Relationship of Indicated Torque with Engine Power available in T-53 Engines

[Greenvalley285]

In Hueys and Huey IIs, T53L13/703 are fitted. Engine Torque is indicated inside cabin, which gives idea of Torque being pulled by helo.

 

Now i have a question, if engine is weak/ under power, what we expect to see on Torque Indicator inside cabin, a higher or lower then normal Torque?

Another indication for a weak engine is a higher indicated EGT/ MGT. But what about Indicated Torque. Does it have any significance to ascertain condition (and health) of engine?

 

Anxiously waiting for advice......

[Gomer Pylot]

Torque has nothing to do with engine power. Torque is a transmission parameter. I many helicopters I've flown you can have 100%+ torque indicated, and still have the engine instruments in the green. Or in some, you can have the engine temp at the redline and still well below max torque. It depends on lots of things, and all you really need to do is keep all the instruments below the redline. If the engine is weak you'll see higher engine temps at a comparable torque indication. As long as the engine temps are below the redline at max torque, you still have more available engine power.

 

But the bottom line is that torque is a transmission paramater, not engine. Evaluate the engine power separately, with a power check.

Edited July 12, 2016 by Gomer Pylot

[Greenvalley285]

Thanks a lot,

But i have a confusion in mind, that, before flight, we check Performance Planning Charts from Dash Ten, and find, max allowable Torque. This Torque is not allowed to be exceeded. Is it a Engine limitation.

[Greenvalley285]

Thanks a lot,

But i have a confusion in mind, that, before flight, we check Performance Planning Charts from Dash Ten, and find, max allowable Torque. This Torque is not allowed to be exceeded. Is it a Engine limitation.

[Greenvalley285]

Thanks a lot,

But i have a confusion in mind, that, before flight, we check Performance Planning Charts from Dash Ten, and find, max allowable Torque. This Torque is not allowed to be exceeded. Is it a Engine limitation.

[iChris]

Now i have a question, if engine is weak/ under power, what we expect to see on Torque Indicator inside cabin, a higher or lower then normal Torque?

 

Another indication for a weak engine is a higher indicated EGT/ MGT. But what about Indicated Torque. Does it have any significance to ascertain condition (and health) of engine?

 

But i have a confusion in mind, that, before flight, we check Performance Planning Charts from Dash Ten, and find, max allowable Torque.

 

This Torque is not allowed to be exceeded. Is it a Engine limitation.

 

If your engine is weak or under powered, it’s working inefficiently. Therefore, the engine must work harder to support its normal workload. Looking at the relationships, you’ll see higher than normal Ng, N1, TOT, TIT, EGT, and Fuel flow readings etc. for the same torque value. Example, you’re normally hovering OGE at your home base @ 75ºF, full fuel @ 39 PSI torque and 608ºC EGT. Over time you’re at the same 39 PSI torque; however, your EGT is how 620ºC, along with a near max Ng.

 

It’s a common problem, low power with high EGT. It is most commonly related to compressor damage, dirty compressor, bleed valve failing to close fully, In the case of the T53, a Bleed band, which is controlled by a slide valve on the fuel control with reference to compressor discharge (P3), and ambient pressure (PA). Additional problems include, excessive air leaks, anti-icing or heat control valve leaks. Normally higher engine inlet temperatures during the summer also amplify the situation.

 

As stated in Gomer Pilot’s post above, the best way to troubleshoot power issues is to start with an evaluation of the engine by accomplishing a power check.

 

Torque available values determined are not limits. Any torque which can be achieved, without exceeding engine, transmission, or other limits, may be used. As shown in the chart below torque is limited by the transmission/drivetrain, which is most often the case.

 

A few words on torque and engine power to ease the confusion. If a force is being applied to cause rotational movement, Work is being accomplished to cause that motion and a torque is being applied. Therefore, in accordance to the physics, there’s a relationship between Work, Power, and Torque.

 

Power is the rate of doing Work. Work = D (distance moved) x F (force applied). By definition, Work is calculated as a vector force, exerted in a straight line. But engines (as well as nuts and bolts when they are tightened or loosened) rotate around an axis.

 

The expression of this rotational or twisting force around an axis is called torque, which is measured in units of force times distance from the axis of rotation. If you have a 1-foot-long wrench and you exert a force of 10 pounds on the end of it then you apply a torque of 10 Foot-pounds (10 ft.-lbs.). If the wrench were 2 feet long, the same force would apply a torque of 20 ft.-lbs. When an engine is said to make 200 ft.-lbs. of torque, it means that 200 pounds of force on a 1-foot lever is needed to stop its motion. This is the relationship between torque and engine power, even though torque is most often referred to only as a transmission or drivetrain limit.

