Today's Message Index:
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1. 08:41 AM - Re: High altitude airport Ops (Bob Turner)
2. 08:53 AM - Re: High altitude airport Ops (Dan Masys)
3. 01:36 PM - Re: High altitude airport Ops (Bob Turner)
Message 1
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| Subject: | Re: High altitude airport Ops |
The usual techniques. Above 5000 DA I lean for takeoff, but richer than best power.
With no cowl flaps my 10s CHTs will go over 420 F unless some extra fuel
is used to keep them down. Flaps in trail.
--------
Bob Turner
RV-10 QB
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=505810#505810
Message 2
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| Subject: | Re: High altitude airport Ops |
I fly my RV-10 routinely between KLHM in the Sacramento valley to South
Lake Tahoe KTVL (elev. 6269, 8000 ft runway but situated in a shallow box
canyon) and Truckee KTRK (elev 5904, two runways each a tad less than 6000
ft.). In the summer the density altitude of both airports routinely is in
the 8500-10000 ft range. Getting there from the valley in the mornings is
usually pretty easy except when winds across the ridges surrounding the
Tahoe basin are over 30kts. The trick is getting back home in the
afternoons. Here is the recipe I have found that so far has worked
safely. It is benefited by having a GRT EFIS that shows percent max power.
1. In flight planning, pay careful attention to the combination of winds
and density altitude. Even for a lightly loaded RV-10, KTVL becomes a one
way in, one way out airport (land to the south, take off to the north
toward the lake). Prevailing winds are from the southwest in the
afternoons, meaning there will be a quartering tailwind on departure. The
FAA guidance is to expect that each knot of tailwind component lengthens
the takeoff run by 3-5 percent, so the multiplier effect of high density
altitude plus tailwind gets very large very quickly, even for an 8000 ft
runway. The common rule of thumb is to abort the takeoff if one doesn't
have 80 percent of rotation speed at 50 percent of runway length, and most
every mountain airport has a midfield marker to use. But if you hit that
decision point it gets pretty scary because your groundspeed is quite a bit
higher than your indicated airspeed by then.
2. If the planning numbers give you a safety margin that works for you,
then optimizing takeoff power goes like this for me:
A. First, you will have had to lean the mixture to even get the IO-540 to
start and run smoothly, and taxi to the runway at high density altitudes.
At the runup area, do a wide-open-throttle runup with the mixture unchanged
from the leaning you did for startup and taxi. If the max percent power is
below about 70 percent, then adjust mixture to get max EGT prior to
initiating takeoff.
B. On takeoff roll, once you get airborne remember that best rate (Vy)
will be a higher IAS than at sea level, and you will have to drop the nose
below your normal pitch angle or you will most likely see your CHTs hit
your alarm limit (mine is set at 400F). Don't attempt to climb at Vx (best
angle) if you can avoid that since it will quickly drive your CHTs up due
to the design of the -10s cowling. In practical terms, sea level best rate
in my -10 is 90 KIAS, and I usually have to climb out at about 110-115 KIAS
to get an acceptable combination of climb rate + CHTs at high DA.
C. Once you are airborne and running at max power, you can drop your CHTs
by slowly enriching the mixture, The IO-540 seems to tolerate this well.
I have not experienced a stumble caused by going richer as long as you are
still running at 2600 rpm or higher, and it is very effective at cooling
the cylinders down. Have never needed to go full rich to get the cooling
effect, so I don't know where the limit to that strategy is, but it
definitely helps in my experience in the -10. Upon leveling off for
cruise, just do what you normally would with respect to finding optimal
mixture.
3. Give yourself some performance margins. Whenever I can, I treat the -10
as at most a 2.5 place aircraft for high DA ops, and don't fill the tanks
to more than you need with usual reserves. There is no benefit to topping
it off in most high DA situations.
This is the ultimate YMMV situation, and others may have a different
recipe, but with 1240 PIC hours in the -10 this has worked well for me.
-Dan Masys
N104LD
Time: 08:50:47 AM PST US
From: Marcus Cooper <cooprv7@yahoo.com>
Subject: RV10-List: High altitude airport Ops
I just relocated to KAPA, Centennial in Denver, CO. I learned about high
altitude
takeoffs long ago, but was wondering if anyone has specific techniques for
the RV-10 with an IO-540?
Thanks,
Marcus
Message 3
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| Subject: | Re: High altitude airport Ops |
Dan, I respectfully disagree with some of your post.
First, be very careful interpreting the GRT power reading. It just works off a
look up table that you entered, and, in particular, does not know the actual mixture
ratio wrt peak egt.
Second, lean to best power, not peak egt, if there is any question about having
sufficient power for takeoff. Best power is about 125 F rich of peak EGT. And
with a long runway, go even richer, to help keep CHTs down.
As you note, caution is needed with downwind takeoffs. I wont accept more than
a 5 knot tailwind component. And while some airports really are one-way, KTVL
isnt one of them. Its a bit tight, but a -10 can takeoff to the south and execute
a left downwind departure. And if it wont climb fast enough, there is a golf
course a bit further south over which you can circle.
Vy (in IAS) decreases, not increases, as density altitude goes up. But you do need
to watch CHTs.
I recommend flaps in trail for these takeoffs.
--------
Bob Turner
RV-10 QB
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=505817#505817
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