hevansrv7a

hevansrv7a

Well Known Member
I'm trying to develop a spreadsheet for modeling engine power in aircraft. I'm taking an approach that I don't think anyone has used yet (or I just missed it). I've done pretty well with Superior and Lycoming stuff, but I need similar data on Conti and Rotax if I can get it:

HP by MP and RPM, S.L. vs altitude, also, if possible.

Can anyone point me in the right direction for this? I've had zero luck with Google.

If I get this finished in time, I will include it with my presentation at AirVenture (Friday 11:30 at HomeBuilder's Hangar).

Thanks.
 
suggestion

I dont know were to get the data for all the engines you discused however in order for the info to be useful to me, I would need HP vs RPM & Torque vs RPM plots for all engines. Horsepower alone is of limited value to me. Good luck, Russ
 
Thanks for the advice?

AK4x4 said:
I dont know were to get the data for all the engines you discused however in order for the info to be useful to me, I would need HP vs RPM & Torque vs RPM plots for all engines. Horsepower alone is of limited value to me. Good luck, Russ
Click to expand...

Russ,
Forgive me if I re-state the obvious, but if you have HP and RPM then you already have torque because RPM x Torque / 5252 = BHP. This is physics and does not change for any engine.

Getting to real HP is both worthwhile and a challenge for a few reasons:
1. We cannot measure it directly in flight without a torque meter and those are either impractical or don't exist for our little GA aircraft.
2. It is a key component in understanding the performance of the aircraft and the efficiency of the propeller. See my previous spreadsheets for more.
3. The advertised power of the engine is not a reliable fact for many reasons.
4. The interpolation of values of Altitude, temperature, RPM and MAP on the manufacturer charts is awkward so a calculator would be useful and many have built them for that reason. And that's if you could believe their stated maximum value.
5. We cannot properly understand engine efficiency (power from fuel) without understanding how much power and how much fuel; the latter is easy, the former is not.

I am working on this problem on two "fronts" at once:
1. be able to read and use manufacturer charts more easily and more precisely and..
2. be able to measure actual power of an engine while it is on an airplane. This will allow using the solution of #1 to get to "truth".


The approach for #1 is why I am requesting chart data for non-Lyco's.

The approach for #2 will be to use the test "club" that Lonnie Prince built for me per the design specifications from Jan Carlsson on the HBA forum.

I think quite a few pilots will find value in this for their experimentation on RV's and even on other aircraft. But that's just me.
 
So are your tables going to include operating on the LOP side of things?

Rich of peak operation HP is determined by mass airflow, LOP = fuel flow.

Just wondering.

I love the science you guys apply to your flying, drag and so on....I must be lazy. :eek:
 
LOP - not useful for this

RV10inOz said:
So are your tables going to include operating on the LOP side of things?

Rich of peak operation HP is determined by mass airflow, LOP = fuel flow.

Just wondering.

I love the science you guys apply to your flying, drag and so on....I must be lazy. :eek:
Click to expand...


Actually, it will be a spreadsheet, but not a table as such - using the ability of the spreadsheet to be a set of data and functions and so on. A program without real programming.

The short answer is "no" because fuel flow and assumed SFC are all you need. Now for the long answer - the one that shows why I'm doing all this.

How do you really "know" what your SFC is? Well, one way would be if:
1. You know the BHP that you are actually using at "best power" setting for a particular flight profile (altitude, weight, speed..).
2. You know the fuel flow for #1 and you sort of know your best power SFC is around .50 pounds per HP per hour.
3. Now you fly the same profile while LOP and check your fuel flow and you can "know" your LOP SFC which can be used to project to other power settings with reasonable (not exact) precision.

Or you can just use 0.40 for the SFC and call it a deal. It's not going to be any better than 0.38 and unlikely to be worse than 0.42. But that's a 10% spread from top to bottom.

BTW - my engine analyzer is probably wrong when it gives me SFC and my guess is that the others are wrong as well because there is no way for them to know your HP except by assuming a SFC to begin with.
 
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