> The biggest draw is probably compressing the air in the cylinders.
> Those pistons are still going up and down, even without the plugs
> firing.
I just thought about it for a minute, and I don't think this is the
case. Let's look at a four-cycle engine's cycles when no fuel is
ignited:
1. comp
Major A writes:
> I'm sure the biggest contribution to the torque with the engine off is
> friction, primarily that of the cylinder sealing rings against the
> cylinder walls, and maybe the resistance of the water cooling system,
> which I guess is driven from the engine shaft.
Most small pla
Can anyone describe briefly how props are modelled in YASim (and
JSBSim, once we're at it)? I get the idea from all those "if"
statements in the code that it's tweaked too much and not really based
on physics.
Andras (physicist, not an aerospace engineer)
==
Erik Hofman writes:
> You know how fast the aircraft goes at a certain propeller RPM.
> Now you want to know the propeller RPM at a certain speed.
It's not quite so simple. A fixed-pitch propeller (or a
constant-speed propeller at any given pitch) has a measurement of how
far the propeller wil
Jon S Berndt writes:
> Any suggestions?
This kind of thing is always hit-or-miss with me, since I don't have a
physics background. Basically, when a fixed-pitch propeller is
spinning slower than its advance speed (is that the right term?), the
propeller starts producing torque from the airstrea
> So we need the amount of force needed to rotate the mechanics (crank
> shaft, bearings, etc.)
Exactly. The most correct model would be possble if we had:
- the torque required to move the mechanics of the engine, as a
function or RPM
- the torque of the combustion at as a function of fuel
Jon S Berndt wrote:
On Wed, 6 Aug 2003 17:41:33 -0400
David Megginson <[EMAIL PROTECTED]> wrote:
you are flying fast enough (i.e. a dive). Any suggestions? JSBSim
does not handle windmilling properly either.
Any suggestions?
Windmilling is basically a reverse calculation.
You know how fast th
David Megginson <[EMAIL PROTECTED]> said:
> Here's the code, with my fix:
>
> // Euler-integrate the RPM. This doesn't need the full-on
> // Runge-Kutta stuff.
> float rotacc = (engTorque-propTorque)/Math::abs(_moment);
> _omega += dt * rotacc;
> if (_omega < 0)
> _om
Erik Hofman <[EMAIL PROTECTED]> said:
> Jon S Berndt wrote:
> > On Wed, 6 Aug 2003 17:41:33 -0400
> > David Megginson <[EMAIL PROTECTED]> wrote:
> >
> >> you are flying fast enough (i.e. a dive). Any suggestions? JSBSim
> >> does not handle windmilling properly either.
> >
> >
> > Any sugges
On Wed, 6 Aug 2003 17:41:33 -0400
David Megginson <[EMAIL PROTECTED]> wrote:
you are flying fast enough (i.e. a dive). Any
suggestions? JSBSim
does not handle windmilling properly either.
Any suggestions?
Jon
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I just checked in a bandaid fix for propeller drag in YASim. Here's
what was happening: the Propeller class would ignore negative RPM but
still send back a torque value for turning the propeller. That torque
value would ratchet up higher and higher negative RPMs until the drag
overwhelmed the pla
Erik Hofman writes:
> So we need the amount of force needed to rotate the mechanics (crank
> shaft, bearings, etc.)
The biggest draw is probably compressing the air in the cylinders.
Those pistons are still going up and down, even without the plugs
firing.
All the best,
David
--
David Me
David Megginson wrote:
Erik Hofman writes:
> You know how fast the aircraft goes at a certain propeller RPM.
> Now you want to know the propeller RPM at a certain speed.
It's not quite so simple.
1500 rpm = 125 fps = 74 kcas
2000 rpm = 167 fps = 99 kcas
2500 rpm = 208 fps = 123 kcas
That
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