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Is my RV3A Slow?

R

RayJr

Active Member
Hello,
Seems you guys talk about higher speeds than I see. At 2700rpm / 7600 DA, I was seeing 159 TAS. Does that seem slow to you? I have an O320 with an after market Injector - The previous owner said 160hp. And a Catto Prop. Not sure which pitch but Catto website says they'll all do the same top speed just at different RPM. This occurred at 1150 pounds.

What are your top speeds? Does it make sense I'm only getting 159?

Thanks

Ray
 
RayJr said:
Hello,
Seems you guys talk about higher speeds than I see. At 2700rpm / 7600 DA, I was seeing 159 TAS. Does that seem slow to you? I have an O320 with an after market Injector - The previous owner said 160hp. And a Catto Prop. Not sure which pitch but Catto website says they'll all do the same top speed just at different RPM. This occurred at 1150 pounds.

What are your top speeds? Does it make sense I'm only getting 159?

Thanks

Ray
Click to expand...
What is your INDICATED airspeed at 7500 feet? How are you converting to TAS?
 
Taltruda said:
What is your INDICATED airspeed at 7500 feet? How are you converting to TAS?
Click to expand...
142 IAS. Dynon is doing the heavy lifting for me there. This picture isn't exactly 2700 and 159 TAS but that was what it flattened out at over a few minutes.
IMG_20240909_161945950_HDR_AE.jpg
 
My RV3b with 160 hp and sensenich metal prop pitched 81" gives an indicated TAS of 172 mph at 7500' and 2300 rpm , according to the AV30 with temperature probe. I may be wrong on the pitch and vaguely recall 83" stamped on the prop during removal and inspection.
Passing by the same towered airport within a couple of hours, east at 7500' and west at 8500' enquired my tracked speed on their end. In both cases the tower operator replied 160 knots (184 mph) I don't know engine rpm at the time, but normal cruise RPM is never greater than 2350 rpm.
 
Richard RG said:
My RV3b with 160 hp and sensenich metal prop pitched 81" gives an indicated TAS of 172 mph at 7500' and 2300 rpm , according to the AV30 with temperature probe. I may be wrong on the pitch and vaguely recall 83" stamped on the prop during removal and inspection.
Passing by the same towered airport within a couple of hours, east at 7500' and west at 8500' enquired my tracked speed on their end. In both cases the tower operator replied 160 knots (184 mph) I don't know engine rpm at the time, but normal cruise RPM is never greater than 2350 rpm.
Click to expand...
Indeed, That is faster than mine. At 2300 I'll see about 155mph/135knots true.
 
The first step is to verify the accuracy of your pitot/static system.

See these excellent articles by Kevin Horton --
https://www.kitplanes.com/flight-testing-static-system-error-theory-and-practice/
www.kitplanes.com

Flight Testing: Static System Error - Theory and Practice, Part 2

Kevin Horton, data analysis, flight-test program, RV-8, www.vansaircraft.com, Van's Aircraft, Jim Weir, ASI, calibrate, instrument error, Dynon, www.dynonavionics.com, D-10A EFIS, D-10A, EFIS, Dynon D-10A EFIS, flight testing, constant wind direction, OAT probe, fresh air scope, calibrated...
www.kitplanes.com www.kitplanes.com

You may discover that your airplane performs just fine...and the "problem" is in the size/shape/location (or some combination of all three) of the static ports.

Good luck!

B
 
Follow up to my previous post, propeller records indicate 83" pitch and I believe the maximum pitch allowed by Sensenich. In spite of the high pitch angle, the 3 still gets off the ground plenty quick enough for me.
 
RayJr said:
Hello,
Seems you guys talk about higher speeds than I see. At 2700rpm / 7600 DA, I was seeing 159 TAS. Does that seem slow to you? I have an O320 with an after market Injector - The previous owner said 160hp. And a Catto Prop. Not sure which pitch but Catto website says they'll all do the same top speed just at different RPM. This occurred at 1150 pounds.

What are your top speeds? Does it make sense I'm only getting 159?

Thanks

Ray
Click to expand...
I have a -3B with 160hp and Catto 2-blade. At 2700rpm and 7500ft my TAS is at least 190mph (165knots) based on GPS. The next time I fly I will double check the numbers to be sure.
 
Last edited:
IMG_3175.jpegIMG_3754.jpeg 160 hp IO-320 with Catto 2b 70” diameter x 75” pitch

8500’ and 13500’ shown in pictures. Both at 2700 RPM.
 
RayJr said:
Hello,
Seems you guys talk about higher speeds than I see. At 2700rpm / 7600 DA, I was seeing 159 TAS. Does that seem slow to you? I have an O320 with an after market Injector - The previous owner said 160hp. And a Catto Prop. Not sure which pitch but Catto website says they'll all do the same top speed just at different RPM. This occurred at 1150 pounds.

What are your top speeds? Does it make sense I'm only getting 159?

