VansAirForceForums  
Home > VansAirForceForums

- POSTING RULES
- Donate yearly (please).
- Advertise in here!

- Today's Posts | Insert Pics


Go Back   VAF Forums > Model Specific > RV-9/9A
Register FAQ Members List Calendar Search Today's Posts Mark Forums Read

Reply
 
Thread Tools Search this Thread Display Modes
  #1  
Old 10-31-2018, 09:11 PM
gfb gfb is offline
 
Join Date: Jul 2014
Location: Madison, WI
Posts: 499
Default Yet another 9A speed thread

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?
__________________
---
RV-9A - started 01/2015, completed 07/19/2018

Last edited by gfb : 11-01-2018 at 10:02 AM. Reason: corrected IAS to TAS & CHT to EGT
Reply With Quote
  #2  
Old 11-01-2018, 05:55 AM
N941WR's Avatar
N941WR N941WR is offline
 
Join Date: Jan 2005
Location: SC
Posts: 11,597
Default

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!
__________________
Bill R.
RV-9 (Yes, it's a dragon tail)
O-360 w/ dual P-mags
Build the plane you want, not the plane others want you to build!
SC86 - Easley, SC
www.repucci.com/bill/baf.html

Last edited by N941WR : 11-01-2018 at 06:04 AM.
Reply With Quote
  #3  
Old 11-01-2018, 07:20 AM
gfb gfb is offline
 
Join Date: Jul 2014
Location: Madison, WI
Posts: 499
Default

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.
__________________
---
RV-9A - started 01/2015, completed 07/19/2018
Reply With Quote
  #4  
Old 11-01-2018, 08:18 AM
MarkW's Avatar
MarkW MarkW is offline
 
Join Date: Sep 2011
Location: Edgewater, FL. KSFB
Posts: 1,047
Default

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.
__________________
Mark
RV9 - N14MW - Flying
G3X - ECI Titan I0-320
Catto three blade prop
http://www.mykitlog.com/MarkW
Reply With Quote
  #5  
Old 11-01-2018, 08:30 AM
gfb gfb is offline
 
Join Date: Jul 2014
Location: Madison, WI
Posts: 499
Default

Thanks Mark. Are you suggesting I increase the prop pitch? This does seem counter intuitive as you mention
__________________
---
RV-9A - started 01/2015, completed 07/19/2018
Reply With Quote
  #6  
Old 11-01-2018, 08:39 AM
MarkW's Avatar
MarkW MarkW is offline
 
Join Date: Sep 2011
Location: Edgewater, FL. KSFB
Posts: 1,047
Default

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.
__________________
Mark
RV9 - N14MW - Flying
G3X - ECI Titan I0-320
Catto three blade prop
http://www.mykitlog.com/MarkW
Reply With Quote
  #7  
Old 11-01-2018, 08:48 AM
lr172 lr172 is offline
 
Join Date: Oct 2013
Location: Schaumburg, IL
Posts: 3,274
Default

Quote:
Originally Posted by gfb View Post
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
__________________
N64LR
RV-6A / IO-320, Flying as of 8/2015
RV-10 in progress
Reply With Quote
  #8  
Old 11-01-2018, 09:01 AM
grubbat's Avatar
grubbat grubbat is offline
 
Join Date: May 2012
Location: Ga
Posts: 577
Default 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 thatís 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. Iíll takeoff at 2700rpm, about midfield when I am at traffic pattern, Iíll dial it back to 2550 to 2650 till 8000ft or so which takes a couple of minutes. I havenít done any speed runs lately but I seem to recall that Bill Repucciís -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.
__________________
Craig

RV-3 Sold
RV-4 Sold
C-140 In a barn
Maule MXT-7 Sold
RV-6a Sold
Twin Comanche - Sold
RV-9 IO-360 CS, Built and Flying
J3-65 Cub - low and slow stuff
Comanche 260 - poor mans RV-10
Reply With Quote
  #9  
Old 11-01-2018, 10:03 AM
gfb gfb is offline
 
Join Date: Jul 2014
Location: Madison, WI
Posts: 499
Default

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
__________________
---
RV-9A - started 01/2015, completed 07/19/2018
Reply With Quote
  #10  
Old 11-01-2018, 10:36 AM
MarkW's Avatar
MarkW MarkW is offline
 
Join Date: Sep 2011
Location: Edgewater, FL. KSFB
Posts: 1,047
Default

Forget EGT's. Just keep playing with it until you get max rpm.
But as Larry says that should be just rich of peak.
__________________
Mark
RV9 - N14MW - Flying
G3X - ECI Titan I0-320
Catto three blade prop
http://www.mykitlog.com/MarkW
Reply With Quote
Reply


Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

vB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Forum Jump


All times are GMT -6. The time now is 02:00 AM.


The VAFForums come to you courtesy Delta Romeo, LLC. By viewing and participating in them you agree to build your plane using standardized methods and practices and to fly it safely and in accordance with the laws governing the country you are located in.