RV-9A performance check, low airspeed

[eumarschner]

Hi all, I've been following the various performance check threads and to this date, haven't been even close to achieving the 160+ kts TAS airspeed suggested by Vans and other pilots in this forum.

I am flying a 2011 assembled RV-9A with a Hartzell CS propeller and a Lycoming IO-320 engine, wheel fairings included.

I've been achieving a 145-150 kts TAS at 8500' DA on flights in the Rio de Janeiro, BR surroundings.

My aircraft was assembled by Flyer in Brazil, who is known for putting a good interior and a bit more weight on the front end of the aircraft.

To verify whether W&B is impacting performance, I share my latest weight and balance measure, to verify whether it stands in line with other aircraft flown elsewhere.

Empty measures:
Right Landing Gear 207.8 Kg (458.1 pounds / 37.6% weight)
Left Landing Gear 210.5 Kg (464.1 pounds / 38.0% weight)
Nose Wheel 135.0 Kg (297.6 pounds / 24.4% weight)
Total 553.3 Kg (1,219.8 pounds)

Can you please share your W&B and performance for verification?

Any additional hints on what else might be impacting performance?

Thank you much folks

 

[D-Dubya]

First off, are you sure that your instrumentation is reading correctly? There are several tests you can perform to confirm that your static ports are reading correctly. There's a calibrated scale you can set up with a manometer to confirm the pitot tube is measuring correctly as well. Has the pitot-static system been checked for leaks? Any of these things could be providing a false indication.

After those things are checked, I'd be looking at rigging and fairings to see if they're slowing you down. 145 knots does sound a little slow at that altitude, even with the IO-320.

 

[Dugaru]

I don't think you're heavy

My RV-9A comes in just a tad heavier at 1137, and I can get 158 to 160KTAS at 8500 DA with a Hartzell CS and a (carbureted) O-320.

I also suspect the instruments. Just for a back of the envelope check, what do the GPS groundspeeds look like when you fly directly into, and then away from, the wind?

Hi all, I've been following the various performance check threads and to this date, haven't been even close to achieving the 160+ kts TAS airspeed suggested by Vans and other pilots in this forum.

I am flying a 2011 assembled RV-9A with a Hartzell CS propeller and a Lycoming IO-320 engine, wheel fairings included.

I've been achieving a 145-150 kts TAS at 8500' DA on flights in the Rio de Janeiro, BR surroundings.

My aircraft was assembled by Flyer in Brazil, who is known for putting a good interior and a bit more weight on the front end of the aircraft.

To verify whether W&B is impacting performance, I share my latest weight and balance measure, to verify whether it stands in line with other aircraft flown elsewhere.

Empty measures:
Right Landing Gear 207.8 Kg (426.8 pounds / 37.6% weight)
Left Landing Gear 210.5 Kg (444.9 pounds / 38.0% weight)
Nose Wheel 135.0 Kg (263.7 pounds / 24.4% weight)
Total 553.3 Kg (1,135.4 pounds)

Can you please share your W&B and performance for verification?

Any additional hints on what else might be impacting performance?

Thank you much folks

 

[DavidHarris]

Another way to sanity check would be to fly a square pattern record GPS ground speed on each leg, then average the speed to get TAS.

David

 

[Finley Atherton]

Empty measures:
Right Landing Gear 207.8 Kg (426.8 pounds / 37.6% weight)
Left Landing Gear 210.5 Kg (444.9 pounds / 38.0% weight)
Nose Wheel 135.0 Kg (263.7 pounds / 24.4% weight)
Total 553.3 Kg (1,135.4 pounds)

Some of your weight conversions don’t seem right. For example 553.3 kg is 1219.8 lb not 1135.4 lb. A well equiped 9A with a Hartzell prop empty weight of 1135.4 lb would be about right, 1220 lb would be heavy.

Fin.
9A.

 

[eumarschner]

Finley, well spotted, thanks. I've corrected the pound converted numbers. Now should be easier to compare. Total weight at 1,219.8 pounds, 297.6 of which in the nose wheel.

Instrument readings were fully tested. I fly with 2 pitot tubes (1 for each instrument), calibrated, and cross-checked with GPS. Doesn't seem to have a problem there.

The speed was achieved with 24' MP and 2400 RPM at 8500' DA, 132 kts IAS and 150 kts TAS at the highest reading.

I assumed there might be a weight&balance or aerodinamic impact.

W&B creating additional drag due to heavier nose. What are you getting on W&B?

What else should I look for in rigging and fairings? Today I fly with the standard Vans wheel fairings.

Thanks again for the help

 

[PilotjohnS]

Intersection fairings

I found the upper and lower gear leg intersection fairings made a surprising difference in speed.

 

[blaplante]

The speed was achieved with 24' MP and 2400 RPM at 8500' DA, 132 kts IAS and 150 kts TAS at the highest reading.

Thanks again for the help

It seems unlikely that you are actually getting 24" MP at 8500' DA. 22 is more likely. At that low rpm I'm not convinced you are actually running at 75% power.

