View Full Version : Required Takeoff EPR?
12-17-2004, 04:58 AM
Hello, first of all: great airliner, the best so far!
Now my question, I couldn't find the answer in the manuals.
How do I figure out the required take off EPR needed? How do figure out the reduced thrust settings? The only table I can find in the manual is a "max take off EPR" setting, depending on pressure and temp. But as I am understaning the subject, T/O EPR is depending on the weight, weather and runway length.
Maybe anyone can help me here.
Thanx in advance.
12-17-2004, 06:28 AM
You were lookng at the correct table Frank. Max take off EPR is the mechanical limit you impose on the engine by choosing to only set the thrust at a given given amount - as opposed to just firewalling it and crossin your fingers :-)
As you said, this limit reflects pressure and temperature. However, runway length and aircraft weight have nothing to do with engine limitations........perhaps you are looking for something that would give you take off roll based on weight and Max EPR?
12-17-2004, 08:01 AM
Hmm thinking ... hold on.
12-17-2004, 08:32 AM
Thanks for your answer.
But how do I then calculate the "REDUCED TAKE OFF THRUST" ?
Normaly you can calculate this thrust by entering the Runway lenght, weather data, T/O flap setting and I believe the weight.
12-17-2004, 08:50 AM
Well, at first I must admit that I am not a real life pilot.
I think you are right but you will need a seperate chart for each runway as far as I know.
Things also depend on obstacles in the climb out path and so on ...
Furthermore it is quite difficult to get a hand on those charts.
12-17-2004, 09:10 AM
Well I hate to mention other addon products but RFP supplies a little tool to calculate the reduced take off thrust. I was just looking for a simular way to compute the reduced thrust for the 727. But I guess it's not that important.
The thing is, that you allways give full thrust for take off.
12-17-2004, 09:29 AM
I know about that EPR calculator for the RFP 747.
Just use the max. EPR table and you are fine - the max. EPR is not equal full thust by the way. I understand this setting as the maximum technical sensible power setting. There is a standard or reduced EPR setting but I don't know how to compute except using those runway charts which I don't have ...
12-17-2004, 11:20 AM
Ok, thanks anyway.
12-17-2004, 10:11 PM
>Ok, thanks anyway.
The boeing727 site (I think the URL is in the DF document) has added more 727 charts. There was also a header "how to save your company $600,000 for hush kits".
It said one could reduce TO EPR to 1.68 and use Flaps 5 (assuming enough runway) and the old turbines would meet noise specs.
While one lands with Flaps 25 and lower EPR at a few kts faster than with Flaps 30.
I tried it and had no problems. I may have used too much of the available runway with my 160,000 lb TO weight, but lifted off some distance before the end of 27L at KORD. Summer temperatures would increase TO distance.
There are lots of charts on TO peformance, I'm not sure what all got in the big DF manual.
If I thought about it I could probably estimate TO distance relative to normal TO Fuel Flow since Thrust is proportional to PPH.
That 727 site also has some 'rules of thumb' for required cruise EPR as a function of weight, etc.
12-18-2004, 10:06 AM
Suffice it to say that the tech data excerpts included with the sim are an extreme simplification of the process needed to derive r/w takeoff perf data. For example, the provided V1-VR-V2 charts do not take into account runway length, RCR, RSC, rwy slope, stopway or clearway available etc. To do it properly, you need the tech data...a 2-3" inch thick volume of charts...and 30 min to an hour to make the trip through a pretty long series of charts...and that's if you know what you're doing. Not exactly practical or appealing to most simmers.
That said, you can estimate a reduced takeoff setting by assuming a temperature approximately 20-40 deg F higher than actual, and use the power settings and VSpeeds for takeoff at the assumed higher temperature. Of course, since we don't have charts that depict rwy required for takeoff, it's possible you may not have enough runway with the reduced setting. Of course it's also possible you don't have enough runway at max TRT either. On a 12000 footer at sea level, it's probably not a problem...but on 6300 feet at 6500 ft field elevation (e.g. KJAC), it's probably not a great idea.
For sim use, a takeoff distance chart (brake release to liftoff) would be a useful flight planning tool.
ATP IMEL Gulfstream II-III-IV-V L-300
12-18-2004, 11:54 AM
>You were lookng at the correct table Frank. Max take off
>EPR is the mechanical limit you impose on the engine by
>choosing to only set the thrust at a given given amount - as
>opposed to just firewalling it and crossin your fingers :-)
>As you said, this limit reflects pressure and temperature.
>However, runway length and aircraft weight have nothing to
>do with engine limitations........perhaps you are looking
>for something that would give you take off roll based on
>weight and Max EPR?
I found a "Boeing 727 TAKEOFF PEFORMANCE Chart" on my HD. It accounts for Wind, runway Slope, Flaps, TO Weight, OAT, EPR and available runway Length. Tricky to use, one has to zig-zag through several charts.
It appears setting 'average EPR' to 2.00, with Flaps 5 is sufficient for 8000 ft of available runway and 167,000 lb TO weight. 15 C, zero wing, zero slope.
I'd assume that's over a specific obsticle, perhaps with quite a safety factor.
Lowest EPR on the chart is 1.96, other lines go over 2.2, I'd expect for higher rated JT8D models. It also goes over 200,000 lb, since some later 727's were rated for that.
It's over 200 kB, too large to attach here.
12-18-2004, 01:10 PM
sounds interesting, Ron - could you send it to me by email ?
Maybe (I pronounce it again, m-a-y-b-e) I can include it in an update of the docs then ...
12-18-2004, 02:10 PM
the chart sounds interesting. Maybe you would like to e-mail it to me too (firstname.lastname@example.org)?
While we are at it. Is there a tool to calculate the needed trip fuel?
12-18-2004, 02:13 PM
check the Planning and Performance Chapter of the manual ...
12-18-2004, 02:29 PM
yeah, I recognized the table. Was just looking for a more convinient way to calc the fuel.
By the way, the documentation is just fantastic. Turned out very well.
12-18-2004, 02:37 PM
glad you like it :-)
I meant the four tools I mentioned in the Planning & Performance Chapter ...
12-18-2004, 02:43 PM
12-18-2004, 02:50 PM
- Flight Operation Center by Urs Wildermuth and Heinz Oetiker
- FS Build by Ernie Alston
- Keroplan by Mario Fiebig (freeware)
- FS Navigator (does it ptovide a fuel calculation ??? I don't know ...)
- Another one: http://www.pmflightplanner.com (freeware and online)
Hope this helps
12-18-2004, 02:58 PM
Oh that you mean. Well I think I'll give FSBuild a try then.
Might be the best way to calc the fuel.
12-18-2004, 04:59 PM
>the chart sounds interesting. Maybe you would like to e-mail
>it to me too (email@example.com)?
Just emailed it to you and Paul.
Hope you can figure it out. ;)
>While we are at it. Is there a tool to calculate the needed
I'm sure there are charts, I think the DF manual has a table of fuel burns for various flights. I imagine one would have to add some extra for winds and also for a standard reserve.
If the AC is flown to the book, fuel consumption should be quite close. BTW, it's a bit lower for the -100; shorter fuselage means less skin drag.
12-18-2004, 05:12 PM
>sounds interesting, Ron - could you send it to me by email ?
Just sent it, I'll find out if the email address I used works.
12-18-2004, 07:05 PM
Look at the "Fuel How Goes It" charts on www.boeing-727.com
Ron...could I trouble you to e-mail that takeoff data chart to me as well?
w6kd AT yahoo D0T com
ATP IMEL Gulfstream II-III-IV-V L-300
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