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Fly_Guy

Does Anyone Know The Reason For "maximum Rate Of Climb" In A 407 Or 214?

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Fly_Guy,

 

I can't speak to the 214 but the rate of climb limitation on the 407 is a result of, like you said, cyclic position and it is not an autorotation issue. This is my understanding and best explanation of the issue.

 

During the 407 certification process, one of the tests involved cyclic position during specific phases of flight. There is an allowable range within the full travel range in which the cyclic must remain, think of it as a box within a box. During rates of climb above 2000 FPM, the cyclic had to be moved aft outside the allowed range to maintain level flight and this required a limitation to be imposed.

 

The cause of the aft cyclic input during rates of climb over 2000 FPM is due to a loss of smooth airflow over the horizontal stabilizers. In spite of the leading edge slots in place to maximize the stall angle, the downwash from the rotor system and airflow from such a high climb speed causes the stabilizers to stall. This decrease of downforce produced by the horizontal stabilizers combined with the increased downforce on the forward fuselage causes a nose down pitching and aft cyclic pilot input.

 

Keep in mind that this limitation is measured by the VSI which reads pressure change and not direct airflow over the fuselage.

 

Hope that helps.

 

Correct. Thats the reason straight from Bell. Has nothing to do with autorotation.

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Yes, until your engine quits and you do not have enough aft cyclic to get the nose up before you hit the ground infront of you......most "American" products will pitch nose down if you lower the collective for autorotation(especially the 500) and if your cyclic motion is limited it will be bad. As the loggers pointed out your option is to turn(even with use of pedals) to get the machine around which may be bad as well. I would tend to just fly it within its rate of climb limits knowing the aircraft should do as expected.

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Another question,if all this happens and you have enough altitude to get your airspeed back is this all redundant?And if so how much altitude would be required?

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Correct. Thats the reason straight from Bell. Has nothing to do with autorotation.

 

Funny ... the Bell test pilot told me they had no problems with climbs at over 2000 fpm. Probably just the old liability issue with a fancy explanation to baffle everone.

 

I don't recall any problem with cyclic location at climbs of 6,000 fpm (might have been higher .... the VSI only went to 6 and it was pegged) but maybe I was doing it wrong.

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I just finished 407 refresher and was told it has to do with both items discussed here.Also was told if you have a lot of altitude you may recover control of the ship if you the rotor rpm doesn't get below 85%.Below that you are riding an anvil and you are as scott mcpile would say SCREWED.At excessive climb rates,ie 2000 fpm and up if you loose the donkey and the fins are in bad air you cannot get the nose of the ship to come down and you still will be climbing with the collective bottomed resulting in rotor drop .Also had same response when asked about it by certain folks in the know as per helicopter jim.

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