What's new
Van's Air Force

Don't miss anything! Register now for full access to the definitive RV support community.

RV9a Performance: Need your x-check

Wahi-Air

I'm New Here
Hi folks,

I am writing you as I need some guidance on where my speed is missing.... :confused::confused::confused:

Summary:
  • I believe to be at least 10-15kt short of TAS at cruise. Question is aerodynamics vs. engine performance... I can´t think of aerodynamics...

  • Would be great if you can let me know where to look for some more knots :)

The plane:
  • RV9A / (Y)O-320-D2G (ordered from Vans), carburated, fixed pitch Sensenich 70CM7S9-0-79, dual mag ignition, all flaps and controls even and on surface, gear boots installed

My performance (all measured with Dynon HDX):
  • 5000ft, 77%, 2500RPM throttle wide open, lean, 35L/h (9.2USgls), 144KTAS (166TAS mph)
  • at take-off on MSL I am reading 2200RPM

The performance of a build-alike RV9a, same config:
  • 6000ft, 77%, 2500RPM, 39L/h, 161KTAS (186TAS mph)
  • 6000ft, 63%, 2300RPM, 34L/h, 145KTAS (167TAS mph)

Here´s a link of a 2.5h flight showing the same data:
https://apps.savvyaviation.com/flights/5752959/45808f9d-3690-458e-bc79-4ef7574aa473

I AM REALLY GRATEFUL FOR ANY THOUGHTS AND INSIGHTS!!!
Cheers
Sunit :):):)
 
Speed?

The performance of a build-alike RV9a, same config:
  • 6000ft, 77%, 2500RPM, 39L/h, 161KTAS (186TAS mph)
  • 6000ft, 63%, 2300RPM, 34L/h, 145KTAS (167TAS mph)

Here´s a link of a 2.5h flight showing the same data:
https://apps.savvyaviation.com/flights/5752959/45808f9d-3690-458e-bc79-4ef7574aa473

I AM REALLY GRATEFUL FOR ANY THOUGHTS AND INSIGHTS!!!
Cheers
Sunit :):):)[/QUOTE]

I have a 9A, same engine but fuel injected. My TAS is essentially the same as your example similar aircraft, that is: pretty close to 186 mph TAS at that power setting and altitude. Mine pretty much holds that TAS at higher altitudes at WOT and leaned to best power, although I seldom run it at best power, normally at LOP about 50 deg F but naturally lower airspeed.

I suspect your indicated (and therefore reported TAS) is not accurate. Have you and this other aircraft flown side by side to verify the airspeed indications correspond?
Ed
 
I have the same engine/set up as you...

and will replicate your conditions and advise. Hopefully today if the weather holds.
 
Altitude?

Is the altitude quoted MSL or DA?

When I had that prop (Sensenich fixed) mounted, 2400 would give me 151 kt TAS AT 6500 ft DA and 21.5”of MAP, approx 71% power per the Dynon...after the static system was corrected. At WOT, 8000’ DA, 2610 rpm, 167 kt TAS, still showing 23.1” MAP. Before correction I would read low. I don’t recall what I would hit at 2500 down low.

Now, wIth the Sensenich GA mounted and set a smidge favoring climb, 8000’ DA and 2700 rpm gives me 166 kts consistently, a little leaning and I can hit 2750 and 169 kts+, with 23.1”-23.2” MAP. Things get busy at that speed. My data consistency got a lot better with the AP. ;).

I seem to be getting good pressure recovery in the airbox. My airbox is not quite standard. All data runs are solo full fuel at TO.

You do have your gear leg and wheel fairings mounted? That was worth 8-10 kt to me. I was shocked.

I suggest a couple three or four ways backed up by GPS before doing anything else.
 
Last edited:
I've got a slow one, IO-320 C/S prop. Looks to be similar to yours. From my last flight:

7500', 22.5", 2350 RPM = 69% Power
34 L/hr
143 KTAS

This is with most of my fairings installed, missing one upper intersection fairing (in a box, just need to install it). I don't think I've ever exceeded 148 KTAS in level flight and that isn't common. I plan 142 KTAS.

