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I was on the ramp the other day watching an R44 about to leave. As they started up the revs went way high, guess they had the throttle full open. It was only for a second, but it made me wonder what should be done maintenance-wise when this happens.

Is it OK if its for 1 second, in which case how long does the throttle have to be fully open before something should be done?

I know there are startup issues to watch for in turbine engines, is there in piston? ???

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There are issues in over reving any rotating mass.

On start up the oil is not where it should be + as it is cold it does not flow as easily, It will damage rockers, cam. valves etc.and can cause damage that appears later in the life of the engine ! and we dont realy want that to happen in flyte.

If you O\R you should report to maintance at least,

     Remember you could be the next to fly the thing

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Different aircraft have different limitations. For instance on the 300CB, without the rotor engaged you can't exceed 1600rpm, but if you do momentarily exceed it you don't have to do any maintenance unless it got higher than 2000rpm. While in flight the rpm limit is 2700rpm, but you can go as high as 2900rpm without maintenance (inspections). The helicopter flight manual (POH) should list any limitations and the action taken if they are exceeded.
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For the most part, *in-flight* RPM, torque, manifold limitations are to protect the drivetrain.  There's very little you can do to damage an engine before you damage the drivetrain (driveshaft, flex coupling, blades, etc.)  Yeah, there are some exceptions, but "for the most part" the above is true.

 

Starting or ground ops without the rotor engaged, the engine can be easily damage.  Temp damage in turbines, RPM overspeeds in pistons (what 500E said).

 

On the case with the R44, I wouldn't worry about the engine, but I would definately get a close look at the drivebelts on the next preflight or 100hr.  Make sure it didn't burn a flat spot onto them or anything.  If it was just for a second, I highly doubt it would have.  But I always checked the belts VERY closely--that is by far the weakest point in Robinson's drivetrain system.

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Not all 300 have goveners, and when starting it is easy for the student to O\R, especialy if a motor cycle user the natural reaction is to turn the WRONG way to shut down
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At Schweizer's maintenance school they show a movie of an engine overspeed (clutch not engaged), actually it's a slow motion video of the short shaft and the thing starts wobble quite violently, clearly showing the kind of damage that can be done.

 

The red line on the CBi is 1600 RPM and the flight manual specifies that maintenance action is required beyond 2000 RPM.

 

With the Robinson's different engine to rotor drivetrain, the limits I think are different, but don't have the specifics. I know that an R22 that was started with the throttle open required an inspection, but I don't know the RPM it got to. But I can guarantee starting an R44 like you saw, with the throttle open, is a very bad thing, could cause damage and must be inspected.

 

Just a golden habit to have, and one I teach every student, is the moment before you press the starter or turn the key, roll it off into the overtravel. With that habit, you can't go wrong.

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Just a golden habit to have, and one I teach every student, is the moment before you press the starter or turn the key, roll it off into the overtravel. With that habit, you can't go wrong.

Absolutely......That goes for any helicopter.

 

If you start a 206L in flight idle position or above, you WILL cook the engine (no if's, and's, or but's).  You cannot close the throttle fast enough.  It's about a $200G+ screw up in under a second.

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For the carburated Robinson or Schweizer, roll it into detent, then "relax" it to idle, just making sure the throttle remains at idle. If you are holding it in the detent position, you might have trouble starting a cold engine. The detent position often nets you a very low idle setting, plus if you are holding against the spring it can be challenging to give the little throttle "blip" you sometimes have to (you may well overshoot and hence overspeed).

 

FI ships (R44-II, 300C/CBi) often require that the throttle be "cracked" slightly to get them started after priming - you have to be vigilant when starting to close the throttle to idle as soon as the engine gets running. In certain circumstances it can be a real coordination drill to run the throttle while pushing in the mixture knob - easy to get crossed up!

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  • 10 months later...
  • 2 years later...

Ok so finally someone talks a bit about the real issue, Yes overspeed is a issue.

But starting with the throttle open dosent mean a overspeed. the main thing is how fast the engine accelerates! the scroll fan cant accel as fast and it ends up twisting the crank. if fan has twisted crank, indicated slippage by alignment marks. the engine needs a tear down and a magnaflux or the liquid penetrant. then x-rayed. and also checked for twist. in the R-22 if you go to 110% you are only turning same RPM as a 300c. no big deal we turn more doing aerobatics all the time the RPM isant that bad!. and the R-44 I turn a equivalent of 110% in my AG wagon

at every takeoff for 1500Hrs befor it takes a crap. ok quite enough

Edited by jaredsega
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  • 4 months later...
<font color='#000000'>I was on the ramp the other day watching an R44 about to leave. As they started up the revs went way high, guess they had the throttle full open. It was only for a second, but it made me wonder what should be done maintenance-wise when this happens.

Is it OK if its for 1 second, in which case how long does the throttle have to be fully open before something should be done?

I know there are startup issues to watch for in turbine engines, is there in piston? ???</font>

Some R44's are a bear to start whenever it gets near or below freezing and we are constantly trying

to avoid over-revving when they finally do start. The fan shaft is one of the first places you can get damage.

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