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  #1  
Old 05-04-2021, 08:04 PM
BealeStAviator BealeStAviator is offline
 
Join Date: Mar 2020
Location: Clovis, NM
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Default Leaning for high DA in a tailwheel

What's y'all's technique for leaning to best power before takeoff given the propensity to tip forward at full power?

I'm based out of a high altitude field and routinely see well above 3000' DA. I was always taught to lean to max RPM at full power in trikes on high/hot days like that. My RV-8 begins to take flight, tail first, well before full power. So how would you recommend leaning to ensure full power at takeoff? Is leaning at run-up RPM (1800) sufficient? Should I just bump it up to the highest safe RPM and do it there?

Thanks in advance!
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  #2  
Old 05-04-2021, 08:29 PM
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Blain Blain is offline
 
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Stick back and tail still comes up?
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  #3  
Old 05-04-2021, 08:36 PM
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koupster koupster is offline
 
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Location: SLC, UT (KBTF)
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Ryan,
I've been to Clovis (Cannon AFB). 25 degrees F gives a density altitude (DA) of over 3000'. A July day gives a DA of over 8300'.

Perhaps, you could check for best power while airborne at different DAs and note the fuel flow, EGT, mixture lever position, etc. From that you could develop a mixture protocol for varying DAs. A bit more fuel flow on takeoff for the sake of better CHTs might be prudent. I'm about to do this before going to Leadville (KLXV) at a DA of 12,000'.

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  #4  
Old 05-04-2021, 08:37 PM
Taltruda Taltruda is offline
 
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Location: Las Vegas, NV
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Quote:
Originally Posted by Blain View Post
Stick back and tail still comes up?
Also would add that if you do a high power static run, be sure the flaps are retracted.

IMO, I don’t feel 3000 feet DA is enough to worry about leaning for takeoff. I would leave it full rich for takeoff, then when at a safe altitude, look over at your egt and make the appropriate adjustments..over time, you may find where to set the mixture at various DA, but an RV has plenty of performance even if it’s a little too rich for best power.
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Last edited by Taltruda : 05-04-2021 at 08:41 PM.
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  #5  
Old 05-04-2021, 08:52 PM
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gyoung gyoung is offline
 
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Location: Spring, TX
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Learn your peak EGT. Lean to within 50-100 deg of it during runup and/or takeoff roll.
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  #6  
Old 05-04-2021, 09:02 PM
BobTurner BobTurner is offline
 
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Quote:
Originally Posted by gyoung View Post
Learn your peak EGT. Lean to within 50-100 deg of it during runup and/or takeoff roll.
50 deg rich of peak is the middle of the "danger zone", probably the worst place to operate. Go to 150 F rich of peak.
I agree, 3000' DA is not "high". Run full rich there.
To keep the tail down, just use your normal run up power. Lean for max RPM (fixed pitch) or 125 F rich of peak (EGT), and pray that the carb or fuel injection works like it should, and keeps you in the same ball park at full power.
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  #7  
Old 05-05-2021, 12:31 AM
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Dan 57 Dan 57 is offline
 
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Location: LSZF
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Yep, interesting problem...

And yes Blain, the tail will come up with that stick held fully back, as low as 2300RPM on my CS.

I regularly fly into “Europe’s highest elevated airport” as they tout themselves, also know as LSZS Samedan http://www.engadin-airport.ch/Airport.9.0.html?&L=1. Fantastic scenery guaranteed
Imbedded in a valley, elevation is 5600ft, and access passes are around 9000ft. Flying LOP at my usual cruise of 12K, I usually enrich about 1” during the approach, for an eventual GA.
I then leave the mixture where it was after landing, and go enjoy a piece of the delicious local nut pie and a coffee
Before starting the engine, the mixture lever is moved another 1/2” towards rich. Run up satisfactory, take off is performed. The runway is some 1800m or 5900ft long, and gives plenty of time to find the best settings whilst rolling or initial flying.
Yes, knowing one’s mount helps.
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  #8  
Old 05-05-2021, 06:30 AM
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Z-EDD Z-EDD is offline
 
Join Date: Oct 2013
Location: Harare, Zimbabwe
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Quote:
Originally Posted by BealeStAviator View Post
What's y'all's technique for leaning to best power before takeoff given the propensity to tip forward at full power?

I'm based out of a high altitude field and routinely see well above 3000' DA. I was always taught to lean to max RPM at full power in trikes on high/hot days like that. My RV-8 begins to take flight, tail first, well before full power. So how would you recommend leaning to ensure full power at takeoff? Is leaning at run-up RPM (1800) sufficient? Should I just bump it up to the highest safe RPM and do it there?

Thanks in advance!
I have lived my entire life, and learned to fly, at 5000' msl with DA regularly above 7000'. I was taught to lean for takeoff from my first lesson, and we did it at run-up RPM. Later I was taught that for a performance critical takeoff a full power run-up, if possible, would yield a more accurate mixture setting but otherwise setting at normal run-up rpm, and erring on the rich side, was acceptable. This served me well for 3000' hours of bush flying, and I never clipped a tree or fried an engine that I know of.

On the certified fuel injected types (C-206, Cherokee 6, Baron) I think they all had altitude bands marked on the fuel flow guages and we would set the corresponding fuel flow on the takeoff roll. I thought I would work out something similar for my FI RV-7 but I find with mixture anything other than full rich CHT is on the high side, and performance is such that it just isn't necessary. The engine runs smooth as silk full rich so I'm doing full rich takeoffs at 5000' feet so far.
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  #9  
Old 05-05-2021, 08:47 AM
ColoradoSolar ColoradoSolar is online now
 
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Location: Westcliffe, Colorado
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Because of engine temps in my 6A I do full rich takeoffs all the time including at Leadville (KLXV) and my home field at 8300msl with no issues. Our RVs have an abundance of power and don't require the same procedures as their certified cousins.
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  #10  
Old 05-05-2021, 08:40 PM
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jcarne jcarne is offline
 
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Quote:
Originally Posted by Z-EDD View Post
I thought I would work out something similar for my FI RV-7 but I find with mixture anything other than full rich CHT is on the high side, and performance is such that it just isn't necessary. The engine runs smooth as silk full rich so I'm doing full rich takeoffs at 5000' feet so far.
Same here, I can go full rich at 5-6k DA no problem to keep the climb CHTs where I want them. Never really notice much of a performance difference.

After takeoff I usually pull back to 2500RPM and then look for my target EGT value if CHTs allow (which they almost always do).
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