Re: [Flightgear-devel] Creating a PA34-Seneca (which FDM to choose?)

[Torsten D. <to...@t3...>]

Am Mittwoch 21 Dezember 2005 19:47 schrieb Dave Culp:

> Looks nice!
Thanks!
> First, does the C-310 model work well?  I've never tried it, so I don't
> know. If it does then I would start with the C-310 config and make changes,
> one change at a time,   Realize that changing one number could effect more
> than one thing, and putting in a wrong number, or a typo,  could make it
> unflyable. 
I tried that first, and I get a flyable aircraft. But its performance data 
does not match the real bird. So I dropped this approach.
> Sounds like you're not getting enough power.  The engine and 
> prop configs in JSBSim can be tricky.   The Aeromatic prop solver isn't
> very good, and I'm waiting to put in a better one, so you might not get
> good thrust figures if you use Aeromatic's prop.  Tell me the engine power
> and prop diameter and I'll send you a prop config for JSBSim.
The Engine is a TSIO360EB, that is a supercharged engine with 200hp at 2575rpm 
at sea-level and 215hp at 2575rpm at 12000ft. It has a wastegate at 42inches 
MP and max. T/O power is at 40inch MP. My JSB engine file looks like this:
<FG_PISTON NAME="TSIO360EB">
  MINMP             6.5
  MAXMP            28.5
  DISPLACEMENT    360.0
  MAXHP           215.0
  CYCLES            2.0
  IDLERPM         800.0
  MAXTHROTTLE       1.0
  MINTHROTTLE       0.2
  NUMBOOSTSPEEDS 1
  BOOSTOVERRIDE 0
  RATEDBOOST1 9
  RATEDALTITUDE1 12000
  RATEDPOWER1 215
  RATEDRPM1 2575
</FG_PISTON>

And the propfile is from aeromatic for a variable pitch with diameter of 
76inches, 2 blades. Props are counterrotating. A better prop-file is highly 
appreciated.

At T/O power (40"MP max RPM, mixture rich at SL), when I look at the 
properties of the engines - and Yes: both engines are running ;-) - each 
engine runs at 2575rpm, fuel flow is 17gph (which should be more, it is more 
than 25 in the real world), thrust_lb is 565 and the thruster/torque is 
-330/+330 for L/R engine.

compared to the c172p, at full power on ground thrust_lb is 325 and 
thruster/torque is 280 at 2180rpm.

When i remember correctly, power = RPM * torque * 2 *PI. If I use this for the 
c172p and my engine, my power is 1.3 times higher than the 172's. Since it 
has 160hp it looks like the developed power is ok (160 * 1.3 = 208).
My thrust is 1.7 times higher than the cessna's, probably due tue the variable 
pitch prop.

So my intention tells me the engines/props are working fine and the propblem 
is in the aerodynamic section. I will dig into this and keep you informed.

More to come 

Torsten