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9A too slow. Frustrated

Earl Findlay

Active Member
My IO-360 RV-9A will not go faster than 148 knots at 2600 RPM. Fixed pitch prop. I’m frustrated constantly hearing others saying they’re 160 or 165 knots. What can I check on my airplane to hopefully fix and make it go faster?
 
Don’t bite on this thread. Same guy said 3 months ago he went 234 kts TAS in his 9.
https://vansairforce.net/community/showthread.php?t=182922

Right. That was in a descent and before I realized that our Vne is a TAS not IAS.

Remember, when people questioned whether I was “real” (I still don’t know how a fake person can write on a web bulletin board) two people came out to the airport to meet up with me and see my RV-14 build. How much more real does it get?

Your message was not helpful, and I do not appreciate you distracting from the assistance that I am seeking.
 
Prop pitch

Well, if it's pitched for climb, then your cruise will be slower.

If it's pitched for cruise, your climb rate will be less.

You can have it one way or the other; not both. The best you can do with a FP prop, is a compromise...
 
Well, if it's pitched for climb, then your cruise will be slower.

If it's pitched for cruise, your climb rate will be less.

You can have it one way or the other; not both. The best you can do with a FP prop, is a compromise...

I can still make 2700 RPM at altitude though.

Is a 10-12 knot speed penalty usual for a climb prop versus a cruise prop? It sounds excessive, but I really don’t have any information to base that on.
 
two people came out to the airport to meet up with me and see my RV-14 build. How much more real does it get?

Yea - still waiting for them to post confirming you’re real.
 
I wish I could get 148 KT TAS out of my 9A (IO-320 C/S). Rest assured you don't have the slowest -9A out there. I max out at about 142 KT at 70% power with all of my fairings installed. Not a chance I can get near Van's published 162 KT at 75%.

My advice, don't worry about the speed. Whatever it is, it is much faster than a 172 and a lot more fun too.
 
Remember, when people questioned whether I was “real” (I still don’t know how a fake person can write on a web bulletin board) two people came out to the airport to meet up with me and see my RV-14 build. How much more real does it get?

I will be in Coeur d'Alene this Friday, at least through the weekend. How about we get together? I'd love to see your -9A, and your -14 build.

I wish I could get 148 KT TAS out of my 9A (IO-320 C/S). Rest assured you don't have the slowest -9A out there. I max out at about 142 KT at 70% power with all of my fairings installed. Not a chance I can get near Van's published 162 KT at 75%.

My advice, don't worry about the speed. Whatever it is, it is much faster than a 172 and a lot more fun too.

I have a -9A with an IO-360, and a fixed pitch prop. I see 147-149 knots true in cruise pretty regularly at 2600 RPM. If I push it up to 2700 RPM, I can get up to about 154 knots. Maybe higher if I was patient... seems that the reported speeds are a bit all over the board.
 
Is the airplane in trim?

Are the fairings on and aligned properly?

Who made your prop? - Some FP props are reputed to give better performance than others.

Can you post a screenshot showing the engine parameters and indicated airspeed and altitude?

Is your static system per Van's plans?

Is the airplane at or under Van's listed gross weight and the CG in range?

Just some things to think of.

Dave
 
I can still make 2700 RPM at altitude though.

Is a 10-12 knot speed penalty usual for a climb prop versus a cruise prop? It sounds excessive, but I really don’t have any information to base that on.

If you don't have anything to base it on, how could that be excessive?

Anyway, that difference could easily attributed to the prop, as well *** everything else posted.

Also, the wheel pants and fairings are worth that much, by themselves...
 
I can still make 2700 RPM at altitude though.

Is a 10-12 knot speed penalty usual for a climb prop versus a cruise prop? It sounds excessive, but I really don’t have any information to base that on.

A climb prop will have flatter pitch and make it easier to get to full RPM. It will also make the airplane slower. 10---12 kt would easily be explained by that.

A good test is to see what RPM you can get at sea level on initial ground roll. A very coarse-pitched "cruise" prop will only be able to turn 2200-2300 RPM on sea level ground roll. Others can say what RPM they get on ground roll with various pitch and diameter.

I think you get higher RPM on initial ground roll at higher altitude.
 
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My IO-360 RV-9A will not go faster than 148 knots at 2600 RPM. Fixed pitch prop. I’m frustrated constantly hearing others saying they’re 160 or 165 knots. What can I check on my airplane to hopefully fix and make it go faster?

Giving a speed in comparison to an engine RPM doesn't provide enough information to analyze whether you have a problem.

Look at it this way.....
If you were evaluate a manual transmission car by driving it an all gears at 2600 RPM on the tach. and record the speeds. The speed in each gear will be different and the amount the accelerator is pressed (throttle position / manifold pressure) for each gear will be different. But all data points will have had the engine at 2600 RPM.

