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  #11  
Old 09-07-2006, 11:01 PM
glenmthompson glenmthompson is offline
 
Join Date: Jan 2005
Posts: 191
Exclamation Timing....NOT MAGS... read on..

There is an all too common cause (read stupid mechanics) of low power output. In the following described instance, you will get close to rated static RPM, but low climb rates and slow cruise.
The cause here, and this is an extreme analysis, but I have seen it in several planes (one that made it to TBO actually, with sucky power) is , believe it or not.....
.
.THE CAMSHAFT/CRANKSHAFT TIMING IS OFF ONE TOOTH!!!!!!!
.
. Yes ladies and gentlemen, this happens, continues to happen and your engine will run and start just fine with this condition. Performance, well that is another story. First my personal history with this, then how to easily see if you are a suffering from this problem.
In my Kitfox, when I built it, in my LYC IO-290, I paid a "reputable" engine builder based out of Lantana airport in Lantana Fl. to put together the bottom end, and he did just that to me.(among many other really bad things, don't get me started)...(PM me for the name of this, umm "mechanic", if you already don't know who it is. STAY AWAY!!!) My flying symptoms were....700 instead of 1100 fpm.....Normal static RPM as expected....Cruise was 122 instead of the expected 135...I tried several props, same thing....
.

Now, easy analysis of this anamoly.....Pull a valve cover off of any cylinder....Pull out spark plug and put piston to TDC of the of exhaust stroke(Look into SP hole to hit TDC, or use timing wheel,..whatever...)..... Rock piston back and forth at TDC.Now, note the exhaust valve and intake valve ( actually note the rockers...) at exactly TDC in this position, the ex. valve should close and the intake should open. ....I am not sure if hydrolic lifters will be exactly like solid lifters at this point....Anybody add here???? Rocking the piston back and forth, with the prop in your hand, will show if you are timed correctly...
I certainly hope this is not it, or the engine will soon be coming off to fix...Just another idea for head scratching/hangar flying....
.
Bottom line here, your climb performance will obviously be more degraded than cruise, since it takes a whole lot of HP to get a little more MPH.
.
.PS, one mechanic said in his humble observation, this happens in at least one out out of 1000 rebuilds. He said he even heard of an engine coming factory new from LYC. in this condition......Also, how much power you lose, depends on whether you are advanced or retarded one tooth........
Glen

Last edited by glenmthompson : 09-08-2006 at 09:24 AM. Reason: text changed and added...Corrected word mag... to camshaft
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  #12  
Old 09-08-2006, 05:17 AM
pierre smith's Avatar
pierre smith pierre smith is offline
 
Join Date: Jan 2005
Location: Louisville, Ga
Posts: 7,840
Default 3 blades...

Leonard,
I didn't tell you that my Catto 76" is a three blade.
Regards,
__________________
Pierre Smith
RV-10, 510 TT
RV6A (Sojourner) 180 HP, Catto 3 Bl (502Hrs), gone...and already missed
Air Tractor AT 502B PT 6-15 Sold
Air Tractor 402 PT-6-20 Sold
EAA Flight Advisor/CFI/Tech Counselor
Louisville, Ga

It's never skill or craftsmanship that completes airplanes, it's the will to do so,
Patrick Kenny, EAA 275132


Dues gladly paid!
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  #13  
Old 09-08-2006, 07:14 AM
gmcjetpilot's Avatar
gmcjetpilot gmcjetpilot is offline
 
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Posts: 4,285
Default Thrust - Drag = Speed

A quikcalc shows that turning 2700 rpm (new prop) you should go 175 mph. That is still about 10 mph slower than spec. The previous post are all interesting, good and possible.

Going to the equations again, speed is a function of drag and thrust. Work on both. The previous post talk to prop and engine issues, which is excellent, but what about the drag part. I understand you have the fairings on.

Do you have any pictures of your plane? Put it out in the middle of a flat ramp, support the tail, for a level flight, naturalize position of all controls (temporarily with tape if needed). Now walk around, a little ways back, get down and get a good look at it with a critical eye. Sometimes you measure stuff within a nats hair in the hanger but out on the ramp you can see that right wheel fairing is a little a skew inboard at the trailing edge. When you fly is your elevator in trail or in other words the elevator counter balanced arm even with the Horz stab in flight? Ailerons even in flight?

Than get up close top to bottom and look for any place air is getting hunk up. Are the engine baffles sealing well. Cooling drag is a big part of the total drag. In a word are all the fairings on straight. Are the controls all in a fair-ed and rigged (even left left to right). Are there any gaps and uneven surfaces.

My guess is a little from here (thrust) and a little form there (drag reduction) you will approach the book speed of about 185 mph 75%, 8000" cruise. I had a similar experience with my RV from the time I first flew it and from the time I had tweaked it over a year or two, gaining at least 10 to 15 mph. Sorry non specifics but a bunch of little things. Recommend back articles by Van in the RVator ('92 thru '94 especially) about increasing speed and the book, Speed w/ Economy by Kent Paser. It's a mph here and mph there.

