Is induced drag modeled in AH?

[Skyyr]

As the title states, does the flight model in Aces High model induced drag?

Thanks!

[Karnak]

Yes.

Take a Mossie XVI with just the 4k bomb.  Test the top speed with the bomb and after dropping it, both tests with the bomb doors closed.  It is faster without the bomb than it is with it.

[Skyyr]

Yes.

Take a Mossie XVI with just the 4k bomb.  Test the top speed with the bomb and after dropping it, both tests with the bomb doors closed.  It is faster without the bomb than it is with it.

Simple enough - thank you very much.

[Brooke]

Another way to know that it does:

Take a plane up and get it going in level flight above, say, 250 mph.  Now do a hard flat turn.  Notice that the speed rapidly goes down.  That's induced drag greatly increasing as you pull g's in the turn.

[MachNix]

The real answer is No, induced drag is not modeled in AH.  The experiments proposed by Karnak and Brooke do happen as they say, but not for the reasons they imply.

Drag in AH is a function of weight and g-loading.  Induced drag, the drag created from generating lift, is a function of indicated airspeed and angle of attack (besides the wing shape).  The experiment you should be using is to take a bird up at try gliding through a certain altitude, like 2,000 feet, at different speeds using the .speed command to keep the speed constant.  Use the E6B to record the descent rates using speeds above and below the best rate of climb speed.  At speeds a few miles per hour below best climb speed, the rate of descent should be at its lowest and start to increase as the angle of attack and the induce drag increases.  But in AH the rate continues to decrease as if parasitic drag where the only drag acting on the model until you near the stall where drag then increases at the buffet.  The flight model is actually quite dangerous if applied to the real world -- you can never get behind the power curve in AH.

Oh, and that thing that is spinning around that looks like a propeller is actually a jet engine in AH.  The faster you fly the more thrust it produces.  The reason there are not really fast top speeds is parasitic drag is increasing at a higher rate than the thrust.  This is why it is sometimes possible to catch a plane that has a higher top speed while flying one with a lower top speed.

[Brooke]

The real answer is No, induced drag is not modeled in AH.  The experiments proposed by Karnak and Brooke do happen as they say, but not for the reasons they imply.

Yes, they do happen for the reasons we say, and if there were no induced drag in AH, turns and extra bomb load would not sap airspeed.

Oh, and that thing that is spinning around that looks like a propeller is actually a jet engine in AH.  The faster you fly the more thrust it produces.

I don't think so, or the performance of the models would be completely off the flight-test data, which it is not.

[BnZs]

Oh, and that thing that is spinning around that looks like a propeller is actually a jet engine in AH.  The faster you fly the more thrust it produces.  The reason there are not really fast top speeds is parasitic drag is increasing at a higher rate than the thrust.  This is why it is sometimes possible to catch a plane that has a higher top speed while flying one with a lower top speed.

If your engine produces more thrust the faster you go, why can't you just hit X and exceed accelerate in level flight till your wings come off?

[Karnak]

Oh, and that thing that is spinning around that looks like a propeller is actually a jet engine in AH.  The faster you fly the more thrust it produces.  The reason there are not really fast top speeds is parasitic drag is increasing at a higher rate than the thrust.  This is why it is sometimes possible to catch a plane that has a higher top speed while flying one with a lower top speed.

You have no idea what you're talking about.

[MachNix]

If your engine produces more thrust the faster you go, why can't you just hit X and exceed accelerate in level flight till your wings come off?

Parasitic drag is increasing at a faster rate then engine thrust.  Where trust equals drag is the top speed for level flight.  This happens at a speed below the wing-ripping-off speed.  For props (in RL) the thrust drops off as you approach the speed of the prop wash -- no more change in momentum of the air passing through the prop disk.

Let us do a little thought experiment.  A constant speed prop is turning at 2500 rpm.  At slow speeds the prop is in fine pitch.  Notice the blades of the prop are wings and they all have their lift vectors pointing nearly forward and creating a lot of thrust.  As the aircraft speeds up, the prop pitch becomes more and more coarse so it is still turning at 2500 rpm.  Now let's go really fast.  The prop is practically feathered.  The lift vectors are now perpendicular to the direction of flight and are not producing any thrust.  All their lift is fighting against the torque of the engine to keep it at 2500 rpm.

If you want to determine thrust, repeat the experiment I outline earlier and compare the differences in rate of climb/descent at the same speeds.  Just to look as some numbers:

Seafire at 6,909 lbs at 2,000 feet:

At 133 IAS (best rate of climb speed), the rate of descent is 1,142 feet per minute with power off giving a drag horsepower of 164.3.  At full power the rate of climb is 2,460 fpm net (thrust minus drag) horsepower of 351.2.  Therefore the prop is producing 515.5 hp of thrust.

At 350 IAS (well above its maximum level speed), rate of descent is 9,939 fpm, rate of climb at full power is -2,703 fpm, giving a prop thrust of about 1,033 hp.

