Addis Ababa, high density altitude takeoff

fuel to flight plan plus reserve

In that region, I would never do that. Where you can get fuel, take as much as you can. These runways are all 3 or 4 kilometres long.

nokicky wrote:

- add 10 knots to the rotation speed

Not quite sure what this would achieve except from using up a lot of runway and risking wheelbarrowing. I would rather apply elevator backpressure to lift the nosewheel ever so slightly and let the plane fly itself off the ground, and/or accelerating in ground effect if necessary.

Once airborne the airplane will fly as it would at that density altitude… I would make sure that the performance is adequate to climb to cruise altitude while clearing any obstacles.

First of all check the REAL DA on the day. As a rule of thumb, every 8C above standard temp equals an increase of 1000ft DA. Second, ensure that your airplane can actually get airborne at that DA. For a Piper, this may present a challenge. Third, as you say, lean for best power. The technique I usually use is: during run-up lean until the engine starts to falter and then enrichen the mixture by two turns. This, as you can tell, is for Cessnas, not sure how to do the ‘enrichen’ on a Piper quadrant. No need to add anything to rotation speed, your ASI will show the correct air speed (as opposed to ground speed). While I have no idea how far you intend to fly on the day, I’d second Bosco’s comment – in that part of the world you want to have as much fuel as you can. Then again, that may make you too heavy. The POH is your friend. Be mentally prepared for a very long t/o run!

Assuming the Dakota has a constant speed prop, you will not lean to max rpm before takeoff at 9000 ft DA. The most basic technique is to lean to roughness at full throttle and max rpm, then enrichen slightly.

Fly all indicated airspeeds as you would at sea level, but be aware of higher ground speed and allow enough room when maneuvering to land. Depending on go around performance you may want to use less than full flaps to reduce potential altitude loss after deciding to go around and adding full available power. Do not lose patience and rotate early on takeoff. Accelerating to best rate of climb speed (Vy) in ground effect is not a bad idea if conditions allow. Vy will be at slightly lower IAS relative to sea level if you really need to extract performance.

I would not recommend adding anything to your takeoff speed. At high altitude, you have to accelerate to a higher ground speed for the same indicated airspeed and you have less power to work with. You will have to lean to keep the engine running when taxiing. I would do a full power run up and set the mixture according to a typical EGT reading on a sea level departure. So if you normally see 1300 degrees as sea level, I would use this as a reference. You will want all the power your engine can muster. Accept the slow acceleration and stay in ground effect until you have increased to best rate climb speed. Your climb will be much more anemic then you normally experience, and you just have to accept what you get. Best rate of climb and best angle of climb converge a little above the service ceiling. If you don’t have a chart the way these speeds change, plot two points at the elevation that your POH describes, one for Vx and the other for Vy. This speed often applies to about 5000 MSL. At your service ceiling from the POH, plot a third point about 1/3 of the distance between the Vx and Vy speeds. Use this point as an Apex and connect it with the other two points, Vx and Vy, and they will give you a good idea of these speeds verses altitude.

So here is how I describe taking off in Cherokee 6 at a 6000 foot MSL, probably 9000 Density altitude.

Full power, airplane starts ground roll, slowly accelerates to the point the ASI indicator comes alive. Speed builds to 40 knots then 45 Knots then 50 Kts then 51 Knots then 51.5 Knots and over an excruciating long time period finally gets to to 60 knots, but more than half of the 10,000 foot runway are now behind me. Begrudgingly the airplane lifts off but you don’t want to climb initially as you need to accelerate to about 70 or 80 Kts before it is willing to climb out of ground effect.

Edit: there is no way I am going to reduce the RPM from red line, every HP available is needed to climb to altitude. So there is no pulling the RPM back to a climb value at these altitudes.

I was in South Africa not too long ago, dealing with similar issues. We had 8,500 ft DA almost every day, we took of with a PA28-140 with 3 people on board, bags and fuel to the tabs. Acceleration was less than stellar, you need a bit of runway.
Dakotas are quite common down there because they can carry so much and have plenty of reserve power. As Bosco wrote above, I’d take all the fuel I can w/i W&B limits.
Lean slighty directly after start (~2cm), lean to peak rpm during the run-up (when the rpm starts to come down, push it back in ~5mm / 1/4").
Rotate at your normal speed, but level off as soon as airborne 2-3m above the runway to pick up speed before the actual climb.

I would agree with the sentiments on fuel. The major rule of flying in remote areas is take as much as you can assuming long enough runways.

I have been flying a Piper Archer 2 from Addis Abeba towards Yemen. The runway was long enough for our overweight aircraft (ferry tank) to rotate, but we had quite some trouble to get over the mountains around it. It can be tricky. Temps can be high. Leaning for max performance helps while trying to climb out. I would take all the fuel you can get.