Chinook & other tandem rotors discussions
As I am a mere Rigga; maybe someone could tell me the difference between Theory of Flight and Principles of Flight?
Have I read the wrong books? Or is it just the wrong language?
Have I read the wrong books? Or is it just the wrong language?
Last edited by Rigga; 21st Aug 2012 at 19:48.
Aha! Looked it up on here:
CH-47 Chinook helicopter - Free Maintenance Manuals, Technical Manuals (TM), Study Guides, and other Publications.
As I thought it was a language thing (to me)
Near the bottom of the page "Theory of Operation". It doesn't explain/show how the double Mixing Unit works, but it does show how the disks move.
CH-47 Chinook helicopter - Free Maintenance Manuals, Technical Manuals (TM), Study Guides, and other Publications.
As I thought it was a language thing (to me)
Near the bottom of the page "Theory of Operation". It doesn't explain/show how the double Mixing Unit works, but it does show how the disks move.
Two questions:
Why is the Chinook so much faster than 'conventional' helicopters ?
Why are there only two wheels at the rear instead of four, surely it would be better to have the opposite arrangement with touchdown on the rear wheels ?
Why is the Chinook so much faster than 'conventional' helicopters ?
Why are there only two wheels at the rear instead of four, surely it would be better to have the opposite arrangement with touchdown on the rear wheels ?
The Chinook originally had two small wheels per landing gear on the rear. When it went to the steerable rear wheel system the Single Wheels were installed in lieu of the double wheels. The much larger tire gives better handling.
The Chinook is fast for several reasons....sheer horsepower is one. Tandem Rotor systems are more efficient than single rotor systems as well.....no loss of power to merely counteract torque of the Main Rotor system.
Third....the top and lower thirds of the fuselage usually have some hydraulic fluid smeared all over them so it is slippery as an eel.
The Chinook is fast for several reasons....sheer horsepower is one. Tandem Rotor systems are more efficient than single rotor systems as well.....no loss of power to merely counteract torque of the Main Rotor system.
Third....the top and lower thirds of the fuselage usually have some hydraulic fluid smeared all over them so it is slippery as an eel.
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the top and lower thirds of the fuselage usually have some hydraulic fluid smeared all over them so it is slippery as an eel
Ah the memories of hot hydraulic fluid, cold hydraulic fluid, pink sticky residue on everything, red hued goat gizzum overing the ramp when doused with rain water made for a skating rink....red tinted flight suits....but she wuz the Queen of the Skies....and still is for kids that could be my Grand Kids.
Except for an EPA waiver....the old girls would require an Environmental Impact Statement for every time they landed somewhere.
Except for an EPA waiver....the old girls would require an Environmental Impact Statement for every time they landed somewhere.
CH-47 Recollections
Now SAS, this is an interesting thread about a truly terrific machine, but can an early ( 1963-1965 ) driver share just a few recollections?
We had three pre-prototypes at the Test Board at Ft Rucker, and they all shared a common hydraulic system reality, which was about an inch of 5606 red stuff being not-so-gently , " shaken, not stirred " by the not inconsequential 3P vibration levels.
Then there was the speed, with a red line set at 130. Fast forward to June 1966 and I started flying a production CH-53A, every one of which was flown to 170KIAS. It held altitude, ( baro or radar ), heading, and attitude, while in the Chinook, one did all that stuff the old fashioned way. My recollection is that it took decades for the CH-47 to catch up, but catch up they did, and in fine style. An effort by Boeing and the Army which we at SA for the most part watched with a little envy, while we limited improvement of the CH-53 to engines, and one gearbox update, until the 53E.
Oh, almost forgot to mention something that surprised me when it happened. After Desert One, and the Army decision to address the special ops requirements in all phases, we saw the development of the MH-60 and MH-47, at 24500 and 54000 lbs respectively. What surprised me was that, at the time they came out, the Hawk had 2-3 kts on the Hook. I cannot comment on what the MH-47 number was based on. I was surprised because at 24000, that Hawk wasn't what one would term.....speedy!
