Do helicopters have to worry about heat soak and roll back from limiters once the temp reaches the limit in the hover or is there some sort of engineering that keeps the engines off the limit?
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Stupid Questions about Naval Aviation (Part 3)
- Thread starter Top_Gun_1_0_1
- Start date
With the T-700 we can reach temp limits for the engines in a hover of flying at max speed. On a hot day we may hit temp limits before we hit tourqe limits.( helo pilots talk % torque numbers for power settings)
The engine will have electronic governing at a certain temp (851 deg C) but the pilots can change that number to a higher number with an over ride switch call Contingency Power. It will rereference the temp limit to 903 deg C.
When we approach the temp limit the computer in the engine will reduce fuel flow to keep you below the temp limit.
What lumpy said is correct. When you hit your temp limit, the motor will stop you by limiting fuel flow thereby causing, in a roundabout way, your rotor to droop.
What I've seen is that you're more likely to hit a torque limit, which is a function of the transmission, or you Ng limit where Ng is the speed of the gas generator turbine.
Power in a hover is higher than the power required for most of the forward flight regime, but that powered required to hover is largely based on gross weight, density altitude, winds, and whether the help is in ground effect or not. Unless you're really fat or really hot/high/humid your power to hover is not going to encroach on your limiters.
Just for the record, I'm not buying any of this until Otto weighs in.
Is it normal to use contingency power? Our engine controller will shift temp/rpm datums up based on nozzle position with each datum having a shorter time limit applied, and we can go through the limiters, but its usually going to result in an over temp if you're already that hot.
And I thought we burned hot at 800C. Guess I was wrong.
And I thought we burned hot at 800C. Guess I was wrong.
Helolumpy, I actually had the same question about the 60. One of our sim guys was saying that, in the 46, going into contingency power could very easily/quickly torch the engine. Is that the case with 60s?
Contingency power use is dependent on the situation, but as the name implies its not for normal use. A few years ago my old type wing SOP dictated certain situations when Cpwr was required. Also, turning Cpwr on is the second step for our generic engine malfunction EP.
While Cpwr does raise the temp limit, it doesn't change your torque or Ng limits, so if you hit one of those limits first, it's not doing anything for you other than turning off your ECS which will give you a little bit more power.
If you lose a motor your torque limit changes so you can pull more power with the good motor and that's where the increased limit may help. Most people who turn the switch on manually would do so to cut out a step of the EP in case you roll a motor in an already risky profile.
The new engine control units have an auto Cpwr function that will automatically increase the temp limit on the good motor when an engine out situation is detected.
When I was towing the flight clearance gave us higher temp limits then you could reach with the Cpwr of so we had to tow with the Cpwr on until our aircraft got the new engine control units.
While Cpwr does raise the temp limit, it doesn't change your torque or Ng limits, so if you hit one of those limits first, it's not doing anything for you other than turning off your ECS which will give you a little bit more power.
If you lose a motor your torque limit changes so you can pull more power with the good motor and that's where the increased limit may help. Most people who turn the switch on manually would do so to cut out a step of the EP in case you roll a motor in an already risky profile.
The new engine control units have an auto Cpwr function that will automatically increase the temp limit on the good motor when an engine out situation is detected.
When I was towing the flight clearance gave us higher temp limits then you could reach with the Cpwr of so we had to tow with the Cpwr on until our aircraft got the new engine control units.
When you turn C power on the air conditioning shuts down.... Therefore, we like to have it off!
All that throwing the switch does is allow the computer to govern the engine at the higher temp limit.
The NATOPS limit for 903 deg C ( upper limit of C power) is 2.5 mins. So, if you fly around at that temp for a while, you will violate a NATOPS limit. What actually is the limiting component inside the engine at that number I have never heard mentioned (and I grew up in the town where the T -700 is built and I have had more than a coupke of beers with folks I went to High School with that actually build them and I've asked them a metric ass- ton of questions about the motor)
In addition to Pags' comments on Engine malfunctions, in HS we may turn it on when we go into an overwater hover when it's hot or we're heavy. We also may turn it on prior to entering an LZ for CSAR flights. It' good head work since it will allow you to get a little more out of the motors when we're fat (both pilots and aircraft!) and it's hot/ high DA days and you are about to enter a flight regime where high power may be required quickly.
As I said the only limitation that flying around with the C power switch on all day is that the ECS (driven off engine bleed air) is shut down and you're left sitting inside a big greenhouse of a cockpit with no windows....
