Units for First Limit Indicator

[simps7b2]

Hello Everyone,

I am learning how to use a First Limit Indicator (FLI) for the AS350 B2. I read up on the patent here: https://www.google.com/patents/US6195598. In the patent it indicates that the units of the FLI display is in percentage of max collective pitch.

Based on this information, my understanding is that the FLI calculates what your "max" collective position is based on the first limit. So if the system projects that the Ng will reach the max continuous rating at 80% of max collective input (where Ng is the first limit), then the display will be calibrated such that the needle is proportional to collective position and displays 100% when the collective reaches 80%. IE - FLI percent = collective position percent * 1.25.

Is this a correct understanding?

Thanks,
Ian

[212man]

The whole point of an FLI is that the origin of the units is irrelevant. If the limit is 10, stop pulling at 10....

[TeeS]

Hi simps7b2

Assuming the B2 works in a similar fashion to the EC135 then collective position does not have any direct effect on the FLI.

3/4 collective pitch will produce completely different Tq/TOT/N1 indications depending on pressure altitude, temperature etc. As 212 says, it doesn't matter whether you are limited by Tq, TOT or N1, if the book says you can pull to 10 for take off, you can pull the lever up until the FLI says 10 - the collective position will be in a different place on different days.

Cheers

TeeS

[Gemini Twin]

Ignore the patent info. it will just confuse you. Check a EC135 flight manual supplement for the LCI kit. It makes more sense when you don't have to make up your own examples.


From an Airbus site:
Technology

The intelligent sensing of an aircraft’s engine parameters is provided by the First Limit Indicator, which supplies the pilot with pertinent information about the engines’ operation based on the phase of flight.
Description

The First Limit Indicator enables pilots to view the appropriate engine instrument data that is most applicable for a particular aspect of an aircraft’s operation. As an example, certain engine instrumentation data is more relevant when starting an engine, and will be made more evident during this phase. Different data will be displayed more prominently when pilots need to be informed of other pertinent information – such as critical power settings or when operating limits are exceeded.

Applications

Aircraft and helicopters.

Value-added benefits

First Limit Indicator display technology significantly improves safety through reduced pilot workload, improved cockpit situational awareness and more rapid identification of engine operating parameters. It takes full advantage of flat-panel glass cockpits, which eliminate individual engine instruments, while assimilating data so that pilots do not have the challenge of monitoring multiple indicators.

Status

Available for use.

[jayteeto]

Units are called bananas by me, seriously.
Don't care what the numbers are, just use the indicated limits.

[simps7b2]

So where would one procure an EC135 flight manual supplement for the LCI kit? Is this something purchased from Airbus directly or available through the interweb? Right now I'm using a AS350B2 manual, but it doesn't have the VEMD. I may invest the $$ to get another manual with the VEMD info in it.

[simps7b2]

Thanks for the replies, but units do matter to me a little. We're working on building a simulator and if the units aren't quite correct then the simulated VEMD will not behave exactly the same way as the real one (except when at 0 or 100%). I don't know if anyone would notice, but a picky test pilot might.

[TeeS]

Unfortunately it just is not that simple. You might be able to get torque and TOT figures with their equivalent FLI figures from the relevant flight manual (for instance for the EC135T2 13.5FLI equates to 128% TQ and 13FLI equates to 125% TQ) However, when you are N1 limited, the maximum N1 will vary depending on pressure altitude and temperature. So, at one location, 10FLI may equate to 99.7% N1 but at another location, or the same location on a different day, 10FLI may equate to 102.2% N1[Note these are completely made up figures].

Sorry I can't be more help but if someone can send you a copy of the limitations page from the RFM for the B2, that might give you a starting point. It's possible that the scales are not even linear.

Cheers

TeeS

[turbinturbin]

Airbus has an app which simulates the VEMD, maybe it will help you understand how it works. It is probably a lot cheaper than a flight manual.

https://play.google.com/store/apps/details?id=air.com.airbushelicoptersinc.vemd

If you search this forum i think you can also find the flight manual.

[simps7b2]

Yeah I've got that app. I don't seem to be able to adjust the units or watch the collective input with it though.

[simps7b2]

@ TeeS:

I do have a flight manual for a B2.

Max transient tq = 107%
Max takeoff continuous tq = 100%
Max cruise continuous tq = 94%
Max transient Ng = 107.5%
Max takeoff rating Ng (no bleeds) = MTP = 101.9%
Max continuous Ng = 98%

Anyways; these values give me places to put the red marks on the gauges, but no way to make the gauges respond correctly to atmospheric changes. It is starting to look like the only way to correctly calibrate a simulated VEMD is to take a test flight. Using the power check chart would be nice, if it was easily discernable: see http://www.pprune.org/rotorheads/540760-trying-decipher-as350b2-power-check-chart.html for that discussion.

Not too worried about T4/TOT, because French engines are designed to not be temp limited is what I've been told.

An interesting side note about the flight manual: it says that MTP = 101.9% = 0 delta Ng. It also says that MCP = 98% = -3.5 delta Ng, but 3.5 + 98 = 101.5???

[simps7b2]

Actually I'm starting to understand the engine performance check chart. I think I'll go ahead and use that to calibrate the FLI needle for now.