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  #1  
Old 10-08-2011, 12:06 PM
humptybump humptybump is offline
 
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Default Performance numbers for RV-8 150hp

Vans does not post performance numbers for an RV-8 with only a 150hp engine but if it's safe to use 150/160ths of the 160hp numbers, then my airplane is about 1% faster than standard

(edit: using the data for 150hp vs 160hp from the RV-4 and RV-6, my plane is about 3% slower than standard for max cruise and 1.5% slower for 75% power at 8000ft.)

I an a buyer not a builder so today I went out and flew all the GPS boxes at 2000ft intervals up to 10,000 ft. The density altitudes were 3400ft up to 12200ft The numbers worked out to 165kts at 3,400ft down to 158kts at 12,200ft.

Throttle was WOT and leaned ROP. It is running a 150HP with a wood prop. Empty weight is 1085lbs (has a pretty massive weight at the prop).

Thanks Van for designing such a well behaved consistent performer!

Last edited by humptybump : 10-08-2011 at 01:21 PM. Reason: New calculations
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  #2  
Old 10-08-2011, 01:07 PM
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Andy Hill Andy Hill is offline
 
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Glad you like the RV-8

Quote:
but if it's safe to use 150/160ths of the 160hp numbers
Doubt it is... The 180HP "top speed (solo wt)" is 214mph. 160/180 x 214 = 190mph, but the 160HP is stated as 206mph.

If you take the ratio to the 3rd power (160/180) ^ 1/3 it gives 96%, and 214mph x 96% is 205.8mph - almost exact as given. So your 150mph top speed maybe should be (150/160) ^ 1/3 * 206mph = 201.6mph?

I'm sure this will provoke someone who knows what they are talking about to come along

Andy & Ellie Hill
RV-8 G-HILZ
RV8tors
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  #3  
Old 10-09-2011, 05:08 PM
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Dennis_I Dennis_I is offline
 
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All these KTS, MPH, KMH in aviation really confuses me
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Grew up with an RV-4, SE-XIO

Now: RV-8, Showplanes Fastback. #83218 Under construction, SE-XXO

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  #4  
Old 10-09-2011, 05:11 PM
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N941WR N941WR is offline
 
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Quote:
Originally Posted by Dennis_I View Post
All these KTS, MPH, KMH in aviation really confuses me
It's simple. In the US, we knots for factory built aircraft but for kitbuilt aircraft we use MPH for performance comparison. When talking to Air Traffic Control, it is always in Knots.

I just wish the US would move to the metric system like the rest of the world and be done with it.
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RV-9 (Yes, it's a dragon tail)
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  #5  
Old 10-09-2011, 06:02 PM
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dedgemon dedgemon is offline
 
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Default not quite

Quote:
Originally Posted by humptybump View Post
Vans does not post performance numbers for an RV-8 with only a 150hp engine but if it's safe to use 150/160ths of the 160hp numbers, then my airplane is about 1% faster than standard
!
The horsepower required increases to the cube of the speed increase so if you add an extra 9% power you should expect the speed to increase roughly 3%.

So the difference in speed from 160 to 150 hp is actually relatively small.
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  #6  
Old 10-09-2011, 07:00 PM
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Ironflight Ironflight is offline
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Quote:
Originally Posted by N941WR View Post
It's simple. In the US, we knots for factory built aircraft but for kitbuilt aircraft we use MPH for performance comparison. When talking to Air Traffic Control, it is always in Knots.
Huh Bill? YOU might use mph for kitbuilts, and a bunch of others do as well....but a lot of us follow the Knots rule for all aircraft. The only real reason to use mph is becasue the numbers sound bigger!

I had an aero professor who'd give you an "F" automatically if you didn't use knots - that was what the industry used, that's what you were going to use as an engineer!
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  #7  
Old 10-09-2011, 08:35 PM
humptybump humptybump is offline
 
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As with all things, what's important is "I'm happy".

All things considered, the plane flies fast and sips fuel.

Trust me, 155kts at under 8gph is a big delta to my other flying favorite - a Stearman going about 100kts and burning 16-18gph. I don't think I'd trade either :-)

Last edited by humptybump : 10-09-2011 at 08:38 PM.
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  #8  
Old 10-11-2011, 09:46 PM
jdmunzell jdmunzell is offline
 
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Quote:
Originally Posted by N941WR View Post
It's simple. In the US, we knots for factory built aircraft but for kitbuilt aircraft we use MPH for performance comparison. When talking to Air Traffic Control, it is always in Knots.

I just wish the US would move to the metric system like the rest of the world and be done with it.
...just so long as we don't change first to altitude in meters and then convert altimetry to QFE down near the ground the way they do in Russia and China!!!! It makes my bunkie a very busy sort during the approach phase, calling out converted numbers and such!
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  #9  
Old 10-12-2011, 03:45 AM
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N941WR N941WR is offline
 
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Quote:
Originally Posted by Ironflight View Post
Huh Bill? YOU might use mph for kitbuilts, and a bunch of others do as well....but a lot of us follow the Knots rule for all aircraft. The only real reason to use mph is becasue the numbers sound bigger!...
Sorry Paul, I was thinking about with regard to marketing and as you pointed out, the numbers sound bigger.
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RV-9 (Yes, it's a dragon tail)
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Build the plane you want, not the plane others want you to build!
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  #10  
Old 10-12-2011, 05:04 AM
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Bob Martin Bob Martin is offline
 
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Quote:
Originally Posted by N941WR View Post
Sorry Paul, I was thinking about with regard to marketing and as you pointed out, the numbers sound bigger.
I'm with Bill on this one!
The one question we as Rv'ers are asked a lot is "how fast does it fly?" and most of these questions are asked by automobile drivers, so it sounds very cool to be able to say "200mph" or just 200. This answer always get responses like WOW.......until some aviator asks the questions about mph or knots? Then we all know the discussion that follows but.......for a brief moment.....it was "200"
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