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Engine Power in Turns and Oil Pressue on the R22


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Hi everyone!

 

I'm having great fun down here with my training, and have finally comfortably found the hovering button :) Took a while but I got there!

 

The other day I was flying (right hand) circuits with my instructor with a fairly strong (say, 15kt) northerly wind, and I noticed that when we turned right from crosswind to downwind, the MAP pressure dropped a little. When I mentioned this to my instructor, he did a couple of rather steep banks to the left and then to the right, while flying with a left crosswind. When he did the steep left turn the MAP climbed quite a bit (say, from 21" to 23"), and when he turned steeply right, it dropped even more than on my gentle right turn (perhaps from 21" to 18").

 

Now, during these turns I didn't change the collective position at all sooo I'm wondering where it comes from. The instructor said if I hadn't figured it out in a few days I should ask.. Now I've been searching left and right and feel a bit lost!

 

I haven't had a chance to see if the effect happens the same way around when the wind is from the other side.

 

Does it have something to do with :

 

* The fact that the air intake is on the starboard side of the R22, and that our turns affect air intake and so the Manifold Air Pressure somehow? (A bit far fetched.. I don't think this is likely..)

 

* That the turn affects the RPM of the main rotor somehow, and that the governor does something (that drastic??) to keep it in the green? But in that case, why does it only happen when turning left or right, wouldn't it be the same both ways (ie. left or right turn both increase/decrease MAP)?

 

* Does it have something to do with the tailrotor in the crosswind? Hmmm, doesn't seem to make sense either.

 

* An effect on the main rotor turning into the wind and out of the wind? This could be likely.. I neglected to check when we were flying on downwind, because then it should be the same either way..

 

You don't have to give me the answer (Yet! :rolleyes:), if you could please just perhaps nudge me the right direction I would really appreciate it!

 

Ok, and my NEXT question is - Where does the "Oil Pressure" come from? Yes, the one they say in the manual should be at least 25psi during your startup checks etc.. In my mind I sort of imagine the oil as being splashed around the the sump around all the needed engine parts -- not really being in some sort of closed loop.. (sorry, I'm not really an engine guy! :) ) But hmmm, it does have to go through the oil cooler -- is that some sort of closed system? Does the pressure have anything to do with the temperature it's at? I guess that would be logical...

 

Thanks so much everyone!

DF

Edited by DigitalFudge
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Ok, and my NEXT question is - Where does the "Oil Pressure" come from? Yes, the one they say in the manual should be at least 25psi during your startup checks etc.. In my mind I sort of imagine the oil as being splashed around the the sump around all the needed engine parts -- not really being in some sort of closed loop.. (sorry, I'm not really an engine guy! :) ) But hmmm, it does have to go through the oil cooler -- is that some sort of closed system? Does the pressure have anything to do with the temperature it's at? I guess that would be logical...

 

Thanks so much everyone!

DF

 

I can't answer your first part, but the oil system, just like in your vehicle, work on the same principle, the oil pump pick up the oil from the sump and pumps it under pressure into the oil tunnels (for the current lack of a better word) the oil pressure sending unit is mounted near this point, the oil flows through out the engine to lubricate the moving parts, starting with the oil cooler for cooling, the oil then drains back into the sump.

 

 

 

 

clear as mud? :blink:

Edited by 67november
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Thanks mate!

 

Now I have a bit of a better idea of how things are put together B) As I said, I'm not really much of an engine guy, unfortunately!

 

Bedtime here now though!

 

Cheers!

 

I can't answer your first part, but the oil system, just like in your vehicle, work on the same principle, the oil pump pick up the oil from the sump and pumps it under pressure into the oil tunnels (for the current lack of a better word) the oil pressure sending unit is mounted near this point, the oil flows through out the engine to lubricate the moving parts, one of those "tunnels" also pushes oil to the oil cooler for cooling, the oil then drains back into the sump.

 

 

clear as mud? :blink:

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Maybe its just me, but I would be thinking about a couple of things that are happening in a turn.

 

One, does the airflow entering the main rotor affect my rotor blades angle of attack? If so, does it take more or less HP to turn a blade with a higher/lower angle of attack?

