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fs2004 air file- engine horsepower setup

MaddogK

MaddogK

Sim Junkie
Greeting all,
I'm hoping someone could help me out with a small headache I'm struggling with. I'm rebuilding one of my air files and tho I've got the max HP, engine drag (about 12% across the board), fuel consumption, prop speed and proper thrust I've discovered my fuel burn rates and HP go WAY below what they should be at cruise setting. My 'J' value is almost constant from 1800-2300, but tho my BHP is correct at full thrust at 2000 RPM I'm over 100HP under what my docs say my output should be. I don't have enough HP even if engine friction was 0. Since the 'J' value barely moves there's not much I can do with prop efficiency and there's not enough points in record 508 to compensate for the quickly falling HP.

Any ideas ?

Its a Curtiss D-12
carbureted
1:1 prop drive
470hp @ 2300 .58 lb per hr per hp << perfectly dialed in
415hp @ 2000 .54 lb per hr per hp << Should be 415/2000 but I'm getting 310hp BEFORE engine drag applies, about 105 pph burn rate
210hp @ 1850 <<< My eco cruise setting is 1850 rpm but 210 HP CANT be right, it should be about 385hp
 
From my experience, 508 (which you have been playing with) & 509 affect output & hence fuel consumption, but also the curves for 511 & 512 will feedback & affect power & hence fuel consumption. Tricky one, just keep experimenting & good luck.
Mind you aircraft attitude & hence induced drag at certain speeds will mess up almost everything!!!
Keith
 
Thanks Dev one, thats exactly what I've been doing, but you're right- my CDi is high and I know it, it's an uncorrected number from my first iteration of this plane that was an arbitrary 'guess' to keep the engine/prop from overspeeding the A/C.

But guess what, after re-re-reading some of Jerry Beckwiths docs I think I see where I'm getting flogged- RPM (by virtue of the prop records 511 and 512) is needed to alter the J on the power and performance charts, but apparently the A/C MUST be moving to compute the J value and the HP as read by AFSD, but 'GASP'- I think Torque is derived directly from the engine performance records, AND

"torque times RPM divided by 5,252 -- to arrive at horsepower"

...Guess I'm chasing the wrong numbers, eh ?

:bump:

First thing I'm doing is dropping the CDi on the A/C (IIRC it's .05 or something) and flattening out the prop efficiency curve so I have more range on J.
 
While I am pretty sure I can set up something like this for Combat Flight Simulator, there isn't a tunable fuel consumption that I have found. Not sure if this would be useful to you for FS 2004.

- Ivan.
 
Ivan said:
While I am pretty sure I can set up something like this for Combat Flight Simulator, there isn't a tunable fuel consumption that I have found. Not sure if this would be useful to you for FS 2004.

- Ivan.
Click to expand...

I'de appreciate it, but I'm gonna have another marathon session again tonight to see if my conclusion about torque is correct. If it is I should be able to manage the rest without putting you out, but I do appreciate the offer. You can adjust the fuel consumption by altering the engine efficiency datablock IIRC.

I'll report back tomorrow.

PS- you dont' have an accurate curve for a Reed R-1 airscrew, do you ? I have a NACA report but the data is hard to transpose into FS.
 
Don't forget that the prop pitch angle can do a lot to restrict/overspeed the engine or aircraft airspeed, rather than play with the CDi all the time. J also then affected.
Keith
 
Perhaps this thread would be helpful to you. It shows much of my basic method.

http://www.sim-outhouse.com/sohforums/showthread.php?77148-Engine-Performance-Tuning-Tutorial

IMHO:
Don't bother tuning the propeller to start. Even the airframe doesn't matter all that much to start.
Set it as a constant speed prop with enough reduction gearing to be able to achieve full engine RPM at the airspeed you are testing at.

That will show you what your actual engine performance (HP / Torque) is with just engine parameters.
Adjust the efficiency, torque drag, supercharger to get correct power at full RPM at SL and at altitude.

You can then adjust efficiency to get the proper cruise HP settings at less than full RPM and manifold pressure.
Be careful here because sometimes the numbers won't actually fit together.
I was once trying to tune a Wright R-2600 and found that once I had the correct cruise setting, I could just raise the manifold pressure at the lower RPM and actually get more power than I was getting at full RPM because the effiiciency was so much better at reduced RPM.

After the HP is set properly, you can adjust the propeller variables. If you mess with the propeller first, all the overspeed and lugging issues are going to mask what your engine settings should be giving you.

Just out of curiosity, What aircraft are you working on? (Simpler question than asking about all the engine specs.)

- Ivan.
 
