Bell 47G - Transfer of Power???

Fx51LP308

Fx51LP308

Major Hide Member
Full Member
Minuteman
    • Apr 8, 2021
    2,361
    3,582
    Tampa Bay, FL
    #1
    For those of you that may have some familiarity with classic Helicopters, I have a question. Re: the Bell 47 (any of the series but "G" in particular - the one featured in the M*A*S*H TV Show), I am aware that it was powered by an internal combustion engine. But how did the torque produced by that engine transfer to the rotor group? For most modern day helicopters (and, including some of the classic Viet-Nam era choppers like the UH-1H Huey), they were Turboshaft Jet Engines where the compressed air produced by the engine feeds the main shaft. For the 47G, I can't imagine a "direct gear" assembly (even with a reduction gear). Perhaps the engine fed a hydraulic pump which, in turn, fed the rotor group?

    Just curious....
     
    #2
    Your understanding of modern helicopter powertrain is incorrect - they mechanically drive the rotors from the output shaft of the turbine engine by using several "passes" of gears with a substantial overall reduction ratio:


    HELICOPTER ACCESSORY GEARBOXES ...THEY GET NO RESPECT | helicoptermaintenancemagazine.com

    helicoptermaintenancemagazine.com helicoptermaintenancemagazine.com

    Piston-driven helicopters generally worked the same way.

    Helicopters are far too sensitive to weight and efficiency for there to be any complexity with regards to energy conversion.
     
    • Like
    Reactions: DuneBoer, Cody S, Keith E. and 1 other person
    #3
    I found some info here: https://www.heli-archive.ch/en/helicopters/in-depth-articles/bell-47g3b-1


    "A two blade tail rotor is installed at the aft end of the tail boom, and is driven by an auxiliary shaft connected to the freewheeling side of the transmission. The upper side of the tail boom supports the tail rotor drive shaft. An aluminium alloy, tubular type rotor guard, is installed to protect the tail rotor blades, and acts as a personnel guard. The main and tail rotor blades are of all metal construction.
    The hydraulic system feeds the boost unit, which is incorporated in the cyclic pitch controls, and the turbocharger automatic control device. The system consists of a reservoir, engine driven pump, two power cylinders with irreversible valves, waste gate control, valves, filter and lines."
     
    #5
    E. Bryant said:
    Your understanding of modern helicopter powertrain is incorrect - they mechanically drive the rotors from the output shaft of the turbine engine by using several "passes" of gears with a substantial overall reduction ratio:


    HELICOPTER ACCESSORY GEARBOXES ...THEY GET NO RESPECT | helicoptermaintenancemagazine.com

    helicoptermaintenancemagazine.com helicoptermaintenancemagazine.com

    Piston-driven helicopters generally worked the same way.

    Helicopters are far too sensitive to weight and efficiency for there to be any complexity with regards to energy conversion.
    Click to expand...

    OK. Is there a "clutch" associated with those MGB/transmission boxes that doesn't engage the rotors until the engine is up to a certain N1? When I see a modern helicopter start, the main rotor (if not also the tail rotor) won't begin rotations until after a certain N1 is reached. And it doesn't have to mean that the engines are "lit" yet. Just that a certain N1 is reached and it will start to rotate. Is the reduction gear multistaged (meaning it switches between different reduction ratios as the engine increases N1? I can't believe there's a complete "direct" connection because I can't imagine how the engine could start if it were.

    I gather then that, as you say, piston engines worked the same, so I'd imagine a "clutch/reduction gear box" doing something similar.
     
    #6
    In the case of the 47, the engine is mounted vertically and torque is transferred via centrifugal clutch, freewheeling unit, and 2 stage planetary transmission. The centrifugal clutch allows the engine to start and idle without the added load of the gearbox and rotors.

    Most piston engine powered helicopters use a similar arrangement of a clutch, freewheeling unit, and transmission to transfer the torque from the engine and also reduce the RPM of the engine to an acceptable range for the rotors. Depending on design and manufacturer, sometimes a belt system does a portion of the reduction and also takes the place of the clutch (in the Robinson R22 & R44 for example, belt tension is relieved to decouple the engine from the drive shaft and transmission for engine startup, and the freewheeling unit is in the upper pulley sheave.)

    Some large piston engine helicopters like the Sikorsky H34 / S58 use a hydromechanical clutch in conjunction with a freewheeling unit linking the engine to the transmission; the fluid coupling allows the engine start and run while decoupled from the transmission and rotors, and the fluid coupling also allows smooth acceleration of the rotor up to engaging speed, at which point the mechanical portion of the clutch engages and directly couples the engine to the transmission.
     
    • Like
    Reactions: Fx51LP308, E. Bryant, Baron23 and 1 other person
    #7
    IMG_6493.jpeg
     
    • Like
    Reactions: Jscb1b
    #8
    Bell 47G

    When originally introduced, the rotor system was aluminum skin over wood, later was all metal.

    Now we use rohacell and honeycomb cores covered by carbon fiber composite or fiberglass composite.

    I can remember the old hands talking about stacking the wooden blocks to build these old blades and how much easier it was to build the new metal/metal.

    IMG_5018.png
     
    • Like
    Reactions: Basher
    #9
    Long ago I worked as a A&P for a shop that would overhaul 47's, they were simple reliable and cheap.
    There was also a full fuselage 47J model produced.

    Crazy thing is the wood blades had no service time limit where the aluminum blades had like a 1500 hour limit.
     