The last comment and have no idea, but possible measurement error is always a possibility? It happens to everyone. The methods are much easier today and assume you used GPS, with three constant course/track runs and used Kevin Horton's spread sheet to crunch the numbers. As far as power estimate you should have both RPM and MAP. The FF is good info, and your sound a little high for 75% power on a 150 hp engine?? Many guys with out FP don't put a MAP gauge in. That is a small pet peeve. You really need a MAP gauge in an experimental plane.

Bottom line you need more thrust and less drag. Think and attack everything that would reduce power / thrust and increase drag. The only thing obvious is the low RPM, which can be a prop, engine or both. Remember this is the fun part, hunting down that extra speed.
__________________
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Raleigh, NC Area
RV-4, RV-7, ATP, CFII, MEI, 737/757/767

2020 Dues Paid

Last edited by gmcjetpilot : 09-11-2006 at 05:08 PM.
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  #14  
Old 09-08-2006, 08:44 AM
osxuser's Avatar
osxuser osxuser is offline
 
Join Date: Aug 2005
Location: Pasadena CA
Posts: 2,484
Default

Quote:
Originally Posted by glenmthompson
There is an all too common cause (read stupid mechanics) of low power output. In the following described instance, you will get close to rated static RPM, but low climb rates and slow cruise.
The cause here, and this is an extreme analysis, but I have seen it in several planes (one that made it to TBO actually, with sucky power) is , believe it or not.....
.
.THE MAG/CRANKSHAFT TIMING IS OFF ONE TOOTH!!!!!!!
.
. Yes ladies and gentlemen, this happens, continues to happen and your engine will run and start just fine with this condition. Performance, well that is another story. First my personal history with this, then how to easily see if you are a suffering from this problem.
In my Kitfox, when I built it, in my LYC IO-290, I paid a "reputable" engine builder based out of Lantana airport in Lantana Fl. to put together the bottom end, and he did just that to me.(among many other really bad things, don't get me started) My flying symptoms were....700 instead of 1100 fpm.....Normal static RPM as expected....Cruise was 122 instead of the expected 135...I tried several props, same thing....
Now, easy analysis of this anamoly.....Pull a valve cover off of any cylinder....Pull out spark plug and put piston to 180 deg out of TDC from comp. stroke, as in top of exhaust stroke(Look into SP hole to hit TDC, or use timing wheel,..whatever...)..... Rock piston back and forth at TDC.Now, note the exhaust valve and intake valve ( actually note the rockers...) at exactly TDC in this position, the ex. valve should close and the intake should open. Rocking the piston back and forth, with the prop in your hand, will show if you are timed correctly...
I certainly hope this is not it, or the engine will soon be coming off to fix...Just another idea for head scratching/hangar flying.
Glen
I'm not quite clear on what you mean by one tooth. The mags are adjustable throughout a certain range by simply loosening them and rotating. If they are off by more than that, they are considered one tooth out, and have to be removed, and the drive gear moved one tooth over. A simple mag timing test would reveal this however, no need to pull a rocker cover off.
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Stephen Samuelian, CFII, A&P IA, CTO
RV4 wing in Jig @ KPOC
RV7 emp built
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  #15  
Old 09-08-2006, 09:21 AM
glenmthompson glenmthompson is offline
 
Join Date: Jan 2005
Posts: 191
Default Hi Mr. Ox Man!!!

Lemme explain a little further...the timing I am refering to, is how the crankshaft gear in the back, inside the accessory case, is meshed with the gear on the back of the camshaft. This is known as "valve timing"..NOT ignition timing. Sorry, I corrected my above post, I DID say mag instead of camshaft, thus how I confused you...sorry, my bad....
As far as the mag timing, yep you are correct, but I speak of the "other" gear meshed with the crank.
...Hard to believe that somebody who works on SEL planes would do this, but....ya never know!
Glen

Last edited by glenmthompson : 09-08-2006 at 09:29 AM. Reason: text changed and added...
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  #16  
Old 09-09-2006, 10:17 PM
osxuser's Avatar
osxuser osxuser is offline
 
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Location: Pasadena CA
Posts: 2,484
Default

Quote:
Originally Posted by glenmthompson
Lemme explain a little further...the timing I am refering to, is how the crankshaft gear in the back, inside the accessory case, is meshed with the gear on the back of the camshaft. This is known as "valve timing"..NOT ignition timing. Sorry, I corrected my above post, I DID say mag instead of camshaft, thus how I confused you...sorry, my bad....
As far as the mag timing, yep you are correct, but I speak of the "other" gear meshed with the crank.
...Hard to believe that somebody who works on SEL planes would do this, but....ya never know!
Glen
Glen,

It all makes sense now. Yep that could do it, although it'd be an outside shot.
__________________
Stephen Samuelian, CFII, A&P IA, CTO
RV4 wing in Jig @ KPOC
RV7 emp built
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  #17  
Old 09-10-2006, 06:36 AM
Mark7986 Mark7986 is offline
 
