Lift and Speed

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Lift and Speed

Postby Bubblehead » Sat Feb 08, 2014 10:03 pm

I'm no pilot but just an avid simmer. When a passenger jet does a bank, let's say 25 degrees, how much lift if any does it lose and does the pilot have to increase throttle to compensate. My second question is: During final approach when the aircraft is off autopilot, how critical is it to maintain required speed? For example if the required speed is 130 knots, how much plus or minus 130 knots does the pilot have to maintain to execute a safe approach and does it require constant adjustment of the throttle?

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Re: Lift and Speed

Postby wifesaysno » Sat Feb 08, 2014 11:04 pm

When an aircraft bank it does lose lift in proportion to the angle of bank. This gets into vector math a bit, but see the following picture to help you visualize the loss of lift.
Image


It is very critical to maintain proper airspeed during ANY phase of flight. Airspeed and flight attitude (angle of aircraft) are ways you gauge the angle of attack. This angle, AoA, or 'Alpha' as it is commonly called, is the angle the incomming air meets the aircraft. Stalls occur at consistent AoA. AoA being a function of airspeed. Therefore during any phase of flight, it is imperative the pilot operates the aircraft at the proper airspeed. During approach, failure to keep airspeed can result in structural damage to gear/flaps (going to FAST) or worse, falling to fast and slamming into the ground by flying to SLOW. Every aircraft has a list of speeds called 'V Speeds' that mark the upper and lower limits of various components and maneuvers.

To help explain these speeds see the following link.
http://x.palmspringspilots.com/content/view/118/167/

Hope I did not overwhelm you too much with technical stuff! Tried to keep it simple :lol:

Tailwinds,
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Re: Lift and Speed

Postby Bubblehead » Sun Feb 09, 2014 12:16 am

I've had a little bit of math and physics to understand what you were talking about although some of the common terms generally used by pilots I have to research to know what they mean. I'm a retired sub sailor so if you any questions regarding the physics of how subs "fly" under water let me know.
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Re: Lift and Speed

Postby Jetranger » Sun Feb 09, 2014 12:52 am

"Retired Sub Sailor", Yes, I'd like to know :D - I'd like to know Alllll, bout' it :roll: :roll:

but - NOT about Submarines :doh:

but - about "Flying Nuns" ! :shock: :D

See when I Twas growin up as a yung'en , there was this der Flyin' Nun

she'd Fly off roof tops, building to building, anywhere she had some kind of "Magical Lift" to her somehow ??

They even managed to catch her Flying several times and showed it on TV !! :o :o :o

she was dubbed the "Flying Nun" :o

I seen it, myself, it was on TV :D

and since it was on TV - why, it had to been true, I seen it ~ ! :shock: :D

Now, my Questin is, How she do that ???

Quite sure theres some Mathmatics involved somehow, but, I'm not good at Math, bout' like dis here Spellin , and you should see me Flyin' Airplanes !

This all sounds intersrestin' :shock:

a Flyin' Nun, really I seen it on TV ~ !!



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Re: Lift and Speed

Postby expat » Sun Feb 09, 2014 3:47 am

Probably not helpful, but my wife's uncle is an ex USMC F4 pilot. He always said, lift and speed were a perspective thing by the fact if you put enough thrust on a house brick you can get it to fly............and they did........McDonnald Douglas called it the F4 :lol:

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Re: Lift and Speed

Postby C » Sun Feb 09, 2014 8:00 am

In simple terms...

Bubblehead wrote: When a passenger jet does a bank, let's say 25 degrees, how much lift if any does it lose and does the pilot have to increase throttle to compensate.


Yes, but not by very much. As and example, the light piston aircraft I fly regularly, at 30deg AOB (in the cruise @100kt) you'll add about 1"MP on the throttle; at 45deg AOB, about 4"MP; at 60deg and above, you'll need full power! The throttle isn't actually increasing the lift though; that's the job of the elevator, which you are using the increase the AoA/"alpha" of the wing as described by Wahubna. The increase in power is to compensate for the increase in AoA.

My second question is: During final approach when the aircraft is off autopilot, how critical is it to maintain required speed? For example if the required speed is 130 knots, how much plus or minus 130 knots does the pilot have to maintain to execute a safe approach and does it require constant adjustment of the throttle?


Again, from past experience in my former life, on approach you'd generally adjust the approach speed depending on the flap selection. With a early stage of flap you may fly at the threshold speed (Vat) + 20 or 30 kts, then as you select further stages of flap bring that closer to Vat. This often depended on the approach profile, and often flap would be delayed to suit ATC minimum speeds and to reduce the noise footprint (more flap = higher power setting = more noise!).
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Re: Lift and Speed

Postby Bubblehead » Sun Feb 09, 2014 11:35 am

Re: The Flying Nun. That was part of the US "skunk" works in Area 51 so I can't tell you anything other than it was top secret.
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Re: Lift and Speed

Postby Steve M » Sun Feb 09, 2014 6:27 pm

I learned something here, lift doesn't go away in a banked turn , it is overcome by various other forces. 8)
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Re: Lift and Speed

Postby PhantomTweak » Sun Feb 09, 2014 11:11 pm

More precisely, it is shifted into a different direction, relative to gravity, so there is an apparent increase in gravity and/or decrease in lift. The lift is still present in just as great a quantity, just pointed a different way, not straight up. Ie: the vector sum of gravity and lift decreases. :geek:

When we were learning vector analysis in highschool, they used exactly the model Adam did to demonstrate basic vectors. Unfortunately, I was bored stiff, having passed ground school at 14 for my glider liscence, about 2 years before that class, but once we got into higher-order vectors it got to be more fun. :D :D Wish I'd stuck with it, Mathematician is a lot easier on the body than Marine is, and I am one lazy SOB, trust me!! :lol: :sleeping-yellow: :sleeping-yellow:

Have a great night all and may the forces lift you ever higher!

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