Ivan said:
Perhaps this thread would be helpful to you. It shows much of my basic method.

http://www.sim-outhouse.com/sohforums/showthread.php?77148-Engine-Performance-Tuning-Tutorial

IMHO:
Don't bother tuning the propeller to start. Even the airframe doesn't matter all that much to start.
Set it as a constant speed prop with enough reduction gearing to be able to achieve full engine RPM at the airspeed you are testing at.

That will show you what your actual engine performance (HP / Torque) is with just engine parameters.
Adjust the efficiency, torque drag, supercharger to get correct power at full RPM at SL and at altitude.

You can then adjust efficiency to get the proper cruise HP settings at less than full RPM and manifold pressure.
Be careful here because sometimes the numbers won't actually fit together.
I was once trying to tune a Wright R-2600 and found that once I had the correct cruise setting, I could just raise the manifold pressure at the lower RPM and actually get more power than I was getting at full RPM because the effiiciency was so much better at reduced RPM.

After the HP is set properly, you can adjust the propeller variables. If you mess with the propeller first, all the overspeed and lugging issues are going to mask what your engine settings should be giving you.

Just out of curiosity, What aircraft are you working on? (Simpler question than asking about all the engine specs.)

- Ivan.
Click to expand...

I'm reworking my Fairey Fox biplane using the early 1920's Mk.1 specs- direct drive prop, NO blower or turbo (completely naturally aspirated carburated). It's here in the warbirds library. I have MUCH more early data than I did when I built it and really want to make it right before I rebuild the visual model. Heck, I have the authentic engine dyno data and prop data as well as the flight test data. I just can't make it work right in FS without lying to it to get the proper numbers. I'm completely hamstrung by the way FS calculates the J value, so with my limited RPM range and speed difference between the two with a 8.5-9 foot prop my J only gives me a range of 0.4 to work in.
:dizzy:
I'll re-read your link as I saw it a couple weeks ago but stopped reading after the first post when I saw you were messing a supercharged, constant speed prop airplane and didn't think what I was looking for applied to my issue. It's looking more and more like I'll need to have some sort low end manifold boost to get the HP and fuel burn rates where I need them. The engine data is hard to find for the early model but I'll be glad to provide and data/docs you may need to get an idea what I'm going for.

edit: I just had a thought, what if I try-
making it supercharged
critical altitude = 0 feet (sea level)
Max intake pressure 29.92 (may have to mess with it to get 29.92 @ full thottle with scaler)
...and define a boost scaler to get me my correct part throttle HP/fuel burn numbers
 
Last edited:
Dev One said:
Don't forget that the prop pitch angle can do a lot to restrict/overspeed the engine or aircraft airspeed, rather than play with the CDi all the time. J also then affected.
Keith
Click to expand...

Thats a thought- the one thing I don't have is the actual prop pitch of the A/C I'm working on. I'm assuming it's close to 21 but it could be much lower. Funny, when I dropped the CDi the J range greatly increased till I started pulling the prop efficiency and power required back into reality, now I'm back where I started but with a plane that'll glide much further.
 
I must admit that on my aircraft I have no idea what the real world prop pitch is, & I dont know how near the FS algorithm is to prop theory! One just has to fiddle & hope to get the end result as near as possible. I'm fairly sure that the FS algorithms are a bit of a fudge - especially when one sees the very long list of items within some FDE'. I have been able on my last few a/c to reduce this down quite a bit, but they are GA 1930's & 40's types.

Jerry Beckwiths free FDWB gives one a bit of an idea, but I find the prop curves can have problems - again maybe aero theory not matching FS theory?
Keith
 
:jump:
Good news- I put a turbo in the FM and with some tweeking the HP is pretty dern close to what I need it to be but the fuel consumption is still a bit off. Luckily FS pins the BSFC to .49 pph per HP so with a fuel scaler I should be able to get the fuel numbers where I need them to be. You were right Ivan, there's noting in the air file that directly alters the fuel burn rates, I had observed the engine efficiency changing the fuel burn rates but didn't really notice the HP values were going up and I was compensating by making the prop loading heavier to keep the RPM down. By lying to FS about the turbo my HP stays authentic and the manifold pressure isn't dropping as fast as the non-turbo FM which seems to be keeping the HP up where it should be. I haven't looked yet but I'm hoping theres a turbo scaler in case altitude starts to throw my numbers off again.

Thanks guys for the ideas that led me to the right path, I think I finally have a handle on this problem.
 
I dunno what I did but it's back to the same as before, even with the turbo the cruise HP is way low ,I'm guessing because the manifold pressure is lower than it should be. Oh well, needed a break anyway- decided to rework the physical model instead and wouldn't you know it my source build is on a different computer that I boxed up 6 months ago and now it's dead. I had to pull the HDD and install it into my new PC so I can get my source models back, then I discover (or remember) that I did the final build in FSDS. Least I was smart enough to export every part as a DXF first. Hard to believe I built this thing 5 years ago.

