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  #21  
Old 09-21-2021, 12:22 PM
Carl Froehlich's Avatar
Carl Froehlich Carl Froehlich is offline
 
Join Date: Dec 2007
Location: Dogwood Airpark (VA42)
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Quote:
Originally Posted by EricTheRV8er View Post
Thanks for the info.

So you converted your -8A from fixed pitch to C/S? I know this engine has a hollow crank, so it could be done. Is there much involved besides the obvious? Did it require a new cowl or a cowl modification? And what speed bump did you see after converting?
In a perfect world you should be able to just replace the prop and make a new spinner (uses a different back and front plate than the FP prop). Spinner available from Vanís.

While there should be no big cowl changes, you might have a spinner to cowl issue - it all depends on what you have now. If so, you may need to do some fit work.

The touchy issues are:
- Do you still have the governor to prop oil line that came with the engine. You will need it. If not you can replace with a braided hose.
- You will need to remove and then replace the rear crank oil seal (the one that gets a hole punched in it if using a FP prop). This is not crazy hard but do not attempt without the help of someone that knows what they are doing and who has the special tools to do it right. The seal is aft of a oil supply tube that if you damage it you will be in the hurt locker.
- You need to buy and install a prop governor, governor control cable and prop control on your quadrant. Assuming you only have a two arm quadrant this will need to be replaced. Parts available from Vanís.

From memory I think I saw 170 knots on a good day at an RPM higher than practical using the FP prop. With the CS prop 180 was easy to hit if you want to burn the gas to do it. Note - donít overlook the value of careful rigging on RV top speed.

On the first takeoff, when your head goes back from the acceleration, you will be rewarded for your efforts.

Carl
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  #22  
Old 09-21-2021, 01:06 PM
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EricTheRV8er EricTheRV8er is offline
 
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Location: Smithfield North Carolina
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Quote:
Originally Posted by Carl Froehlich View Post
Note - donít overlook the value of careful rigging on RV top speed.


Carl
I'll be looking into rigging and finishing our gear leg root fairings before making a prop change.

It would be nice to get the same cruise speed at lower RPM, but I probably wouldn't do the conversion without feeling confident the rest of the plane was sorted, and the prop is the weak link. I know there are other benefits with takeoff/climb performance, but in those regards the plane performs satisfactorily for my purposes. I just feel it should be faster than 160kts at 70% power. I was expecting 170-175kts out of it.

You are the only report I've read of a speed bump going from FP to CS.
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  #23  
Old 09-21-2021, 04:02 PM
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Laird Laird is offline
 
Join Date: Feb 2007
Location: SoCal
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Default Mo Speed

Quote:
Originally Posted by EricTheRV8er View Post
You are the only report I've read of a speed bump going from FP to CS.
I can confirm a speed increase, as well as ROC, take off and landing roll, reduced fuel burn, and a tremendous grin factor. And if you're interested in formation flying, it SO much easier with a CS prop.

As a friend said "stop on the side of the road and pick up alum cans, eat PBJ sandwiches, sell yourself...do whatever you need to do to buy a CS prop".

I switched my FP Sensenich (O-360) to a CS after 200 hours...what a different airplane!

Also, it doesn't need to be a new BA Hartzell. Some of the older models work very well too.

Laird
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  #24  
Old 09-21-2021, 04:35 PM
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EricTheRV8er EricTheRV8er is offline
 
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Location: Smithfield North Carolina
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Originally Posted by Laird View Post

I switched my FP Sensenich (O-360) to a CS after 200 hours...what a different airplane!


Laird
Thanks Laird. If you recall, what were your cruise speeds before and after?
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  #25  
Old 09-21-2021, 06:53 PM
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Laird Laird is offline
 
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Originally Posted by EricTheRV8er View Post
Thanks Laird. If you recall, what were your cruise speeds before and after?
It was 20 some years ago, so that information has been overwritten, and I've misplaced my flight test data years ago, but I do remember that it was something like 10mph, maybe more, maybe less.

I do remember that I had the 83" pitch, which was a bit of a climb prop, so I couldn't use all the throttle at cruise. I think they recommend the 85 or 87 now.

Speed isn't the only thing you get with a CS prop, it's all the other stuff that really changes the airplane. I used to say when I added the CS prop, I got the last 30% of performance out of the airplane.

