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Bell 205 tail-rotor

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Bell 205 tail-rotor

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Old 29th May 2011, 16:21
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Bell 205 tail-rotor

Does anyone know why Bell has made some the 205's with the tail-rotor on the right side of the stabilizer?

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Old 29th May 2011, 18:42
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The switch from pusher to tractor was made to overcome LTE at high DAs (due to the impact of MR downwash on the TR). The switch was introduced on the HH-1H and retained for late-model UH-1Hs (and 205A-1s, as shown in the photo above), plus the Huey II and 210. Fuji-built 204B-2s also used the tractor tail rotor.

I/C
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Old 29th May 2011, 18:51
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Would that be LTA?
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Old 29th May 2011, 21:05
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It was to make better use of the tail rotor - instead of trying to get lift from an aerofoil moving downwards in a downwards-moving airflow, they flipped the whole gearbox to the other side to get an upwards-moving rotor blade in a downwards-moving airflow. A lot more V squared for little effort.

I think they called it the flip-flop tail rotor for a while.
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Old 29th May 2011, 21:55
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Mmmm ....

And 212s and 412s share the same configuration .....
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Old 30th May 2011, 00:52
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Cool! Many thanks for your help
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Old 30th May 2011, 03:10
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How many years after the Bell 47 came out did they figure this out? Bell innovation at its best!
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Old 30th May 2011, 08:07
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Ascend Charlie, if they flip the rotor to the other side one or the other then surely there is still going to be one blade moving up into the down-wash in either case so why does it matter?

With the tail rotor is aft of the disc, is the down-wash going to catch that much of the tail rotor anyway?

What about the effect of the vertical stabiliser on the efficiency of the tail rotor? Is it better to be blowing air onto the stab or sucking air around it? Does it matter if the vortices generated by airflow past the stabiliser are being drawn into the blades or being created on the outside of the stabiliser?
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Old 30th May 2011, 08:27
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Seem to remember they made the same mistake with the early Lynx?
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Old 30th May 2011, 09:05
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And the Hind and the Hip have had flipped tail rotors!!!

It's better to had a pusher tail rotor so that the high pressure air is not impacting on the vertical fin. However, manufacturers sacrificed this when they realised they had to solve problems with a tail rotor where the FRONT tail rotor blade goes down through a downwards flow from the main head. The rear blades are not in the same flow.

It's easier to reuse the same tail rotor and flip the gearbox, rather than redesigning the whole tail rotor and keeping it as a pusher.

The critical bit of flight is left sidewards flight for American turning heads. The tail rotor can get into vortex ring and the foward tail blade up setting helps. Buy Prouty's book off amazon as it explains it much better than me.
 
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Old 30th May 2011, 09:06
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Krypton John - the TR blade that is nearest to the MR is the one that is most affected by the MR down wash and it is this one that needs to be going upwards into the downwash to give max V squared.

As old beefer said, it made a huge difference to the TR effectiveness on the Lynx, from something that would often pirouette at high power to something that can deal with 120 deg per sec and beyond rates of yaw and remain controllable.
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Old 30th May 2011, 09:51
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I flew first flew the Huey with the T/R on the left side and later the Bell 205 A1 with it on the right side. There were absolutely no problems with yaw control in the A1 version at high DA, whereas it was forever a challenge in the Huey.

Also, the A1 basically had a 212 T/R drive train, with rods replacing cables and reducing the chances of various kinds of T/R control failure.

The 205 A1 was, perhaps, my favourite helicopter - flown for 10 years in Oman.
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Old 30th May 2011, 18:24
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KJ,

Check out the 210's with Fin Mods....and compare to the stock Huey.


I nicked this photo from the Northwest Helicopters/Olympia, Washington website.


Last edited by SASless; 31st May 2011 at 03:18.
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Old 30th May 2011, 18:30
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Enstrom did the same thing with the F28A. It started life with the T/R on the R/H of the tail boom and changed to the L/H later on. There are still some Enstroms out there with the R/H gearbox.
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Old 30th May 2011, 21:26
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Ah, I see - the TR is not in a uniform down-wash. Thanks guys.
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Old 31st May 2011, 14:39
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Krypton John - you can see by comparing the 2 photos in the above posts that the TR still rotates anti-clockwise regardless of which side of the pylon it is - that means the rest of the drive train can stay the same whilst the TRGB swaps sides and gives an upward moving forward blade.

Because the tail pylon on the Huey is relatively narrow there is little difference between changing it from a pusher (mounted on the port side) to a puller (mounted on the starboard side).

On other aircraft with wider/bigger pylons, the Tr 'downwash' can act against the pull of a puller/tractor TR or can suffer from pylon blanking in the case of a pusher TR.
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Old 1st Jun 2011, 06:18
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strey,

Don't confuse a 205 with a UH-1 and vice versa.

205A LHS of which they only made about 39. L-11 engine.

205A-1 RHS which makes up probably all of the fleet as they will have been all converted. ~ about 360 aircraft in total. 212 T/R. L-13 engine.

The conjecture on here regarding the whys and wherefores of why it works better is interesting! If air would only move in straight lines like in the classroom and not get tied up in knots as it really does!

Hell even Ray Prouty is not too sure why - Rotor and Wing Article
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Old 1st Jun 2011, 08:29
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RVDT

The 205A-1's at Bristow Duri had the TR on the RHS but they were not 212 TR's. I seem to remember that some later 205's had 212 drive trains but what they were called escapes me.
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Old 1st Jun 2011, 18:48
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@RVDT

I hear you, the question came up when I was at school one day. They have a 205 there which is used for utility work. Then I noticed the tail-rotor issue. Since nobody could give me an answer (not even the guys flying the thing) I engaged this beatiful forum
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Old 2nd Jun 2011, 09:59
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DURI 205A1s

OLD LAE

You may be confusing the field mod removing the cable and chain pitch change mechanism to the 212 push pull rod system. It took quite some time, enough for the BHT Tech Rep to "fall in love". Interesting as well that the first tail boom we chose to modify was SN 002, which was itself a modified tail boom from the 204 series. As I remember, this caused some measuring problems, but was eventually sorted out.
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