What's new
Van's Air Force

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

Why is my RV-9A so slow?

Just bought an RV-9A w/ O-320-D2A.
Seller stated it trued-out at 8,000ft at 140kts and 7.5gph.
Everywhere I've looked indicates this is at least 5kts and more like 10kts slower than most folks report.

So, I took it up to 8000ft, leaned it out, and checked ground speed in 3 cardinal directions.

Sure enough, it came out to 140kts and 7.5gph.
Just had a condition inspection, and everything appears to be rigged properly.
Any ideas what could cause this?

Thanks for your help!
 
Is it an all-wood prop or wood-core composite? Catto is refining its designs all the time, and no doubt there's greater efficiency/speed to be had with the improvements.

Is your engine 150 hp or 160 hp?

Mine's an IO-320-D1A (160 hp) with a circa-2014 Catto 70x70 prop that will nudge 170 KTAS under the right conditions, but that's spinning at 2850 rpm. My usual performance cruise at about 10,000' DA is 155-157 KTAS at 2700 rpm, burning between 7.5 and 8 gph.

What is your max static rpm?
 
Last edited:
Тише едешь дальше будешь

Just bought an RV-9A w/ O-320-D2A.
Seller stated it trued-out at 8,000ft at 140kts and 7.5gph.
Everywhere I've looked indicates this is at least 5kts and more like 10kts slower than most folks report.

So, I took it up to 8000ft, leaned it out, and checked ground speed in 3 cardinal directions.

Sure enough, it came out to 140kts and 7.5gph.
Just had a condition inspection, and everything appears to be rigged properly.
Any ideas what could cause this?

Thanks for your help!

Looks normal to me. You can repitch the prop to get those extra few knots folks are reporting but do you need them? The 9 is a wonderful machine for its purpose congratulations and enjoy.
 
Looks normal to me. You can repitch the prop to get those extra few knots folks are reporting but do you need them? The 9 is a wonderful machine for its purpose congratulations and enjoy.

I agree...love my 9, and I'm going to fly the heck out of it.
I was just concerned if there was something fundamentally wrong with mine, as no one reports speeds these slow.
 
Prop

My 9A has the Sensenich 70CM7S9-0-77 FP that was repitched to 79" in 2008 in front of a Lycoming 0320E2D (150 hp). It will cruise about 10kts faster than you are reporting but climb performance is poor at best. I typically cruise above 10,000 msl so it will take me 11 to 15 min to get there. I commute about 460 miles to KC weekly and glad for the cruise performance. Every good thing comes at the expense of something else.
 
You are in good company. Mine is a little slow too. After over a decade of enjoyment (160hp C/S hartzell), I've only just recently started to ponder where my other 5kts went. I recently spent a weekend checking that the amateur builder rigged it straight. Found nothing there.
 
Could be it's really draggy, could be poor engine performance or low compression, could be pitch on prop. Most folks don't brag on slow speeds, so you are likely seeing the best-performing numbers and at higher rpm.
 
160hp
rpm is between 2300 and 2400.
I have no idea of manifold pressure.

I don't think 140 knots at 2350 rpm is strange for a -9. Is the RPM limited because it won't turn more, no matter how hard you lean on the throttle, or are you intentionally limiting RPM with throttle setting?
 
160hp
rpm is between 2300 and 2400.
I have no idea of manifold pressure.

At 8000' DA, you should push the throttle full forward, spin it up, and lean it. That should give you ~75% power.

If your Catto is pitched properly, it should stop accelerating around 2750 rpm.

Do your speed runs at that power setting and report back.

PS. The engines are designed to make TBO at 75% power while spinning on the redline. (Invoking the Mahlon Russell.)
 
Last edited:
My 9A has the Sensenich 70CM7S9-0-77 FP that was repitched to 79" in 2008 in front of a Lycoming 0320E2D (150 hp). It will cruise about 10kts faster than you are reporting but climb performance is poor at best. I typically cruise above 10,000 msl so it will take me 11 to 15 min to get there. I commute about 460 miles to KC weekly and glad for the cruise performance. Every good thing comes at the expense of something else.

I?m based at LXT.
Love to catch up some time when you?re in town!
 
At 8000' DA, you should push the throttle full forward, spin it up, and lean it. That should give you ~75% power.