Thanks

Ray
Click to expand...
I would level off but keep it WOT and see what it’ll do. The prop rpm might go to 2800 or 2900, that’s ok, but throttling back is the reason you are going slow. Perhaps you have a climb prop.. you really need to fly your power settings based on manifold pressure. Trying to use RPM on these planes varies too much with airspeed. For what it’s worth, I find a good rule of thumb to calculate IAS to TAS is to multiply 2 percent per thousand feet.. 7500 is 15 percent (7.5x2) and multiply your IAS by it (142x1.15=163 knots TAS) or almost entirely is based on altitude and not temperature so much.
 
bjdecker said:
The first step is to verify the accuracy of your pitot/static system.

See these excellent articles by Kevin Horton --
https://www.kitplanes.com/flight-testing-static-system-error-theory-and-practice/
www.kitplanes.com

Flight Testing: Static System Error - Theory and Practice, Part 2

Kevin Horton, data analysis, flight-test program, RV-8, www.vansaircraft.com, Van's Aircraft, Jim Weir, ASI, calibrate, instrument error, Dynon, www.dynonavionics.com, D-10A EFIS, D-10A, EFIS, Dynon D-10A EFIS, flight testing, constant wind direction, OAT probe, fresh air scope, calibrated...
www.kitplanes.com www.kitplanes.com

You may discover that your airplane performs just fine...and the "problem" is in the size/shape/location (or some combination of all three) of the static ports.

Good luck!

B
Click to expand...
Thanks for that. I tried the flight test described in here last night. It seems like I was showing slower airspeeds than my average ground speeds. Though, only by maybe 3 knots or so. It could be part of my issue.
 
RayJr said:
Thanks for that. I tried the flight test described in here last night. It seems like I was showing slower airspeeds than my average ground speeds. Though, only by maybe 3 knots or so. It could be part of my issue.
Click to expand...
On my -7, the paint shop messed up the transition from the skin to the static port orifice, which resulted in a 7kt error (low). The fix involved a .032” washer and new “domed” ports.
 
My RV-3 will exceed redline in level flight at 8,000’ density altitude at 2700rpm. 193 knots true airspeed. This has been verified by 3 and 4 way speed runs and flying alongside (racing) a friend in his RV-8 with a fully tested and verified Garmin G3x system. [He’s about 3 knots faster, btw.] Yes, I have an IO-320 and a constant speed prop, but a correct fixed pitch prop and appropriate mixture settings should still come close!

Have I mentioned that I love my RV-3?!?
 
193 knots! Wow. I am working on an RV-3 engine, IO-320-D1A, some where in the range of 160-170hp is what I am aiming for. Constant speed prop for sure. Maybe an MT or WW?
RV-3 with FP props are a hard problem to solve. We had an RV-3B with 180hp and a FP catto prop. It would go 234mph but it would not hardly climb like a normal RV-3. One of the best FP props we've had on RV-3's (2 out of the 4 built) was an Ed Sterba wood prop. It would climb well, was smooth and the airplane would top out at 215 at 2700 rpm. My dad said that it would turn in over 200mph block times airport to airport (this was before GPS was in every plane). So that included TO, Climb to ALT and then enroute distance to the next airport. Props can slow an airplane down if its set up for Climb instead of climb/cruise.
If you have one that is more of climb prop, you are going to lose speed at cruise. Even running 2600 rpm, you may only get 170mph out of your RV.
Some other items to look at are fairing. Tight fitting fairings are a must. Loose fairing that have gaps could cost you 3-5mph. Do you have the older wheel pants or the newer style? There is 2-3 mph difference there. Are they straight? What do you have for gear leg fairings? Metal or Fiberglass?
Have you looked at the angle of incidence on the Horz stab? Some people have incorrectly rigged their stabs and it cost them 10 mph. Once corrected, the plane gained it's advertised speed back. I would check the thickness of your shim under the horz stab. This has happened quite a bit, especially in the tandem airplanes with a larger CG range.
Is you canopy sealed up nicely? This will eat us some MPH if you have large gaps/cracks.
Lastly, is you engine sagging more than normal. Older engine mount isolators can let the engine sag down too much and you thrust line is off compared to a new engine mount/isolator setup. I personally rigged my engines to be square to the datum when in the level position. This requires you to get the airplane in the level position and then put a level on the crank flange. I put small shims under the bottom engine mount isolators to get it into position. This is a trick used by most folks at the Reno air race scene. Mooney used it to make some of their birds faster too. It works!
You could have one large item that is slowing you down or a combo of many smaller items.
 
I have a 0-320 with a Sterba cruise prop, and at 8,000', 2600rpm I will see 170kts (195mph). I would look at the rigging of the plane to make sure everything is true, this will affect the speed as well. You can gain as much as 10mph just by correcting the stab set-up, also check for gaps, is your canopy sealed tight. as MENTIONED ALOT OF LITTLE THINGS ADD UP. BTW I love my -3 too!
 
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