validator

Hello,

I'm kinda lost among some information for a study im trying to complete.

We know that TS engines have 30s, 2min and continuous OEI power limits, Take off and continuous AEO limits.

Performance class 1 and 2, so category A requires that, in the event of a power failure in an engine; the other engine has to either make a safe landing or continue the operation at hand.

Imagine I am a pilot and my halicopter is capable of commencing cat-a operations, and i have an engine failure after TDP, and i decided to carry out the operation at hand.

I raised to 1000ft height, set to OEI max. continuous power to reach the destination.

Ok this was the scenerio uptil now. my question ( comes from now on =) )

Does the OEI(max. continuous) power means that im running my engine at %100 capability? (hence 30sOEI is about %110-%120, and 2minOEI is about %105-%110) (similarly AEO TO and AEO continuous are about %100 - %90 capability, respectively)

lastly, does the usage of any of the above power ratings (30sOEI, 2minOEI, max.cont.OEI) requires a maintainance on the engine? or are these values in these time intervals are completely safe?

I know questions are pretty easy and fundemental, but I have to validate the answers in order to continue with the assumptions im making in my study.

any help is appriciated =) thanks in advance

Thomas coupling

Hello Validator.
What r u doing in Turkey - one asks?

Your question is ambiguous. In that if you continue to fly after OEI (why continue?) and you fly at Max Con, then that figure is decided by the OEM to provide a margin of safety for the turbine temperature and blade centrifugal speeds. I don't believe it is based on engine output performance although this is a side effect.
You could, of course, pull to the 30sec and 2min OEI for those durations and then immediately back off to max con and then re-apply the 30sec and 2min once more - continuing with this cycle ad infinitum!
I'm not sure what you mean by "capability"?

Your second Q: Each OEM will lay down in the Maint Pubs, what checks must be carried out (if any) when applying and sustaining these engine/gearbox limits [30sec/2min/max cont]. Because at the end of the day you are stressing the turbine blades.

In some a/c, reaching and sustaining max cont or beyond in excess of the laid down limits, requires one to reject that entire engine

ShyTorque

"Ad infinitum" isn't possible for all turbine engines, it depends on what the manufacturer says. Some are certificated only for a defined cumulative time, after which the engine needs an overhaul.

HeliComparator

It depends on the manufacturer I suspect, but for French engines you normally need maintenance checks after exceeding OEI continuous. Probably depends on the duration but I think if you used 30 secs of the 30 sec rating, it would be overhaul time.

This is why, for an intentional in-flight shutdown eg for a Chip, our pilots are encouraged to be careful to back the power off before shutting it down, so that the remaining engine doesn't run above OEI continuous. Otherwise you have 2 engines to change after landing, not just the one!

212man

Not really. The term 'capability' doesn't really mean anything in this context, and the limits for the different conditions may be based on different parameters - Ng, TGT (N1, T4 for HC...) or Torque. They will also be determined with respect to the overall engine life and reliability and frequency of use.

It will - as stated - vary between engine manufacturers, models and varients of models. I believe the Makila 1A1 allows 10 minutes of cumulative time spent in the 2.5 minute range before maintenance action, for example. If you look at the Ariel 2 series, the 2S1/2C1 model requires an engine (well, hot end module) change after even 1 second in the 30 second range, whereas the 2S2/2C2 model allows 30 second cumulative time within that band.

riff_raff

All powerplant ratings specified by the aircraft OEM (MRP, MCP, IRP, 30sec/2.5min OEI, etc.) are by definition 100% of engine capability. These are the ratings that the powerplant installation was certified to under regulations like FAR part 33. While the OEI horsepower ratings are typically around 10-15% higher than the AEO MCP rating, the engine speed associated with the OEI rating may be well below the max operating speed limit of the power turbine.

Once again, operating the engines within the limits/conditions specified by the OEM should be safe by definition. That's why aircraft designs are put through a rigorous certification process. However, with most modern turboshaft engines, once they are operated even briefly at OEI conditions they immediately require certain inspection and maintenance procedures. The reason for this is that modern turboshaft engine designs are very high performance, and as a result many of their components have very small margins for excessive dynamic loads or temperatures. In order to produce the higher engine power output needed for OEI conditions, the only practical approach is to burn more fuel, which increases the TIT. The high TIT produced during OEI operation is extremely hard on the turbine nozzles and blades.

After OEI operation it may also be necessary to perform inspection and maintenance on some parts of the transmission, such as the overrun clutch or the bearings and bevel gears of the input stage.

Here is the relevant section of FAR part 33 if you'd like to read up on the subject.

Shawn Coyle

There are ratings, and limitations.
The ratings are for the power produced, and the limitations are for protecting the engine to allow continued use.
Some engines have cumulative limits on OEI use - the P&W 206/207 engines that use 30" ratings, for example, have a cumulative life of 2 minutes at 30" power, and then the engine comes out for maintenance.
The same engine can be used in different airframes with different ratings - some airframes use 2 minute and 30" ratings, which have very tight tolerances on exceeding the limitations in those ranges, while another airframe may use 30 minute and 2.5 minute ratings which have more generous exceedence limits.
Confused yet?

[email protected]

As Nick Lappos used to say - regard your engine as a jar full of beans - you can use the beans slowly (operate within normal limits) or use the beans quickly (using contingency power) but when the beans are gone, they are gone and it's time for overhaul.

vfr440

Crab, I like that . Perhaps I may use it on occasion with young ab-initio trainees (and maybe also more mature disbelieving customers) It is a particularly aposite analogy, and cheers for bringing it up! - VFR

AnFI

If an engine, which has shared the same history as one which has just failed, is asked to make more power than it ever has before (ie the 30 second rating) is the risk of it's failure in that 30second period still only 1 in 100000 x (3600/30) - ie 1 in 12,000,000 (based on the oft used 1:100000 per hour failure rate) ? (I don't think so)

If an old engine is at 10% of its beans remaining, and 30seconds burns all the beans of an engine life, then there might be some beans missing!

TeeS

Hi Validator

As a general rule, the twin engine takeoff power limit will be to protect the gearbox, it may not be capable of absorbing the combined power of both engines at more than this power setting. Either engine will probably be very capable of producing more than this power continuously, if fitted in a single engine helicopter for instance or if the other engine fails.

TC's comment that you can keep 're-applying' the 2 minute or 30 second power is incorrect - for instance on the EC135 (with TM engines) the engine is designed to provide three bursts of 30 second power in their lifetime (if memory serves me correctly).

Cheers

TeeS

validator

thanks for all the answers, I have been reading too much lately, especially on the reliability of TS engines, what you guys wrote here helped me a lot.

take care