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Inertial Particle Separator & TO Distance

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Inertial Particle Separator & TO Distance

Old 12th Aug 2015, 03:40
  #21 (permalink)  
 
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[QUOTE=SPUDO;9078533]Torque limiter in action. It acts by limiting the fuel flow.


Not in the PT6 - unless your definition of "metering computing section" is very broad. The cable from the power lever goes to the speeder spring tension. Nowhere else.

Oh what about the speed scheduling cam. Or dose that not matter. Which in turns sets the fcu fuel schedule for the computing section of which it is a part off. Prehaps you could enlighten us of what p3, px , py air dose and how it's use in the computing section and how it's changes effect the wf or is that too detailed. What I said what broadly speaking. If you like a full detail I'll let you know.
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Old 12th Aug 2015, 04:53
  #22 (permalink)  
 
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Oh what about the speed scheduling cam. Or dose that not matter. Which in turns sets the fcu fuel schedule for the computing section of which it is a part off.
You're talking about beta/reverse. SPUDO was probably referring to the flight range. Yes, there is mechanical linkage from the power lever to the fuel control unit, but it only applies during beta/reverse. Captain Nomad gave us this information a few posts ago.

A question for you, yr_right: What is the purpose of that mechanical linkage (which only applies during beta/reverse)? I know the answer, but am giving you the opportunity to put it.
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Old 12th Aug 2015, 08:25
  #23 (permalink)  
 
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Pre haps you should tell me what the reverse lever pickup dose on the topping gov. Ive only held a engineering lic on the whole PT6 series for a bit over 20 odd years work on them in extremely remote areas of the world and Australia. here is your chance to shine.
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Old 12th Aug 2015, 08:40
  #24 (permalink)  
 
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how come when I push it forward more it stays and never goes above 96% on a certain PT6 I've flown?


Torque limiter in action. It acts by limiting the fuel flow


Whilst the Tq limiter removes fuel via air py bleed air line the fact of 96% is not a case of tq limiting. This is a fact of either engine condition or environment conditions. And with out have the details I would think more engine condition. Generally Tq limiter is set around 104% and above, it differs for each aircraft model. For example a tbm which has a derated engine will never over tq the engine but can over Tq the airframe.


So saying the tq limiter is in action is completely incorrect.
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Old 12th Aug 2015, 10:27
  #25 (permalink)  
 
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Originally Posted by yr right View Post
how come when I push it forward more it stays and never goes above 96% on a certain PT6 I've flown?


Torque limiter in action. It acts by limiting the fuel flow


Whilst the Tq limiter removes fuel via air py bleed air line the fact of 96% is not a case of tq limiting. This is a fact of either engine condition or environment conditions. And with out have the details I would think more engine condition. Generally Tq limiter is set around 104% and above, it differs for each aircraft model. For example a tbm which has a derated engine will never over tq the engine but can over Tq the airframe.


So saying the tq limiter is in action is completely incorrect.
Spot on yr right
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Old 12th Aug 2015, 14:50
  #26 (permalink)  
 
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Generally Tq limiter is set around 104% and above, it differs for each aircraft model.
yr right, Torque limit is not, and cannot, be based on engine speed. There is no direct relationship between engine speed and torque. On a cold day, for example, an engine in good condition could achieve max torque at a speed much lower than some other engine, in lesser condition, on a hot day. There is no direct relationship.

The same engine, even, under two different sets of ambient conditions could reach the torque limit at different speeds. For example, a takeoff at low elevation in cold temperatures and a takeoff at higher elevation in hot conditions on the same day. The Ng is guaranteed to be different between these two scenarios. How can a torque limiter possibly be based on engine speed, given such typical circumstances?

So saying the tq limiter is in action is completely incorrect.
The poster gave almost no supporting information, so SPUDO was quite justified in giving the *most likely* reason as torque limiter, given that this is the only time, on a properly operating PT6 engine, that power lever advance should have no effect.

The next most likely reasons are mis-rigged power lever, crook Ng governor or instrument error.

GTang, some more information please. What aircraft type? Does it achieve rated takeoff torque? Have you flown other aircraft of the same type? If so, how do they compare?

Last edited by FGD135; 12th Aug 2015 at 15:09. Reason: Added the "PT6" qualifier
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Old 12th Aug 2015, 21:28
  #27 (permalink)  
 
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Originally Posted by FGD135 View Post
yr right, Torque limit is not, and cannot, be based on engine speed. There is no direct relationship between engine speed and torque. On a cold day, for example, an engine in good condition could achieve max torque at a speed much lower than some other engine, in lesser condition, on a hot day. There is no direct relationship.

