Primarily for general aviation discussion, but other aviation topics are also welcome.
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By Rob L
#1859703
Very early in my flying experience in the 1990s, I attempted a take-off from Nuits-Saint-Georges with my then 65-hp Taylorcraft and fully loaded with two on board plus all the camping gear and full fuel. It was very hot and the grass was long; the wind was favouring a westerly take-off and there were big electricity pylons off the departure end.

At the half-way point we were still too slow, so I aborted (the first time I had ever felt the need to do so). We ended up waiting a few hours for the temperature to drop, and then took off the other way with a slight tailwind but with no tall obstacles in the way.

Lessons learned: don't rush density altitude; make a decision point early.

Roll forward 20 years, and I departed an airfield in the USA with a 9600' density altitude with no problem (but it was a lot longer and tarmac!) Both aircraft the same: 65hp Taylorcraft with no mixture control.
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By Paul_Sengupta
FLYER Club Member  FLYER Club Member
#1859714
Rob L wrote:Both aircraft the same: 65hp Taylorcraft with no mixture control.


At Big Bear, in a 180hp injected 172, at a slightly lower density altitude, I couldn't even get it to idle properly on full rich, let alone take off.
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By PeteSpencer
FLYER Club Member  FLYER Club Member
#1859715
Paul_Sengupta wrote:
Rob L wrote:Both aircraft the same: 65hp Taylorcraft with no mixture control.


At Big Bear, in a 180hp injected 172, at a slightly lower density altitude, I couldn't even get it to idle properly on full rich, let alone take off.


Yeah but high DA power checks immediately pre take-off involve leaning at full power till peak then back rich a bit for take-off. :thumleft:
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By Rob L
#1859717
Paul_Sengupta wrote:
Rob L wrote:Both aircraft the same: 65hp Taylorcraft with no mixture control.


At Big Bear, in a 180hp injected 172, at a slightly lower density altitude, I couldn't even get it to idle properly on full rich, let alone take off.

I don't think you should even be idling a 180 Lycoming at sea level "on full rich", let alone at Big Bear altitudes. You should be running as lean as you can (on the ground at low rpm) to keep the plugs clean.

Rob
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By PeteSpencer
FLYER Club Member  FLYER Club Member
#1859719
Our arrer (200HP) plugs have been known to oil up on full rich idle in the 20 minute queue to depart the Duxford airshow....

Fortunately caught in time: pulled out of the queue for a quick aggressive lean and all was sweetness and light.

ILAAFT. :oops:
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By Rob L
#1859724
When I rented a Cessna 150 many moons ago from Phoenix Deer Valley airport to fly to Sedona, the rental agency advised me a little bit about density altitude (this was winter time; it was very cold & dry so DA was not too much of an issue; nor was carb ice).
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By Josh
#1859736
Most eye opening takeoff I ever did was after the Brazilian GP in São Paulo a few years ago. Very full 777 was at performance limited takeoff mass after offloading some freight. 36 °C at 2500’ elevation on a 3600 m runway.

V1 was 175 KIAS and the amount of runway left was frightening.
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By Rob L
#1859739
Josh wrote:Most eye opening takeoff I ever did was after the Brazilian GP in São Paulo a few years ago. Very full 777 was at performance limited takeoff mass after offloading some freight. 36 °C at 2500’ elevation on a 3600 m runway.

V1 was 175 KIAS and the amount of runway left was frightening.



Why was the freight loaded in the first place, if it required offloading?
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By Josh
#1859746
In this case it was hotter and there was less wind when we departed than when they initially ran the numbers. It’s very rare to encounter this sort of issue and we are talking needing to offload 1-2 T in an aircraft with a MTOW of 340 T.
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By Paul_Sengupta
FLYER Club Member  FLYER Club Member
#1859758
Rob L wrote:I don't think you should even be idling a 180 Lycoming at sea level "on full rich", let alone at Big Bear altitudes. You should be running as lean as you can (on the ground at low rpm) to keep the plugs clean.


I started it full rich, and then quickly leaned when it wouldn't run properly.

I always tend to start the engine full rich.
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By A4 Pacific
#1859861
Why was the freight loaded in the first place, if it required offloading?

Even when ambient conditions remain constant, the freight is often loaded before the crew have selected the amount of fuel they require. Which may, for perfectly valid reasons, be more than flight plan.
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By MichaelP
FLYER Club Member  FLYER Club Member
#1859912
@Josh the B777 is not as good as a Russian aeroplane... 8)

You also don't know the actual weight of the passengers until a male/female split is done at closeout.

I have noticed that some women are bigger than their men these days. Then there’s the relative baggage load!

At Baotou, 1,000 metres elevation, we never put the mixture to full rich, maybe 2/3rds on start. (Diamond DA40-180).
Then leaned to 100F rich of peak at full throttle during the run up and left it there.

When I do aerobatics above 3,000 feet I lean the mixture at full throttle to achieve maximum power if I need it.
Then fly aerobatics with power set as required.
In a Super Decathlon this means 2400 RPM, and anything between 22” and 25” for most manoeuvres.

Full rich at high altitudes means less than full power is available.
But I do take the point about monitoring the CHTs, and using a richer mixture for cooling.
Like everything, it’s a compromise.

With the DA40, the mixture will lean a little more as you throttle back on levelling off, but the additional altitude and that pre-set 100F buffer mean it doesn’t go over lean.
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By MichaelP
FLYER Club Member  FLYER Club Member
#1859915
Another thing I do that is different to many is to lean on the ground.
This is taught in Canada!

For the engine runup I set the RPM a little below the required and lean the mixture to see the rise in RPM to that required for the mag check.
The mixture is left slightly rich of peak for the mag check and carb heat check, and this results in the plugs being kept clean.
I hate the business of thrashing an engine on the ground, leaning it to remove lead that was usually caused by someone not knowing how to use the mixture properly.

Then for takeoff ensure it is rich or set as required.
A reds blues check is good to do before commencing the takeoff roll.

On a hot day, short strip, leaning to max rpm might be a good idea if you are confident in doing this. The extra fifty RPM might make all the difference.

To be pre-warned, look at the aircraft exhaust before you fly.
Black may indicate a possible mag drop, rich.
Sand coloured is ideal.
White, a little over leaned.
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By Paul_Sengupta
FLYER Club Member  FLYER Club Member
#1859922
MichaelP wrote:Another thing I do that is different to many is to lean on the ground.
This is taught in Canada!


I never had a plug fouling issue with the Bulldog, ever.

Then Michael insisted I lean on the ground. So I did. And got my first instance of plug fouling. So I gave up on leaning on the ground. Plug fouling not an issue again. So then I decided to lean on the ground again, and got plug fouling again...

Make of that as you will... :D