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Author Topic: [Released] Cessna 172A  (Read 31180 times)

bomber

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Re: [Released] Cessna 172A
« Reply #45 on: August 10, 2015, 04:23:08 am »

I've a simple question on spinning that I've never asked..

In a clockwise spin,  which wing is trailing?
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FarlanderMiG

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Re: [Released] Cessna 172A
« Reply #46 on: August 10, 2015, 02:22:25 pm »

I believe that would be the inner wing of the spin, the one that is stalled. There's always only one wing that is stalled in a spin, the outer wing is still "flying".
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bomber

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Re: [Released] Cessna 172A
« Reply #47 on: August 10, 2015, 02:45:42 pm »

Nobody attempts to model stall forces, there's some unwritten rule that it's too complicated....

I larf in the face of complication.

That said... half the problem with modelling a stall is trying to understand what the heck is actually happening.. and I'm struggling to find a description of creating a stall that's not 2nd hand.

you fly gliders, yes...... could you talk me through a clockwise stall

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"If anyone ever tells you anything about an aeroplane which is so bloody complicated you can't understand it, take it from me - it's all balls" - R J Mitchell

FarlanderMiG

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Re: [Released] Cessna 172A
« Reply #48 on: August 10, 2015, 03:56:38 pm »

Alright. So a spin happens when a wing drops (looses lift) and the other wing keeps flying "around" the stalled wing. But to get it into a spin in the first place it needs some yawing into the stalled wing. A spin is not something that automatically happens every time you stall. I am able to stall an airplane and still keep the wings level using rudder for the most part. all the controls become very sluggish when you approach stall, and it starts to shake quite alot. but a wing usually stalls from the wing root out (wing root has a higher AoA than the wing-tip.), so you will still have some slight control.

But anyways, If i am going to simulate a spin i'm going to put my nose up (engine to idle if it's an engine aircraft) slowly apply full elevator and when i'm quite slow
i will kick full rudder to the direction i want to spin. I will keep holding full elevator and rudder into the spin until i want to recover. i'm not going to do anything with the ailerons, but if i want to keep the spin longer i will add a bit aileron to the opposite side of the spinning to keep it going. when i want to get out of the spin i put elevator back to neutral, and apply full opposite rudder for the rotation to stop. when the rotation slows down and the nose comes down the aircraft will pick up speed and you end up in a steep dive that you have to recover from before you overspeed (an engined aircraft will most likely not have too much problems with overspeeding).

But in the real world a spin would most likely come when you are in a turn and get too slow. the wing drops, and you already have some rotation to get the spin going.

And yes, scripting a flight model is basically mission impossible. Hope this helps somewhat, and if you have any more questions just tell me :)

( a clockwise and an anti-clockwise stall is basically the same. a clockwise stall in a cessna that has throttle on can be a bit more violent becuase of the torque i would guess.. but if you want more information about that i can ask about it)
« Last Edit: August 10, 2015, 04:00:15 pm by FarlanderMiG »
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bomber

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Re: [Released] Cessna 172A
« Reply #49 on: August 10, 2015, 06:38:14 pm »

Farlander, thanks for the reply, I can't begin to tell you how helpful it's been...

Can I ask you to consider something, with regards your understanding of a stall, and it may sound backwards to you.. It might be that what you've written is genuinely what you believe is happening, you might even have been told this is what's happening by more experienced pilots, or even read it..... But can I ask you to consider that it doesn't quite fit with what it feels like is happening when you personally enter a spin..

I'm quite happy if you say, no Simon my description is how I feel..... or you might say, you know Simon I have had a nagginf feeling that the description doesn't quite tally with how it feels..

And bare in mind it's only for a fraction of a second we're talking about here.

You''ve already explained something to me, like why the Rudder has such a large deflection... say 30 degs left or right, which is massive overkill to what's needed to correct any yawing.

Anyway, just think on the force normal being generated by a wing at hight AoA and the vectors in the X and Z co-ords

Regards

Simon
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"If anyone ever tells you anything about an aeroplane which is so bloody complicated you can't understand it, take it from me - it's all balls" - R J Mitchell

FarlanderMiG

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Re: [Released] Cessna 172A
« Reply #50 on: August 10, 2015, 08:06:27 pm »

Im sorry if there was something i misunderstood... i try my best with my English, but it's not always sufficient.

But what i described was the "procedure" to get a spin in the L-23 and almost any other airplane.

sorry if i misunderstood.

EDIT:

If what you meant to say was that the higher AoA on the inner wing of the spin would create more lift, then that is acually the opposite. The inner wing is stalled out because of the low speed of it and the high AoA it has. it results in lower lift that the outside wing, and more drag than the outside wing.

The best video we've found demonstrating a spin:
« Last Edit: August 10, 2015, 08:39:32 pm by FarlanderMiG »
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FarlanderMiG

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Re: [Released] Cessna 172A
« Reply #51 on: August 10, 2015, 08:52:02 pm »

Im sorry if there was something i misunderstood... i try my best with my English, but it's not always sufficient.

But what i described was the "procedure" to get a spin in the L-23 and almost any other airplane.

sorry if i misunderstood.

EDIT:

If what you meant to say was that the higher AoA on the inner wing of the spin would create more lift, then that is acually the opposite. The inner wing is stalled out because of the low speed of it and the high AoA it has. it results in lower lift than the outside wing, and more drag than the outside wing.

The best video we've found demonstrating a spin:

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JNelson

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Re: [Released] Cessna 172A
« Reply #52 on: August 10, 2015, 08:54:01 pm »

Farlander, thanks for the reply, I can't begin to tell you how helpful it's been...