The same engine, even, under two different sets of ambient conditions could reach the torque limit at different speeds. For example, a takeoff at low elevation in cold temperatures and a takeoff at higher elevation in hot conditions on the same day. The Ng is guaranteed to be different between these two scenarios. How can a torque limiter possibly be based on engine speed, given such typical circumstances?

The poster gave almost no supporting information, so SPUDO was quite justified in giving the *most likely* reason as torque limiter, given that this is the only time, on a properly operating PT6 engine, that power lever advance should have no effect.

The next most likely reasons are mis-rigged power lever, crook Ng governor or instrument error.

GTang, some more information please. What aircraft type? Does it achieve rated takeoff torque? Have you flown other aircraft of the same type? If so, how do they compare?
Clearly you don't understand how and why the Tq limiting works and how it senses it. I would suggest that you find out how it works before you make any more comments. This is because you are incorrect with your statements.
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Old 12th Aug 2015, 22:12
  #28 (permalink)  
 
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You obviously have never done a preformance run for maintenance either. The difference between two engines with different Tq is more than likely the condition of the engine. It's a lot easier to see a engine loosening power on a twin as you can see the them together as you run them. This is where trend monitoring comes into play.
When you fly what do you set too.
You don't set to N1. However this is the first thing as an engineer we look for , this tells us what the condition of the engine is. For a set Tq ,np , wf we should have a N1 in a region if it's out we ethier have a sad or good engine.
Tq is in the power section in the prop reduction gearbox. Helical gears that allow the disc to move. The more Tq the more it moves. It will not vary the Np when it's in the governed range. Hence you set Np then add power Tq will rise Np will say at the set range. N1 will rise itt wf will rise. Np will stay the same.
If the engine is running to 96% and is itt limited it's a sign of a poor gap seal at the compressor turbine. Not Tq limited
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Old 12th Aug 2015, 23:11
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Getting back to the original question. Could it be that the 3% difference separator on/off is due to account for the change in mass flow through the engine? With the separator on even though the same torque and rpm may be set for take off the mass flow through the engine could be less. Is residual thrust provided by the gas generator exhaust ? ( I'm not familiar with the PT 6 or 750TX installation)
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Old 13th Aug 2015, 00:37
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It's an tired Pt6-34 on a PAC XL750. I've flown it in conditions on takeoff from max torque 58psi to much less and Ng will not go above 96%. Also done runs with the engineer. This is the only XL I've flown but the other pilot has over 4000 hours in XLs and the newer engines perform better. Yr right is right on this point.
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Old 13th Aug 2015, 01:15
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The 3% loss is what I first said. It's the loss of ram air affect. This means that now you air bypassing air and the engine is basically sucking air in. With the bypass in the closed position the air is being rammed into the inlet. This is where the gain is.

I'll make this clearer. Tq limiter is set via oil px from the Tq ring in side the prg. The Tq oil px equals at over Tq at around the 104%ish mark. Tq limiter wf loss before this is a problem with the limiter and not the engine or and indication problem. You will never over Tq at 96%.
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Old 13th Aug 2015, 01:16
  #32 (permalink)  
 
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Getting back to the original question. Could it be that the 3% difference separator on/off is due to account for the change in mass flow through the engine?
That reduced mass flow can be compensated for by just pushing the power lever slightly further forward - provided the engine is not already at one of its limits (torque, ITT or Ng). Most of the time, it will be possible to make such compensation.

Does an open separator create slightly more airframe drag? This could be the reason for the 3% factor.

GTang, thanks for that. What happens when you continue to advance the power lever beyond 96%? Does ITT, fuel flow and torque continue to rise, or do they also cease increasing?

If the answer to this is YES, then clearly you have an Ng instrument error.

If the answer is NO, and the torque is less than the limit (if the aircraft has a torque limiter fitted), then clearly the Ng governor has a fault.
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Old 13th Aug 2015, 03:53
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Originally Posted by FGD135 View Post
That reduced mass flow can be compensated for by just pushing the power lever slightly further forward - provided the engine is not already at one of its limits (torque, ITT or Ng). Most of the time, it will be possible to make such compensation.

Does an open separator create slightly more airframe drag? This could be the reason for the 3% factor.