One of my all time favorite helicopter pictures is the CH-47 in Iraq (Afghanistan? ) with it's rear wheels on the roof of a small mountain-side building, while the cockpit is hanging out over the slope to the valley floor. Certainly speaks to the quality of both the aircraft and those indomitable Army pilots.
Thanks,
John
We had three pre-prototypes at the Test Board at Ft Rucker, and they all shared a common hydraulic system reality, which was about an inch of 5606 red stuff being not-so-gently , " shaken, not stirred " by the not inconsequential 3P vibration levels.
Then there was the speed, with a red line set at 130. Fast forward to June 1966 and I started flying a production CH-53A, every one of which was flown to 170KIAS. It held altitude, ( baro or radar ), heading, and attitude, while in the Chinook, one did all that stuff the old fashioned way. My recollection is that it took decades for the CH-47 to catch up, but catch up they did, and in fine style. An effort by Boeing and the Army which we at SA for the most part watched with a little envy, while we limited improvement of the CH-53 to engines, and one gearbox update, until the 53E.
Oh, almost forgot to mention something that surprised me when it happened. After Desert One, and the Army decision to address the special ops requirements in all phases, we saw the development of the MH-60 and MH-47, at 24500 and 54000 lbs respectively. What surprised me was that, at the time they came out, the Hawk had 2-3 kts on the Hook. I cannot comment on what the MH-47 number was based on. I was surprised because at 24000, that Hawk wasn't what one would term.....speedy!
One of my all time favorite helicopter pictures is the CH-47 in Iraq (Afghanistan? ) with it's rear wheels on the roof of a small mountain-side building, while the cockpit is hanging out over the slope to the valley floor. Certainly speaks to the quality of both the aircraft and those indomitable Army pilots.
Thanks,
John
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Last edited by Matari; 16th Feb 2014 at 02:21. Reason: sp
John,
I would say that despite the US Army...the Chinook became a graat helicopter.
The CH-34/CH37 had a great autopilot in the thing....but the next generation of helicopters, the UH-1/CH-47 were not equipped with any autopilot....and the great leap forward in the 47 Series....the C Model only added a Pitch Sas Channel that had some sort of Pitch attitude hold capability.
It was not until the advent of the MH-47 did the Army get its head out its ass and consider the Chinook as being something more than a flying Five Ton Truck.
When the UH-60's arrived....they did so without an Auto-pilot. They had a Flight Director system....but it was hand guided.
It took Aviation becoming its own Branch....and Officers being dedicated Aviators rather than Cannon Cockers, Grunts, and worse of all....Truck Drivers....seconded to Aviation for the Army to really progress and begin to embrace technology to improve the capability of the helicopters.
If you remember the wonderful "Tactical Instrument Rating" created by a General Tolson....I once got to remind him of the limitations of that system in a pickup truck ride from halfway between Charlotte and the Adjutant General's office in Raleigh one rainy, murky, ugly day after we parked a Huey in a cow pasture. Shortly after that we began to get all sorts of slots at the Instrument Flying Course where we obtained "Standard Instrument Ratings".
I would say that despite the US Army...the Chinook became a graat helicopter.
The CH-34/CH37 had a great autopilot in the thing....but the next generation of helicopters, the UH-1/CH-47 were not equipped with any autopilot....and the great leap forward in the 47 Series....the C Model only added a Pitch Sas Channel that had some sort of Pitch attitude hold capability.
It was not until the advent of the MH-47 did the Army get its head out its ass and consider the Chinook as being something more than a flying Five Ton Truck.
When the UH-60's arrived....they did so without an Auto-pilot. They had a Flight Director system....but it was hand guided.
It took Aviation becoming its own Branch....and Officers being dedicated Aviators rather than Cannon Cockers, Grunts, and worse of all....Truck Drivers....seconded to Aviation for the Army to really progress and begin to embrace technology to improve the capability of the helicopters.
