Chinook & other tandem rotors discussions
Join Date: Dec 2004
Location: UK
Posts: 785
Likes: 0
Received 0 Likes
on
0 Posts
can it auto-rotate on one rotor
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?
'nough said
Join Date: Sep 2002
Location: Raynes Park
Age: 58
Posts: 1,025
Likes: 0
Received 0 Likes
on
0 Posts
I take it you arent a helicopter type of chap?
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:
Cheers,
amofw
Join Date: Dec 2004
Location: UK
Posts: 785
Likes: 0
Received 0 Likes
on
0 Posts
Take it the other engine was taking some of 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:
Join Date: Apr 2000
Location: West Midlands, UK.
Age: 73
Posts: 294
Likes: 0
Received 0 Likes
on
0 Posts
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 ..
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 ..
Join Date: Dec 2004
Location: UK
Posts: 785
Likes: 0
Received 0 Likes
on
0 Posts
Because when both engines are working hunky dory, the max normal power is 100%. I think its all about norms and visual perception.
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.
Thats my spin on it. You would need to ask Westland and Rolls Royce for the definitive.
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.
Thats my spin on it. You would need to ask Westland and Rolls Royce for the definitive.
'nough said
Join Date: Sep 2002
Location: Raynes Park
Age: 58
Posts: 1,025
Likes: 0
Received 0 Likes
on
0 Posts
You hadnt just nicked a Cavalier SRi had you??
- 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:
Join Date: May 2000
Location: uk
Posts: 268
Likes: 0
Received 0 Likes
on
0 Posts
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.
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.
'nough said
Join Date: Sep 2002
Location: Raynes Park
Age: 58
Posts: 1,025
Likes: 0
Received 0 Likes
on
0 Posts
"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." 
Will that do?
"In short, bloody good show and can't wait to see it again next year."
Will that do?
Combine Operations
Join Date: May 2005
Location: U.K.
Posts: 687
Likes: 0
Received 0 Likes
on
0 Posts
Can Chinooks auto-rotate?
can it auto-rotate on one rotor ?
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.
Join Date: May 2000
Location: uk
Posts: 268
Likes: 0
Received 0 Likes
on
0 Posts
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.
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.
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.
Join Date: Dec 1999
Location: UK
Posts: 2,584
Likes: 0
Received 0 Likes
on
0 Posts
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!
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!
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!
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!
Join Date: May 2005
Location: Europe trying to enjoy retirement “YES”
Posts: 372
Likes: 0
Received 0 Likes
on
0 Posts
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
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
'nough said
Join Date: Sep 2002
Location: Raynes Park
Age: 58
Posts: 1,025
Likes: 0
Received 0 Likes
on
0 Posts
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?
Cheers
amofw
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?
Cheers
amofw
Join Date: May 2005
Location: Europe trying to enjoy retirement “YES”
Posts: 372
Likes: 0
Received 0 Likes
on
0 Posts
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
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
Purveyor of Egg Liqueur to Lucifer
amanoffewwords,
I see you're not from the Midlands!!!!
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!!
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?
I see you're not from the Midlands!!!!
While I'm here, here's another that was buzzing over me:
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!!
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?