Can Chinooks auto-rotate?

[amanoffewwords]

These things keep buzing over my house every other day - sometimes as a pair in close formation (never when I have my camera handy of course). A question that's been nagging me (not that I wish to sound fatalistic) but what happens if it should have to shut down an engine - can it auto-rotate on one rotor ?

http://www.ecusb.net/att/chinook.jpg

Just curious,

amofw

[wg13_dummy]

can it auto-rotate on one rotor

No.

I think you may have a misunderstanding as to how the Chinook works. It is twin engined and tandem rotor'd.

But the engines go into a gearbox providing power to both rotors. So, either engine and both engines power the blades (via the gearbox). If one engine fails, the remaining engine automatically takes up the power, feeds power through to the gearbox thus still turning both sets of blades. Even if both engines failed, both sets of blades will still go round under autorotation (so long as you dump the lever quick enough!). I take it you arent a helicopter type of chap?

[amanoffewwords]

I take it you arent a helicopter type of chap?

Nope, I'm in IT but I like the concept of helicopters - if I could start again...

So in essence it's the same principle as a Sea King perhaps? Saw one on TV the other with an engine failure during a rescue but managed to carry on for a while while looking for a suitable landing spot. Take it the other engine was taking some of the load?

Thanks for your prompt and interesting response.

While I'm here, here's another that was buzzing over me:

http://www.ecusb.net/att/police.jpg

Cheers,

amofw

[wg13_dummy]

Take it the other engine was taking some of the load?

If one had failed, the remaining would be taking all the load.

Think about it as a car having two engines going into one gearbox. Using a clever free wheel arrangement, both engines provide power to the gearbox in roughly equal amounts. Power from the gearbox then goes to the wheels (Rotor and tail rotor). If one engine failed, the other needs to provide double the power to keep the wheels turning at the same speed. (A constant rotor speed is what is required).

For example, a Lynx helicopter (twin engined) in the cruise would be showing approx 70% torque (power indication). Thats both needles (one for each engine) showing 70% each. If one engine failed, the failed engine torque needle would fall to zero and the remaining engine torque would effectively rise and read 140%. Because it has now had to double its power to maintain rotor speed (a governor senses a drop in rotor rpm and puts more fuel into the remaining engine to compensate). You are now thinking 'how can you have 140%??' Simple. Think of the '70%' twin engine torque as 35% in real terms. Ie; its working at 35% of its capacity. An engine fails, it then- in real time, is working 70% (so you still have about 30% to go on one engine before you run out of power on that engine). Thats the theory! With me?

It's just a way of making the indications more readable.


While I'm here, here's another that was buzzing over me:

You hadnt just nicked a Cavalier SRi had you??

[Cron]

wg - bear with me I'm a bit dim.

Genuine Q.

Why don't the gauges just show 35% on each when all is normal and 70% on one gauge when delivering double the power...

I think I'm missing something ..

[Heliport]

There's a mine of information on flying Chinooks here (http://www.pprune.org/forums/showthread.php?s=&threadid=163538).

[wg13_dummy]

Because when both engines are working hunky dory, the max normal power is 100%. I think its all about norms and visual perception.

http://img.villagephotos.com/p/2004-12/915521/CXQHR-BXKCF-IIGIC-DSCF0116.JPG

The gauge is showing no1 engine at 95% and no2 at zero (the picture was actually taken on the ground, power/bty off and the gauges read random values). If this was in flight, and you had other indications of an engine failure, you would expect that under twin engine conditions, you would have been pulling about 45-50% Tq.

Most of the other engine related gauges in the Lynx (that have a % value) read plus of 100%. I think it is because 100% is used to interpret the 'norm'. However, the NR and NF (rotor rpm and free power turbine speeds. Pic below) sit together at about 107% in normal flight. Dunno why.

http://img.villagephotos.com/p/2004-12/915521/YBIEK-DSCF0120.JPG

Thats my spin on it. You would need to ask Westland and Rolls Royce for the definitive. ;)

[amanoffewwords]

You hadnt just nicked a Cavalier SRi had you??

Nope :) - that one was taken at Brooklands during an emergency services day show - it came over us on the way to a shout, did a 360 over the event and buzzed off.. 'twas very impressive.

Here's the buzzing off version:

http://www.ecusb.net/att/police1.jpg

[Max Contingency]

amanoffewwords

When ever you witness an impromptu air display it is always good manners to write a short thank you note to the Chief Pilot of the organisation concerned. Be sure to include comments like

"how nice it was that they turned up completely unexpected"

"how the crew amazed the crowd with such skill at low level"

"how you were previously unaware that a rotor craft could be manoeuvred in such extreme ways"


The aircrews will really appreciate it and it is the polite thing to do. Go on... write today.

