Welcome, Guest. Please Login or Register
YaBB - Yet another Bulletin Board
  We've upgraded to YaBB 2!

FFDS Home | TIPS Section | Tutorials Section | Resources Section | Utilities Section

Military | FSDS | Jetliners | Real Planes Section | Gmax | Rotorcraft | Business | Civilian

  HomeHelpSearchLoginRegister  
 
 
Page Index Toggle Pages: 1
Send Topic Print
working on piston engine (Read 2499 times)
9th Aug, 2010 at 5:27pm

dmaher   Offline
Spline Extruder
I love YaBB 1G - SP1!

Posts: 229
***
 
Hi, so I've copied the propeller from the Mooney, it has a similar air speed range (~200mph).
And, now I’m trying to setup my engine, it's a common Lycoming IO360 (180 hp)

I’m a little unsure about how to read the power listed in AFSD (below).
And which power should correspond to the published Hp numbers.

AFDS list power in 4 steps…
  • Indic power(hp)
  • Friction power(hp)
  • Shaft Power(hp)
  • Thrust Power(hp)
When the manufacture says, “Max. Continuous Brake Horsepower: 180”; does that correspond to Shaft Power (in AFDS)?
What’s Indic power, Is that some sort of abstract ideal power?

Multimedia File Viewing and Clickable Links are available for Registered Members only!!  You need to Login or Register

Multimedia File Viewing and Clickable Links are available for Registered Members only!!  You need to Login or Register

Multimedia File Viewing and Clickable Links are available for Registered Members only!!  You need to Login or Register

Danny
« Last Edit: 9th Aug, 2010 at 7:07pm by dmaher »  

Multimedia File Viewing and Clickable Links are available for Registered Members only!!  You need to Login or Register&&&&&&
IP Logged
 
Reply #1 - 9th Aug, 2010 at 10:26pm

Au-MaV   Offline
Inspecteur des Polygonnes
Whatcha lookin at
Adelaide South Australia

Gender: male
Posts: 1956
*****
 
Hi
I read it as
Indic power/engine made HP - Friction power = Shaft Power
shaft Power + or - prop table/pitch = Thrust Power
Meh I could be wrong though Smiley
I tend to use Mr Beckworth's test panel for this kinda stuff Multimedia File Viewing and Clickable Links are available for Registered Members only!!  You need to Login or Register
There is less to take in and so long as the gauge numbers read right the rest tends to fall into place  
Wozza

 
IP Logged
 
Reply #2 - 10th Aug, 2010 at 1:30am

dmaher   Offline
Spline Extruder
I love YaBB 1G - SP1!

Posts: 229
***
 
Thanks Wozza, that makes sense.

I don’t see why there are two tables (508 and 509) that affect power.
It would be much easier if there was just one Wink

I’m guessing the relationship might be something like this…
Shaft power = Power * efficiency (tbl508) – shaft friction (tbl509)

The c172 also has an io360-180hp so to start I’ve copied 508-efficiency and 509-shaft friction from there.

Does anyone understand the formula for estimating 509-shaft friction?

The AAM tip says,
Quote:
Friction HP per Cyl=RPM*Torque/5252
Total about 12% of BHP at 2400 RPM.


It also says calculate shaft friction first, then adjust 508-efficiency to get the correct HP.

This is from the C172's IO360
Multimedia File Viewing and Clickable Links are available for Registered Members only!!  You need to Login or Register
 

Multimedia File Viewing and Clickable Links are available for Registered Members only!!  You need to Login or Register&&&&&&
IP Logged
 
Reply #3 - 10th Aug, 2010 at 8:16am

Au-MaV   Offline
Inspecteur des Polygonnes
Whatcha lookin at
Adelaide South Australia

Gender: male
Posts: 1956
*****
 
Hi Mate
You lost me a bit Smiley ....why are you focusing so much on friction/shaft speed?
If the aircraft engine is rated at 180 hp and your Indic power is 165 then you need to look at the engine params in the cfg
check the number_of_cylinders,compression ratio,cylinder_displacement, max_rated_rpm are close to real world figures.Then test to see how close the engine is in sim to your real world tables.Also min and max mp wont work unless you have turbocharged=1 (if under accel you also have to check the supercharger params to get the correct HP)
Once your engine is generating the ball park hp,then move onto shaft speed/friction, prop tables,drag,lift yada yada Smiley

To the question "Friction HP per Cyl=RPM*Torque/5252
Total about 12% of BHP at 2400 RPM."
the equation is "RPM times torque divide by 5252" as in "hp = torque * RPM / 5252"..... 5252 is a ball park maths for rotation mass
if you want to read more on it(explains it better than I can) have a look here Multimedia File Viewing and Clickable Links are available for Registered Members only!!  You need to Login or Register
its mind expanding stuff Wink 
Cheers
Wozza

                                                     
 
IP Logged
 
Reply #4 - 10th Aug, 2010 at 3:12pm

dmaher   Offline
Spline Extruder
I love YaBB 1G - SP1!

Posts: 229
***
 
Thanks, I’m pretty sure the engine config parameters are ok…triple checked & verified –for what that’s worth Wink
The chart above might have confused things a bit – it compares turbo vs. normal – but I’m using normal.
So the drop in power is good…
But the numbers posted were at 8000ft and I was playing with the engine tables at the time.

The engine performance is definitely in the ball park.
Like, 29mp and 2700rpm gives 170hp at sea level.

MS’s c172 IO360 sets friction to:
  • 25ft-lbs at 500rpm
  • 31ft-lbs at 2700rpm
I guess I was hoping there was some universal way to estimate the shaft friction at different RPM’s.
Literally “12% of BHp at 2400” only describes one point, 2400. So I was confused.
But I guess the 12% part is the point.

wikipedia also says,
Quote:
...shaft horsepower can be...estimated from the indicated horsepower and a standard figure for the losses in the transmission (typical figures are around 10%).


If I use 10% friction (IndHp/10) and I want 180bhp shaftPower at 2700rpm

IndHp = SftHp + FHp
IndHp = 180hp + IndHp/10
IndHp = 200hp

so
FHp = 20hp at 2700rpm

or
F torque = 39ft-lbs at 2700rpm

I'm not sure if that's right...but I think it's an ok place to start.

Actually now I see, (12% of shaftPower) pretty much equals (10% of indicatedPower) and the math is much simpler.
« Last Edit: 10th Aug, 2010 at 8:58pm by dmaher »  

Multimedia File Viewing and Clickable Links are available for Registered Members only!!  You need to Login or Register&&&&&&
IP Logged
 
Reply #5 - 11th Aug, 2010 at 3:10am

Au-MaV   Offline
Inspecteur des Polygonnes
Whatcha lookin at
Adelaide South Australia

Gender: male
Posts: 1956
*****
 
Hi
I tend not to worry to much about whats in the cfg air file numbers wise, so long as the aircraft gauges are in the ball park when flying that's good enough for me Smiley
When I was doing the Texan airfile I was using the pilots manual and no matter how hard I tried I couldnt get the numbers I wanted...later I found a forum that had a discussion on flying the texan today, I was amazed that the figures/settings the pilots said they used/getting  was so close to what I was getting in the sim I was stoked Cheesy
Cheers
Wozza
 
IP Logged
 
Page Index Toggle Pages: 1
Send Topic Print