 

[PilotjohnS]

Might have to go fly....

Well i might just have to go fly and test mine out.

I haven't really done a speed run since the engine was broken in. I have been too busy flying cross countries at 11500' and higher at LOP. This whole $7/gal gas stuff. But maybe a 2 hour speed run at 8500' to see if I can meet Vans numbers.

But first, need to calibrate Otto so we don't get into hand to hand combat down the localizer as it tries to overshoot the centerline while skirting Class bravo on one side..... And redo the airspeed calibration using the GPS method.... ands fly to the end of a rainbow for some more gold to buy gas...

 

[Desert Rat]

You've mentioned wheel fairings, but do you have gear leg and intersection fairings? If not, that's likely part of your problem.

It's little counterintuitive but without fairings, round gear legs and sharp acute angles at the top and bottom create more drag that the wheels hanging out there on most airplanes. I'm not flying mine yet but I imagine RV's are the same.

 

[eumarschner]

For fairings, I might be missing the upper intersection between the leg and the fuselage. See a picture of my plane.

Also, how impactful can weight be on cruise performance?

 

[D-Dubya]

Well, it appears you ARE missing the upper intersection fairings. That might be worth a few knots, so I'd look at getting some and fitting them in place. But it won't make up for all of the difference you've stated. But every little bit helps.

 

[Desert Rat]

You keep circling back to the weight, but I really don't see how that could be your issue.

Within cg limits, an aft CG will be slightly faster than a forward CG. but not 10-15 kt faster. As far as your empty weight, your useful load might not be as high as with a lighter airplane, but as long as your gross weight isn't more than max gross, it seems like you should be getting the same numbers as an equivalent airplane at the same gross weight.

Vans published numbers for an RV9A with 160hp, a Hartzell constant speed prop, 75% power, and 8000' only vary by about 1 kt between 1400 lbs and 1750 lbs

1400 = 187 mph (162.5 kts)
1750 = 186 mph (161.6 kts)

 

[liuk]

Finley, well spotted, thanks. I've corrected the pound converted numbers. Now should be easier to compare. Total weight at 1,219.8 pounds, 297.6 of which in the nose wheel.

Instrument readings were fully tested. I fly with 2 pitot tubes (1 for each instrument), calibrated, and cross-checked with GPS. Doesn't seem to have a problem there.

The speed was achieved with 24' MP and 2400 RPM at 8500' DA, 132 kts IAS and 150 kts TAS at the highest reading.

I assumed there might be a weight&balance or aerodinamic impact.

W&B creating additional drag due to heavier nose. What are you getting on W&B?

What else should I look for in rigging and fairings? Today I fly with the standard Vans wheel fairings.

Thanks again for the help

How did you test your instruments against the GPS? Two independent pitot tubes agreeing with each other does not really exclude the possibility of instrument error. For example, two instruments could share the same static source which might be wrong. Or it might be the OAT that has a problem.

The easiest way is to keep the same IAS and fly a rectangular course, then take the average of the GS from the four legs.

 

[BillL]

As mentioned ASI calibration and when trying to compare to book run at 8000 density altitude, know your gross weight at the time, and record the ambient temps too. You will want to know if it is above normal standard temp. Then, run at rated engine speed, and rich. Experiment with mixture to ensure you are at maximum power. I just adjust .1gph at a time until the airspeed is a maximum.

Typical things like checking for full throttle plate opening etc. . . the basics.

Your hartzell CS - is it a new BA airfoil or used from a certificated airplane? The prop efficiency is a significant factor.

Once these are addressed, let the tweaking commence.

 

[eumarschner]

Bill, the temperature was ISA+12 at the time. Can the higher temp reduce speed drastically? I was flying at 130kts IAS and 6900' Indicated Altitude, reaching 8500' Density Altitude.

My Hartzell CS is dated 2011, when it was installed brand new.

Flight data uploaded to FlyGarmin. I have the speed tests done there. Instrument readings are correct.

 

[Richard Connell]

Bill, the temperature was ISA+12 at the time. Can the higher temp reduce speed drastically? I was flying at 130kts IAS and 6900' Indicated Altitude, reaching 8500' Density Altitude.

My Hartzell CS is dated 2011, when it was installed brand new.

Flight data uploaded to FlyGarmin. I have the speed tests done there. Instrument readings are correct.

I don’t want to beat a dead horse here but how have you done your “speed tests”? Using the NTPS method?
if you’ve done the NTPS PEC testing what are your PEC values at your test altitude/speed/power settings? Zero?
That also makes no sense.
Can you definitely rule out static position error? I’ve seen plenty of RVs with 10kt position errors over the years. Everyone was adamant that something was wrong with their plane when they just had a dodgy static port shape (and in one case location)

 

[PilotjohnS]

Just me

After reading the thread, I got concerned my plane was also “slow”.

So yesterday I did some flight testing. My objective was to
1)recalibrate the autopilot. (Last flight back from grand canyon, Otto and I were having a fist fight down the localizer)
2) figure out if my prop pitch could be improved
3) figure out why my plane was so slow.