Oh... by the way, the technical term for "doing a 360" as you put it, is a "loop". Probably best to use the right terminology in your letter.

:E :E :E :E

[diginagain]

At least it wasn't SilsoSid.


Or was it?

[amanoffewwords]

"And how they endagered the safety of the craft by such pointless manoevres which, as a professional bystander I can further testify, compromised the safety of several large aircraft landing at London Heathrow nearby. The untold panic caused to the attending crowd, which included several pregnant women, a whole contigent of soldiers from Chelsea hospital, several Heads of State, Jimmy Saville and other priceless jewels, is an unquestionable reason for dismissing the crew of this valuable tax-payer owned piece of equipement alas piloted by the equivalent of reckless joyriders, nay, pirates of the air." :*

"In short, bloody good show and can't wait to see it again next year." ;) :ok:

Will that do? http://www.planetsmilies.com/smilies/happy/happy0007.gif

[Farmer 1]

Can Chinooks auto-rotate? can it auto-rotate on one rotor ? I don't think this question has been answered.

Not that I've ever flown one, but I guess after losing one of its rotors a Chinook would autorotate about as well as a conventional helicopter would after losing its main rotor.

[Max Contingency]

The first picture shows quite well how a Chinook's blade paths are inter meshed between the two rotor heads. Failure of one rotor will leave the other one flying unmolested for a maximum of 1/3 of an Nr!


It was a synchromesh problem that brought down a North Sea variant in 1986 with considerable loss of life and ultimately led to the North Sea operators switching aircraft types.

Having only had a 'wee shot' in one, I don't claim to be an expert. However one of my more qualified colleagues told me that they have to self impose a 5000 fpm ROC. The reason for this is that at any higher rates of climb and they would not be able to establish an autorotative 'rate of descent flow' through the blades before the Nr decayed to critical levels in the event of an engine or transmission failure.

[Thud_and_Blunder]

From 1989 to 1998 (my time on the beast) the RoC limit was 3000 fpm. We were told it had nowt to do with establishing autorotation and everything to do with a 3-axis "shuffle" the aircraft exhibited in climbs above this rate. As the shuffle couldn't be explained, it was decided to avoid putting the aircraft into that configuration.

[Agaricus bisporus]

Can Chinooks Autorotate?

YES of course they can. They would never be allowed to leave the ground if they could not!

In fact the Chinook autorotates more gently than any other I have flown, even a LongRanger, in fact it floats like a thistledown with, if memory serves, quite lively Nr. The technique at the end of an EOL is quite different from a conventional helo in that there is no check in the sequence; flare, check, level... in fact you just flare it onto the deck on its back wheels rather like an aeroplane using the collective to control the Nr and it tends to float. float float. Wheels on and keep the nose up until it sinks down onto the front gear too, then use the brakes. This uses up a lot of distance. They may autorotate well, but you sure need some space to stop one one on the ground!

I hope after all these years my memory isn't playing tricks - this is how I seem to remember it!

[Arm out the window]

If it takes up so much distance in the run-on, and the descent's so gentle, why not zero speed it!!!



;)

Just a tongue-in-cheek question; I've got about 0.5 in them thanks to a good mate's generosity, so actually know bugger-all about them really!

[MightyGem]

While I'm here, here's another that was buzzing over me:
Chinooks do anything but buzz!!

[outhouse]

Hi amanoffewwords,
Would have really liked to follow the link you included in your post but it seems under the censorship restrictions operating in Qatar it’s banned and blocked!!! (Good advert for Qtel though) By the internet provider. So if it was not porn it must have been considered controversial? Any hints please.

outhouse

[amanoffewwords]

Hello outhouse,

I'm not providing weblinks, just image links and a couple of smilies linked from another site. Is it the latter that you can't see/access?

:confused:

Cheers
amofw

[outhouse]

Hi again amanoffewwords
Thanks for coming back, all I see at the end of your text after the smiley is the standard Qtel censorship page saying the link is blocked as inappropriate. This censorship system is generally used to block porn and other web facilities that whoever controls the system wish to block. So it can control all aspects, including communication systems (and have at this time) on the web, information gathering and the ability to choose how you use the internet.
Total control, still we are in the year 2005 not 1984? Seems to ring a bell regarding a rather good book.

outhouse

[SilsoeSid]

amanoffewwords,

I see you're not from the Midlands!!!!

While I'm here, here's another that was buzzing over me:

http://www.ecusb.net/att/police.jpg

http://bestsmileys.com/lol/1.gif

Max Con is obviously completely ignorant in the operation of Police Helicopters.

