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Always start left engine first?


Yurgon
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From the in-game tutorial and various Youtube tutorials, I get the impression that we're usually supposed to start the left engine first.

Wouldn't that cause more wear on this engine, resulting in unequal engine performance over time? In Casmo's latest video, he also explains that the first engine that's started has to work a lot harder than the second engine, because the first one has to get the rotor spinning.

If I recall correctly what Ed Macy wrote about the British AH Mk-1, they would start the left engine first on odd days and the right engine first on even days to pretty much equal out the wear and tear over time.

So the question is, what would be the recommended and typical engine start order for our 2005-ish AH-64D, and is there any downside in DCS to alternate between left engine first and right engine first? (Not that wear and tear would be a factor for us, but maybe there's some stuff added later in Early Access that I'm simply not aware of, hence the question).

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Good question. Personally always go with the start order of No1 then No2. Normally you will find that an engine manufacturer caters for most scenarios, and doesn't care about starting order, as it would have been designed to cope with a start under load (direct drive to the transmission) if say on a single engined aircraft. Alternating starts may effect engine life cycles, which in turn will effect maintenance and overhaul - potentially leading to No1 Eng undergoing maintenance more often if No1 is always started first - albeit dependent on how long it is between No1 and No2 starting... . The alternating method may have been a 'local order' from the maintenance section to help alleviate supply and stores issues to try to align running hours.

It also does depend on how the user records usage - whether operating hours, airborne hours, hours above a certain % Ng or Np...the variables are endless and quite often co-dependent on the end user.

In the case of the British Army - up until the AH appeared the helo of choice was a Lynx - with the ability to run No1 engine in an accessory drive mode, so whilst  burning and turning was not providing any drive to the main transmission - but all the while was running up operating hours resulting in maintenance if the metric was op hours and not flight (under load) hours.

Apologies but you did ask!

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Not sure how startup on idle power and no torque would cause any extra wear, compared to the required full power performance over a few-hour flight. For a mil-spec engine designed to fly the whole helicopter alone, I'd say it's neglible. Regular maintenance on flight hours would take care of it.

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19 minutes ago, PlainSight said:

Not sure how startup on idle power and no torque would cause any extra wear, compared to the required full power performance over a few-hour flight. For a mil-spec engine designed to fly the whole helicopter alone, I'd say it's neglible. Regular maintenance on flight hours would take care of it.

Yup - agree. Only things that may effect wear would be possible 'chattering' due to lack of load - but minimal in terms of wear. However - if you look at the AH start as soon as you accelerate No1 to GI it starts turning the rotor - indicating more load - though I would believe that load/wear would be more borne by the MGB input drives and not the engines.

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  • ED Team
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In normal operations, AH-64D's in the US Army were/are always started with the left engine (No 1) first.  It's not an absolute requirement, it's just common practice unless there is some other reason, like a maintenance test pilot evaluating certain things on the right engine (No 2) without the need to start the left, etc.  I can't speak for British Apaches since they have a different engine setup than US AH-64D's, but any un-equal wear and tear on the engine or nose gearboxes by starting the left engine first is statistically insignificant compared to the stresses the engines and powertrain routinely experience in flight, which is within its design tolerances.


Edited by Raptor9
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Afterburners are for wussies...hang around the battlefield and dodge tracers like a man.
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2 hours ago, Raptor9 said:

In normal operations, AH-64D's in the US Army were/are always started with the left engine (No 1) first. [...]

Awesome, thanks for your answer, that's exactly what I was looking for! 🙂

2 hours ago, key_stroked said:

Pfft I start both at once. Equal wear and tear! And 1/2 the time spent starting up. 👍

Good one! 🙂


Edited by Yurgon
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I'm not sure of the TBO's on these engines, but on commercial airliners, with the typical requirement to achieve the highest possible cycles/hours on wing before servicing, there is a requirement to alternate the starting engine - given that engines are serviced based on hour spent running, and no attention is given to what kind of running (except limit exceedences), we have to 'spread the joy' otherwise over time, a significant hour buildup will occur on one engine.

 

Our company starts the downwind engine first during pushback, which randomly spread the time over both (in theory). I can understand that the military might just keep things the same though, the difference is indeed almost insignificant (especially with such a short startup cycle in the Apache - an airliner start cycle can be a lot longer: even only one days operation might result in 5-6 minutes difference in engine running times......multiply that over 365 days of operation, and one year means ~33 hours of time difference).

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6 hours ago, ARM505 said:

I'm not sure of the TBO's on these engines, but on commercial airliners, with the typical requirement to achieve the highest possible cycles/hours on wing before servicing, there is a requirement to alternate the starting engine - given that engines are serviced based on hour spent running, and no attention is given to what kind of running (except limit exceedences), we have to 'spread the joy' otherwise over time, a significant hour buildup will occur on one engine.

 

Our company starts the downwind engine first during pushback, which randomly spread the time over both (in theory). I can understand that the military might just keep things the same though, the difference is indeed almost insignificant (especially with such a short startup cycle in the Apache - an airliner start cycle can be a lot longer: even only one days operation might result in 5-6 minutes difference in engine running times......multiply that over 365 days of operation, and one year means ~33 hours of time difference).

I've flown airliners in flight sims for many years, and I've heard of many company SOPs stating that the downwind engine would normally be started first. If memory serves me, on aircraft such as the 737 it's also common to alternate which igniters are used.