To meaningfully analyze your performance, there has to be enough information to determine what amount of power your engine is producing in the condition your are quoting.

So at the very least, you need to provide engine RPM and manifold pressure.
Additionally helpful would be fuel flow and density altitude in the condition being quoted.

It is entirely possible that your prop is way under pitched and you are pulling the throttle back so far to have an RPM of 2600, that you are actually at only 60% power.
 
You also need to insure your tack. Is reading properly. Your mixture, and throttle are making full travel. So meny outher peramiters, not withstanding.
 
First step is to

The first step is to confirm that your measurement system is accurate. In this case, your static lines, airspeed indicator, and so forth. Prior to that, do a 3-way GPS run, full throttle, at 8500 ft or so. Record outside air temp.Fly one gps direction with autopilot on, record gps and indicated, change gps direction 120deg and once stabilized record gps speed and indicated, and change gps direction another 120deg and once stabilized record gps speed and indicated. Land and average the gps speed. Average the indicated speed. Calculate TAS from the indicated and then compare with gps speed. Note the error if any. Repeat except this time do the procedure at say 80kts or so. Is your indicated error greater at slow speed than cruise speed? Or vice versa? Is your Calculated TAS average the same as GPS average or is it different? What is the difference? Report back grasshopper and we can better advise you on what steps you need to do.
 
My 9-A consistently cruises at 160 knots true at about 5000 ft. and 2600 rpm. I have a 160 hp Lyc with two mags and a 3-blade Cato. My brother has a 160 hp with e-mags on his RV-4 and when we go WOT in formation, neither of us pulls on the other, a dead heat. You should definitely be as fast as me since you have the 180 hp. I would first be suspect of the prop, but you could also have any number of aerodynamic problems. Even your gear leg fairings need to be exactly streamlined into the trust line. Be sure both ailerons are streamlined when in level flight and slip ball centered. Good luck!!
 
STATIC ERROR

I had the slowest RV10 in the world once too.......Static error. Once corrected all was normal.

I test flew an RV9A with an IO320 and FP prop (Sensinich-Vans) and at 7-8000' it would TAS 159-160 LOP.
 
I can still make 2700 RPM at altitude though.

Is a 10-12 knot speed penalty usual for a climb prop versus a cruise prop? It sounds excessive, but I really don’t have any information to base that on.

Absolutely yes, depending on the pitch. I have a Sensenich ground adjustable carbon fiber prop on my -9a. When I set it up initially after talking to Sensenich they gave me a very conservative number for the pitch pin. It climbed like a homesick angel - 2000FPM+, but top end was around 142 true. I also could easily exceed 2700rpm at altitude. Readjusted to more of a cruise pitch and was able to get about 152kts. Adjusted one more time, now I can easily cruise at 155kts true at 2500rpm, and can hit 165kts by going WOT at 8000ft.
 
I’m with DeltaFox...

I hit 2700rpm at 165 kt true at 8000DA at WOT. I have a few more RPM with leaning. I usually cruise between 2420 and 2450 RPM, seeing 147-150kt true. I consider my current setup a little biased towards climb, but I like it.
 
0-320 w/3blade Catto fixed pitch prop.

145 knots 9 gph @ 8500’.

Well short of Vans claims......

Throttle setting? RPM?

Right

As I posted previously in this thread, when comparing performance #'s, it is impossible to get a meaningful data point from just an RPM.

What if your prop is way under pitch for your airplane? If you are pulling the throttle back well below what would produce a manifold pressure that would equate to 75% power, to keep you RPM at 2600, then your airplane should be slower than the spec'ed max. cruise speed.

I always tell builders to install a manifold pressure gauge even if they are going to have a fixed pitch prop. It makes it quick and easy to set power settings without chasing an RPM and it is useful for knowing what your power output actually is.
 
0-320 w/3blade Catto fixed pitch prop.

145 knots 9 gph @ 8500’.

Well short of Vans claims......

Do a 3 or 4 leg GPS GS run 120 or 90 degrees apart respectively...average the indicated TAS and ground speeds and compare them. If they're off check your static system starting with the port type because a leak will cause airspeed to read high. The standard Vans pop-rivet static port is the most accurate but even those can be off.

Once you figure out they're off use the NTPS spreadsheet (or Kevin's) to actually dial in the exact TAS (the method above is only totally accurate in calm air)

My 9A would only go 148 TAS max WOT at 8500 with Sensenich cruise prop (79) turning ~2550 rpm. Unit I found out my flush static port was causing a 10-11 KIAS error. Solo with full fuel I'm now indicating my actual 158 KTAS and my airspeed indicator is 0.2 Kts off. Very close to Van's numbers and the difference I'm chalking the up to my wing rigging being off slightly.
 
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