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Why no lower than 57 kts in moderate+ turbulence?

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Why no lower than 57 kts in moderate+ turbulence?

Old 12th Dec 2012, 22:04
  #21 (permalink)  
 
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Perhaps you should read this. Note that it refers to a flight envelope least likely to induce mast bumping and Main Rotor stall (well in their opinion anyway - where that opinion originates I have no idea) and also note that your manual refers the limitation to a pilot of less than 200 hours experience with 50 on type and has not completed certain awareness training.

The rest of us who have to operate in that environment (moderate turbulence) for all day every now and then, usually work out how to do it safely as we often have to go slow to shift recalcitrant cattle and surprisingly, land occasionally for a refuel and a pee.

This answer from Soave Pilot would have sufficed.
Because that is the airspeed it is most stable at.
In the meantime should you suddenly encounter moderate turbulence, please don't suddenly lower the collective and or suddenly move the cyclic aft.

Cheers maayte
tet
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Old 13th Dec 2012, 06:32
  #22 (permalink)  
 
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JB77UK,
Re-read the answer you were given again, and see if it still makes sense. How can 57 kts be the minimum speed at 10,000 ft if it is the Vne? The inference is you must fly above Vne (as crab highlights.) The logic in the answer is flawed - I suggest you e-mail RHC directly (then post their reply here )
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Old 13th Dec 2012, 21:24
  #23 (permalink)  
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@212Man - logic...

Hey 212Man, I see what you are saying and why it may seem that way, but I let me try to explain why I still think it is right.

Firstly - lets be very clear - this is JUST talking about why the number is 57 knots - this is not a discussion on if you should be flying at 10,000 ft at 30C or what you or I do personally when flying in turbulence - this is just about the FAA approved number in 2-15 of the Limitations section of the R22 POH.

So lets run a couple of scenarios:

#1
4,000' PA, 0C
Vne is 102 kts. We are flying along at 100 kts when we come across moderate turbulence - according the POH 2-15 we reduce airspeed to between 60 kts and 71 kts (102 Vne x 0.7).

#2
8,000' PA, 30C
Vne is 69 kts. We are flying along at 65 kts and hit moderate turbulence again - doing the math we should be flying between 60 kts and 48 kts (69 Vne x 0.7) but wait, 48 is lower than 57 kts and the POH section 2-15 says "...but no lower than 57 KIAS..." - so it should be between 57 kts and 60 kts.

#3
10,000 PA, 30C
Vne is 57 kts (the lowest Vne on the chart) so although we may be flying along at 57 kts, we should not go any faster as we would be exceeding limitations and likely soon experience retreating blade stall. Lets say we flying along at 53 kts (best climb speed), trying to get max performance to be able to stay up at 10,000....Now we hit moderate turbulence again (been a bad day for it) and we do the math - between 60 kts and 40 kts (57 Vne x 0.7). 40 kts is lower than the minimum 57 kts mentioned and we shouldn't be going 60kts as that is above Vne, so according to the limitations we should speed up to 57 kts.

Does that make sense as far as number go?

If that still doesn't make sense and you want a better explanation, give Robinson Helicopter a call. I spoke to a guy called Pat Cos (not sure of the spelling).Let us know what you hear.

Like I said this is just a discussion of where the 57 comes from - in reality I don't think I would be trying to fly an R22 at 10,000 at 30 C.

p.s. I am referencing those numbers from the latest R22 POH - available at robinsonheli.com/r22_poh.html
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Old 13th Dec 2012, 23:20
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Yeah I think it's Pat Cox, he's one of the gurus as I understand it.

What did he say?
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Old 13th Dec 2012, 23:48
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Humm...Blade stress, power limit but over all, can it have anything to do with safe min autorotative air speed ..

Can't beleive this...Where's the basic !
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Old 14th Dec 2012, 07:42
  #26 (permalink)  
 
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Hmmmm - and just how accurate is that ASI again? Can you really fly at exactly 57 kts, especially in turbulence? Any gust would take you straight past VNE and most likely into RBS.

Sounds like Robinson need to take a closer look at their advice and reference it to the real world.
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Old 14th Dec 2012, 10:30
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can it have anything to do with safe min autorotative air speed
Nup,
Recommended is 65 knots, not as easy is 53 knots, specially on a hot day and heavy doing a standard - 1 flare.- 2.pitch pull - 3 level and cushion - and fixed attitude, quite safe as low as 35 knots, don't miss the pull. That done in the cool is easier on the nerves

Sounds like Robinson need to take a closer look at their advice and reference it to the real world.
Yup.
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Old 14th Dec 2012, 16:07
  #28 (permalink)  
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Yeah I think we can all agree trying to fly 10,000' at 30C in turbulence is a very dangerous place to be in an R22 - with very tight margins of safe flight.
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