"how nice it was that they turned up completely unexpected"
Sorry, we'll give the crims a phone call in future so they can make a getaway!

"how the crew amazed the crowd with such skill at low level"
It's not difficult to impress the unknowing.

"how you were previously unaware that a rotor craft could be manoeuvred in such extreme ways"
Well, I hope you have now learnt from the experience! Join us on our next inner city pursuit!

I'll just get this hook out from my cheek!!http://bestsmileys.com/fishing/1.gif

By the way, it's not a 'loop', but a low speed route reversal!! ;)


wg_13,

Isn't the torque value based on the gearbox limitation and not the engine!!! Even at a 100% TQ, isn't the engine still only working at about 60% of its capability. It's a powerful engine the Gem!

The Nr & Nf needles are set at '107% Nr' as that is the result of the SSL selection after start up. Bonk tuning?
As your pics show, at 120kts the SSL should be adjusted to give 104.8%. Primarily, isn't this to give 104.8%NR in order to reduce airframe vibration and therefore a smoother flight?

[wg13_dummy]

Slow day at the office SS?:rolleyes:

I was attempting to keep it simple mate.:8

If you wish to have a limitations quiz, give me a shout and I'll send one over. :ok: (I'll make sure you get above 60% this time (30% real time)) :E

It's a powerful engine the Gem!
It is but we work out single eng perf based on PPI not gearbox. :ok:

Tell the rest of the bonk tuning criteria then?? C'mon, you'll not get away that easily!

[SilsoeSid]

Slow day at the office SS? Sorry, I don't know, but I can find out for you! Nice of you to ask though.
memo to self: must remember passwords for tax return, then I won't be drawn towards PPRuNe !

As for the quiz, if you can get one here for Friday in time for my OPC that would be great. It would be the correct type I trust!?

Thanks for the results, I didn't know back then that they were that low! With 'Above Average' gradings back then, I wonder what I would get if I scored higher in the MPQ! :p

By the way, I never got the last question on each MPQ paper corect.
What 'was' the telephone number for Aviation Standards at M.Wallop? I do hope the questions are more relevant these days!

we work out single eng perf based on PPI not gearbox. But surely that is still a transmission torque limitation!!!

:confused: ;)
SS

[wg13_dummy]

Papers in the post ;)

But surely that is still a transmission torque limitation!!!

Forgotten how and why we do a PPI already, Sid??

You've still not furnished me with the rest of the bonk setting criteria:rolleyes:

QHI's.....c*"ts the lot of 'em!:E

[Thud_and_Blunder]

wg13,

Cu*ts are useful and pleasant to be around, aren't they?

Sid,

What's a tax return?! :cool:

[SilsoeSid]

It seems then wg, that my memory is fading faster than a cat can lick it a$$!!

When working out the single engine performance figures, I always used to refer to the charts in the back of the ODM. The figures were based on Temp/Press/Wt. At no time did I go to the BATs office and get the latest PPI figures.


These days, we do a PAC (Power Assurance Check) daily, and still when working out the figures for Cat A Ops, do not go and check the daily PAC sheets. The Performance data charts still only needs a combination of Temp/Press/Weight to give me the required values.

Perhaps it is you that doesn't know why you do a PPI in the first place!

:ok:
SS


Thud,

Time for you to come home, the Sun must be getting to you!!

http://bestsmileys.com/expressions/6.gif
SS

[MightyGem]

memo to self: must remember passwords for tax return, then I won't be drawn towards PPRuNe !
Hmmm...shouldn't that have been done by the end of September?

[wg13_dummy]

Power Assurance Check

And that gives you the limitation for the gearbox??

So you wouldnt use the PPI figures from the 700 to establish where to start on the graphs then? Remember all the different graphs relating to 96% PPI (clean etc), 98% PPI (Clean etc), 100% PPI (blah...).

At no time did I go to the BATs office and get the latest PPI figures.

So why do we bother to go out and do a Comp wash/PPI (comp wash to clean comp blades to give us the best state) if it has no bearing on the figures you calculate each sortie? You are suggesting that all engines are the same and produce the same power with the only variables being wt, press, temp?!?!

Surely the performace of the engine (well, since its last PPI) is quite relevent to what we could expect the engine to produce should the other donk stop?

(........1013 set, S+L, CAC out, friction on, ECL brief, 1 back to check 2, pull to 100 %, allow to settle, read OAT, Alt, NR, TQ, T6, NH....blah..... See if its T6, NH or NR droop limited?? REMES calculate to give the errr Power Performance Index so that we can calculate the errr Sin Eng Perf!!) Jog any memories, Sid?