Edited by frostycab
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Yup, the 737 igniters get alternated - we start using the right first (due to the right igniters being connected to the AC standby bus, and it's slightly more critical that they work, thus we run them first), then switch as we go.

 

Sorry, off topic, but thats the reason.

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3 hours ago, frostycab said:

I've flown airliners in flight sims for many years, and I've heard of many companies' SOPs stating that the downwind engine would normally be started first. If memory serves me, on aircraft such as the 737 it's also common to alternate which igniters are used.

Which engine is "downwind"

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20 hours ago, key_stroked said:

Pfft I start both at once. Equal wear and tear! And 1/2 the time spent starting up. 👍

You realise that when you break down and the mechanic plugs in the ECU they'll tell you that you've invalidated the warranty, right?

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21 hours ago, ARM505 said:

I'm not sure of the TBO's on these engines, but on commercial airliners, with the typical requirement to achieve the highest possible cycles/hours on wing before servicing, there is a requirement to alternate the starting engine - given that engines are serviced based on hour spent running, and no attention is given to what kind of running (except limit exceedences), we have to 'spread the joy' otherwise over time, a significant hour buildup will occur on one engine.

 

Our company starts the downwind engine first during pushback, which randomly spread the time over both (in theory). I can understand that the military might just keep things the same though, the difference is indeed almost insignificant (especially with such a short startup cycle in the Apache - an airliner start cycle can be a lot longer: even only one days operation might result in 5-6 minutes difference in engine running times......multiply that over 365 days of operation, and one year means ~33 hours of time difference).

Not doubting your expertise but wouldnt it be preferable to have all the engines at a different cycle, that way, you only have to change one engine rather than all 4 or 2 at the same time?

I suppose the detail is in the cost modelling, ie. taking an aircraft out to do 2 or 4 engines at the same time is relatively less time off line than bringing it in twice to do smaller amounts of work?

On 4/3/2022 at 5:04 AM, Yurgon said:

If I recall correctly what Ed Macy wrote about the British AH Mk-1, they would start the left engine first on odd days and the right engine first on even days to pretty much equal out the wear and tear over time.

 

Great book, his descriptions of the Flechettes (spelling.) made my toes curl.

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They actually do almost all the work on the engine 'on the wing' as it were, and a lot of it is 'on condition' as well. It's only really major stuff that necessitates an engine being removed from the wing entirely. I think it's more to be able to plan that, on average, engines will last approximately the same time before servicing if they started off together - but this is absolutely out of my domain as a normal line pilot, you're right 🙂 The engineering dudes handle that side - we're just taught how to operate them, and do so as per SOP's, which the company decides on, I'm assuming for the reasons I've stated. When the aircraft goes in for a C or D check, it's easier and more cost effective to just do all the work on both engines while you've got them there as opposed to taking the aircraft off the line again.

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Just to add to this, some here have said about minimal wear on the engine when running in a minimal torque setting. Starting a gas turbine is a rather stressful event for various components as follows:

1. During startup the engine accessories gearbox receives higher loading as it is have to drive the entire gas generator (GG) rather than being driven by GG. The intial rotation puts quite a torque loading on the accessory drive shaft and drivetrain to the starter. All while lubricants are at sub optimal temps and pressures ...see point 2.

2. Oil system becomes quite loaded as well as the oil is at sub optimal temperature, this creates high pressures while warming up and stresses the pumps and delivery system. The oil system is also (briefly) bypassing the cooler and filters at these pressures to prevent damage to the narrow oilways in these components. You can see these pressure spikes on the ENG page during startup. 

3. Bearings, a gas turbine has numerous sets of ball, roller and taper roller type bearings along the main shafts of the GG and Free Power Turbine shaft , these require lubrication, at sub optimal Ts and Ps these bearings wear a lot faster also a lot of the time these bearings are sealed by labyrinth seals where air ducted from the compressor seals (and cools) the bearing. Again at intial startup this oil is just flashing past the bearings back to scavenge as there is very little sealing air until the rpm increases.

4. Combustion chamber and turbines. Due to the low levels of mass flow at startup the combustion chamer and turbines receive a spike in temperature at light off. This is why you'll often see a Turbine Inlet Temperature limit that is higher for start than the limit for normal continuous operation. Exacerbating this is that the free power turbine is static through these high transient temperatres (until you see the blades start to turn) which creates uneven temperature distribution on the blades.

In summary this is why engine lifing is far more complicated than just hours run. Components have lives based on starts, GG cycles, FPT cycles, hours run, autorotations, One Engine Inoperative time etc etc.

 

During engine replacements we'd quite often try and make sure to even things out by giving engines that had been number 1 a bit or a rest by popping them in the number 2 position (if only it was as easy as "popping" them in!!)

Hope that helps and gives some insight.

Former Apache, Gazelle, Wildcat Mechanical Engineer.

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Personally in game I prefer to start the right engine first, because otherwise the left power lever will obstruct the clickspot for the right starter switch somewhat. 

As has been mentioned in this thread, British do the alternating routine, depending if it's even or odd day of the week, at least according to Ed Macy's book.

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Guess its not enough stress to make a difference but even if it was it would encourage to always use a specific one since that one would have an altered maintenance scheldule because of that while not having to check on both more often (or would even have some extra reserves built in to help with that)

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