 

Second, am I using my pedals in the turn? Does left or right pedal use change the angle of attack on my tail rotor..and if so, how? When hovering, do you notice the power requirement change for a right pedal turn vs a left pedal turn?

 

If none of this rings a bell for you then go do this on your next lesson.

 

Keeping the power setting ( collective ) exactly the same in a hover, do a left pedal turn. What happens to your altitude? Why? Now try a right pedal turn..

 

hope this helps.

 

Goldy

 

PS...forget the whole air intake on one side idea !!!

Edited by Goldy
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Hey there Goldy!

 

Thanks for the suggestions! Personally I do not think that it's the same effect as you get when doing pedal turns in the hover. When I bank while in flight it's almost entirely cyclic, and I only use a tiny bit of pedal to compensate for slipping/skidding etc.

 

If I were to do a left pedal turn in the R22, I would start descending a bit (because the TR is using some of the engine's power) - so do compensate for that I have to pull some collective. However, if I were just hovering and doing the turn, but NOT compensative for it (ie, leaving the collective in the same position) the MAP should stay exactly the same, right?

 

I just got up and it looks like a lovely day for flying, so I'll go and check :)

 

The blade AOA changing in the turn sounds interesting! I think I'll go and chip away at that for a while ;)

 

Cheers,

DF

 

Maybe its just me, but I would be thinking about a couple of things that are happening in a turn.

 

One, does the airflow entering the main rotor affect my rotor blades angle of attack? If so, does it take more or less HP to turn a blade with a higher/lower angle of attack?

 

Second, am I using my pedals in the turn? Does left or right pedal use change the angle of attack on my tail rotor..and if so, how? When hovering, do you notice the power requirement change for a right pedal turn vs a left pedal turn?

 

If none of this rings a bell for you then go do this on your next lesson.

 

Keeping the power setting ( collective ) exactly the same in a hover, do a left pedal turn. What happens to your altitude? Why? Now try a right pedal turn..

 

hope this helps.

 

Goldy

 

PS...forget the whole air intake on one side idea !!!

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Like it, like it! I love a good discussion.

 

When I mentioned this to my instructor, he did a couple of rather steep banks to the left and then to the right, while flying with a left crosswind. When he did the steep left turn the MAP climbed quite a bit (say, from 21" to 23"), and when he turned steeply right, it dropped even more than on my gentle right turn (perhaps from 21" to 18").

 

I wonder if 'C of G' cares to comment on this!?

 

Maybe someone could also confirm the opposite happening in a clockwise rotating helicopter such as the EC120?

 

Is there a corresponding drop in MP whilst leveling from the left bank?

 

Lastly, I wonder what happens with a helicopter without a govenor?

 

This might help you on the way to the answer!

 

Joker

Edited by joker
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I can't answer your first part, but the oil system, just like in your vehicle, work on the same principle, the oil pump pick up the oil from the sump and pumps it under pressure into the oil tunnels (for the current lack of a better word) the oil pressure sending unit is mounted near this point, the oil flows through out the engine to lubricate the moving parts, starting with the oil cooler for cooling, the oil then drains back into the sump.

 

 

clear as mud? :blink:

 

Maybe I misunderstood but I was taught that the Lycoming O-360-J2A was splash lubricated and has no oil pump. 67's explanation applies to a reciprocating engine with an oil pump system. Now I'm curious too, where does the oil pressure come from in an R22?

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Maybe I misunderstood but I was taught that the Lycoming O-360-J2A was splash lubricated and has no oil pump. 67's explanation applies to a reciprocating engine with an oil pump system. Now I'm curious too, where does the oil pressure come from in an R22?

 

The crankshaft and camshaft are splash lubricated, but the oil going to the valves and their associated components is under pressure, otherwise it couldn't get where it needed to go. Also, the oil wouldn't flow through the oil coolers if it wasn't under pressure. I don't know about the J2A specifically, but it would be fairly difficult to lubricate the push rods without a pump. If you have the chance, sit around and watch the next time the mechanic(s) rip apart an engine.

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Torque Rise in Turns

 

Well it seems that no one is going for it, so i'll put my neck on the line!

 

* That the turn affects the RPM of the main rotor somehow, and that the governor does something (that drastic??) to keep it in the green? But in that case, why does it only happen when turning left or right, wouldn't it be the same both ways (ie. left or right turn both increase/decrease MAP)?