GTang, thanks for that. What happens when you continue to advance the power lever beyond 96%? Does ITT, fuel flow and torque continue to rise, or do they also cease increasing?

If the answer to this is YES, then clearly you have an Ng instrument error.

If the answer is NO, and the torque is less than the limit (if the aircraft has a torque limiter fitted), then clearly the Ng governor has a fault.
Omg

By facts given it is tried. Sounds more like A HSI is required. I would think that your trends should be looked at. That will tell you your proplem straight up.
If you know your troubleshooting and how to find what the problems with indicated instruments it's not hard to figure out.
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Old 13th Aug 2015, 03:56
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Please explain the location of the NG gov.
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Old 13th Aug 2015, 10:31
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Originally Posted by FGD135 View Post
That reduced mass flow can be compensated for by just pushing the power lever slightly further forward - provided the engine is not already at one of its limits (torque, ITT or Ng). Most of the time, it will be possible to make such compensation.

Does an open separator create slightly more airframe drag? This could be the reason for the 3% factor.

GTang, thanks for that. What happens when you continue to advance the power lever beyond 96%? Does ITT, fuel flow and torque continue to rise, or do they also cease increasing?

If the answer to this is YES, then clearly you have an Ng instrument error.

If the answer is NO, and the torque is less than the limit (if the aircraft has a torque limiter fitted), then clearly the Ng governor has a fault.
Yes, itt, fuel flow and tq increases. When they changed the vane class, Ng and tq improved slightly.
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Old 13th Aug 2015, 14:44
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Yes, itt, fuel flow and tq increases.
GTang,
If this is what you see when doing a static engine run, then it can only be an instrumentation fault. It is physically impossible to get a further rise in those parameters without the Ng also further increasing (in the case of a static engine run). You may be seeing the indicated Ng cease rising, but the actual Ng must still be rising.

On a takeoff roll however, it is perfectly normal to get a rise in those parameters whilst Ng stays constant - this is the ram effect.

Please explain the location of the NG gov.
It may not be called that, but I am referring to the mechanism with the speeder spring and flyweights that signals the FCU to increase/decrease fuel flow.

The 3% loss is what I first said. It's the loss of ram air affect.
No. I think you will find that the performance tables for this aircraft make the assumption that rated torque is achieved by the engine for every takeoff, including those with the separator open (this can be confirmed by a 750 pilot - he just needs to confirm that the AFM gives one torque value for all takeoffs).

In practice, this is achieved, for a separator-open takeoff, by just slightly increasing the Ng (thus compensating for the reduced air flow). The pilot does what he always does for takeoff - advances the power lever in order to set the target torque.

With the separator open, of course, he may notice a slightly higher ITT. If he is really sharp-eyed, he may notice the Ng is also slightly higher.

That 3% factor on the TO distance, queried by FoolCorsePich, can only be due to the aerodynamic drag of the open separator.
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Old 13th Aug 2015, 23:24
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[QUOTE=FGD135;9081079]GTang,
If this is what you see when doing a static engine run, then it can only be an instrumentation fault. It is physically impossible to get a further rise in those parameters without the Ng also further increasing (in the case of a static engine run). You may be seeing the indicated Ng cease rising, but the actual Ng must still be rising

Completely incorrect. If the wrong class ngv is installed you can have itt and Tq within parameters and a low n1. And if they changed the ngv recently this may be the problem. Once again look at your trends. It will tell you the problem
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Old 14th Aug 2015, 04:46
  #38 (permalink)  
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That 3% factor on the TO distance, queried by FoolCorsePich, can only be due to the aerodynamic drag of the open separator.
That's an interesting thought. Thank you.
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Old 14th Aug 2015, 07:10
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That 3% factor on the TO distance, queried by FoolCorsePich, can only be due to the aerodynamic drag of the open separator.


How do you figure that. If anything the drag will be less not more.
This extra required length in takeoff is consistant of every aircraft I know off fitted with a separator.
The reason for this is simple. Please read.
It's the loss of ram air effect. Nothing more nothing less. And like I said. In a b200 if you fit a raisebeck ram
Air recovery you don't loose any engine preformance with the inertia separator in the open position. If there was a case of drag then this would not make any difference.
This the separator open you loose toque. By memory in a b200 it's around 40lbs. Hence the lose of preformance.
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Old 14th Aug 2015, 07:59
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Yr right, so the reduction in thrust as a result of losing the ram air effect cannot be recovered in any way?
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