If your Catto is pitched properly, it should stop accelerating around 2750 rpm.

Do your speed runs at that power setting and report back.

PS. The engines are designed to make TBO at 75% power while spinning on the redline. (Invoking the Mahlon Russell.)

Dang it!
Wish I saw this before flying this evening!
I?ll do that and report back.
Seems fuel burn would be higher then expected though if I have throttle wide open. Like 8.5 to 9gph.
Anyway, I?ll report soon.
 
If wishes were horses..... (we'd all go 300)

A stock Lyc will do no better than .43 lbs per HP per hour. In the real world, it'll be closer to .45-.48, properly leaned. It's there to read, in any Lyc performance/altitude chart. If you do the math, 7.5 GPH just won't get you 75% power in an O-320/160HP engine.

7.5 (gph)*6 (lbs per gal)=45 lbs per hour.

X hp * .45= 45
solving for x:
X= 45/.45
X=100 HP

Optimistically (absolute best case, according to Lycoming),
X hp * .43=45
solving for X
X=45/.43
X= 104.65 HP

It violates everything you've ever read on the interwebs, so Lycoming can't be right, right?
 
Test run

So I am also curious what would happen if you push the throttle full forward and let the rpm wind up and let the fuel flow be what it wants to be.
 
Looks normal to me. You can repitch the prop to get those extra few knots folks are reporting but do you need them? The 9 is a wonderful machine for its purpose congratulations and enjoy.

If wishes were horses..... (we'd all go 300)

A stock Lyc will do no better than .43 lbs per HP per hour. In the real world, it'll be closer to .45-.48, properly leaned. It's there to read, in any Lyc performance/altitude chart. If you do the math, 7.5 GPH just won't get you 75% power in an O-320/160HP engine.

7.5 (gph)*6 (lbs per gal)=45 lbs per hour.

X hp * .45= 45
solving for x:
X= 45/.45
X=100 HP

Optimistically (absolute best case, according to Lycoming),
X hp * .43=45
solving for X
X=45/.43
X= 104.65 HP

It violates everything you've ever read on the interwebs, so Lycoming can't be right, right?

These are good numbers.
Also, adding in from the Lycoming manual that the O-320 generates 76.2% power at 8000ft.

160HP x .762 = 122hp
122hp x 0.45 lbs/hp / 6lbs/gal = 9.1gph

I'll let it go WOT and see if 9.1 gph is what I see!
Also, will report KTAS.
 
Yeah, you can't find anyone who cut their teeth in C-172's or Cherokees who will believe you when you tell 'em that 75% is 9+ GPH. They're so used to flying around at 55% and *thinking* it's 75% (because the extra power does nothing in those planes), that they can't believe real numbers. :)
 
My -9 did 153 kts at 8,000' at 75% power and less than WOT, with a Catto. And my -10 does 150 kts at 8,000' at 55% with 10 g/hr. Not bragging, just facts.

Michel
 
My -9 did 153 kts at 8,000' at 75% power and less than WOT, with a Catto. And my -10 does 150 kts at 8,000' at 55% with 10 g/hr. Not bragging, just facts.

Michel

Not sure what mine will do at 8,000 since I hardly ever fly that low going someplace - but at 16,500 it will do 150 knots true on 6.5gph. I like getting up there where it's cool and smooth.
 
I was intentionally limiting the throttle to keep fuel burn at 7.5gph
There you go. As you found out by the other posts, you weren't at 75% power.

Dang it!
Wish I saw this before flying this evening!
I?ll do that and report back.
Seems fuel burn would be higher then expected though if I have throttle wide open. Like 8.5 to 9gph.
Anyway, I?ll report soon.
When I used to fly a C172 with a 160 hp O-320 we would plan on 9.6 GPH at 75% power. The engine doesn't know what plane it is in, so 75% is still 75% power and you should see over 9 GPH at that power setting.

So I am also curious what would happen if you push the throttle full forward and let the rpm wind up and let the fuel flow be what it wants to be.
Give it a try and find out!

For comparison, my -9 taildragger will do 175 knots at 8,000' DA at 2700 RPM but it is drinking fuel to do that. My typical flight is anywhere between 150 and 165 knots and substantially lower fuel burns. The sweet spot seems to be around 155-160 knots at 7 GPH LoP.