 

 

Edited July 17, 2016 by iChris

[Greenvalley285]

Thank You iChris

 

Still i have some doubts.

Torque indicated inside cabin (through Torque Indicator) is what

• Is it the Torque produced by engine? OR
• Is is the Torque imposed by Transmission, to engine. Means its the Counter Torque imposed on engine by Transmission, or helo weight configuration?

In that case, the question is, If the Torque displayed inside cabin, is less then normaly displayed in same configuration and conditions, what does it mean.

• A healthy engine, since more margin is available to engine before it gets into Yellow/ red limits (more green arc is available)? OR
• incase is it the Counter Torque indicated, then Counter Torque is more imposed, and thus most of the torque produced by engine is taken to resisit this Counter Torque.

I am still confused.....

[Rupert]

Huey's take the torque (Nq) reading from the engine. Power checks compare the N1, pressure altitude and outside air temperature against the amount of torque produced by the engine under those conditions. One of the few systems that will bleed rpm at topping. For that reason, Bell rigged the system to operate at slightly higher than optimum rpm, so that if the pilot got in trouble and needed to pull more power, the rotor would bleed down into the more efficient range, 96%. An excellent system for relatively low time pilots. Hueys have regularly done the impossible because of this. The high point of helicopter development.

[Wally]

Thank You iChris

 

Still i have some doubts.

Torque indicated inside cabin (through Torque Indicator) is what

• Is it the Torque produced by engine? OR
• Is is the Torque imposed by Transmission, to engine. Means its the Counter Torque imposed on engine by Transmission, or helo weight configuration?

In that case, the question is, If the Torque displayed inside cabin, is less then normaly displayed in same configuration and conditions, what does it mean.

• A healthy engine, since more margin is available to engine before it gets into Yellow/ red limits (more green arc is available)? OR
• incase is it the Counter Torque indicated, then Counter Torque is more imposed, and thus most of the torque produced by engine is taken to resisit this Counter Torque.

I am still confused.....

 

Torque measures the power being delivered, an air frame or transmission limit, regardless of engine capability. You could encounter an engine limit (temp or turns) before you reached a torque limit, a weak engine or external conditions- high and hot for instance, where you need more collective and thus more induced drag for the same amount of lift at lower, cooler altitude.

As to "counter torque" (anti-torque load?), most torque measurements are 'picked' at the engine, more collective means more anti-torque required. If the Tq pick is at the transmission, this would not be the case.

[Gomer Pylot]

Torque is power delivered to the transmission. The transmission does not impose torque on the engine. The engine produces power by burning fuel. The transmission only changes the speed and direction of the power and thus spins the rotorblades. The gears inside the transmission can only absorb so much power, so the power the engine is allowed to provide is limited. If the engine is allowed to produce too much power, it could cause a catastrophic failure of the transmission. In most helicopters, under most conditions, the engine(s) can produce much more power than the transmission can safely absorb. This isn't always the case, and sometimes an engine limit can be reached before the torque limit, which again is a transmission limit. This should have been thoroughly explained to you during your pilot training. It is basic information.

[iChris]

Thank You iChris

 

Still i have some doubts.

 

Torque indicated inside cabin (through Torque Indicator) is what?

 

It’s the torque produced by the engine. In fact, the torquemeter is an integral part of the T53-13 engine’s oil system via a torquemeter boost pump mounted on the front of the N2 gearbox.

 

Moreover, Bell leaves little room for doubt in their description of the system in regards to the T53-13 engine installed in the Bell 205A-1:

 

MAXIMUM POWER (TORQUEMETER PRESSURE) CHECK

The purpose of this check is to determine whether or not the installed engine will deliver torquemeter pressure (power) equal to or greater than a minimum specification engine. Since the minimum specification engine is capable of delivering 1400 horse- Power, and the engine as installed in the helicopter is de rated to 1250 horsepower, care must be taken not to exceed the power limitation (54.0 PSI torquemeter pressure). This "full throttle" power check, in order to be conclusive, must be made at conditions of altitude and temperature at which full throttle will produce no more than 54.0 PSI torquemeter pressure. Ref Bell 205A-1 Flight Manual

 

In that case, the question is, If the Torque displayed inside cabin, is less then normally displayed in same configuration and conditions, what does it mean?