My RV-6 has a max cruise (8000' DA, full throttle, 150deg rich of peak) of 183kts. Generally, I flight plan for 165kts door to door at 9 ghp which I usually beat.

Last edited by Laird : 09-21-2021 at 06:58 PM. Reason: added speed
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  #26  
Old 09-21-2021, 07:16 PM
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rjcthree rjcthree is offline
 
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Location: Bay Village, OH
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Default PA vs DA

At the start of your thread, it looks like youíre targeting 7500í pressure altitude. For the 75% test, shouldnít it be 7500í density altitude?
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  #27  
Old 09-22-2021, 06:20 AM
judoka5051 judoka5051 is offline
 
Join Date: Aug 2010
Location: McAlpin, FL
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Default CS vs FP again?!

Hey Eric,

I've got a FP (Whirlwind) prop on my 8, and I can tell you it's plenty fast. I cruise at 215mph at 2550, and hit VNE at 2750 at 7500ft. On the other hand I only see 2050 static.

This is with a fuel injected, dual P-Mag o360 with 9:1 pistons. The fastest it's gone is 243mph, but that was with mods that don't work for normal flying. Home made tailwheel pant that covers the wheel AND vertical socket, No external antennas, and a few other doodads.

When I built the plane I was planning on racing it, but then I saw the two RV8s that were in the 270+mph club and gave up on that.

The plane light at 1006 lbs, so that helps with the climb. A CS prop would help with the climb, but I don't think it would help the top speed.
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Scratchbuilt Biplane
Preceptor N3 - Sold
Zenith Zodiac 601HD - Sold (good riddance)
Kitfox IV - Sold my share, but loved that plane
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  #28  
Old 09-22-2021, 07:59 AM
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EricTheRV8er EricTheRV8er is offline
 
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Location: Smithfield North Carolina
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Quote:
Originally Posted by judoka5051 View Post
Hey Eric,

I've got a FP (Whirlwind) prop on my 8, and I can tell you it's plenty fast. I cruise at 215mph at 2550, and hit VNE at 2750 at 7500ft. On the other hand I only see 2050 static.

This is with a fuel injected, dual P-Mag o360 with 9:1 pistons. The fastest it's gone is 243mph, but that was with mods that don't work for normal flying. Home made tailwheel pant that covers the wheel AND vertical socket, No external antennas, and a few other doodads.

When I built the plane I was planning on racing it, but then I saw the two RV8s that were in the 270+mph club and gave up on that.

The plane light at 1006 lbs, so that helps with the climb. A CS prop would help with the climb, but I don't think it would help the top speed.

Sounds like you have a very fast plane. I'm not intending or expecting this to be a 180kt plane, but I figured it would do a little better than 150-155kts at moderate power settings. It seems most report 165-175kts at similar power settings and altitude.

I am seeing 2200 static, and 2300+ about rotation speed. It's pitched at 85", which seems on the more cruise prop end of the spectrum to me, but 2200 static seems high for a cruise FP. Catto lists their cruise prop pitched at 78". I know there's probably more that goes into it than pitch, but still.

Would probably learn a lot borrowing a Catto someone has laying around and do some comparisons.

Last edited by EricTheRV8er : 09-22-2021 at 08:04 AM.
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  #29  
Old 09-22-2021, 11:05 AM
Tbone1 Tbone1 is offline
 
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Location: Kenly NC
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Check the RPM with a digital tach, sounds like you may have a climb prop ?
Whatís your ground roll, and vertical climb rate ?
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  #30  
Old 09-22-2021, 11:23 AM
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EricTheRV8er EricTheRV8er is offline
 
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Location: Smithfield North Carolina
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Originally Posted by Tbone1 View Post
Check the RPM with a digital tach, sounds like you may have a climb prop ?
Whatís your ground roll, and vertical climb rate ?
According to Sensenich, it's labeled a "Standard" prop at -85. They offer what they label a "climb" prop as a -83 and a Cruise prop as -86.

On climb out with full fuel and just me, OAT surface 23C, I'm seeing about 1000fpm with a constant IAS of 125kts from SL up to 5500'.

I haven't recorded numbers at a Vy climb, but I would guess about 1200-1400 on average warm day.
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