Setting Prop Efficiency/Thrust

[AER_DaddyO]

Hello all,

When opening airfile section 511 with AirEd 1.52, the "info" in the drop down menu indicates that there is a research doc on how to set values for Propeller Efficiency in Section 511 and Thrust Coefficients in Section 512. I've looked high and low and can't locate the research doc. Lol.. it's most likely right under my nose, and I'm just not seeing the forest for the trees. Does anyone out there know the whereabouts of the research doc ?

Thanks In Advance, AER_DaddyO

[fliger747]

Welll.......

My Aired donn'a tell me, ah..... much. The mysterious prop tables. I suppose someone around here like Jerry Beckwith, Rom Friemuth or Milton Shupe might have some vague (or better) idea what the entries mean in the table and be able to raw edit with predictable results. For many of us it is a bit like a dog looking at a calander.

Given how the Microsoft Flight Simulator approximates reality, it is amazing that these tools, and the sim itself do as well as they do!

As a practical matter, Jerry's Workbook or Airwrench, seem to be a good way to generate values that are useable. Or go steal a table from a plane that seems to be appropriate.

What would be great would be a really comprehensive reference on all of the ins and outs of the FM and it's editing. Some partial explanation lists do exist which are quite helpful.

Sorry for not really answering your question.

[sparks]

I wrote the paper you're looking for, and I'm sure I've got a copy of it somewhere. I'll dust it off and post a copy on my website. Stay tuned...

[sparks]

I've leaned out the original paper (written 6 years ago) and posted it on my website:

http://www.mudpond.us/fs_props.pdf (http://www.mudpond.us/fs_props.pdf) (41kb)

[fliger747]

Thank You sir!

The mathematical method by which FS calculates THRUST seems straightforward enough. It's the raw table values, which one is often exposed to, which in numerical, tabular presentation, as opposed to your graphical presentation, seem a bit less than illuminating.

Cheers!

[sparks]

The charts in the paper were made by dumping the air file data to a text file with AirUpdate, loading the text file into a spreadsheet, and using the tools in Excel to plot the data. With the data charted, it's a lot easier to recognize for what it is and manipulate it.

The process can also be reversed with AirUpdate. Data can be cut from a spreadsheet, pasted into a text file, and used to update an air file - which is basically how the Flight Dynamics Workbook functions. :)

[AER_DaddyO]

Thanks for your responses. Using the formula supplied in your document, I was able to rethink the advance ratio on a CFS2 SPAD XIII, and ultimately get the result I was looking for. She will now maintain the correct engine speed of no more than 2100 RPM from take off, clear up to ceiling. She'll now also do an extended dive approaching 200 MPH and not gain any additional RPM over 2100. I am continually amazed at the knowledgeable and helpfull folks that I see on this forum.

AER_DaddyO

"Don't just stand there...get one up!"

[magoo]

AER_DaddyO
She'll now also do an extended dive approaching 200 MPH and not gain any additional RPM over 2100
....The big fixed pitch prop could easily drive SPAD's engine into overspeed while diving.

Most of these old mills like the Hispano V-8 could exceed their max "rated" rpm/hp quite easily.....but the odds of them holding together was the real issue. ( The difference between the Hisso 180 hp and 220 hp was essentially an engine that could better hold it's parts together rather than any major improvement in efficiency.

An interesting exercise in WW-1 flightsim model might be a fixed pitch aircraft that could maintain rated HP/RPM in a climb at max (safe) engine temp, but could scream into overspeed and potential engine failure if the pilot let 'er go in a dive/fast descent. (We'll not get into wings tearing off....) :)