When I had the O-290D2 in it, I would cruise at 140 knots at 6.4 GPH RoP. That little engine didn't like to run LoP, so I simply ran it RoP all the time. That worked out to be 65% power for the O-290.
 
Beware with the answer. Greg is "special", as will be his number.

ofR.png


I had just finished a climb on this one and the cylinders were not cool yet, but there it is. And I've been called worse things than "special" :D
 
Just so Greg knows he is not alone.

Yeah, yeah.... Bill has done a lot more drag reduction than I have. I'm lazy. :cool:

Bill is making slightly more power than I am at the same conditions, he's running 100LL on Pmags (variable timing) and I'm running 8.7:1 compression with 91E10 premium autofuel on fixed timing. My fuel costs me $2.53 per gallon though, so it all works out.
 
Last edited:
These threads inevitably turn into comparing who is the fastest, but as somebody else mentioned there is usually a selection bias because people with faster planes are more likely to talk about speeds. As a data point, 140ktas is generally what I plan for at 6.5 gph in my 150hp 9a in that 8-10k altitude range.

Our slightly slower speeds could be attributed to lots of little things, like cooling inefficiency, slightly out of alignment wheel pants, less than ideal prop, etc. My fixed pitch prop is rpm limited so I know I will never get peak efficiency out of it. Drag reduction will be the biggest bang for your buck in terms of time spent, I would imagine, assuming your engine is in good shape and the prop is pitched properly.

And don’t compare your speeds to those with 180hp and constant speed props.

Chris
 
...

And don?t compare your speeds to those with 180hp and constant speed props.

Chris

Ummm, I have a fixed pitch Catto two bladed prop.

My real point is that people complain about "slow" RV's when the issue is they don't spin their Engines up to 75% power.
 
New Data

I had a plan to go gather data at 6000, 8000, and 10000, but we had an overcast layer today, so I only got data at 6000.

I'm not sure it makes sense, and as soon as this layer clears up, I'll go get the rest. Here's what I found:

Altitude: 6000
Throttle: wide open
%hp: 72%
MAP: 23.4
gph: 8.2
rpm: 2550
Speed (000 heading) 144 kt
Speed (270 heading) 156 kt
Speed (180 heading) 167 kt
KTAS: 155 kts @ 8.2 gph

There's such a discrepancy from my last attempt (probably due to WOT vs 2300rpm), that I have to go finish this out at 8000 and 10000.
But if this is true, this is a world of difference.
Also, I don't currently have a nose wheel pant on...in the process of building a new one. But I don't think that affects it by more than a kt or two.
 
Wheels are the worst

Add a parachute the same size as a wheel and the effects will be about the same, in my opinion. I think Wheels are one of the draggest shapes that can thrown thru the air.
I suspect the 4-5 knots gain due to wheel pants is probably not too far off.
 
Ummm, I have a fixed pitch Catto two bladed prop.

My real point is that people complain about "slow" RV's when the issue is they don't spin their Engines up to 75% power.

I wasn't referring specifically to you, but I do believe that with a FP prop, once the OP is at WOT, the RPM will be limited by excessive drag and may not spin as much as you'd like it do, so in order to make sure you are getting that full 75% power, or more, you need to make sure thing like wheel pants are aligned, etc.

I had a plan to go gather data at 6000, 8000, and 10000, but we had an overcast layer today, so I only got data at 6000.

I'm not sure it makes sense, and as soon as this layer clears up, I'll go get the rest. Here's what I found:

Altitude: 6000
Throttle: wide open
%hp: 72%
MAP: 23.4
gph: 8.2
rpm: 2550
Speed (000 heading) 144 kt
Speed (270 heading) 156 kt
Speed (180 heading) 167 kt
KTAS: 155 kts @ 8.2 gph

There's such a discrepancy from my last attempt (probably due to WOT vs 2300rpm), that I have to go finish this out at 8000 and 10000.
But if this is true, this is a world of difference.
Also, I don't currently have a nose wheel pant on...in the process of building a new one. But I don't think that affects it by more than a kt or two.