Can I ask you to consider something, with regards your understanding of a stall, and it may sound backwards to you.. It might be that what you've written is genuinely what you believe is happening, you might even have been told this is what's happening by more experienced pilots, or even read it..... But can I ask you to consider that it doesn't quite fit with what it feels like is happening when you personally enter a spin..

I'm quite happy if you say, no Simon my description is how I feel..... or you might say, you know Simon I have had a nagginf feeling that the description doesn't quite tally with how it feels..

And bare in mind it's only for a fraction of a second we're talking about here.

You''ve already explained something to me, like why the Rudder has such a large deflection... say 30 degs left or right, which is massive overkill to what's needed to correct any yawing.

Anyway, just think on the force normal being generated by a wing at hight AoA and the vectors in the X and Z co-ords

Regards

Simon

What do you mean how it feels?

I can concur with what farlander is saying.

I would recommend looking at some of the testing done by NASA
https://www.youtube.com/user/NasaCRgis
These videos may help with some of your programming.
Aerodynamics are normally extremely complicated and not intuitive.
So good luck! :)
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bomber

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Re: [Released] Cessna 172A
« Reply #53 on: August 11, 2015, 06:22:20 am »

Aerodynamics are normally extremely complicated and not intuitive.

This is what I mean.... that it's not intuitve but that the explaination as above attempts to make it intuitive, and because of that gives a false impression of what's actually happening.... yet is good enough because its all happening in a fraction of a second and a pilot doesn't really need to understand the mechanics of the situation..... just what to do in the situation...

So there's nothing wrong with the above if it helps you get into and out of a stall safely...

The problem comes when attempting to model the forces acting at the moment of spin, within a simulation...

For example of what I mean by mis-conception lets look at a simple case within normal flight.

We want to roll to the right, we apply a bit of right stick, the left aileron goes down the right up... and the left wing will rise and the right drop...

A question...... which wing is generating more force ?

Simon
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"If anyone ever tells you anything about an aeroplane which is so bloody complicated you can't understand it, take it from me - it's all balls" - R J Mitchell

FarlanderMiG

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Re: [Released] Cessna 172A
« Reply #54 on: August 11, 2015, 07:39:35 am »

Ok, i'll try to explain it as best as i can. As far as my training this is how i got it.

When you first apply left stick the the right wing will have aileron down, and the left will have the aileron up. The changes to the wings will be as follows: outboard right will increase AoA, lift and increased drag. inboard right will stay the same. outboard left will decrease lift, and the inboard left will stay the same. This lifts the right wing up and the left wing is pushed down, but at the same time it rotates/yaw the aircraft to the right.

And my understanding is that when the bank is set the outer wing is creating more lift than the inner wing because it's travelling faster. this explains why you need right stick in a left turn to keep the bank angle.

I highly suggest you invest some money into getting a proper book for aerodynamics to tell you about all the details though.

EDIT: I've thought about it for along time now, and what i said about the sustained turn dosen't feel right... i'll see if i can find some other sources than my own flight book.
« Last Edit: August 11, 2015, 08:24:39 am by FarlanderMiG »
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bomber

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Re: [Released] Cessna 172A
« Reply #55 on: August 11, 2015, 08:49:46 am »

Thanks for the reply.... and please understand everyone,  I know sometime I come across as condencending within forums, but please be assured I'm not, and I'm not trying to make anyone look foolish or lose face... I just love these sort of conversations.

I would say that this is a key sentence... "but at the same time it rotates/yaw the aircraft to the right."

If the centre of pressure is behind the CoG then to yaw the plane to the right, the right wing would have to be generating more force...ie more X & Y vectors, which yaw the plane.... but also more Z vector which means more lift on the right wing... which is droping at the time.

Simon...
« Last Edit: August 11, 2015, 12:46:57 pm by bomber »
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"If anyone ever tells you anything about an aeroplane which is so bloody complicated you can't understand it, take it from me - it's all balls" - R J Mitchell

FarlanderMiG

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Re: [Released] Cessna 172A
« Reply #56 on: August 11, 2015, 09:31:47 am »

Alright :P

Anyways, i think i agree with you, but could you specify x,y,z?
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bomber

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Re: [Released] Cessna 172A
« Reply #57 on: August 11, 2015, 09:42:32 am »

X vector +ve towards the nose
Y vector +ve towards the right wing
Z vector +ve downwards

Basic right-hand rule.
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"If anyone ever tells you anything about an aeroplane which is so bloody complicated you can't understand it, take it from me - it's all balls" - R J Mitchell

FarlanderMiG

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Re: [Released] Cessna 172A
« Reply #58 on: August 11, 2015, 10:40:48 am »

But what if im left-handed ;)

Anyway.. thanks for the clarification
Nevermind... re-reading it i now understand what you were saying... at first i thought you meant the left wing in a left roll had the most force...
« Last Edit: August 11, 2015, 11:15:37 am by FarlanderMiG »
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bomber

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Re: [Released] Cessna 172A
« Reply #59 on: August 11, 2015, 11:33:00 am »

Nevermind... re-reading it i now understand what you were saying... at first i thought you meant the left wing in a left roll had the most force...

but that is exactly what I'm saying and is the only thing that meets the requirement that the nose rotates to the left....

Simon

p.s. Can we please stick to ethier rolling to the right or left, swapping like this can lead to confussion, in an already complex situation.
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"If anyone ever tells you anything about an aeroplane which is so bloody complicated you can't understand it, take it from me - it's all balls" - R J Mitchell
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