Bell 412 Tail Rotor Manual Rotation
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Bell 412 Tail Rotor Manual Rotation
Recently I've observed a mechanic manually spinning the 412's tail rotor during a preflight.
I remember eons ago, during my initial helicopter training reading something about the fact
that this procedure puts too much stress on the TR links and shaft, therefore it is a better idea to rotate the Main Rotor instead, to inspect both TR blades.
Is there any specific written documentation or reference for helicopters in general and a Bell 412 in particular?
Many thanks!
I remember eons ago, during my initial helicopter training reading something about the fact
that this procedure puts too much stress on the TR links and shaft, therefore it is a better idea to rotate the Main Rotor instead, to inspect both TR blades.
Is there any specific written documentation or reference for helicopters in general and a Bell 412 in particular?
Many thanks!
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I have not yet seen a chopper that you can't turn the tail blades - with or against direction of rotation - CAREFULLY during a preflight - the ones you can reach anyway.
Obviously not good airmanship to "throw" or violently get the blades going.
Sorry I don't know where or if this is written down.
Obviously not good airmanship to "throw" or violently get the blades going.
Sorry I don't know where or if this is written down.
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Years ago when I did my Bell 205/Iroquois course, we were taught to turn the t/r blades only in the direction of rotation, to avoid turning the generator in the wrong direction, and thus potentially chipping the brushes.
Later, on AS350's there was no limitation on direction of rotation.
I have never heard about damage to linkages(?)
Later, on AS350's there was no limitation on direction of rotation.
I have never heard about damage to linkages(?)
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Well the generator idea wouldnt be valid as its connected to the N1 and when you turn the blades you are only turning N2.
Its always a good idea with the Allison engine series to turn the blades backwards to tie the blades down as it helps clean carbon off the knife edge seals in the turbines, unless its locked up which can happen.
Ive never heard of the idea of not turning the TR, but yeah do it gently.
Its always a good idea with the Allison engine series to turn the blades backwards to tie the blades down as it helps clean carbon off the knife edge seals in the turbines, unless its locked up which can happen.
Ive never heard of the idea of not turning the TR, but yeah do it gently.
as spanner90 said on the Iroquois UH1-H we were told not to turn the rotor in reverse as the xmsn driven generator(only one hyd system gen driven from top fwn of xmsn) had angled brushes and you could damage them if turned backwards, but that is the only helo I've heard about with that , the 205 had 2 hyd systems and the main gen was eng driven.
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The 412 has basicly got the same Tail Rotor & drive shafts as the 212 205 & 204 (yes I know the T/R was on the other side on a 204).
People have been using the T/R to turn the rotors since the Huey entered service & they have had very few T/R failure problems.
There is nothing in the flight manual or the maintenance manual prohibiting this.
However, be gentle when you do.
People have been using the T/R to turn the rotors since the Huey entered service & they have had very few T/R failure problems.
There is nothing in the flight manual or the maintenance manual prohibiting this.
However, be gentle when you do.
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yeah i forgot about that. The "generator" is on the txmsn so yeah if you turned the blades backwards the brushes could be damaged.
But if your generator isnt on the txmsn (and is then a starter/generator) it wouldnt matter which way you turned the blades as its not connected.
We do it all the time on 412s as well
But if your generator isnt on the txmsn (and is then a starter/generator) it wouldnt matter which way you turned the blades as its not connected.
We do it all the time on 412s as well
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Harlem Globe Trotters (H)
I've observed a mechanic manually spinning the 412's tail rotor
All the 412's that I have flown in the offshore role have been on the High Skid option and as a 6'2" midget - I find that I can't reach the bloody thing anyway so need steps to do a thorough pre flight (or rely on the much more highly qualified Engineer to carry that out and rely personally on a thorough visual inspection including checking for cracks i.a.w. the recent Airworthiness Directive)
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Yes I do mean slowly turning, but I want to say that my gut feeling is that it shouldn't be done by pushing on the blade tips, rather as close as possible to the center of rotation (shaft). I can't find any written reference and my gut feelings have been wrong before, therefore this post.
On a totally different topic, it seems to me that the recent AD has been posted as a quick fix for a machine that is not at the top of Bell's priority list.
If the same problem would've developed on a newer series...well, probably a whole different story..
On a totally different topic, it seems to me that the recent AD has been posted as a quick fix for a machine that is not at the top of Bell's priority list.
If the same problem would've developed on a newer series...well, probably a whole different story..
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Iroquois MM, Chap 39, Page 1, Para 3 CAUTION
"The main rotor should not be turned backwards as damage to the main generator brushes may occur."
Interesting to note that this Caution is not in the Ground Handling section of the same manual. I don't have access to a -6, or POH.
Good to know my memory hasn't quite failed yet.
I can't find any other limitations.
As mentioned by others (thanks) this is only relevant for aircraft where the generator is connected to the txmn. Due to this feature, you can still have full electrical power when in engine off auto (landing light for night autos....don't even want to think about that!)
"The main rotor should not be turned backwards as damage to the main generator brushes may occur."
Interesting to note that this Caution is not in the Ground Handling section of the same manual. I don't have access to a -6, or POH.
Good to know my memory hasn't quite failed yet.