These numbers indicate a power setting of more than 74% - I would estimate around 82% based on the lyc charts, although we don't know density altitude. But they do make sense otherwise, and are similar to what I see, maybe a tad faster. Looks like you are doing fine.

Chris
 
Wheel fairings are worth more drag reduction at RV speeds than most people realize but the biggest drag reduction is from the gear leg fairings.

The nose wheel fairing will give you a bit more speed which would in turn give you a bit more RPM, but WOT at 6000 having only 2550 RPM indicates your prop pitch is too course.

On an RV, if you want the best overall performance (Meaning good climb and cruise, but not the fastest cruise possible), your prop should be pitched such that you need to reduce manifold pressure to maintain RPM below 2700 until you are at least about 10K feet.

An RV should not be pitch like a typical Cherokee or Cessna with a fixed pitch prop where you can never approach red line on the tach except when the nose is pointed straight down.
You should be able to easily exceed red line at lower altitudes (below 10K). Any RV with a fixed pitch prop that can't, will always be slower (and climb more poorly) than one that can.

If you only fly in the flat lands and will never go above 8000 ft, then a prop that peaks at 2700 at WOT, at that altitude will be fine, but it will still climb a bit slower and will probably still be slightly slower than a fixed pitch RV with an optimized prop, flying at 12000.


I had a plan to go gather data at 6000, 8000, and 10000, but we had an overcast layer today, so I only got data at 6000.

I'm not sure it makes sense, and as soon as this layer clears up, I'll go get the rest. Here's what I found:

Altitude: 6000
Throttle: wide open
%hp: 72%
MAP: 23.4
gph: 8.2
rpm: 2550
Speed (000 heading) 144 kt
Speed (270 heading) 156 kt
Speed (180 heading) 167 kt
KTAS: 155 kts @ 8.2 gph

There's such a discrepancy from my last attempt (probably due to WOT vs 2300rpm), that I have to go finish this out at 8000 and 10000.
But if this is true, this is a world of difference.
Also, I don't currently have a nose wheel pant on...in the process of building a new one. But I don't think that affects it by more than a kt or two.
 
Even More Data

OP Here...overcast layer lifted, so I was able to gather the rest of the data.
Here it is:

10,000 ft, 2500 rpm, WOT, 7.5 gph, 20.1 MAP, 62%, 150 KTAS (3 dir: 129kt, 158kt, 172kt)

8,000 ft, 2620 rpm, WOT, 8.6 gph, 21.8 MAP, 68%, 155 KTAS (3 dir: 130kt, 146kt, 180kt)

6000 ft - I think I need to redo. RPM seems low compared to 8000.

All-in-all, I'd say, I'm going to get 150-155 kts on 7.5 - 8.5 gph.
I'm pretty happy with that...way different than the 140kts at 7.5 gph I was thinking. Also, will report the difference the nose wheel pant makes when I get it put on.
 
I?ve had my Rv for only a year. Bought it built. I haven?t done any of these tests. I just run mine at 2400 rpm, regardless of altitude. I usually get 7-8.5 in cruise. I ever even thought about running at a higher rpm. My skyview usually shows about 53-54% power at that point and I?m true at about 155kts. I?m in a 6A btw. I lean to about 1350. Usually one cyl above and the rest right around there. I?ve never figured out the lean assist on the skyview. This thread makes me think I could go faster and probably manage the engine better than I do.....
 
You're right there in the middle of the mix, nothing wrong with your plane.
 
Wheel Pants

Also, I don't currently have a nose wheel pant on...in the process of building a new one. But I don't think that affects it by more than a kt or two.[/QUOTE]

Flew mine without wheel pants or leg fairings and I wont ever do that again! I was extremely surprised how slow it was. For what its worth my numbers are very close to yours. Couldn't be happier 265hrs in less than two years
 
Thanks everyone for your input.
I?m taking a lot of your advice, and planning to fly the heck out of this plane.
First long XC (LXT to IDA and back) in a couple weeks.
Can?t wait to see how it performs.
 
Thanks everyone for your input.
I?m taking a lot of your advice, and planning to fly the heck out of this plane.
First long XC (LXT to IDA and back) in a couple weeks.
Can?t wait to see how it performs.

Get it up high - you'll love the way that wing reacts to thinner air.
 
Back
Top