
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More estimates

Humbly accepting that Kevin is always right :)o), 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.
 
Bob Axsom said:
Some people don't like company and will go to great lengths to avoid it.

IMG_1127.jpg


Bob Axsom
Click to expand...

Judging by the number of cars parked on the street, and people walking to/from the house, it would seem they crave the views more than the privacy. It must be some scenery from...any room with a window. :)
 
Need for speed...

Nice post! I like seeing true speed numbers posted with the corresponding fuel flow. My 16 year old HR2 with 285 HP and GAMIs, large tires, caked mud (from my strip) and 2 more cylinders cooking easily tops 200 knots in level flight burning 14 Gph. I wonder how the 7 would perform with a 540 up front...

There's no substitute for HP...:)

Smokey

PS: The photo is a pvt resort.
 
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smokyray said:
Nice post! I like seeing true speed numbers posted with the corresponding fuel flow. My 16 year old HR2 with 285 HP and GAMIs, large tires, caked mud (from my strip) and 2 more cylinders cooking easily tops 200 knots in level flight burning 14 Gph.

There's no substitute for HP...:)

Smokey
Click to expand...

Indeed you're right, Smokey. But 14 gph? I see that on takeoff and cringe.

Last weekend, I was heading home from a fly-in and wasn't in any hurry so I pulled it back to 21". As I recall, it was drinking something like 6 gph. I thought, "Gee, I don't think I slowed down very much ..." and looked to see that I was still doing 145 kts! Sounded slow to me, but when I realize that most other bug-smashers are tooling along quite happily in their 172s and Cherokees happy to hit 130 kts balls-to-the-wall, I couldn't help but smile.

That said, I'd still rather see 200 kts. :D
 
Meteora

kentb said:
I would like to drop-in for a visit.

Kent
Click to expand...

The structure I photographed there is a monastery of Meteora just north of Kalambaka but there are private homes there built on huge vertical walled "rocks" in the same manner and style. We visited there on a Trafalgar tour called "The Best of Greece". It was a great trip by the way.

Bob Axsom
 
Cool.

Bob Axsom said:
The structure I photographed there is a monastery of Meteora just north of Kalambaka but there are private homes there built on huge vertical walled "rocks" in the same manner and style. We visited there on a Trafalgar tour called "The Best of Greece". It was a great trip by the way.

Bob Axsom
Click to expand...

I will be in Greece mid November, but don't know if this is on our schedule. I hope so.

Kent
 
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hevansrv7a said:

Let's start with power. I calculate you are getting (23 x 2600) roughly 74% at those numbers = 155.5 BHP. If I'm right about that, then your best power SFC is .516. Conversely, if your SFC is the normal .500, then your BHP is 160.9 = 76.6%. I won't go into detail here, but based on my airplane, the 155.5 is more likely to be correct. This balances to your fuel burn at .516 SFC.

Now that we have that, we have the minimum drag, too (skipping the details, I used my spreadsheet, linked below). Your minimum drag should be a little less than mine (7 vs 7A) plus or minus individual airplane issues. I used 146.4 pounds at 110.5 mph for your airplane. Close, but probably not perfect. It matches my 150# corrected for the difference in nose wheel using Van's delta. I've ignored weight here, but my specs and yours appear to be a solo weight so the differences are small.

Taking an academic chance, if we use those numbers for a guesstimate, your Thrust HP at 215 at 8000 is 135.42 and that makes your WW 200RV prop 87.1% efficient. Considering that the prop was designed to be about 90% efficient at 8000 and 150 HP, but for an RV8 going 220, this is very close to design specs. Even if your BHP is the higher figure, your efficiency is 84.2%. If I use your 75%, it is 86% efficient.
Click to expand...

Yeah, 220... 221, whatever it takes...
:)
 
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