If you remember the wonderful "Tactical Instrument Rating" created by a General Tolson....I once got to remind him of the limitations of that system in a pickup truck ride from halfway between Charlotte and the Adjutant General's office in Raleigh one rainy, murky, ugly day after we parked a Huey in a cow pasture. Shortly after that we began to get all sorts of slots at the Instrument Flying Course where we obtained "Standard Instrument Ratings".
CH-47
Yes, SAS, I do recall the Tactical Instrument Rating, which came after I graduated from flt school. We got 6 hrs of hood time in an H-19, but luckily, I had a great mentor at the Test Board and the opportunity to practice instruments in our three Chinooks, and I think I could have passed a checkride, but that was beyond the flexibility of the Army system.
Good thing I did that too, because a few months later, due to a tactical emergency situation, our company commander at Pleiku had us saddle up and he led the company out into the monsoon, where 15 minutes later, all 22 of us were in the clouds executing that inadvertent IFR procedure. That nobody died I always considered as one of the missing Augustinian " Proofs for the Existence of God ". ( Another one being that the Pope wasn't killed when he took a ride in the Phillippine UH-60 ).
Thanks,
John
Good thing I did that too, because a few months later, due to a tactical emergency situation, our company commander at Pleiku had us saddle up and he led the company out into the monsoon, where 15 minutes later, all 22 of us were in the clouds executing that inadvertent IFR procedure. That nobody died I always considered as one of the missing Augustinian " Proofs for the Existence of God ". ( Another one being that the Pope wasn't killed when he took a ride in the Phillippine UH-60 ).
Thanks,
John
Remember all those hours practicing a Tactical Figure Eight Instrument Approach.....that no one ever...ever dared try as it was absolutely certain you would get Vertigo or get lost in space in some dark, foggy, nasty place?
Re the photo of the Chinook landing on the roof top.....it actually is much easier than it appears.
You position the aircraft over the landing spot so the rear wheels hit the right spot.....lower the Thrust Lever....Collective to the Not Knowing....until the gear touch....bring the cyclic back to the "Two Inch Mark" on the Cyclic Stick Position Indicator (actually about two inches aft cyclic or so....) then simply maintain pitch attitude with the Thrust Lever and yaw control using pedals.....a piece of cake as it replicates the takeoff from the ground maneuver where you do exactly the same thing in reverse.
We used to ground taxi using that method to include backing up....kinda like making Jumbo dance at the Circus....it happens slowly and with some good delay between inputs and outcomes.
The only trick to the landing is if you are sitting out over the wide, wide World on a mountain top or atop a cliff....and then as you cannot see behind you to know where you are relative to the ground....it can get a bit interesting....but that is why you have to trust and rely upon the Crew in the back to help you out by talking you down.
Re the photo of the Chinook landing on the roof top.....it actually is much easier than it appears.
You position the aircraft over the landing spot so the rear wheels hit the right spot.....lower the Thrust Lever....Collective to the Not Knowing....until the gear touch....bring the cyclic back to the "Two Inch Mark" on the Cyclic Stick Position Indicator (actually about two inches aft cyclic or so....) then simply maintain pitch attitude with the Thrust Lever and yaw control using pedals.....a piece of cake as it replicates the takeoff from the ground maneuver where you do exactly the same thing in reverse.
We used to ground taxi using that method to include backing up....kinda like making Jumbo dance at the Circus....it happens slowly and with some good delay between inputs and outcomes.
The only trick to the landing is if you are sitting out over the wide, wide World on a mountain top or atop a cliff....and then as you cannot see behind you to know where you are relative to the ground....it can get a bit interesting....but that is why you have to trust and rely upon the Crew in the back to help you out by talking you down.
Last edited by SASless; 30th Aug 2012 at 18:53.
Reality Check
SAS: Tactical Instrument Approaches? In an H-19 with a 2.5 inch, pull to cage attitude indicator and a 6 inch diamer compass card? The 6 hours was spent trying to keep the greasy side down!
This is way off the CH-47 thread axis, but in 1964 I had to ferry an Army H-19 from the West Coast back to Alabama, and got stuck at the San Diego Coast Guard station, where they flew their H-19's IFR. But their instrument panel and radio/nav equipment was far different than what I had. In fact the USCG pilots seemed to be amazed that anyone would actually operate a machine such as I had.
