Cadstat

Cadstat

Well Known Member
My slider 6A doesn't deliver the numbers I was hoping for. I'm only 170-172 mph @ 8k tops. I'm the third owner. The plane has over 30 'stick on' applique decals of flames as you can see in the photo. They have a slight texture that you can feel. I can't believe they are slowing me down but who know? What else can I do to improve speed.
Its a IO-320 160 hp once turbo'd with 745 hours, 2600 rpms max. Bendix mags. Good compression and doesn't use oil. Hartzel C/S, 1175 pounds empty.
 
Are the gear leg fairings & wheel pants properly aligned? A tech counselor told me a similar tale once and fixed the issue by re-aligning those fairings. I filed that tidbit away for future reference...
 
John,

Some more data would be useful in diagnosing. What MAP/RPM/ fuel flow are you seeing? How are you leaning? Is 8K pressure or density alt? How are you measuring the speed? ASI, True ASI, GPS 3 way run verified?
 
Cadstat said:
I'm only 170-172 mph @ 8k tops.

Its a IO-320 160 hp once turbo'd with 745 hours, 2600 rpms max. Bendix mags. Good compression and doesn't use oil. Hartzel C/S, 1175 pounds empty.
Click to expand...

Looking at the above numbers...... let's take 8K and make 8K DA. and then convert 172 indicated into TAS...... now we are going 194 MPH. Not bad for a motor that will only turn 2600rpm.

To produce 75% power at 8K da, you will need about 22' of MP. You need to find out why your motor will not produce 2700 rpm. Timing. Cam timing, flat cam?

Good luck.
 
More info

The speed is by GPS as well as the altitude. And the numbers have been the same over many test checks with two GPS.
Timing unknown. The previous owner said the rpm is limited by the governer.
I do get a 350 rpm drop each side on the mag check. Plugs are brand new.
Shows 22 Manifold pressure @8k, rpm doesn't change the speed. 2200-2400 no change in airspeed. No fuel flow but digital EGT at 1300.
 
Cadstat said:
The plane has over 30 'stick on' applique decals of flames as you can see in the photo.
Click to expand...


Strange, the flames should speed you up. Maybe because they are decals and not paint, only the commitment of painted flames can give you those extra few knots.

Have you tried racing stripes?
 
Can't use GPS speed

Also, you can't go by GPS speed because that is relative to earth, not relative to the local wind you are flying in. What's important is air speed. Above it was suggested to use TAS adjusted for altitude and temperature from indicated. You may be doing better than you think.
 
John,

How exactly did you do the GPS check? You should go out and fly three (or four) legs at 90? to each other (in smooth air and carefully holding altitude), and correct for the wind using one of the formulas linked on Kevin Horton's web page:

http://www.kilohotel.com/rv8/phplinks/index.php?&PID=49

If the speed is indeed low, there might be more than one cause. I'd start with getting the mags checked or overhauled; 350 rpm is way too much drop. It also sounds like either the prop or the governor needs adjustment; you should be able to turn 2700. While you're at it check to make sure the throttle and mixture cables are adjusted correctly.

From there I'd look at alignment of the gear fairings and control surfaces. The airplane is also very heavy for an RV-6A which will affect speed a bit, but I'd only expect this to be on the order of a couple of knots.
 
Cadstat said:
The speed is by GPS as well as the altitude. And the numbers have been the same over many test checks with two GPS.
Timing unknown. The previous owner said the rpm is limited by the governer.
I do get a 350 rpm drop each side on the mag check. Plugs are brand new.
Shows 22 Manifold pressure @8k, rpm doesn't change the speed. 2200-2400 no change in airspeed. No fuel flow but digital EGT at 1300.
Click to expand...


This is definatley not normal.

As was mentioned before too, gear leg fairings dragging you sideways will cause a lot of drag as well. The stickers, while you may get some turbulent flow it wouldn't be 15-20 mph worth of drag. I'd start with the mag drop, that is way out of tolerance.
 
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Cadstat said:
I do get a 350 rpm drop each side on the mag check. Plugs are brand new.
Click to expand...

350 RPM drop during a mag check? That is too much, and should be investigated. Lycoming SI-1132B specifies an RPM drop of 175 RPM for fixed wing aircraft.
 
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Good point

Very good point Rocket Bob. I didn't think about that. I may not have 160 hp to start with. Kind wish I still had a turbo now.
 
It's likely you have more than one issue at work and probably a few things are compounding to make the plane what it is. Definately the mag drop is Quite BAD. The compression is easily fixed with 4 new pistons if indeed it's low, but then again we don't know that to be a fact. The RPM is suspect, but again we dont know if its the governor or the prop. The Stickers probably aren't helping either. Overall I'd focus on one thing at a time; first get the engine healthy because something ain't right with it! Then focus on the other things.

My 2 cents as usual,

Stein
 
CG

I read in another post your plane is a bit nose heavy? I can think of a few things that would most-likely cause drag trying to maintain level flight.
 
Are you leaning for your mag check? If you are doing your mag checks full rich at your altitude, that would cause the large mag drops. I usually throttle to 1700 rpm and then lean to 1800-1850 rpm for a mag check at my 5800' altitude.
 
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