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View Full Version : Why no lower than 57 kts in moderate+ turbulence?


JB77UK
9th Dec 2012, 19:53
Hi all,

I understand in moderate+ turbulence we want to reduce airspeed to reduce structural loads, but why do you think in the R22 POH it states 57 kts as the absolute minimum?

R22 POH Limitations Section:
"Adjust forward airspeed to between 60 knots indicated airspeed (KIAS) and 0.7 Vne, but no lower than 57 KIAS, upon inadvertently encountering moderate, severe, or extreme turbulence."

I guess it is probably a performance issue - to be able to maintain best climb maybe, but that number is 53 kts...

Any ideas?

Without understanding more I think I would just aim for 60kts and try to keep the ship level.

Many thanks for your thoughts,

Jay

JohnDixson
9th Dec 2012, 21:02
Suggestion: Call up Robinson, get the test pilots office and ask them. They will know.

Soave_Pilot
10th Dec 2012, 01:02
Because that is the airspeed it is most stable at. :ok:

nz66fan
10th Dec 2012, 01:24
Its because 57kts ias is at the bottom of the power curve, when you encounter severe turbulence its the t/r thrust that tries to roll the helicopter leading to mast bumping (very simplified statement I know). Thus the less power in use equals the less amount of roll which. thats why when you encounter low g, not only do you use the gentle aft cyclic you also lower the collective.

Anthony Supplebottom
10th Dec 2012, 08:09
Because Robinson require operators to do a lot of strange things to keep their products from falling out of the sky!

Hughes500
10th Dec 2012, 08:15
Supple

Oh dear, I hope you have a Kevlar helmet and are about to retire to your trench in the back garden, as you will have a lot of " incoming" from the I love Robbie brigade, good luck:eek:

Anthony Supplebottom
10th Dec 2012, 08:29
Ha ha - let them rain down their abuse, I'm ready!

People don't love Robinsons by choice. They defend it because the helicopter school they went to had nothing else and so they themselves had no choice.

Then, as they gain awareness of the industry they suddenly realise "Oh my God, I've been duped, they're teaching me to fly in a souped-up lawn mower" and so they have no alternative but to defend the heli or to deny that they have ever flown one - most defend it.

So, flying schools all over the world - have pity on your students this Christmastime and buy a decent training helicopter.

I hear they are still producing the Bell 47.

Hughes - now that should attract some flack! :ok: ;)

Hughes500
10th Dec 2012, 08:39
Now I know of a secret nuclear bunker not to far from you:ooh:

nigelh
10th Dec 2012, 09:04
Supplebum ......Now we are all showing our age banging on about 47,s . Do i think it is a great training ship ...Yes . Would i love to have one in the garage just for those summer evening going 50 miles down the road for lunch ...Yes . Most of these guys flying Robbos will never have had the chance to even sit in one and if they did would be all over the place with the throttle . I think the 300 is probably the best now .
Getting back to turbulence in a Robbo .....do you really have to cyclic back and REDUCE collective in low G .....i would have expected to raise collective ....so i would be another Robbo statistic straight away .....

hostile
10th Dec 2012, 11:26
as low is your airspeed, your maneuvers (control movements) increasing and keeping the aicraft stable is harder. So simple, I think. Try it in some flight device in IMC and you know the difference.
:8

JB77UK
10th Dec 2012, 17:58
Thank you all for your input. Now, side-stepping the anti/pro Robbie hijack of the thread (;)) I have been given what I think is the definitive answer to the original question (Why specifically 57 kts?):

The answer was provided by Raven on another forum:

The airspeed you fly in turbulance is a range. 60 is the low point 71.4 (0.7 of 102) is the high point. If 0.7 of any other Vne (remember it goes down with altitude and tempurature) is less than 60, you must go 60. However, at 10,000 feet and 30 degrees, you cannot go 60, because your Vne is 57! Hence the one exception, "no lower than 57".

Learning something new, one post at a time - thanks to Raven :D and all that tried to help answer this one.

nigelh
10th Dec 2012, 18:07
What sane person would go to 10,000 in a R22:eek::eek::eek:

Tailboom
10th Dec 2012, 20:22
I've been there, and auto'd down for an engine off fantastic!!

MartinCh
10th Dec 2012, 23:21
auto from that altitude 'all the way down' somewhere low, the ears must hurt from the sudden pressure change. Make sure you swallow saliva a lot..

Anthony, I'm (so far) pure Robbie pilot and I wish the job market and RELATIVE affordability were otherwise, for people paying from own pocket/inheritance/years of savings, and I'd have gladly jumped to 269/300 instead from the scratch. We work with what we can/have to.

Other than R44 charter/sightseeing, fewer and fewer countries have fresh CPL guys going straight to copilot seat. Then again, 22 time is useful for 44 jobs getting towards turbines.