    #11
    Basher said:
    “The metal remembers.”
    Click to expand...

    Composites supposedly have an infinite life, but they fatigue and erode, just much less than their metal counterpart. Corrosion is usually the killer of metal rotor systems and of composite systems that have a metal component.

    I have seen alot of weird stuff in 28yrs that was/is not explainable.
     
    #12
    Fx51LP308 said:
    and, including some of the classic Viet-Nam era choppers like the UH-1H Huey), they were Turboshaft Jet Engines where the compressed air produced by the engine feeds the main shaft.
    Click to expand...
    I take expectation over the remark “classic Viet Nam era”. Classic refers to ancient and I, being a Viet Nam era veteran, am somewhat taken aback by being considered ancient. Classic or certainly classy, but definitely not ‘old.’ :D.

    Flew many a mile hanging off the side of those birds. Left LZ Chippewa one evening with SIXTEEN GI’s aboard. Thought the pilot was going to have a heart attack. I nearly had a heart attack seeing just how close that skid came to the wire as we struggled to get aloft. One of those times when my life nearly came to an end. Good man flying that bird though. Like to think when I got my Private, I was a tenth as good as he was.

    Nothing better than the sound of a Huey coming to pick us up, bringing a hot meal, flying as a nighthawk, or maybe my all time favorite the Viet Nam Era Cobra.
     
    • Like
    Reactions: Darryle
    #14
    Dead Eye Dick said:
    Nothing better than the sound of a Huey coming to pick us up, bringing a hot meal, flying as a nighthawk, or maybe my all time favorite the Viet Nam Era Cobra.
    Click to expand...

    I'm curious about that "sound of a Huey." Do you find that particular sound to be something that might be a bit problematic for your fellow veterans that are suffering from Viet-Nam era PTSD? Believe it or not, my HS football team would often play in a large field, and one of my fellow alumni was wealthy enough to come to the games in his own Sikorsky S76 (this was in the 90s). He was kind enough to land it near the field, close enough to let it be used for medivac purposes if need be (and, thankfully, it never was).

    But I often wonder what might happen if he had a refurbished Huey instead of an S76. Given the number of Viet-Nam era vets that attended the games as alumni, would the use of that Huey for such a purpose be a problem for some vets PTSD wise? That said, I do see a lot of vets that are still flying give rides to various groups of citizens as a demonstration of what it was like to fly in one. So that's a good sign, I guess.





     
    Last edited:
    #15
    Fx51LP308 said:
    I'm curious about that "sound of a Huey." Do you find that particular sound to be something that might be a bit problematic for your fellow veterans that are suffering from Viet-Nam era PTSD?
    Click to expand...
    The sound of a Huey is the most relaxing sound a vet can hear. It means safety. It means going back to the rear with hot chow, a actual cot that is much like a bed, it means a shower, it means a cold beer from the PX (depending how big the rear area is) it means going home.

    We love that Huey, that night hawk, that Cobra.
     
    • Like
    Reactions: Fx51LP308 and UKDslayer
    #16
    10 years too young at the time in the 60's for Viet Nam but remember warm summer nights in Whitt TX at granddaddy's farm watching the pilots train at an airfield that abutted his farm. Would lay on the cool flat sheets taking it all in feeling amazed and safe. He'd leave at 0400 to drive transport busses and fuel helicopters at Ft Wolters. The pilots would hover over his pecan trees for him when they were ready for picking to bring in the crop. At 65, I now see those days as irreplaceable and special.
    God's blessings on those pilots and the troops they carried.
     
    Last edited:
    • Like
    Reactions: Baron23
    #17
    Dead Eye Dick said:
    I take expectation over the remark “classic Viet Nam era”. Classic refers to ancient and I, being a Viet Nam era veteran, am somewhat taken aback by being considered ancient. Classic or certainly classy, but definitely not ‘old.’ :D.

    Flew many a mile hanging off the side of those birds. Left LZ Chippewa one evening with SIXTEEN GI’s aboard. Thought the pilot was going to have a heart attack. I nearly had a heart attack seeing just how close that skid came to the wire as we struggled to get aloft. One of those times when my life nearly came to an end. Good man flying that bird though. Like to think when I got my Private, I was a tenth as good as he was.

    Nothing better than the sound of a Huey coming to pick us up, bringing a hot meal, flying as a nighthawk, or maybe my all time favorite the Viet Nam Era Cobra.
    Click to expand...

    Thank you for your service sir!

    Friends, Coworker's and Extended family served in VN, all said they came by the name slick legitimately, especially if you were being evac'd and tossed in on a hot LZ, you'd mostly slide out the other side if there wasn't someone or something to stop you.
     
    • Like
    Reactions: Dead Eye Dick
    You must log in or register to reply here.

    Similar threads

    gr8fuldoug
    New Products Intel from Camera Land
    Replies
    3
    Views
    1K
    Brettdec
    B
    P
    Maggie’s Combat and Chivalry in the War-Torn Skies of World War II
    Replies
    4
    Views
    1K
    aur0ra145
    aur0ra145
    V
    John McPhee Aerial Marksmanship - June 2012 - MT
    Replies
    0
    Views
    636
    va_dinger
    V
    V
    John McPhee Aerial Marksmanship - Oct 2012 - MT
    Replies
    0
    Views
    635
    va_dinger
    V
    sinister
    Sports Illustrated at Camp Perry
    Replies
    9
    Views
    2K
    NativeCraft
    N
    Top Bottom
    Back
    Home
    Forums
    Merch
    Alerts