Thanks,
John
This is way off the CH-47 thread axis, but in 1964 I had to ferry an Army H-19 from the West Coast back to Alabama, and got stuck at the San Diego Coast Guard station, where they flew their H-19's IFR. But their instrument panel and radio/nav equipment was far different than what I had. In fact the USCG pilots seemed to be amazed that anyone would actually operate a machine such as I had.
Thanks,
John
Tactical IFR Rating
SAS or some of the younger guys better answer this as to the details.
All I can add is that beginning in 1966, the new pilots right out of Ft Rucker had this training, and from personal observation, the training in basic instrument flying was very sound. If one had a new kid for a night flight, no moon and iffy weather, and assuming it was ash and trash or something non-adversarial in nature, so to speak, you put the new guy in the right seat and treated the situation as if you had an audio-command auto-pilot. My sense was that it was the basic IFR flight tasks from a standard ticket type of training syllabus, but less the civil nav and approach tasks.
Discussions about this rating tended to be loud and polarized, in my failing memory.
Thanks,
John
All I can add is that beginning in 1966, the new pilots right out of Ft Rucker had this training, and from personal observation, the training in basic instrument flying was very sound. If one had a new kid for a night flight, no moon and iffy weather, and assuming it was ash and trash or something non-adversarial in nature, so to speak, you put the new guy in the right seat and treated the situation as if you had an audio-command auto-pilot. My sense was that it was the basic IFR flight tasks from a standard ticket type of training syllabus, but less the civil nav and approach tasks.
Discussions about this rating tended to be loud and polarized, in my failing memory.
Thanks,
John
The basic difference was the Tac Ticket got no ILS training and very little VOR work but lots of ADF, GCA, Holds, IMC takeoffs from the ground (No outside reference at all)....and standard NDB approaches and lots of Tactical NDB approaches that included NDB and FM Homing Figure 8 approaches.
For the sake of a few hours training on ILS's and a few hours less on the Figure 8 approach....we could have all had Standard Instrument Tickets.
Standard Instrument Ratings were usable in Civilian Airspace....Tactical Instrument Ratings not. In Vietnam did not mean much but once back in real World environments....it meant a huge difference.
The figure 8 approach was one where you did a figure 8 pattern with constant heading segments 15 seconds long after passing overhead the Beacon or the FM radio location (think down to Platoon Level untis using back pack radio's and keying the Mike for you to home to.
You descended all during the approach to arrive at decision height as you approached the beacon or homer transmitter.....200 feet was the minimum as I recall. Visibility was not a factor. Either you could see to land or not....and visual guidance would be assisted by Smoke Grenades, Flares, Flashlights, Zippo lighters or sometimes guys laying on their backs in small holes waving an index finger if it was a really Hot LZ.
I preferred to find the trees....and then home to the location or map read to the place or in extremes do the old "You are getting warmer talk down method".
For the sake of a few hours training on ILS's and a few hours less on the Figure 8 approach....we could have all had Standard Instrument Tickets.
Standard Instrument Ratings were usable in Civilian Airspace....Tactical Instrument Ratings not. In Vietnam did not mean much but once back in real World environments....it meant a huge difference.
The figure 8 approach was one where you did a figure 8 pattern with constant heading segments 15 seconds long after passing overhead the Beacon or the FM radio location (think down to Platoon Level untis using back pack radio's and keying the Mike for you to home to.
You descended all during the approach to arrive at decision height as you approached the beacon or homer transmitter.....200 feet was the minimum as I recall. Visibility was not a factor. Either you could see to land or not....and visual guidance would be assisted by Smoke Grenades, Flares, Flashlights, Zippo lighters or sometimes guys laying on their backs in small holes waving an index finger if it was a really Hot LZ.
I preferred to find the trees....and then home to the location or map read to the place or in extremes do the old "You are getting warmer talk down method".
Thank you John.....but you ruined my evening! Mere sight of the "Ladder" sends shivers down my spine yet today!