The autopilot calibration went well and I had really poor gain setting on the roll axis. The pitch and altitude capture gain needed tweaking, but was reasonable.

The speed run was done at 4500’ wide open, and riched for peak power while maintaining CHTs below 400F. Plane trued out at 161 ktas. Which is right at 185 mph. Engine rpm was about 2500 to 2600 IIRC. At 8500’ 153 ktas (175mph) at 2510rpm. And I know I have a 1% indicated airspeed error from phase 1 testing.

In all I am happy with the speed. It seems my plane is “slow” because I choose to fly it up in the teens, lean of peak, and not burn so much gas.
I think the prop pitch is fine because with a lower pitch, I might get a few more knots, but then on descent from altitude I could easily overspeed. If I had to do it over with another prop, I think I would consider a larger diameter, but with same pitch due to my fondness for high altitude cruising. JMHO

 

[lr172]

I’ve seen plenty of RVs with 10kt position errors over the years. Everyone was adamant that something was wrong with their plane when they just had a dodgy static port shape (and in one case location)

This is way more common than most would suspect in my experience.

 

[Dugaru]

Thread creep

If you’ve got the Garmin autopilot, I’d love to know the settings you ended up with. I also need to do a recalibration and it would be great to have something to compare to.

After reading the thread, I got concerned my plane was also “slow”.

So yesterday I did some flight testing. My objective was to
1)recalibrate the autopilot. (Last flight back from grand canyon, Otto and I were having a fist fight down the localizer)
2) figure out if my prop pitch could be improved
3) figure out why my plane was so slow.

The autopilot calibration went well and I had really poor gain setting on the roll axis. The pitch and altitude capture gain needed tweaking, but was reasonable.

The speed run was done at 4500’ wide open, and riched for peak power while maintaining CHTs below 400F. Plane trued out at 161 ktas. Which is right at 185 mph. Engine rpm was about 2500 to 2600 IIRC. At 8500’ 153 ktas (175mph) at 2510rpm. And I know I have a 1% indicated airspeed error from phase 1 testing.

In all I am happy with the speed. It seems my plane is “slow” because I choose to fly it up in the teens, lean of peak, and not burn so much gas.
I think the prop pitch is fine because with a lower pitch, I might get a few more knots, but then on descent from altitude I could easily overspeed. If I had to do it over with another prop, I think I would consider a larger diameter, but with same pitch due to my fondness for high altitude cruising. JMHO

 

[PilotjohnS]

OK

If you’ve got the Garmin autopilot, I’d love to know the settings you ended up with. I also need to do a recalibration and it would be great to have something to compare to.

OK I will update this reply with the data today. I meant to write them down, so this will force me to.

The recalibration went exactly as outlined in the latest installation manual. I was expecting a classic damped oscillation as in normal oscillatory systems, but Garmin apparently did some tricks in the software and it really becomes a very great damped response once it is dialed in.

EDIT 11/2/23 OK the gain for pitch was too high. On my last cross country, the pitch was wallowing up and down. I had to turn gain down on pitch to 0.75.

 

[Dugaru]

Thanks!

I really appreciate it. Just updated my Garmin software so with any luck I'll have smooth sailing as well.

OK I will update this reply with the data today. I meant to write them down, so this will force me to.

The recalibration went exactly as outlined in the latest installation manual. I was expecting a classic damped oscillation as in normal oscillatory systems, but Garmin apparently did some tricks in the software and it really becomes a very great damped response once it is dialed in.

 

[PilotjohnS]

Stuff

Posted pics in previous reply of Otto’s selfie

 

[Dugaru]

Thanks again!!

I really appreciate it.

Posted pics in previous reply of Otto’s selfie

 

[PilotjohnS]

gain adjust

See edit in post above . I had to reduce the pitch gain quite a bit to keep from porposing during cruise.

 

[Dugaru]

Got it

And thanks again. This is one problem I’m trying to solve, I’m getting porpoising (but only at high altitudes). I also seem to have overly aggressive roll.

See edit in post above . I had to reduce the pitch gain quite a bit to keep from porposing during cruise.

 

[PilotjohnS]

Slow Pitch

And thanks again. This is one problem I’m trying to solve, I’m getting porpoising (but only at high altitudes). I also seem to have overly aggressive roll.

I think the pitch gain can be quite slow. The transitions from climb to cruise seems like it will be gentle. I think only if one uses Otto when flaps are lowered would the pitch gain need to be finely tuned. I typically fly the approach on Otto until the flaps come down, then I am hand flying.

 

[Dugaru]

Very interesting

I ended up where I am after trying to fix altitude loss during turns. Starting to think I overdid it in every axis.

I think the pitch gain can be quite slow. The transitions from climb to cruise seems like it will be gentle. I think only if one uses Otto when flaps are lowered would the pitch gain need to be finely tuned. I typically fly the approach on Otto until the flaps come down, then I am hand flying.