I'd love to find a few more knots for my long cross country flights, but I don't really need it most of the time.
 
My speeds

My 2003 RV9a with constant speed prop and o-320 DIA engine, faired fully with wheel pants runs 149 kts at 7500 feet MSL at 2400 rpm. I don’t usually run 2500 rpm as I don’t like the extra vibration and fuel burn. I think my plane is pretty average for an RV 9a.
 
speed

The performance of a build-alike RV9a, same config:
  • 6000ft, 77%, 2500RPM, 39L/h, 161KTAS (186TAS mph)
  • 6000ft, 63%, 2300RPM, 34L/h, 145KTAS (167TAS mph)

Here´s a link of a 2.5h flight showing the same data:
https://apps.savvyaviation.com/flights/5752959/45808f9d-3690-458e-bc79-4ef7574aa473

I AM REALLY GRATEFUL FOR ANY THOUGHTS AND INSIGHTS!!!
Cheers
Sunit :):):)

I have a 9A, same engine but fuel injected. My TAS is essentially the same as your example similar aircraft, that is: pretty close to 186 mph TAS at that power setting and altitude. Mine pretty much holds that TAS at higher altitudes at WOT and leaned to best power, although I seldom run it at best power, normally at LOP about 50 deg F but naturally lower airspeed.

I suspect your indicated (and therefore reported TAS) is not accurate. Have you and this other aircraft flown side by side to verify the airspeed indications correspond?
Ed[/QUOTE]

Just to clarify my post. The numbers I show here are based on the results of my flights usually by myself, about 1/2 fuel, no other baggage, so I am light. I dont recall my best speeds at near gross at best power since I normally fly LOP and accept the speed loss. I have never actually determined best speed at max gross. Also, my aircraft is polished, only paint is on the fiberglass parts. Also not sure if it makes any difference, but I have a slider, not tip up. I wonder if it makes any difference?
Ed
 
-9A, painted, tip-up, all fairings installed except upper main gear intersection fairings. YO-320-D2G, FP Prop. Dynon avionics.

My numbers from yesterday:

5000' MSL
2500RPM
75%
9.2 g/hr
185mph TAS

6000' MSL
2300RPM
62%
7.7 g/hr
165mph TAS

6000' MSL
2500RPM
77%
10.1 g/hr
183mph TAS

This was a quick flight - might try again and take several data points.

To the OP - would be curious what you find if you continue to investigate your aircraft's performance.
 
Best Speed Altitude

Typically Best Speed will be at 7500' Density Altitude and Wide Open Throttle, which should give very close to 75% power.

Higher or lower than that will not be as good. NOTE, DA, not MSL.

If you are only turning 2400 rpm at that altitude then I don't think you'll see 75%.

All the gear fairings are important. Wheel pants (all 3), gear leg fairings (all 3) and intersection fairings (all 5). With none of that you'll be down around 15 mph.

Rigging can be huge. Make sure you don't have flap or aileron droop.

Run a 3 leg GPS test and plug it into the NTPS spreadsheet. [Search the forums...]
That will give you actual ground speed not some +/- 5% airspeed....

Took me a while, but I have book numbers now!
 
thanks guys, really much appreciated.
Next week I will do a long X-country where I can test several settings. Will also check on the 3-leg flight test (though I am not expecting to see a huge change as my GS is always quite close in no wind conditions and does not show me the numbers like 160kts either...).

Will come back to you in a few days.
Cheers
Sunit
 
The basic checks are,

1. Do you have the Van's static ports? If no then your static reference will account for most of the error. It is the outside shape that is critical, doesn't matter how you hook up to the tubes inside. Verify by using the GPS calibration method.
2. Calibrate your tacho and fuel flow.

If you are really turning the Sensenich prop 2400 or 2500rpm and have all your fairings installed and straight then you should be achieving close to Van's posted speeds.
 
Back
Top