Using Pedals in an AUTO?

[hooked4life]

So I'm studying for Commercial right now and one of the FAA questions I'm having trouble understanding is this:

 

Using left pedal to assist a left turn during an autorotative descent will probably cause the rotor RPM to?

and the correct answer given in the ASA test bank is:

increase and the aircraft nose to pitch down.

 

 

the explanation they give for this is:

 

Use of antitorque pedals to assist or speed the turn causes loss of airspeed and downward pitching of the nose, especially when the left pedal is used.

 

Where does the increase in RPM come in? I thought that using left pedal in an auto would DECREASE RPM...I was under the impression that you're kind of robbing inertia from the Main rotor to power the tail rotor when you use left pedal with out the engine driving the rotors.

I don't really understand the whole concept and was hoping that someone could clarify what exactly is going on in this situation.

[Darren Hughes]

It would depend on how much left pedal you use. If you only use a small amount you are reducing the amount of negative pitch that are on the tail rotor blades needed to offset the torque produced by the in the transmission which is in the opposite to the torque produced by the engine during powered flight and much smaller.

 

If you put in a lot of left pedal you would be going past the "zero thrust produced" point on the tail rotor and will start producing thrust in the direction needed for powered flight. That will then cause a reduction in rotor RPM during the auto.

[Tom22]

Kudos to the FAA for providing a detailed explanation of this aerodynamic phenomenon experienced in an autorotation.

[jaredsega]

Tomorrow morning I will pull the 44 out and report back in 24 HRS!

[r22butters]

The last time I was down at Robinson the instructor had me put in full left pedal during our last auto. The helicopter turned completely sideways, and shortened the glide pretty good. I had my door off, so watching the runway numbers rush straight up at me was a little un-nerving, but wicked cool!

[Little Red 22]

I'm also studying for the CPL written and stumbled over this question. My training has all been in the 22 and 44, with emphasis on staying in trim for all auto entries. Under what circumstances would you use the antitorque pedals in this way?

 

LR22

[500E]

Not flown a 22 but I also understood you were dissuaded from flying out of trim, but it will shorten glide!! appreciably, sometimes it is better to auto to what you can see rather than hope the longer glide will find better ground, if enough hight vertical auto will shorten distance, a lot of pilots laugh when you say vertical auto.

[Trans Lift]

Yeah those left pedal autos are a nice maneuver to practice and are practical too. Really makes a huge difference in the length of the glide. I used to teach them to my commercial students.

 

Just remember to hold the same attitude when "sideways", you don't want to come back around too low with not much airspeed. I found students tended to get fixated on looking down at the spot only, keep an eye on that attitude too!! The ASI won't be indicating an accurate airspeed, if any.

Edited March 14, 2010 by Trans Lift

[Little Red 22]

So if you initiate the auto in trim can you apply left pedal later to shorten the glide?

[Trans Lift]

Yes. It gets windy, especially if you have the doors off. You apply enough pedal pressure until you have reached about 90 degrees left (you should be looking down at the spot through the door). It shortens up the glide dramatically. Just don't forget to scan and keep en eye on your attitude as this will not change.

 

I always initiated the maneuver between 1500 and 2000 feet AGL. You want to be coming back around into trim no later than 600ft, you can do earlier if you judge it necessary to make the spot. Once back into trim, you will see the airspeed indicator coming back up to 55-60kts (300CBi). It will not read accurately during the maneuver.

 

Fun maneuver to do and works well. Good co-ordination practice for students too.

[Inferno]

Its always fun to do with both doors off. Turns the cockpit into a wind tunnel.

 

TBH though, s turns are usually just as effective and easier if you're trying to shorten your glide to make the spot....