Increasing power required with altitude.. what's a good plain english explanation?

I was trying to explain to a non-pilot why increased power is required with
altitude. She said "isn't the air thinner up there so there isn't as much
resistance?" I said "yes, but the plane needs to fly fast enough for the air
over the wings to feel like it does down low. So the speed required goes up
you get higher. More speed need more power."

This didn't really do the trick.

Can someone think of a better way of putting it without resorting to
mathematics and an explanation of IAS and TAS?

TIA

"xerj" wrote in message
...
I was trying to explain to a non-pilot why increased power is required with
altitude. She said "isn't the air thinner up there so there isn't as much
resistance?" I said "yes, but the plane needs to fly fast enough for the
air over the wings to feel like it does down low. So the speed required
goes up you get higher. More speed need more power."

This didn't really do the trick.

Can someone think of a better way of putting it without resorting to
mathematics and an explanation of IAS and TAS?

TIA


There isn't as much air for the prop to grab, so it slips more.

xerj wrote:
Can someone think of a better way of putting it without resorting to
mathematics and an explanation of IAS and TAS?

Just say it is "PFM"...

Or tell her that the squirrels under the cowling can't breathe as well
at high altitudes...

Personally, I prefer to just claim it all is just PFM though...

Here's my attempt at an easy layman explanation: "To stay up, the
plane must push down a certain quantity of air. A plane pushes air
down, by flying forwards. If there is less air, the plane must fly
forwards faster to push down the same total amount of air, so you must
add more power to do so."

On Feb 2, 7:18 am, "James Sleeman" wrote:
Here's my attempt at an easy layman explanation: "To stay up, the
plane must push down a certain quantity of air. A plane pushes air
down, by flying forwards. If there is less air, the plane must fly
forwards faster to push down the same total amount of air, so you must
add more power to do so."

Uhhhhh, I hate to bust anyones balloon, BUT, more throttle at higher
altitude does not mean you are getting more power than you were
getting with less throttle at lower altitude...

denny

Denny writes:

Uhhhhh, I hate to bust anyones balloon, BUT, more throttle at higher
altitude does not mean you are getting more power than you were
getting with less throttle at lower altitude...

Indeed, if you work out the numbers, you'll find that you can fly with
less power at higher altitudes, even though the throttle may be set
higher.

--
Transpose mxsmanic and gmail to reach me by e-mail.

The reason that explanation did not do the trick is because it simply
is not true. You don't need more power at higher altitude. You need
less power (for the same performance) because the air has less
resistance. Your non-pilot was correct.

Think about it. Your engine power (normally aspirated) drops with
altitude. But the airplane moves faster despite the power drop. If you
can maintain constant power (turbo charging), you get better and
better performance with altitude.




On Feb 2, 6:51 am, "xerj" wrote:
I was trying to explain to a non-pilot why increased power is required with
altitude. She said "isn't the air thinner up there so there isn't as much
resistance?" I said "yes, but the plane needs to fly fast enough for the air
over the wings to feel like it does down low. So the speed required goes up
you get higher. More speed need more power."

This didn't really do the trick.

Can someone think of a better way of putting it without resorting to
mathematics and an explanation of IAS and TAS?

TIA

If you
can maintain constant power (turbo charging), you get better and
better performance with altitude.

The TAS will increase, but say you want to hold a specific angle of attack
and its attendant IAS (maybe for range), you will need more power to do that
as you get higher.

On Feb 2, 4:24 pm, "xerj" wrote:
If you
can maintain constant power (turbo charging), you get better and
better performance with altitude.

The TAS will increase, but say you want to hold a specific angle of attack
and its attendant IAS (maybe for range), you will need more power to do that
as you get higher.

That is correct, but that was not your original question.

The TAS will increase, but say you want to hold a specific angle of
attack
and its attendant IAS (maybe for range), you will need more power to do
that
as you get higher.

That is correct, but that was not your original question.

Well, it's related to the original question, I think it's fair to say.