Sheesh, when it rains, it pours.
 
MaddogK said:
I dunno what I did but it's back to the same as before, even with the turbo the cruise HP is way low ,I'm guessing because the manifold pressure is lower than it should be. Oh well, needed a break anyway- decided to rework the physical model instead and wouldn't you know it my source build is on a different computer that I boxed up 6 months ago and now it's dead. I had to pull the HDD and install it into my new PC so I can get my source models back, then I discover (or remember) that I did the final build in FSDS. Least I was smart enough to export every part as a DXF first. Hard to believe I built this thing 5 years ago.

Sheesh, when it rains, it pours.
Click to expand...


Would you mind posting a copy of the air and cfg.
 
I thought I had a problem yesterday after playing with my .air files & the changes would not work using the saved flight system. I then opened up using the standard Cessna then changed to my latest WIP & the changes worked OK - same in FS9 & FSX.

As for fuel consumption I'm a bit on the low side at the moment, but HP & Thrust, hence speeds are correct. I have also now been able to mess about with the curves in table 511 to achieve prop aerodynamic braking when reducing rpm.....I have made the curves 'avalanche' above a J value of 0.95, so that the efficiency falls almost immediately to -2.0 - this does mean making the values of J very close together (every 0.01) for a few values above 1.0.

I think tables 508 & 509 affect fuel consumption & power values - especially 509, but one must balance between the two. Thats my next experimentation!
HTH
Keith

BTW - those links for the prop values are not much good to me as they quote the prop pitch in inches, whereas MSFS quote them as degrees, but they do not specify at what prop dia that angle refers to. So I find it best to try different values in the .cfg & then empirically test!
K
 
google prop pitch calculator. there are a couple out there. other wise you would have to to do the math. if you can get all of the measurements that is.

you are using AirEd correct. you can also use airwrench, it will give you some info based on your changes to the air file. it the free version you can't make very many changes. Make sure your CFG matches the Airfile. I'm not sure about FSX but in some of the earlier FS sims the fuel settings need to match in order for everything to work right.

Does FSX have a FSedit? if so rename the cfg then run FSedit. it will make a new cfg based on the Airfile. Some things may be set wrong or missing but from that you can fill in the blanks.

without looking at the files that all I have. sadly I don't have FSX so I can't be a test pilot for you. hopefully there can be some inspiration in the what I have given.
 
Blood_Hawk23 said:
Would you mind posting a copy of the air and cfg.
Click to expand...

Sure, I'll try to get it posted tonight (provided storms don't knock out my power again), and BTW, I ran the calculators on the sites you provided below and my 'guess' was pretty dern close- the calculated pitch I should be running is 20.36 and I've been using 21 on this model. It's about as close to documented performance as it gets at wide open throttle, but part throttle performance is a complete headache because I can't keep manifold air pressure up where I need it so that HP and fuel burn rates remain as documented.
 
Blood_Hawk23 said:
Would you mind posting a copy of the air and cfg.
Click to expand...

Here's where I'm at ATM. I disabled the turbo because it stopped boosting low end manifold pressure and was causing some high end calibration problems, I also have the engine efficiency scaler set way too high @ 1850 trying to get the HP value up, but it's still not high enough and is causing unrealistic acceleration problems at takeoff. Fuel consumption isn't a real issue now that I know FS9 has pinned the fuel flow to .49 pph/hp so I can compensate with a scaler. My target performance specs are as follows:

2300 RPM / 155 mph / 470 HP @ sea level,
2100 RPM / 435 HP
2000 RPM / 425 HP
1850 RPM / 400HP (cruise setting) aprox 135 mph
Time to 2000 ft - 1.8 min , to 15000 ft - 21.5 minutes (max speed @ 14k-140MPH)
Range - 500 miles with 75 gallons fuel @ 130MPH
Service ceiling 17,000 ft.
This is a completely natural aspirated engine- NO turbo, NO supercharger, NO prop reduction gear, Carburated.
It should be noted that this aircraft was expected to have a range of 1750 miles with 175 gallons of fuel in the 1934 macrobertson race (Curtiss D-12 'Felix'). I calculated the optimum prop for a 2300 RPM motor at 8.25 feet, but looking at actual pics of the AC show it to be every bit of 9 feet or larger. I settled for 9 feet because I have the NACA test data for the 9 foot Reed prop on a Curtiss D-12 from the early 1930's so I thought it was a good match since Fairey mounted Reed props on this aircraft at that time, tho I gave up trying to reconstruct the prop tables in FS9 from the published test data curves. Trying to match the RPM to FS's 'J' variable was a bit beyond my math skills.

Lemme know if you see anything that I overlooked, or botched badly. I have until early October to wrap this up in order to get it qualified for our annual Macrobertson re-enactment. Thanks for looking.
 
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