 

I am still confused.....

 

What does it mean? Again, Bell leaves little room for doubt when describing the outcome of any check:

 

If this check is satisfactory, it can be concluded that the installed engine is at least as good as a minimum specification engine and that full power can be obtained. If this check is not satisfactory, there is reason to believe that the engine has deteriorated to the extent that published performance may not be obtained. If this occurs, the cause of the deterioration should be determined. Ref Bell 205A-1 Flight Manual

Edited July 23, 2016 by iChris

[whoknows idont]

Torque indicated inside cabin (through Torque Indicator) is what

• Is it the Torque produced by engine? OR
• Is is the Torque imposed by Transmission, to engine. Means its the Counter Torque imposed on engine by Transmission, or helo weight configuration?

 

My understanding is that as long the RPM remains constant, torque and counter torque are equal.

∑M = 0

[Eric Hunt]

I think what he is really asking is, if the torque is low, is the engine more healthy?

 

Most likely NOT.

 

If normal flight is at 96% N1 to produce 40psi for a cruise, but the same N1 is now only giving 38psi, then the engine is working harder than it should - usually due to a dirty compressor, or a faulty bleed band.

 

As has been said, Torque is a measure of the power coming out of the engine, done using pressurised engine oil being forced between 2 plates - just a way of getting a "number". This is presented as psi of oil pressure, or a percentage of the 100% maximum normally allowed.

 

The engine's job is to maintain the RRPM at 324 or 100% (or 107% in an S76 or some other random number). If more collective is pulled to generate more lift, the drag increases and the blades want to slow down. The N2 governor detects this, and tells the FCU (N1 governor) to lift its act and pours more fuel into the engine to raise N1 and bring the N2 back up to normal. So the constant N2 (and RRPM) is held there by a variable N1. A good engine needs less N1 to hold the revs.

 

But if the compressor is dirty, or the bleed band is leaking some air, the N1 has to work harder to maintain N2.

Edited July 25, 2016 by Eric Hunt

[Mbrowner1]

So is the HIT Check a condensed version of the Topping Check?

[iChris]

So is the HIT Check a condensed version of the Topping Check?

 

The term Topping Check has become rather ambiguous in its usage. Topping has confusingly been equated to many other non-relating checks. The HIT is a procedural check outlined in the Pilot’s Flight Manual. Topping, most often referred to as N1 topping, is a procedure outlined in the Maintenance Manual.

 

It is possible under given condition that your HIT check maybe within limits without the N1 Topping being optimized to its maximum. Ensuring optimized topping will result in improved HIT results overall.

 

Therefore, never assume or attempt to equate any one test to another. HIT Checks, Power checks, Power Assurance Checks, etc. referenced to in the Pilot’s Flight Manual lets you know your engine’s performance is within the specification ballpark. Topping or Max N1/Ng checks, referenced in the Maintenance Manual, pinpoint your engine’s exact performance level in that ballpark and stand as a starting point to optimizing overall performance. Fuel controller adjustments and/or throttle rigging are determined from these types of maintenance checks.

 

As an example, the Engine Health Indicator Test (HIT) is the method by which a pilot, in day-to-day flying, monitors the aircraft engine condition. The pilot selects an N1 setting (%) based on the existing outside air temperature (OAT) observed on the aircraft OAT gauge. The Turbine Temperature indicated at that N1 setting must then relate to the predicted value (Baseline Turbine Temperature Value) found on the HIT Log. Turbine Temperature variations from the baseline values are logged by the pilot on the HIT Log. This log, is then used by maintenance personnel to monitor engine health trend data.

 

In contrast, Topping, as an example in the Bell 412, relates to a maintenance action, Automatic Mode maximum gas producer speed check and AFCU maximum N1 stop adjustment. As stated in the maintenance manual:

 

“Maximum gas producer (N1) speed (topping) is achieved when N1 ceases to increase and N2/NR droops as collective is further applied. Do not droop below 90% N2. The observed reading at this point should be 99.8 to 100.8% N1. A minimum value of 99.8% N1 is required to assure in flight topping at 103.4% N1...”

 

“Maximum N1 topping checks should only be performed after engine control rigging is adjusted or when any of the following components are replaced: (two power sections and reduction gearbox), power section, AFCU, MFCU and fuel pump…”

 

The main point here is to never equate any one test to another without knowledge to their relationship to the specific helicopter engine.

Edited September 10, 2018 by iChris