[Mongoose]

Oh, and that thing that is spinning around that looks like a propeller is actually a jet engine in AH. 

  No, it's a fan to keep the pilot cool.  If you don't think so, make it stop and watch him sweat!!!   

  (I know, old and stupid joke, but I though it fit)

[BnZs]

At 133 IAS (best rate of climb speed), the rate of descent is 1,142 feet per minute with power off giving a drag horsepower of 164.3.  At full power the rate of climb is 2,460 fpm net (thrust minus drag) horsepower of 351.2.  Therefore the prop is producing 515.5 hp of thrust.

At 350 IAS (well above its maximum level speed), rate of descent is 9,939 fpm, rate of climb at full power is -2,703 fpm, giving a prop thrust of about 1,033 hp.

Wait, wait, wait...this sounds like a series of non-sequiturs to me...are you saying these figures mismatch what a Seafire should actually be able to do? Because frankly the claim that AHII has modeled thrust and drag in a completely bogus way, yet each and every  plane has speed and climb performance close to that of their historical counterparts, well, that would seem like an awfully lucky series of coincidences.

Also, if AHII doesn't model induced drag, why do the planes lose energy in turns? That is the mechanism by which planes loose speed in turns. If there is no induced drag, why can't a P-51 be flying along at 360 IAS, pull 5gs for a 180 degree level turn, and still be going 360 IAS at the end of the turn???

[hitech]

MachNix is incorrect.

First AH Absolutely  models induced drag. What do you think makes your plane slow down when you turn?

2nd Thrust decreases with speed once the "Stall speed of the prop" is reached, normally around best climb speed.

For normal estimation.

Thrust = Power / Speed;



A description of "Prop stall speed"

When a plane is standing still the prop is at a finer pitch but a very hi AOA, probably pass stall. When in this state increasing prop witch will increase torque required, but decrease thrust.

Once a plane starts moving forward the airflow from the forward movement is also creating lift on the prop blade and increases drag/torque require.  As the plane is accelerating the AOA of the prop is decreasing but since the prop is in a stalled state, the lift is increase. Once the speed is reached that crosses the stall boundary the thrust will start decreasing linearly with the speed (ignoring the small efficiently change do to not all points in the prop having the same AOA).


This "Prop stall" is why the paddle blade prop was created, it lowered the stall speed of the prop which was faster then best climb speed. This lowering increased thrust at best climb speed hence increasing climb rate. It is in essence the same as a helicopter. With long enough blades you can produce more thrust when standing still. But similarly if a helicopter is sinking fast (like moving backwards in a plane) a point can be reached where the propeller/rotor stalls. This is called settling with power. And can not be recovered from by applying more collective but must be recovered from with forward motion.

I have 10 hours rotary instruction logged and have practiced the recovery.


HiTech

[BnZs]

Yes, my next  question was going to be, if induced drag in AHII is simply a function of Gs, why do some planes bleed Gs faster than others? The fact that the  Ta-152 with those high aspect ratio wings holds energy so well in turns DESPITE one of the highest wingloadings        leads me to believe induced drag is probably *very* well modeled in AH.

[MachNix]

First AH Absolutely  models induced drag. What do you think makes your plane slow down when you turn?

Induced drag is a function of the amount of lift produced.  Lift is a function of airspeed and angle of attack.  Therefore induced drag is a function of airspeed and angle of attack.

In AH the drag does increase in a turn and the flight model works very well in having the aircraft slow down, but the model has the dragged hooked to something other then angle of attack.  What makes me say this is at speeds 20 to 30% slower then the best climb speed, where induced drag should start dominating the power required curve, there is only a small increase in drag.  The fact that there is an increase may mean there is indeed induced drag modeled, but is not as strong as one may expect. 

For the Seafire, power required goes from about 151 hp required at 109 IAS, which is its lowest, to only 154 hp at 91 IAS near the stall.  A 3 hp change in the power requirements is not much considering how much the angle of attack changes between those two speeds.

Am I saying to change the flight model?  Definitely not!  Everyone would have a cow.  But if Skyyr comes in trying to fly the P-51 like he does his A-4 where he is used to unloading the aircraft to increase the acceleration force he feels shoving him in his lower back, he is going to be disappointed.  And if he engages in a stall fight thinking he is in a high-drag environment due to induced drag, he is going to be at a disadvantage.

Thanks for responding Hitech and I like your reference to the rotary-wing world where you have to move out from under that column of descending air.   

[hitech]

but the model has the dragged hooked to something other then angle of attack. 

I can 100% guaranty  you that Induced drag in AH is a function LiftCo which is a function of AOA.

From wikii


the code cut and pasted from AH.

double simpwingCalcWingIndDragCO(simpWING * Wing)
{
return Wing->IndDragCO * Wing->WingForce.LCO * Wing->WingForce.LCO;
}

Note in the equation from wiki the 3 divisor terms are all constant for a given airframe. My variable (Wing->IndDragCo ) is simply the bottom part of that term.
HiTech