Join Date: Jul 2006
Location: Fairmont MN
Posts: 41
Default

Quote:
Originally Posted by glenmthompson
There is an all too common cause (read stupid mechanics) of low power output. In the following described instance, you will get close to rated static RPM, but low climb rates and slow cruise.
The cause here, and this is an extreme analysis, but I have seen it in several planes (one that made it to TBO actually, with sucky power) is , believe it or not.....
.
.THE CAMSHAFT/CRANKSHAFT TIMING IS OFF ONE TOOTH!!!!!!!
.
. Yes ladies and gentlemen, this happens, continues to happen and your engine will run and start just fine with this condition. Performance, well that is another story. First my personal history with this, then how to easily see if you are a suffering from this problem.
In my Kitfox, when I built it, in my LYC IO-290, I paid a "reputable" engine builder based out of Lantana airport in Lantana Fl. to put together the bottom end, and he did just that to me.(among many other really bad things, don't get me started)...(PM me for the name of this, umm "mechanic", if you already don't know who it is. STAY AWAY!!!) My flying symptoms were....700 instead of 1100 fpm.....Normal static RPM as expected....Cruise was 122 instead of the expected 135...I tried several props, same thing....
.

Now, easy analysis of this anamoly.....Pull a valve cover off of any cylinder....Pull out spark plug and put piston to TDC of the of exhaust stroke(Look into SP hole to hit TDC, or use timing wheel,..whatever...)..... Rock piston back and forth at TDC.Now, note the exhaust valve and intake valve ( actually note the rockers...) at exactly TDC in this position, the ex. valve should close and the intake should open. ....I am not sure if hydrolic lifters will be exactly like solid lifters at this point....Anybody add here???? Rocking the piston back and forth, with the prop in your hand, will show if you are timed correctly...
I certainly hope this is not it, or the engine will soon be coming off to fix...Just another idea for head scratching/hangar flying....
.
Bottom line here, your climb performance will obviously be more degraded than cruise, since it takes a whole lot of HP to get a little more MPH.
.
.PS, one mechanic said in his humble observation, this happens in at least one out out of 1000 rebuilds. He said he even heard of an engine coming factory new from LYC. in this condition......Also, how much power you lose, depends on whether you are advanced or retarded one tooth........
Glen
The crankshaft timing was one of the things Sensenich recommeded to check, it was right on

Mark
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  #18  
Old 09-10-2006, 07:31 AM
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tc1234c tc1234c is offline
 
Join Date: Sep 2006
Location: Port Orange, FL
Posts: 1,020
Default

I just found this thread and since I have a similar problem I am posting my problem here.

I have 30 hours on my RV-9A with new O320-D2A engine from Aero Sport Power and a 79 pitch Sensenich metal propeller. I don't have my wheelpants neither leg fairing on yet. I have not received my manifold transducer, thus only rpm is recorded. I verified my TAS using Kevin Horton's spread sheet. Following are my numbers:

at 8,500 ft (leaned ROP)

rpm TAS (kts) gph
2080 117 5.3
2190 121 7.7
2290 132 8.4
2420 139 10.0

at 3,000 ft (not leaned)

rpm TAS gph
2080 114 8.0
2290 130 10.1

Yesterday at 6,000 ft, full throttle, I had 144 kts at 2,450 rpm.
At cruise the ball is slightly on the left and the elevator slightly pointing down (I could see an inch of counter-balance/tip above the HS). People on the ground also report a whistling sound from my airplane. During the climb out my #3 CHT could go as high as 450 degree F. At cruise, it is around 390. #1 and #2 are around 310-330. My GRT EIS 4000 reports a carb temperature of 127 degree F. But, I don't see any leaks in my airbox. This might be a sensor/installation problem. I set my idle to 500 rpm per recommendation of Mike Seager and adjusted idle mixture accordingly. Magneto timing has been checked and both side are set at 25 degrees.

Apparently I have problems with my low rpm at full power and the higher than normal fuel flow. I am a newbie to engines and still learning.

I will look into suggestions already given on this thread. Any additional suggestions will be appreciated.

Ted
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  #19  
Old 09-10-2006, 09:30 AM
Kyle Boatright Kyle Boatright is offline
 
Join Date: Aug 2005
Location: Atlanta, GA
Posts: 4,219
Default

Ted,

I think your aircraft's performance is within reason for an RV-9 without fairings or wheelpants. The fuel burn numbers look high, but that could be a product of several different issues - tach accuracy, rich mixture, etc.
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Marietta, GA
2001 RV-6 N46KB
2019(?) RV-10
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  #20  
Old 09-10-2006, 09:47 AM
Bob Axsom Bob Axsom is offline
 
Join Date: Mar 2005
Posts: 5,685
Default For the original

In a fixed pitch prop situation, with a common design airplane with known performance characteristics, well built and rigged, at a set RPM with an accutate tach how can it be anything but a bad prop?

Bob Axsom
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