[humptybump]

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!

 

[Andy Hill]

Glad you like the RV-8

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

 

[Dennis_I]

All these KTS, MPH, KMH in aviation really confuses me

 

[N941WR]

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.

 

[dedgemon]

not quite

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.

 

[Ironflight]

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!

 

[humptybump]

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

 

[jdmunzell]

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!

 

[N941WR]

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.

 

[Bob Martin]

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"

 

[smokyray]

No substitute?

Hi Glen,

Glad to see another 150HP RV out flying around. I get a chance to fly many RV's and just delivered a 200HP C/S RV8 from Portland OR to FL. Longest leg was CO to MS (750NM)) I set 15"and 2300 RPM at 9500' (7.8GPH) and 155 Knots. I repeated the same leg last week in my 150HP wood propped RV-6X burning 8.2GPH at WOT 9500' and 165 KTAS (OK Paul I won't discuss Mach numbers The fuel bill after 4 hours was nearly identical. My 285HP HR2 at 160 TAS burned, you guessed it 8.0 GPH. To me they all fly great but the memorable ones are the light ones.

Hmm, maybe those Engineer types know what they are doing eh?

Smokey
www.fly-4-life.com

PS: You can go faster, but you'll pay for it...

 

[humptybump]

maybe those Engineer types know what they are doing

yeah - that's the conclusion I've come to

I'm looking forward to getting out on a few cross cow try flights this winter. I've been up to Maine a couple times this summer. Perhaps south to the Keys may be in order !