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Yet another 9A speed thread

gfb

Well Known Member
OK, so finally finished my wheelpants and dialing in the prop.
RV-9A, Titan IO-340 180hp, WW GA-200L prop

75% 2650rpm 9.2gph 164kts TAS 8500' (189mph)
65% 2540rpm 7.9gph 154kts TAS 8500' (177mph)
56% 2440rpm 6.8gph 149kts TAS 8500' (171mph)
50% 2400rpm 6.0gph 146kts TAS 8500' (168mph)

I was expecting a bit more at the top end; I was at full throttle, peak EGT.
Van's website numbers for 160hp list 186mph at 75%, I figured the extra 20hp would buy me 10mph?
 
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Did you mean "True Airspeed"?

What is important is True Airspeed at 8,000' density altitude. That is the benchmark to use.

I think you will find your numbers will go up.

Also, why 2650 RPM? Is that all your engine could turn? At 9.2 GPH, I don't think you are producing full power. An O-320 will burn 9.6 GPH at 75% power.

At 8,000' DA, my O-360 spinning a Catto cruise prop will spin up to 2750 and my -9 taildragger will top out right at 175 knots TAS. To do that, I am burning a but more than 12 GPH, So I don't fly it at those speeds.

Good luck!
 
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Good catch, I corrected IAS to TAS as that is the number I was actually reading.

The engine dataplate indicates 180hp at 2700rpm. The prop is limited to 2700rpm. I was trying to get the prop pitch to show 2700 rpm at full throttle around 8000'. I hadn't considered DA, I'll go out and re-do the test at 8000' DA and see what I get.
 
gfb,
Since i believe that is a ground adjustable prop you may find a little better speed at a little lower RPM @ 8500' and 75%.
I think the CS prop guys see better speeds at a little lower RPM.
I know sounds counter intuitive.

I typically fly around 8000' (9k-9.5k DA) and lean back to about 152- 155 kts and 7gph. If I look for best speed I can see around 160 kts at that altitude but my rpm is 2500.
This gives me enough prop that at the lower altitude and WOT I push the 2700 limit.
My guess is you would over rev at lower altitudes with your current prop setting.
 
Thanks Mark. Are you suggesting I increase the prop pitch? This does seem counter intuitive as you mention :)
 
Yes.
I would want to get input from CS prop guys but as I said I believe that they pull rpms back a little for best speed.
Plus I would assume you are over rev limit down low @ higher power percentage if you are 2650 @ 75%.
I bet you have very good climb with the current prop pitch.
 
OK, so finally finished my wheelpants and dialing in the prop.
RV-9A, Titan IO-340 180hp, WW GA-200L prop

75% 2650rpm 9.2gph 164kts TAS 8500' (189mph)
65% 2540rpm 7.9gph 154kts TAS 8500' (177mph)
56% 2440rpm 6.8gph 149kts TAS 8500' (171mph)
50% 2400rpm 6.0gph 146kts TAS 8500' (168mph)

I was expecting a bit more at the top end; I was at full throttle, peak CHT.
Van's website numbers for 160hp list 186mph at 75%, I figured the extra 20hp would buy me 10mph?

Assuming you mean Peak EGT. The represents economy cruise and is not full power. richen it up to 80-100 ROP for full power. I would guess that Van's uses that setting for their advertised speeds and this is loosely validated by backing it out of their endurance numbers.

20 HP should only buy you ~5 MPH.

Larry
 
Good question

I seem to recall the late Bob Axsom using max rpm of 2700 when racing to get peak HP and fastest speed. My engine produces max hp at 2700 rpm and I am limited by prop mfg to not exceed the rpm past that point. Also, my Vetterman trombone exhaust is tuned to 2550 to 2650 rpm. So, what does one to do? Horsepower and torque is a function of rpm and that?s one big factor to go fast. Another critical factor is prop rpm limitations and prop efficiency. I heard years ago that most fixed pitch props had peak efficiency around 2500rpm but who knows. I?ll takeoff at 2700rpm, about midfield when I am at traffic pattern, I?ll dial it back to 2550 to 2650 till 8000ft or so which takes a couple of minutes. I haven?t done any speed runs lately but I seem to recall that Bill Repucci?s -9 had me beat on top speed with his craft and that wonderful Catto prop. His prop is just good. Craig Catto should be proud.
 
Another good catch. I meant to say EGT.

Today I'll go out and re-run things at 8000' DA and 80-100 ROP. Stay tuned :)
 
Forget EGT's. Just keep playing with it until you get max rpm.
But as Larry says that should be just rich of peak.
 
data point

5.7 gph, 153 kt TAS, ~20 in HG, 11.5K ft, 2250 rpm

riding the wind

IMG_20180306_094225_zpsbu2pknf9.jpg
 
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I ran several different generations of Catto 3 blade props on my IO360 equipped 9a for many years. Also spent a lot of time testing prototype units for Craig. All testing was at 8k density or higher and the 9 wing really liked slightly higher when testing for TAS performance. To set max power I would go to altitude wot, level, let things stabilize, and then set egt on my #4 (first to peak) at around 100 rop and again let things stabilize. The next step was to move the red knob VERY slowly richer until the rpm peaked. I did this several times to insure it was repeatable and took the egt at peak rpm as my set point for best power. Mine usually peaked the rpm at around 120-130 degrees rich of peak. This way when testing for TAS I could simply go to the same density altitude and set 120-130 rich of peak egt and know I was pretty close to peak power.

BTW, with a fp prop this HAS to be done in smooth air--the least amount of turbulence really makes this task difficult if not impossible.

Hope this helps.

You are gonna love that RV9/180/Catto combo--smooth, efficient, fast, and low maintenance.

Cheers,

db
 
These speeds look really good compared to what I'm getting right now. I don't have pants or leg fairings yet and I'm running a lot slower.

Recent flight #1:
  • 7400' DA
  • 64% Power
  • Peak EGT (best economy)
  • 7.0 gph
  • 122 KTS TAS

Recent flight #2:
  • 9100' DA
  • 66% Power
  • ~140 ROP (A little too rich)
  • 9.3 gph
  • 133 KTS TAS

I really hope I can get at least 20 KTS more in these conditions once I put my pants and fairings on. I think that may be a pipe dream. In any case, don't want to hijack this thread - I'll start my own sometime.
 
I really hope I can get at least 20 KTS more in these conditions once I put my pants and fairings on. I think that may be a pipe dream. In any case, don't want to hijack this thread - I'll start my own sometime.

That's about what I picked up so it's not a pipe dream. You'll also run quite a bit cooler CHTs, thanks to faster speeds.

To keep with the thread topic. I generally run my -7A

8500-11500
160 KTAS
8-8.2 GPH
LOP

Maybe I should try burning a little more gas to go faster.
 
Don't Be Disappointed

Claude don't think something is wrong if you don't see that 18-20 knot increase. Raymo appears to be running a fp 3 blade Catto--per your signature you are running a 200RV CS prop. When Raymo installed his fairings and got them lined up he benefitted by removing drag from the airframe and the plane flew faster. Since the airframe had less drag he also reduced the load on the engine prop combo and the rpm went up--therefore producing more hp and again flying faster. With a constant speed prop you would get the first benefit (lower airframe drag) from your fairings but you can already produce max available hp via use of the blue knob therefore you may not see as dramatic an increase as a fp RV.

BTW, back when I built my 9a (2003-2006) I had a fp 3 blade Catto and saw 16-17 knots increase with the install of the fairings. If memory serves my rpm at wot also went up well over 100 rpms.

Hope this helps.

Cheers,

db
 
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