Quick Cruise Altitude Question

[Peter Grey]

Short meaning under 150-200 NM.

On a flight from KSNA to KSFO you'll most likely reach your optimum cruise altitude.

At 200 NM

200/6 = 33 or FL330

Past FL330 you are quickly going over the optimum cruise of any aircraft (short of military stufff).

This calculates the "climb till you reach TOD" part of the altitude calculation. It doesn't factor in optimum altitude at all. If you reach optimum altitude you level off.

It is cruise altitude in thousands of feet (didn't indicate that).

[Nelson L.]

Ah, ok - see it now. Thanks for the explanation.

[par2005]

Climb wise climbing the extra 10000' costs you 4.2 gallons. However it takes 25 minutes to do so. In that 25 minutes at 2000' you would burn 4 gallons. So it's a wash until you factor in 1 last part the descent. You can either keep 110 kts TAS in the descent (and burn less fuel then you would at 2000') or you can go faster and farther for the same fuel. This means you save fuel with a climb to descent.

Hey Peter,

Could you explain how do you figure out how much it costs you to climb extra 10000' (with the cost of 4.2 gallons) ? I also assume you're using Vy for climbing calculations?


And one more thing - people keep saying that 12500 so high for small pistons. Is it so uncommon to climb to those altitudes with Piper Cherokee or C172/C182 for longer legs in real life?

[Peter Grey]

Could you explain how do you figure out how much it costs you to climb extra 10000' (with the cost of 4.2 gallons) ? I also assume you're using Vy for climbing calculations?

I have access to real world C172 performance charts (as I use to fly the thing daily). So it's taken from the real world climb performance chart. It does assume a Vy climb.

And one more thing - people keep saying that 12500 so high for small pistons. Is it so uncommon to climb to those altitudes with Piper Cherokee or C172/C182 for longer legs in real life?

I don't know why people say that. 12,500 is a little high as it's in the oxygen required range, but I've flown the C172 (and even a C150) at 10,500 and 11,500 on a regular basis. I also operated out of a 5,000' field so it wasn't actually that high above the ground. I used 12,000 as it's the highest cruise chart available for the C172.

Note the official ceiling of a C172 is 14,100.

[par2005]

hm, I thought 12500 is still under oxygen requirements..

Sec. 91.211

Supplemental oxygen.

(a) General. No person may operate a civil aircraft of U.S. registry--
(1) At cabin pressure altitudes above 12,500 feet (MSL) up to and including 14,000 feet (MSL) unless the required minimum flight crew is provided with and uses supplemental oxygen for that part of the flight at those altitudes that is of more than 30 minutes duration;

[Peter Grey]

True, but you need to think about it. Note the rule is pressure alt, not true alt. So if the altimeter is below 29.92 you need it at 12500 true. So its a consideration.