Author Topic: Heavier vs Lighter TOP SPEED (Read 519 times)

MANDOBLE · « **on:** April 05, 2002, 06:26:57 PM »

Why here a lighter (less fuel) D9 has a faster TOP level speed than a heavier one? A miracle?
Probably it is even true for all the planeset...

Please, dont tell me that a 420 mph your 2100 HPs are used to keep your plane flying against the gravity, and so the lighter one has more power to fight against drag ...

Tac · « **Reply #1 on:** April 05, 2002, 06:37:49 PM »

inertia?

MANDOBLE · « **Reply #2 on:** April 05, 2002, 06:41:44 PM »

favouring the lighter airplane????

Sikboy · « **Reply #3 on:** April 05, 2002, 06:45:47 PM »

http://www.aero.upm.es/es/servicios_generales/jefatura_estudios/jefest.html

If you have some time and money.

-Sikboy

FDutchmn · « **Reply #4 on:** April 05, 2002, 06:46:49 PM »

Forward motion of the plane gives the lift. Assuming that the two planes you say are in level flight, both planes have the same power but the heavier plane has more drag because it would need more lift to keep it in the air. Isn't it not?

Citabria · « **Reply #5 on:** April 05, 2002, 06:52:05 PM »

if your not sure what your talking about, consider for a minute that maybe HiTech knows more about this stuff than you, me and a lot of other people that fly aces high.

MANDOBLE · « **Reply #6 on:** April 05, 2002, 07:06:50 PM »

That is true for low speeds, but for 500 mph your lift is much greater than your weight. You may stop your engine (0 Hp), center your controls. and your plane will start climbing for a while.
At these speeds you need to counteract your lift with your elevators to keep flying at level. The heavier plane will need to compensate less than the lighter one, that should mean more drag from the controls of the lighter plane to keep flying at level. At the end that may imply a slower top speed.

All these considering that less fuel doesn't imply a redistribution of the weight in reference with the CG.

Sikboy · « **Reply #7 on:** April 05, 2002, 08:33:08 PM »

If you wanted some travel, you could come over here (in case you didn't want to stay in Madrid).

http://web.mit.edu/aeroastro/www/academics/undergraduate/degrees.html

Just trying to help

-Sikboy

ra · « **Reply #8 on:** April 05, 2002, 08:44:05 PM »

<>

For all speeds your weight is equal to your lift in level flight. If the plane is heavier it requires more lift, so more drag at any speed.

ra

Tac · « **Reply #9 on:** April 05, 2002, 08:49:52 PM »

"favouring the lighter airplane????"

doh, understood yer post the other way around.

Karnak · « **Reply #10 on:** April 05, 2002, 10:37:16 PM »

Citabria and Ra explain it as I understand it.

It makes sense to me.

ccvi · « **Reply #11 on:** April 06, 2002, 07:01:34 AM »

Instead of visiting expensive courses it might be enough to read a book

See How It Flies

MANDOBLE · « **Reply #12 on:** April 06, 2002, 08:23:50 AM »

Quote

Originally posted by ra
[BFor all speeds your weight is equal to your lift in level flight. If the plane is heavier it requires more lift, so more drag at any speed.[/B]

Lets suppose we have a plane with 75% of fuel flying at 450 mph and needing 2 degrees elevator down to keep flying straight and level and the same type of plane with 50% of fuel needing 7 degrees elevator down to keep flying straight and level at that speed. Which one is, normally, suffering more drag?

john9001 · « **Reply #13 on:** April 06, 2002, 08:51:32 AM »

i would say they both need to adjust their trim

if you need 7 deg DOWN elevator to fly level you got something wrong, (unless your flying upside down)

2Late4U · « **Reply #14 on:** April 06, 2002, 09:09:21 AM »

Its not that hard to understand

The heavier an object the more lift is required to maintain a given altitude. No wing is 100% efficient, and so the more lift, the more drag, more drag is less speed. Now of course the acceleration of a hevier object is reduced, but no matter how long you wait, a hevier plane will not be a fast as a lighter one in level flight (or climbing of course).