Newbie question

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Rneuwirth

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Rneuwirth
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Just started my PPL training, with 8hrs in so far (and loving it).
My question: it would seem that with a heavier weighted plane, sudden movements would increase the angular momentum and stress the wing/fuselage junction more than a similar but lighter loaded aircraft. Why then is the VA higher as the weight goes up?
Thanks in advance.
 
Here's a hint.... inertia. Think about what Va means, and think of acceleration, remembering that G-load is an acceleration load.

Then come back and tell us if you got any new insights.
 
Rneuwirth said:
Just started my PPL training, with 8hrs in so far (and loving it).
My question: it would seem that with a heavier weighted plane, sudden movements would increase the angular momentum and stress the wing/fuselage junction more than a similar but lighter loaded aircraft. Why then is the VA higher as the weight goes up?
Thanks in advance.
Click to expand...

Tim's hint is good. And above, you just stated the key to understanding this.

Think about it this way... if you hit a beach ball (light) and a bowling ball (heavy) with the same amount of upward force with your hand, which one displaces further?

Now, extrapolate that to an airplane getting bumped around by turbulence / up and down drafts. How does increased weight affect the amount the aircraft gets displaced? As the airplane gets lighter, does it get bounced around more? :yesnod: Thus, as we slow down (lower Va with decreased weight) we limit the impact of that displacement on the aircraft structure.

On a road full of potholes, I must drive a smaller car slower than I could drive a bigger truck over that same surface.
 
Troy,

How will I know you when I see you at the airplane graveyard tomorrow? I'm 62, 6' tall, 180 pounds, bald as a cue ball but will probably be wearing a US Army cap.

Doc
 
I'll be with my white-haired father in law, and I'll be wearing a bright blue "I've got plans" homebuilder's t-shirt.
 
I tried the beachball/bowling ball trick and now I have a huge cast on my arm. Shouldn't you include a disclaimer? ;):rofl:

Bob Gardner
 
What color bowling ball did you use? A blue bowling ball is lighter than a green bowling ball right? Isnt that why the sky is blue, and the sky is above the grass?

:goofy:
 
This is a great explanation. I remember asking my instructor about this when I had to list "V-Speeds" on my pre-solo take home quiz and noted that some speeds varied based on things like how much the aircraft weighed at the time.

Thanks,

Kimberly
 
Here's the way I explained it to my last student (who hopefully gets to solo tomorrow)

The airplane stalls at an angle of attack of about 17°. A lightly loaded plane might fly along at a 3° angle of attack at gross Va, which allows 14° of abrupt movement before stall and the unloading of the wings, and therefore a high load factor. A heavily loaded plane might wallow along at 12° angle of attack while at Va and you are unable to put enough abrupt movement in before the wings unload. If you slow down in the lightly loaded plane, you increase your constant angle of attack, and reduce/eliminate the chance of the abrupt movement exceeding the load limits before the wing unloads. That's why Va goes down with weight.



Note: These numbers were used for illustrative purposes only and may not reflect the true angles of attack at stall, or at cruise.
 
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TangoWhiskey said:
Think about it this way... if you hit a beach ball (light) and a bowling ball (heavy) with the same amount of upward force with your hand, which one displaces further?

Now, extrapolate that to an airplane getting bumped around by turbulence / up and down drafts. How does increased weight affect the amount the aircraft gets displaced? As the airplane gets lighter, does it get bounced around more? :yesnod: Thus, as we slow down (lower Va with decreased weight) we limit the impact of that displacement on the aircraft structure.
Click to expand...

Then why doesn't maximum structural cruising speed (Vno) change with the weight (or mass) of the airplane?

I think the above explanation can cause confusion because it refers to turbulence - not to control movements. Otherwise Vno and Va would be referring to the same thing. In the eyes of design engineers (or the FAA; some concepts originate from them rather than the physics of the situation) they are different values.

I'd post a clarification if I understood the difference myself, but am too lazy/busy to sort through CFR section 23.335 and its related kin. Besides, I'm not an aeronautical engineer and don't know anyone who is.
 
Jim Logajan said:
Then why doesn't maximum structural cruising speed (Vno) change with the weight (or mass) of the airplane?

I think the above explanation can cause confusion because it refers to turbulence - not to control movements. Otherwise Vno and Va would be referring to the same thing. In the eyes of design engineers (or the FAA; some concepts originate from them rather than the physics of the situation) they are different values.

I'd post a clarification if I understood the difference myself, but am too lazy/busy to sort through CFR section 23.335 and its related kin. Besides, I'm not an aeronautical engineer and don't know anyone who is.
Click to expand...

Because Vno is based on things like flutter and resonance, not load factors.
 
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