I can't find any other limitations.
As mentioned by others (thanks) this is only relevant for aircraft where the generator is connected to the txmn. Due to this feature, you can still have full electrical power when in engine off auto (landing light for night autos....don't even want to think about that!)
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Tail Rotor DoR
Do you know what was wrong with the direction or rotation of the tail rotor on early Huey's which was corrected by simply rotating the TR gearbox so the blades were on the opposite side of the boom?
The forward blade on the UH-1 series went downwards with the main rotor down wash so it wasn't as effective.
Reversing the rotation meant that the forward blade went upwards through the downwash, effectively increasing the airspeed seen over the blade, making the tail rotor for effective.
Changing sides on the tailboom was the easiest way to do this, but it also changed it from a pusher tail rotor into a tractor tail rotor, so instead of sucking dirty air around the fin, it operated in clean air and just had to push it around the fin.
That is my understanding of it anyway.
Reversing the rotation meant that the forward blade went upwards through the downwash, effectively increasing the airspeed seen over the blade, making the tail rotor for effective.
Changing sides on the tailboom was the easiest way to do this, but it also changed it from a pusher tail rotor into a tractor tail rotor, so instead of sucking dirty air around the fin, it operated in clean air and just had to push it around the fin.
That is my understanding of it anyway.
you are correct sir. The most aerodynamically efficient T/R rotation is opposite to the M/R vortex, or, the blade closest to the disk is moving up. The original UH-1 design had it moving the other way. The easy fix was just to rotate the 90 deg G/B to the other side of the fin, which effectively changed the direction of rotation. This "fix" was implemented on the AH-1G (the Cobra used the T/R drive train of the UH-1H) in mid 1970 during "in-country" depot maintenance. The U.S.Army never did the mod to the UH-1 series. Ultimately all of the AH-1 series were modified/manufactured to this configuration with the AH-1S series utilizing the 212 drive train. The tractor (puller) T/R is aerodynamically less efficient than the "pusher", but the change in direction proved to out weigh that inefficiency. With the 206 series, Bell was aware of the concept and got it right at the beginning.
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but I want to say that my gut feeling is that it shouldn't be done by pushing on the blade tips, rather as close as possible to the center of rotation (shaft).
What you will find with the entire Huey series is that when manipulating the tail rotor by hand there is initially some slack before the drive-train begins to rotate. First take-up this slack and then rotate the tail rotor using smooth/even pressure (not jerking it) and rotate the blades to the desired position.
The AGUSTA 139 requires a significant difference in force to rotate the rotor in the direction of rotation as opposed to rotating in the opposite direction. I believe this is caused by back pressure in the hydraulic system.
I would say that where you turn the tail rotor can make a difference. Again in the case of the 139 you are turning the blades with a long lever arm, no centrifugal force to hold the blades in position and driving through the elastomeric bearings.
Practicaly we all turn rotors by hand and gently does it is the way forward.
However being aware of any cautions in the flight/maintence manuals in relation to rotor systems is important e.g the R22 caution not to pull down main rotor blades.
How often do you see aircraft main blades tied down so tightly as to be outside the manufacturers recommendations.
I would say that where you turn the tail rotor can make a difference. Again in the case of the 139 you are turning the blades with a long lever arm, no centrifugal force to hold the blades in position and driving through the elastomeric bearings.
Practicaly we all turn rotors by hand and gently does it is the way forward.
However being aware of any cautions in the flight/maintence manuals in relation to rotor systems is important e.g the R22 caution not to pull down main rotor blades.
How often do you see aircraft main blades tied down so tightly as to be outside the manufacturers recommendations.
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Speaking of blades being tied-down; I remember an occasion, quite a few years ago now, when a pilot started the first engine of a 212 and got it to flight idle before he realised the main rotor was not turning. Not being able to diagnose the problem he shut-down, got out and then noticed that the tail rotor was still tied-down. He then promptly removed the tie-down and proceeded with the flight. No discrepacies with the drive-train were found after his return.
So yes, the drive train is very robust - but as many have commented here - gently does it when turning the main rotor by the tail rotor.
So yes, the drive train is very robust - but as many have commented here - gently does it when turning the main rotor by the tail rotor.
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Practicaly we all turn rotors by hand and gently does it is the way forward.
I am deviating from B412 info here but for the benefit of ericferret,
FYI RE: AW139
Straight from the IETP (Maintenance Manual)
CAUTION
Do not push or pull the tail rotor blades to turn the tail rotor. It is easy to cause damage to the tail rotor blades if you push or pull them. Turn the tail rotor driveshaft or the main rotor to set the tail rotor to the necessary position.
I see the maintenance industry as a whole do this on the AW139...yet it clearly states not to do in the IETP.
Anyway-just for your info
SS
FYI RE: AW139
Straight from the IETP (Maintenance Manual)
CAUTION
Do not push or pull the tail rotor blades to turn the tail rotor. It is easy to cause damage to the tail rotor blades if you push or pull them. Turn the tail rotor driveshaft or the main rotor to set the tail rotor to the necessary position.
I see the maintenance industry as a whole do this on the AW139...yet it clearly states not to do in the IETP.
Anyway-just for your info
SS