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-   -   Manifold Pressure R22 (https://www.pprune.org/rotorheads/539005-manifold-pressure-r22.html)

ETL2GO 8th Sep 2008 20:18

Manifold Pressure R22
 
It seems to me that with the large amount or derating on these engines, resulting in more power available at higher altitudes etc, could the MP limitation be theoretically raised for operations at lower alts, lower disc loadings etc etc....

comments?

the beater 8th Sep 2008 20:23

You can pull what you like from the engine, it's the transmission that'll suffer.
That's why the engine's limited.:ok:

Tarman 8th Sep 2008 20:33

The main danger is that you'll over pitch the blades, if you have an engine hiccup or a magneto cough the rotor will stop in the blind of an eye. They're de-rated for a reason !!:ok:

the beater 8th Sep 2008 20:54

Words fail me!
Are you just saying this to wind us up?
Just excuse me for a short while whilst I consult Roger's Profanisaurus for a suitable reply.
Are you really saying that it's designed-in to cover the possibility of a magneto problem?
No, it's no good, I really have to lie down.

Bloody hell!

helimutt 8th Sep 2008 21:01

The redline on the MAP gauge, is just that, a red line on a guage. We all know it'll pull more than that:eek:

tegwin 8th Sep 2008 21:11

In theory, yes you can pull more power than red line on the MAP guage in an R-22, but you WILL over torque the transmission....


Oh, and if you try that trick on the R44 your going down quick!.....They have NO power left once you get to red line!

the beater 8th Sep 2008 21:14

Aye, but there's the rub.
We all know that there's a red line on the gauge, but what most don't realise is that there is a graph up in the roof that doesn't have a red line. But it does have a manifold limit.
I still contend that this graph is needed to preserve the integrity of the transmission. So does Frank Robinson.
Not of significance to those backing-up into cranes and ordering bacon butties:eek:

JimBall 8th Sep 2008 21:26


Oh, and if you try that trick on the R44 your going down quick!.....They have NO power left once you get to red line!
Tosh. The 44 has a stack of power that isn't used - just read the POH. As has been said above, the red line is there for a reason and it isn't a lot to do with the engine. However, the 2200hrs of life is based on operating within manufacturer limits.

It's a question of whether you care enough about the next people to get in the heli. And the next. And the next. Most overspeeds, overstresses and exceeding of limits don't show up for a few more hours.

ELT2GO : are you really a pilot ? Your thought process is somewhat worrying.

mikelimapapa 8th Sep 2008 21:38

There have been cases of blades failing in the R22 with as little as 6-700 hrs on them. Its one thing to momentarily exceed manifold pressure to get out of a bad situation.......its entirely different to do it on purpose just because its there :=:=:=

Mike

winged hunters 8th Sep 2008 21:48

If you are talking about the ag machine in New Zealand that was a slightly different situation. He used the 'big twist and heave' t/o method. That means he opened the throttle (well ABOVE the red section on the tacho) and heaved the collective up until it's 'light on the skids' so they can do a cushion creep t/o. It's quite a standard procedure in NZ ag circles and quite nessecary when overloading by 200-300 lbs is standard practice. Only in NZ...

HillerBee 8th Sep 2008 22:02

Basically the question is why are there red lines on the gauges, they are only blocking the vision!!!!

With an attitude like that, I highly recommend you to refrain from flying.

heliduck 8th Sep 2008 22:26

ETL2GO,
I'll assume your enquiry is genuine so at the risk of repeating what some have already said, here's my 2 cents worth. The manifold pressure guage gives you an indication of the torque being produced by the engine -
Yes, you can ignore the guage & pull power in any model R22 until the RRPM droops.
Yes, you will get away with it for a while.
Yes, the drive belts will shred & depart the scene eventually.

206Fan 8th Sep 2008 22:33

Theres no call to pull more power than the red line indicates..

the coyote 9th Sep 2008 01:25

With any exceedance, you can lie to your boss, and you can lie to yourself, but you can't lie to the machine...

ETL2GO 9th Sep 2008 01:32

as i expected a wide range of input, some even intelligent.....I come from a part of the world where practicality is more often required, things are not always done by the book.
I'm not saying I condone it, personally I strive to remain within any limitations, thinking about not just the transmission, but the whole machine, especially the drive train, grips, spindles, feathering bearings, blades, TR d/s...the list goes on....and obviously the future pilots and more especially the future pax who use the machine........

however, back to my original question....surely there is a great deal less stress on all these components in lower disk loading / torque manouevers than others...

i'm interested in hearing from designers perhaps who have a working knowledge of the principles here....

also it would be nice if we could act a bit like grown ups and share some opinions, instead of casting petty aspersions.....

puntosaurus 9th Sep 2008 04:49

I believe Mr. Lappos has a certain reputation in the field of design so maybe his words on
this thread will help you.

topendtorque 9th Sep 2008 12:25


I believe Mr. Lappos has a certain reputation in the field of design so maybe his words on
this thread will help you.
when that fails try this recipe.


also it would be nice if we could act a bit like grown ups and share some opinions, instead of casting petty aspersions.....
an' if you still canner make sense of it even by this method


I come from a part of the world where practicality is more often required, things are not always done by the book.
then here's the fail safe method.

do it by the book
cheers tet

bladewashout 9th Sep 2008 12:32

ETL2GO

My grown up opinion is that if your interest is simply academic, it's interesting, but you should never knowingly exceed the gauge other than in a life-threatening situation and should disclose it every time.

If your purpose is at all to conceive of scenarios where you might, at some time in the future, use your freedom of choice as a pilot in command to pull more MAP than permitted in what you consider to be a practical and safe manner, please have the decency to leave a list of machine names you use so the rest of us can have the freedom of choice to avoid them.

That's not a petty aspersion, just a statement of fact that a lot of us who rent aircraft depend on the fact that everyone before us has acted according to the POH for their own and their passengers safety.

BW

scooter boy 9th Sep 2008 13:02

When I had my beloved little R22 beta II my belly was a bit bigger than it is now. (Ironically now that I have lost weight I fly a 44 II).

I recall taking off one day from my garden with 2 fat boys on board when I was faced with a choice - it was either trim the rotor blades on a telegraph pole or exceed the limitation. I chose to exceed the limitation.

A chat with the engineer later on reassured me that all was well.

Both the 22 and 44 have more power available than the red line indicates.

It is there on the rare occasion that you need the extra power to prevent rolling the machine up into a ball.

SB

JohnDixson 9th Sep 2008 13:34

R-22 manifold Pressure Limitation
 
Suggest you write a letter, or call the Chief Test Pilot at Robinson and just ask about the derivation of that limitation. He will know and will be happy, I'm sure, to pass it along.

Thanks,
John Dixson


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