 

Significant cyclic deflection towards the retreating side will result in rise in power demand.

 

Why:

 

Increased total drag on the rotor disc.

 

Why:

 

Reduction of pitch on retreating side (notwithstanding all the phase lag and gyroscopic precession stuff). This reduces drag (on this side) according to the drag forumala -

 

frmldcdpv2s.gif

 

Increase of pitch on advancing side increases drag on that side.

 

Conclusion:

 

Due to the V(squared) property of the formula (exponential differential in velocity between advancing and retreating sides) the increase in drag is greater than the reduction in drag, thus the total drag on the rotor disc as a whole increases. This requires more 'power' to maintain an given rpm, thus MP goes up.

 

Discussion:

 

In a non-governed engine, presumably with no pilot input, there would be a slight reduction in rpm instead, as there is no governor to compensate for the extra drag. Maybe someone can check this. When doing so, don't discount 'disc loading', 'coning' and coriolis, as all of these suggest that a the initiation of a hard bank (in either direction) will load the disc and thus see either a rise in rpm, or (in a governed-engine) a drop in MP. However, this is not the situation being discussed here.

 

Of course the biggest differences will be from one extreme to the other. So you could set up a 30 degree left bank and check the numbers. Then set a 30 degree right bank and check the numbers. The demonstration doesn't have to be done quickly, as it is a function of cyclic pitch settings (bank angle), not aggressiveness of banking (rate of roll) that causes the difference in drag.

 

This is a torque rise due to cyclic pitch setting. Once equilibrium between power and rotor drag is acheived (as in a steady turn) the MP requirement will stabilise?

 

I don't think the wind azimuth has anything to do with this situation.

 

Also, for a really steep turn, then pedal application will have an effect, to the same as Goldy suggested. However, I think this is negligiable for most turns and for the purpose of answering this question.

 

Just my layman's guess. I wonder what Goldy would have said. It seems to me we were on the same lines.

 

Joker

Edited by joker
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I think some focused too much on the tail rotor question. The real question isnt what would happen....but why? Doesnt a change in the AOA of a blade change the amount of power required to turn it? Thats the direction I was trying to get to with the tail rotor question.

 

But what the heck...after a while you just fly and when the RPM drops you raise it and when it gets over 100% you lower it, and I think many times you arent even thinking why !! I'm usually more concerned about a fixed wing flying into me (since the pilot has his head down in his new GPS toys)..

 

 

I do recall one night flight where I noticed a change in MP..and it didnt seem right to me. I instinctively pulled full carb heat in the R22 and once I reduced carb heat things went to normal power settings. The change in MP was masked by the governor but I felt a throttle increase under my hands and it caused me to check the MP....that was probably an auto waiting to happen.

 

Goldy

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After reading this discussion I went and flew a helicopter that has no governor, and a clockwise rotating rotor, and tested to see what would happen to the manifold pressure if I made a steep turn one way or the other.

I very carefully fixed the collective in one spot so as not to inadvertantly nudge it up or down during the turns.

After making several steep turns in both directions I viewed no change in the manifold pressure.

I did however lose some altitude because of the fact that vertical lift was vectored horizontally and no up collective was given to compensate for the decrease in vertical lift.

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Hello southernweyr,

 

Good on ya for going out and trying things out....you can now call yourself a 'test pilot'!!!

 

However, look at my last post carefully. Particularly this line...

 

"In a non-governed engine, presumably with no pilot input, there would be a slight reduction in rpm instead. "

 

So, when you went out in your 'non-governed' aircraft, I was predicting that the MP would stay the same. This is what you saw, yes? Did you look carefully at the RPM though? Did this change or not?

 

I actually did some experimentation of my own yesterday whilst flying the line. Indeed, there is a 1-2% torque rise when doing a left turn in S76. Opposite is true for a right turn. So the total difference between left deflection of cyclic and right deflection is about 2-4%!!

 

Any other 'test pilots' out there, care to comment.

 

BTW, I have edited my original explanation, to be a little more accurate. It is not the hardness of the turn, but the degree of cyclic deflection that matters. It can be demonstrated with a gentle turn to the same bank angle too. (That's what I found.)

 

Joker

Edited by joker
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