They were one of those grand ideas that Engineers come up with that should never make it past the pipe smoke!
By the time you found a clearing big enough to safely use the things.....you could land the Chinook to the ground instead of using the ladders.
Drop the darn things off the Ramp and stick them down into a hole in the Jungle....usually one that had been made by some sort of Explosive device....with all the attendant broken Tree Limbs sticking out in all directions....and odds were you would leave them there as you left.....having cut them away with Bolt Cutters.
The Ladders looked so festive decorating the Trees around the LZ.
Also....imagine the Troops climbing up the darn things...hot, tired, scared, and some rather anti-social locals shooting at them as they clamber up the thing.
All the while....there we were....looking at sure signs we were disturbing folks in the area.
Then for real kicks....do that at night!
People wonder why I drink!
Dropping Para's was always fun.....for us.
Slow right down....just above ETL....with all that rotor down flow pouring down behind the Chinook....very interesting parachute openings to be seen! I am sure I have converted some Heathens to Religion doing that!
Advice to you Para's....always make sure the Pilot knows you mean AGL.....not MSL!
They were one of those grand ideas that Engineers come up with that should never make it past the pipe smoke!
By the time you found a clearing big enough to safely use the things.....you could land the Chinook to the ground instead of using the ladders.
Drop the darn things off the Ramp and stick them down into a hole in the Jungle....usually one that had been made by some sort of Explosive device....with all the attendant broken Tree Limbs sticking out in all directions....and odds were you would leave them there as you left.....having cut them away with Bolt Cutters.
The Ladders looked so festive decorating the Trees around the LZ.
Also....imagine the Troops climbing up the darn things...hot, tired, scared, and some rather anti-social locals shooting at them as they clamber up the thing.
All the while....there we were....looking at sure signs we were disturbing folks in the area.
Then for real kicks....do that at night!
People wonder why I drink!
Dropping Para's was always fun.....for us.
Slow right down....just above ETL....with all that rotor down flow pouring down behind the Chinook....very interesting parachute openings to be seen! I am sure I have converted some Heathens to Religion doing that!
Advice to you Para's....always make sure the Pilot knows you mean AGL.....not MSL!
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Single AFCS on CH47D
I have always wanted to know why is there a 100 kts limitation on the CH47 when operating on single AFCS. Any instructors can enlighten me please?
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That Limitation is similar to many aircraft with two AFCS systems....the airspeed limit might vary but the concept is the same.
In the "A" model with the "sharp" ended Aft Pylon...when you lost SAS the Yaw Divergence could be extreme particularly if in a turn and out of trim to some degree. The subsequent Models with the "Blunt" end to the Aft Pylon were much more docile but still required some attention when SAS was lost.
Supposedly, the Squared off Aft Pylon gave the aerodynamic effect of 31 feet of Tail Fin in yaw stability. It was very noticeably different than the A Model.
The Bell 412 for instance, has a similar limitation re AFCS.
In the early A Models of the Chinook, it was not all that uncommon to hear the Droop Stops pound when "skidding" after the SAS was turned off with no Warning. Usually, an Instructor only did that once in his career and afterwards there was plenty of warning to the Student. Few of us were really Suicidal or that Masochistic to do it on purpose after a really good fright the first time.
In the "A" model with the "sharp" ended Aft Pylon...when you lost SAS the Yaw Divergence could be extreme particularly if in a turn and out of trim to some degree. The subsequent Models with the "Blunt" end to the Aft Pylon were much more docile but still required some attention when SAS was lost.
Supposedly, the Squared off Aft Pylon gave the aerodynamic effect of 31 feet of Tail Fin in yaw stability. It was very noticeably different than the A Model.
The Bell 412 for instance, has a similar limitation re AFCS.
In the early A Models of the Chinook, it was not all that uncommon to hear the Droop Stops pound when "skidding" after the SAS was turned off with no Warning. Usually, an Instructor only did that once in his career and afterwards there was plenty of warning to the Student. Few of us were really Suicidal or that Masochistic to do it on purpose after a really good fright the first time.