RRPM in Auto's with Pedal inputs..

[LostHeliBoy]

Autorotation

add pedal

Left or Right

Does it increase or decrease Rotor rpm?

 

The drive system is a solid state it hopefully keeps a steady RPM. But, increase or decrease the pitch on the tail rotor and what will happen..

 

I've done a bit of research into the topic and will go explore in the machine later

 

I would like to hear about this from some of the others.. thoughts?

 

I'll add my .o2c later as I want to see what replies come this way..

Edited November 14, 2007 by LostHeliBoy

[Sparker]

Increasing AoA on the tail rotor would lower rpm unless a tid bit of power is applied, but I'm confused because you say "in autos" but you say "engine powers it at a hopefully steady RPM"

 

If you decrease AoA on the tail rotor that would leave the engine with extra power as there is now less drag on the tail rotor... thus unless power is decreased the main rotor (maybe both rotors?) would gain speed unless somehow drag is increased on the main rotor, ie collective, blah blah...

 

But if it is in actual autos I don't know.... the drag would have to be equalized between both rotors... ie, if drag is decreased on tail rotor, drag would have to be increased on the main rotor as there is no way to decrease engine power, eh?

 

 

This is mostly an educated guess...

Edited November 13, 2007 by Sparker

[C of G]

The question is not so easily answered, but simply increasing the T/R pitch will decrease the RRPM. Having said that, in autorotation, depending on forward airspeed, each pedal input could actually increase the drag on the t/r either in positive pitch or in negative pitch. depending on the extreme to which you apply the pedal. To take it a bit further, what is driving the rotor in autorotation? It is purely external forces. What is the RRPM referencing? Let's just say it's referencing each time a blade passes the nose. Now, take a zero speed autorotation where the helicopter is descending vertically. If you were to do left pedal turns, the RRPM would decrease, because the nose is now spinning in the direction of blade rotation, and even thought the local blade velocity doesn't change, the reference for the RRPM does, so it artificially decreases the RRPM, but doesn't effect the lift. Same goes for a right pedal turn, and if you were to do a 360 pedal turn in 6 seconds, your rotor would go up about 10 RPM in a right turn, and it would decrease as you stopped the turn. If you were not in a vertical descent, but say a 60 knot auto, the pedal wouldn't have as significant of an impact as the increased parasite drag would once established in a slipping attitude.

[Eric Hunt]

Why would you "stomp on the pedal"??

 

Stay in balance. In an R22, if you are significantly out of balance, the ASI misreads badly, so you will not know if you are at 60kt or 40 kt, it just reads zero.

 

As a theoretical question, it is a waste of brain processing power. As a practical question, forget it. Bad technique.

[clay]

Why would you "stomp on the pedal"??

 

Stay in balance. In an R22, if you are significantly out of balance, the ASI misreads badly, so you will not know if you are at 60kt or 40 kt, it just reads zero.

 

As a theoretical question, it is a waste of brain processing power. As a practical question, forget it. Bad technique.

 

Actually it isnt a waist of brain power, or bad technique. in the right situation, with the right circumstances, it is a needed procedure. if you are going to overshoot your target, you can kick the helicopter out of trim, and it will slow you down. if your out in the middle of the woods and your only clear spot is in front of the chin bubble, i'd sure kick it out of trim to get down to it, instead of over shooting

[lelebebbel]

Actually it isnt a waist of brain power, or bad technique. in the right situation, with the right circumstances, it is a needed procedure. if you are going to overshoot your target, you can kick the helicopter out of trim, and it will slow you down. if your out in the middle of the woods and your only clear spot is in front of the chin bubble, i'd sure kick it out of trim to get down to it, instead of over shooting

i talked to a RHC factory instructor pilot about this, and he told me he would not recommend that at all. It puts a lot of stress on the tailboom and on the tail rotor blades. He let me try it briefly in a practice auto to show me it was not very effective, too.

Also, the same can be achieved by applying aft cyclic, or flying an S turn.

Edited November 15, 2007 by lelebebbel

[LostHeliBoy]

Alright ....

 

Enough ...

 

the original question was about the RRPM in an AUTOROTATION..

 

not about the strength of the tail cone mounting during large out of trim moments.. Robinson has addressed this..

 

The question is not a "waste of time" it is a theoretical exercise..

 

we know that in a hover the addition of left pedal requires more engine power so ignore the Gov. in the R22.. and think Bell47 instead and think

 

---well I just added left pedal and the helicopter is sinking.. hummmm,. The additional load of the pitch that was required to turn this large and ungainly helicopter to the left needed more engine power.... roll on throttle MASH head----

 

I rant a bit when I want to get the point across..

 

-- So take the same theory and apply it to a R22 in an AUTO.. yes the engine is disengaged from the rotor system .. the freewheeling unit is working its heart out and the auto is going SMooth.. I trim the RRPM's will stay nicely in the green with little pilot effort if you have reacted quickly enough and appropratly.. Take the Above experiment in the B47 and apply that to the situation in the R22 and the RRPM's will decrease?

 

C of G had great input and so did sparker after getting over my now corrected typo.. or loss of thought process..

 

 

C of G

but simply increasing the T/R pitch will decrease the RRPM. Having said that, in autorotation, depending on forward airspeed, each pedal input could actually increase the drag on the t/r either in positive pitch or in negative pitch. depending on the extreme to which you apply the pedal.

 

I think he nailed the question but is this the real Why?

[clay]

i talked to a RHC factory instructor pilot about this, and he told me he would not recommend that at all. It puts a lot of stress on the tailboom and on the tail rotor blades. He let me try it briefly in a practice auto to show me it was not very effective, too.

Also, the same can be achieved by applying aft cyclic, or flying an S turn.

 

nevermind... not going to start anything....

Edited November 15, 2007 by clay

[K-38]

That's interesting because when I took the Robinson Safety Course taking the aircraft out of trim in an auto to reduce glide distance was one of the maneuvers I was taught.

[clay]

im glad a robbie guy jumped in and approved that basic maneuvers.