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  #21  
Old 03-20-2020, 10:39 AM
lr172 lr172 is offline
 
Join Date: Oct 2013
Location: Schaumburg, IL
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Quote:
Originally Posted by RV10inOz View Post
Why on earth do people persist with this 25/25 OWT.

If you knew its origins, you would laugh. If I told you, it would make you think I was taking the <insert naughty word>.

So in summary, the engine is slightly worse off for you doing this. Is it critical, no, but it is real.

The most efficient climb-cruise-descent profile is achieved like this.

1. Takeoff at WOT/2700/full rich. At higher fields you may need to lean to about 1300dF (based on mags not EI's)
2. Climb WOT/2700/ Target EGT (1300 in these planes) and at Vz which is 120-125KIAS
3. Cruise WOT / 2300-2500 (pick a smooth spot, many use about 2300-2400) and appropriately LOP. That is 10-20dF at higher levels, 25-40 mid levels and 50-80 at sea level to say 3000'. A well executed Big Mixture Pull will be fine at any level.
4. descent .....nose over, maybe remove a few hundred RPM, back the throttle off to remain out of the yellow arc.......Mixture leave well alone unless there is any sign of stumbles, then only tweak it enough to smooth them out. Land, ICO at the hangar or ramp. If you really cant do the lean landing, go full rich and then lean again for taxi.

The engine is rated at full power all day long. 25/25 was borne out of old WWII pilots who became instructors and they had to find a power reduction from METO in their old warbirds......there was not one, so when they found a recommended cruise climb of 25/2500 (marketing blurb not engineering based) they had discovered what was missing. That was it!

I know it sounds too silly to be true, but my friend and training partner John Deakin lived back in those days and lived through it. Probably in the engine articles on Pelicans Perch he will have written about this OWT. If not, here it is now.

Hope that is helpful.
As I experiment in my 10, i am finding that at 8000í and WOT (2400) i am having to be around 100* Lop or more to get the economy fuel flows that i want. This causes a rougher running engine with a very occasional miss. I have instead pulled the throttle back to get to a point where i am 40* Lop. Curious how others are setting up for a 165 kt speed with 10.5 to 11 gph flow.

Larry
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  #22  
Old 03-20-2020, 01:14 PM
BobTurner BobTurner is offline
 
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Location: Livermore, CA
Posts: 6,445
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To achieve well lean of peak, smooth running, you need to adjust your injector nozzles so all cylinders reach peak egt at the same fuel flow.
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  #23  
Old 03-20-2020, 01:56 PM
lr172 lr172 is offline
 
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Originally Posted by BobTurner View Post
To achieve well lean of peak, smooth running, you need to adjust your injector nozzles so all cylinders reach peak egt at the same fuel flow.
I have. 5 of the cylinders are a .2 spread and the last is another .2 from that range. It was the best I could do. Unfortunately, I can't get that last cyl in line. It is either .3 richer or .3 leaner than the base line average across the other 5.

I guess I wouldn't call it rough, just not as smooth as 50 lop or richer. It was mostly the occassional miss (every couple of minutes) that bothered me.
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Last edited by lr172 : 03-20-2020 at 01:59 PM.
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  #24  
Old 03-20-2020, 06:17 PM
bpattonsoa bpattonsoa is offline
 
Join Date: Apr 2005
Location: Indepenence, Oregon
Posts: 332
Default Riching up to peak speed

When I richen to peak speed at cruise, I use my Dynon to first lean until all EGT drop and note the fuel flow spread (GAMI number that Dynon has as part of its lean routine ) just for interest. It has been reasonably consistent since it was new, around .2 to occasionally.5 GPH. If it ever changes a bunch, will look for the cause.

After stable at cruise on autopilot I note the TAS and richen about 1/3 turn. Wait a couple of minutes and recheck TAS. It does not respond quickly. After a couple of iterations I only richen 1/4 turn. After a bit the TAS will drop a touch, so go a bit leaner.

Takes a while, but cruise is boring and there ainít many exciting things to do. Every hour or so I may lean it up a bit and do it again out of boredom.

It generally gets me 2-4 knots and a bit more fuel, but the -10 does long legs, about my bladder limit.
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  #25  
Old 03-21-2020, 07:25 AM
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N941WR N941WR is offline
 
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Location: SC
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Quote:
Originally Posted by rvbuilder2002 View Post
Since there is obviously a lot of passion regarding correct power settings for climb I won't get mixed up in that, but hopefully people will at least keep noise signature in the back of there mind. It is a much bigger problem than most of us are willing to admit. Particularly on RV's without mufflers.
Scott, has Van's done any noise testing with the same aircraft, with and without mufflers?
Just curious what the quietest results are.

(My neighbors continually comment on how quiet my FP -9 is on takeoff and when entering the pattern and I do not have mufflers. Probably because I have to reduce power way back to get it slowed down in the pattern.
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