It's easy to slag off stuff you don't need to use/train/work with and have little to no experience of. I don't bitch about your negativity, I just put things in context. What you 50-60yo+ 'oldies' know about breaking into civvy industry without having rich background, lucky to be in certain countries (at the right time) with 0-CPL cadet schemes for helicopters or going through basic training in the military or similar, NOWADAYS?

ShyTorque
11th Dec 2012, 00:21
I can't help drawing a parallel....

_bIn_ZgHJaE

fadecdegraded
11th Dec 2012, 02:02
I reply to you martinch.

Just because someone is 50/60 years old dosent mean we never had it easy when we were starting out. Just because we have the experience to know a cheap and nasty helicopter when we see one isn't a bad thing either no good getting older if you don't get wiser with it.

Now by the sounds of it you are one of these "young" blokes that want it handed to them on a plate because you have some idea that you are owed it just because.

We learnt in what was around at the time just as you probably have we were just a bit luckier having helicopters that were a bit more robust, just as underpowered as the r22 and maybe even more underpowered.

Anyway point being none of the old hands had it any easier than you in fact probably harder.

Bellrider
11th Dec 2012, 10:03
@<hidden>:{
Best Video ever, parallel R22/normal!
Thanxx!

topendtorque
11th Dec 2012, 10:57
Subtle nigelh, subtle, they will still be working that one out re the collective.

And yes the G5 parked out back with a built in vertical to make it real would be very nice.

I agree, the CBI is probably the most versatile, hardest to hurt yet very handy machine around at the moment, still with a bit of a requirement to test the vacant space between the ear lobes regarding throttle control and some room to move to set up - "things".

JB77UK

Give us a break mate that's all gobbledegook.You seem bent on feinting with a question then supplying the answer which may or may not have substance. For mine, and i have been in just a tad of turbelence around thunderstorms and the like over the years at low level amongst largish hills, you can stick your 57 knots where the monkey put the peanut. Slow right down as nigelh says and get the collective well up at slow airspeed.. Positive - Power - Control.

Martins ch,

Bell 47 G2's had far less power to weight ratio than any marque of the Robinson family and were far far harder to get into translation and out of trouble if one ventured near it.
The trouble is nowadays the blessed Robinson is so easy to fly that qualified, ahem, I mean licensed pilots from them have so much to learn in the real world that they're pretty much useless for a long time.

cheers tet

11th Dec 2012, 14:00
JB - the other reason that the answer you got is flawed is that if your VNE is 57 kts at 10,000 feet and plus 30 - you won't want to be flying at VNE in turbulence! Unless you like RBS that is.

Nigel is right re collective - don't lower it except to slow down.

JB77UK
12th Dec 2012, 19:26
@<hidden>TopEndTorque:

Not sure why the attitude - it was an honest and sincere question. And to be clear all I was asking was "WHY is the number 57 knots mentioned in the R22 POH as the minimum, as opposed to 60, 53, etc" I wasn't talking about what you or anyone else ACTUALLY does in turbulence, I was just hoping the vast cumulative hours of experience and knowledge that comes from the pilots that use this forum might help me find the answer...

I had posted the same question on another forum where Raven5 posted an answer that to me, made perfect sense and answered the question of why 57 kts and so I posted the response - simple as that - I hope that addresses your "You seem bent on feinting with a question then supplying the answer"

As for your accusation of "that's all gobbledegook" and "supplying the answer which may or may not have substance" - I truly thought it was correct, but did say "I have been given what I think is the definitive answer to the original question...". The answer was also confirmed by other posters on other forums.

But to make sure I called Robinson Helicopters in California and they confirmed that is EXACTLY the reason the 57 KIAS is in there. Enough substance for you?

I got to say I come to this forum for respectful advice, so I respectfully quote you TopEndTorque when I say "Give us a break mate!" [insert Australian accent] ;)

topendtorque
12th Dec 2012, 23:04
Perhaps you should read this (http://rgl.faa.gov/Regulatory_and_Guidance_Library%5CrgAD.nsf/0/91BE0874983FB92686256A4D0061449D?OpenDocument). 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. http://images.ibsrv.net/ibsrv/res/src:www.pprune.org/get/images/smilies/thumbs.gifIn 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

212man
13th Dec 2012, 07:32
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 :ok:)

JB77UK
13th Dec 2012, 22:24
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

topendtorque
14th Dec 2012, 00:20
Yeah I think it's Pat Cox, he's one of the gurus as I understand it.

What did he say?

Pendulum Artist
14th Dec 2012, 00:48
Humm...Blade stress, power limit but over all,:ugh: can it have anything to do with safe min autorotative air speed ..:8

Can't beleive this...Where's the basic ! :eek:

14th Dec 2012, 08:42
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.

topendtorque
14th Dec 2012, 11:30
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.

JB77UK
14th Dec 2012, 17:07
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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