All that throwing the switch does is allow the computer to govern the engine at the higher temp limit.
The NATOPS limit for 903 deg C ( upper limit of C power) is 2.5 mins. So, if you fly around at that temp for a while, you will violate a NATOPS limit. What actually is the limiting component inside the engine at that number I have never heard mentioned (and I grew up in the town where the T -700 is built and I have had more than a coupke of beers with folks I went to High School with that actually build them and I've asked them a metric ass- ton of questions about the motor)
In addition to Pags' comments on Engine malfunctions, in HS we may turn it on when we go into an overwater hover when it's hot or we're heavy. We also may turn it on prior to entering an LZ for CSAR flights. It' good head work since it will allow you to get a little more out of the motors when we're fat (both pilots and aircraft!) and it's hot/ high DA days and you are about to enter a flight regime where high power may be required quickly.
As I said the only limitation that flying around with the C power switch on all day is that the ECS (driven off engine bleed air) is shut down and you're left sitting inside a big greenhouse of a cockpit with no windows....
That's because you like to fly the new-fangled things with televisions in them. Legacy Seahawks were more temp limited than Tq limited. For whatever reason, the new birds seem to never run out of temp, just Tq and Ng, even with an engine that isn't a 1.0+. I haven't figured out why that it is.
Historically, there did seem to be a difference between "when" to turn on C-Power between the HSL guys and the HS guys. For HSL, if you are approaching or leaving the boat, it's on. I've flown with HS guys that will say, "then you're expecting an emergency." I think that over-simplifies it, but I get the point. Forgetting the Hotel for a minute (I know it's heavy), I was wondering if it was a difference in weight/performance between the Fox and the Bravo. W/ 3-4 Hellfires, a GAU and a bunch of ammo (and maybe some AIRBOC), you would need C-Power to get off the boat comfortably in a Bravo. I'm curious if that's the case with a Fox.
I think it may have more to do with the fact that for the carrier, we typically can take off up the angled deck, so we are in translational lift before we go out of ground effect. I know I've had to side-step off the carrier and for those (depending on weight, temp, DA, etc) I've used C-power.
For our typical landings (Plane Guard) will have under 2K in gas and not much stores, so gross weight and the fact that we have more physical space to land means C-power is not normally required.
As to the "expecting emergency" I can see what that pilot meant, but I think we'll both agree turning on C-power before something happens is just good headwork. But the use of C-power is obviously a community specific issue due to the different environments that we will take off and land from. Having been a DLQ instructor at HS-10, I've routinely turned on the C-power for the first landing just to ensure we had that little extra, if needed.
As for weights in a hover, I know I have had to burn down some gas before we tried to dip and that was without a torp or a large load of buoys. But the Foxtrot is a lot lighter than a Bravo, so it's not as much of routine issue as you guys have to deal with.
That is unrelated to C-power. He is talking about what was in the -46 called emergency throttle (but would have been better named manual throttle) which when activated allowed manual control of fuel flow to the engines via rocker switches on the collective. The closest -60 equivalent is when you lockout the DECU on an engine.
Does the legacy tgt limiting have to do with old ecus? The 60S all had what HSL guys would call IDECUs but we just called them DECUs. The EDECUs have further increased the TGT limits so instead of IRP we have Mil Power. Also, the 60R/S have higher torque limits then the 60B.
The places where our wing SOP mandated Cpwr use were all mission areas where there was an increased risk exposure. It's been three years, but I think they were:
-shipboard
-couplers
-first auto
-cals
-high alt lzs
I think there was one more, but I can't remember it. I tend to think that the very name let's you use it under extenuating circumstances that aren't necessarily emergencies. If it was only meant for emergencies it wold have been called emergency power.
When I started we had ECU's. Then the DECU's came out and it had 6 functions over the ECU (now, I'm calling on brain cells I thought I killed off a long time ago) Hot start prevent, auto-relight, Fault Detection (tq codes), fault isolation, Tq spike elimination, 400 Hz Airframe Power.
The DECU's were later incorporated with an change to provide Droop Compensation (collection position and rate of collective pull will increase fuel flow to expect a high power demand).
I can't speak to the IDECU's in the Sierras.
I came in when the Foxtrots and Hotels were new and now those aircraft and I can be classified as "Legacy".... For some strange reason, I find great comfort in that fact!