My, you have been away too long!:rolleyes:




When working out the single engine performance figures, I always used to refer to the charts in the back of the ODM. The figures were based on Temp/Press/Wt. At no time did I go to the BATs office and get the latest PPI figures.

'Above average' eh?

:p :p :p

[SilsoeSid]

Hmmm...shouldn't that have been done by the end of September? Not on line!! 30 December 2005



And that gives you the limitation for the gearbox?? No, the PAC is a means for the pilot to determine, prior to take off, that each engine is capable of developing specification power!!
Running parrallel on this thread, Torque limitations are based on the transmission are they not? An engine can easily overtorque a transmission.

I guess when I said, "At no time did I go to the BATs office and get the latest PPI figures" I must have been thinking about that cat licking its a$$. OK, wrong again, sorry! http://bestsmileys.com/foot_in_mouth/1.gif

Now was that anti-icing and cabin heating off or not? What if I have anti-icing off and cabin heating on? AFCS Height hold disengaged or not?

Anyway, I still stand by "When working out the single engine performance figures, I always used to refer to the charts in the back of the ODM. The figures were based on Temp/Press/Wt." But must add, the chart used was decided by the PPI results found in the 700. But isn't that just for finding MinSELF?

Do/Did you feel safe in an aircraft giving you 94% PPI?

'Above average' eh? Everytime! All types!
You never did make PSI did you? Only now by default!

;)
SS

[wg13_dummy]

Apology accepted. ;)

No, the PAC is a means for the pilot to determine, prior to take off, that each engine is capable of developing specification power!!
I guess its a similar thing for most twin engined helis. But with the Lynx it goes for the most current figure as opposed to what the manufacturer spec says it should be? Is the PAC figure a fixed book figure?

Running parrallel on this thread, Torque limitations are based on the transmission are they not? An engine can easily overtorque a transmission.
Yes quite true. Thats why we have a TQ guage. TQ limitations are set in stone. But with a low PPI engine or a 'bad performance day' there is no guarentee that the TQ limit will be reached before the MSELF. Hot & High it will more than likely be the T6 or even the NH.

When working out the single engine performance figures
But isn't that just for finding MinSELF?
Think youve answered your own question.:E


Do/Did you feel safe in an aircraft giving you 94% PPI?

More than. :ok:

As to your last question......YES! Cheeky git!

[SilsoeSid]

One of those weeks, just trying to get the 3rd thing to go wrong, in order to reset everything.
(This thread seems to have done the trick!)
Thanks for the help________wghttp://bestsmileys.com/kick/1.gifSS________

Is the PAC figure a fixed book figure? Opening up to contradiction on different types here, but I think that the PAC way keeps everything 'tidy'. As mentioned before, the PAC ensures that the engines are capable of developing specification power, if they are producing within spec then all is well. It is a check afterall, as opposed to an index figure.

The check is a monitor for power trends and should a trend develop, indicating power loss, then it is investigated further from that point. Rather than having lots of starting pages (moving posts!!), ie 104%, 100%, 94% anti ice & cabin heating on or off, sand filters fitted, etc.

Wouldn't it be easier in the Lynx to work off one set of charts, lets say the 94% figure, and if you have 104% or 100% PPI, bonus! ?
How about also a system where should an engine fail, the cabin heating (and air conditioning!) automatically switches off in order to utilise maximum power from the remaining engine, with an override for use when back in a safe OEI condition?

Maybe on FLynx!!! http://bestsmileys.com/animals/6.gif


SS exits stage left ________________________ http://bestsmileys.com/eek/3.gif

[wg13_dummy]

How about also a system where should an engine fail, the cabin heating (and air conditioning!) automatically switches off in order to utilise maximum power from the remaining engine, with an override for use when back in a safe OEI condition?

It's taken us nearly thirty years to get an intermitant wiper button on one cyclic!!!

There are even more graphs in the back now, Sid. I think the reason why there is so many is firstly, we operate in slightly more varied environments than was the case 15 or so years ago. I'm talking hot. :ok: And secondly, if we just went for the lowest, it may take away a potential landing site when in fact it could be made. Ie. Taking the lowest PPI, 94%, we may come up with a MSELF of 50 knots (not impossible in some theatres). Having a MSELF as high as that would also give us quite a high run on speed (prob over 30kts). This may push us into a decision to go elsewhere if we didnt have a suitable length or surface of area to run on to. You may think 'well, thats working well on the safe side'. True it is but the greater array of figures and calcs means that we can more accuratly get a realistic figure. Ie, more flexibility.

I'm guessing in the civy side, the PAC gives you a greater safety margin hence it being a set figure?


Maybe on FLynx, I'll let you know. :ok: