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HeliTorque :: View topic - Secondary Effects of Yaw - Why?
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HeliTorque Forum Index » Flight Dynamics

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Secondary Effects of Yaw - Why? Goto page Previous  1, 2, 3, 4, 5  Next
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animalsticks
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PostPosted: Sun Feb 15, 2009 4:04 pm    Post subject: Reply with quote

i'm just thinking if that is what happened at 70 kts ias that's quite a dangerous thing to do - you would have climbed, rolled left a lot, thrown a huge airflow at the back of the TR disc, the oncoming wind would have caught the underside of the horizontal stabiliser stressing the tail.

Can the R22 take the stresses of flying sideways into a 70 kt wind?
i guess it can if you're still here to write about it - dont think i'll try it though Very Happy good topic
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PostPosted: Sun Feb 15, 2009 4:18 pm    Post subject: Reply with quote

Thats the only way I can see him achieving it. I've never used full left pedal at 70kt in a 22, but I'm not sure you could get it that sideways. Bags not trying.
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PostPosted: Sun Feb 15, 2009 5:34 pm    Post subject: Reply with quote

You can't. The aerodynamic forces on the vertical stab are too much and it'll want to keep you straight. Plus Robinson now states that the R44 should not be flown out of balance deliberately with left pedal, which made filming tasks harder. And flying sideways to the left down a golfcourse at 40kts is not easy!
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PostPosted: Sun Feb 15, 2009 6:39 pm    Post subject: Reply with quote

Interesting topic. On my instructor course part of exercise 4 was to show the effect of applying too much left pedal or right pedal in forward flight. It was only a quick demo to prove that the airspeed indicator does not give a correct indication when completely out of balance but I don't really like doing it for more than a split second - I am aware of the AD regarding flying out of trim for prolonged periods and I can't see it doing the aircraft much good if done too often.

I must admit immediately as you throw in a left pedal input it does seem to roll left, but maybe I'm instinctively making a correction on the cyclic. Next time I'm flying this exercise I'll pay more attention to what my right hand is doing!

I've just looked at the course notes from my instructor course and it does actually say "left pedal, yaws left, rolls left, nose pitches down". I might bring this one up with my FIC instructor when I go up for my LPC next week!

Sarah
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PostPosted: Sun Feb 15, 2009 6:51 pm    Post subject: Reply with quote

If GashJ is reading this, maybe he can put this one to a certain FIE tomorrow...
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PostPosted: Sun Feb 15, 2009 7:35 pm    Post subject: Reply with quote

I agree, he'll give us the right result.
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PostPosted: Mon Feb 16, 2009 11:35 am    Post subject: Reply with quote

Sarah,

Quote:
course notes from my instructor course and it does actually say "left pedal, yaws left, rolls left, nose pitches down


I dusted off my FIC notes and they say the same as yours Smile

PoF was never a strong point but:

Applying left pedal causes aircraft nose to yaw left - No arguements there

Rolls Left - 50KIAS on to the right hand side of the aircraft as the nose goes left could easily have that effect.

Nose pitches down - The horizontal stabiliser on the tail produces a downward force. Remove that airflow by being out of balance, the downward force provided by the tail reduces and the a/c nose willl now tip forwards.

I've always liked to 'Keep it simple', but will wait for a fully techie answer Laughing [/quote]
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PostPosted: Mon Feb 16, 2009 11:52 am    Post subject: Reply with quote

Quote:
Rolls Left - 50KIAS on to the right hand side of the aircraft as the nose goes left could easily have that effect.


Fling - would this effect not roll the aircraft to the right?
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PostPosted: Mon Feb 16, 2009 12:14 pm    Post subject: Reply with quote

FW,

Interesting. Perhaps we had the same FIC instructor Laughing Laughing

Anyway, it's always rolled left for me at around 60kts with enough left pedal to throw the ball completely out to the right. Have the day off today so can't test the theory but next time...

Sarah
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PostPosted: Mon Feb 16, 2009 12:27 pm    Post subject: Reply with quote

WG, does it roll left only momentarily and then settle into a right roll?
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PostPosted: Mon Feb 16, 2009 12:30 pm    Post subject: Reply with quote

HW,

My FIC notes say different. Although like I said PoF was never a strong point.

As an aside I can give you a new definition of confusion. Five onshore IFR pilots (including an FIE) all discussing what will happen if left pedal is applied in forward flight Very Happy

We're agreeing on the nose left, nose pitches down. Now it's just the debate over which way the aircraft rolls. At this rate we'll be checking in the 109 when we next fly Rolling Eyes
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PostPosted: Mon Feb 16, 2009 12:40 pm    Post subject: Reply with quote

Just had second-hand word from a very senior FIE, and I'm havig to retreat at the moment.
He says it will roll left on application of left pedal by design. ie it must do this to pass certification. The reason is that there is more surface area above the C of G than below. I have no more details on it than that.

This said, it must be transitive other wise the ball would go left...

If it is transitive, then its a mixture of the above and flapback. The reason the ball would move right instantaneously would be the decelleration forcing the ball over, then does the fusilage settle over right?

Still open to arguments here.
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PostPosted: Mon Feb 16, 2009 12:41 pm    Post subject: Reply with quote

Hahaha! I'd like to be a fly on your crewroom wall FW. Laughing Laughing

I guess as experienced pilots we don't even think about this anymore as it's not something we deliberately do in normal flight. As I say to the students exercise 4 is not about how we intend to fly a helicopter, it's merely a demo of the "effects" of the controls and once they've seen the effects happening they proceed to flying the helicopter "properly" and probably forget about some of the less significant effects.

Now, what about rotor-rookie's other question...?

Quote:
While we're on the subject, what is the reason for the nose trying to come up as you increase power in forward flight? Is it that there's more flapback with more pitch on the blades, or is it the downwash pushing down harder on the tail? Or is there another reason that this happens?


I'm no aerodynamicist - just going on what other people have taught me, but I've actually heard experienced FI's and FIE's discussing this one. Be interesting to hear other people's views!

Sarah
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PostPosted: Mon Feb 16, 2009 12:45 pm    Post subject: Reply with quote

I'm still standing on my disymmetry of lift causing flapback on that one.
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PostPosted: Mon Feb 16, 2009 12:49 pm    Post subject: Reply with quote

Agreed, but I think what he's asking is at a constant speed in forward flight, when you raise the lever, does the nose pitch up because there is more flapback with the higher pitch on the blades or does it pitch up because the amount of downwash pushing down on the horizontal stabiliser has increased.

Perhaps rr could come back and confirm if this is what he meant...

Sarah
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