Takeoff EPR for Spey engine

[clavel9]

Hi all

I'm wondering about the following. While I know most One-Elevens and Tridents were typically fitted with Thrust Index gauges (David Maltby's included!) I was wondering if anyone knew what a typical takeoff EPR setting would be for a Rolls Royce Spey engine. I do know that 727's using JT8D's had a takeoff setting in the range 2.00 - 2.02. One-Elevens for the US market seem to have been fitted with EPR gauges.

Thanks in advance,
Brendan.

[DaveB]

Hi Brendan,

This is a question that's been asked before and is not particularly easy to answer as the EPR (Thrust Index) setting is dependant on a number of factors. Two basic ratings are used.. A and B. Rating A gives 3% less than the maximum Spey 512 defined thrust level and can be used to reduce engine wear when sufficient takeoff distance is available. This equates to 12,650HPrpm and 595degC. Rating B is max power.. 12,800HPrpm and 600degC. Overspeeds up to 13,290HPrpm are allowed as long as the total time above 12,800HPrpm is no greater than 20seconds.

To complicate this further, the charts are different for pod engines and again, for pod engines with anti-ice on plus, centre engines (on the Trident) and again, centre engines with anti-ice on. All in all, there are 8 charts to cover all of the above scenarios and then you add the pressure and temperature components to arrive at your thrust index :o

To make it easier and give you an example, I've chosen 'a' pressure setting of 1010mb and an ambient temp of 0degC and this is what you get..
Rating A - pod engine - engine ice off - 137
Rating A - centre engine - engine ice off - 116
Rating A - pod engine - engine ice ON - 138
Rating A - centre engine - engine ice ON - 117
Rating B - pod engine - engine ice off - 153
Rating B - centre engine - engine ice off - 131
Rating B - pod engine - engine ice ON - 153
Rating B - centre engine - engine ice ON - 132

Note that for each of the above settings, the variation ranges from -40decC to +10decC and 840mb to 1100mb so there is room for deviation from these Easily though, you can see a differential of around 20degC between Rating A and Rating B and with/without engine icing ;-)

ATB

DaveB :tab:

[clavel9]

Hi DaveB

Thanks once again for your prompt reply!

I do have a set of Thrust Index tables for the Trident 1E. I suppose what I don't understand is the correlation between Thrust Index (expressed as a percentage) and EPR (expressed as a ratio!). I DO know that an EPR reading of 1.0 equates to zero thrust and I do know that Thrust Index needs to read 100% or over for takeoff. What I don't know is what a typical takeoff EPR would be.

All very confusing...

Brendan.

[DaveB]

I thought that myself Years of mixing with the elite on here that does it ;-)

ATB

DaveB :tab:

[MALTBY D]

And he taught me all I know about it.
Which explains a lot.

American Airlines used to have a P7 EPR gauge, rather than the thrust index.
It displayed in inches of mercury. Sadly the manual I have doesn't contain the tables giving minimum P7 for takeoff.
It does mention reaching around 44 in by a certain point in the takeoff run, but I assume the level would rise after that.

What is almost certain is that if you plug in a bog standard EPR gauge into the 1-11, it will be very unlikely to show an accurate reading.
I've never had need of true EPR readings on my panels yet & so don't ever get to see what FS reckons the value to be.
I suspect that there will be some kind of scalar in the air file that you can adjust to get a better reading. Another FS illusion.
My thrust index gauges don't use the FS EPR value.

DM

[DaveB]

Hi DM..

In between work and work, I nipped up and found the relevant section in the AA Flight Manual and of course.. it isn't there If anyone has a copy of the 1-11 Flight Performance Manual, that publication lists the relevant P7 figures ;-) In fact, the AA 1-11 manual describes it as EEP (Engine Exaust Pressure) not EPR but my uneducated guess is that they're one and the same ;-)

Now then.. were we talking 510 takeoff procedure or 511! :o :roll: :partyman:

ATB

DaveB :tab:

[DispatchDragon]

Because the first two Dan Air 1-11s XCK/XCP were ex AA and fitted with P7 gauges - In typical DAE fashion ALL 1-11s after were
fitted that way - David your numbers are spot on and of course His lordship is totally correct - I have the an AA manual
I bought at a wonderful store in San Diego (Ocean Beach) which I bought only because it has my mothers initals in it as
being the original BAC compiler in 1963 -

For Brendan (and anyone else who enjoys the level of realism afforded by Lord Maltbys models)

The P7 and EPR values are indentical - Dave I hope you dont mind - for those NOT familar with what
we are talking about may I suggest http://www.grc.nasa.gov/WWW/K-12/airplane/epr.html
It gives a graphic representation of how the EPR/P7 values are worked out.

Tonks NOT sure how you do it on the Queen of the Skies - But on the DAN 1-11s The PNF would put his hand below the
PFs on the throttles and inch them forward until the correct P7 value was reached where he would tap the PFs hand
so he didnt have to look at engines gauges - The PNFs job during takeoff was to monitor those

The same applies to just about every Airline Ive worked for over here - the PNF sets EPR using the ATOGs (Take Off
performance charts for specific runways by weight/temprature and pressure) and then monitors them

As a silly aside with the MD80 using JT8Ds (217/219) the values are simply given as a max and min EPR setting giving a
band of .05/07 on the setting requiring that one maintains power within that band for takeoff.

Cheers

Leif

Sorry got all excited by real airplane talk - AA Manual says 1.72 Hgb to 2.09hgb max operating then as Dave says
operational settings by Density Altitude and bleed functions operating - (amazed to see there were no pack-off
values in the table)