Author Topic: Question to HTC: Does propwash affect controls? (Read 1494 times)

Krusty · « **on:** December 21, 2007, 12:39:10 PM »

I've got a question. I know AH doesn't have propwash or turbulence or wakes or anything. What I want to know is if the propwash forces are modeled on the controls, even if not on the air itself.

For example, the plane moves through the air, and the speed determines what effectiveness the rudder will have. Only, what if you're in a zoom? When your speed drops and your nose is up, the "forward speed" forces on the rudder would be almost none. BUT.... the downward blast of the roaring engine would keep the rudder and elevators very effective.

I'm thinking about the hammerhead move. I've seen little stunt planes do it, and even at zero miles per hour their rudder is so effective it can whip around in-place.

Try that in a 109 and you're more likely to flop over than do a pivot. I have always wondered if this is because the flight model is only counting your forward speed, and NOT the prop wash, when calculating rudder effectiveness.

So, even at almost no forwrad speed the rudder should be highly effective in some cases, but it doesn't seem that way at times. Also, gunning the engine while taxiing with full rudder should swing you around, but it requires forward motion before it really does this.

I also wonder how this would affect elevators, flaps (prop wash over wing roots or wings for twin engines) and so on.

dtango · « **Reply #1 on:** December 21, 2007, 02:56:20 PM »

AH does model propwash. You can readily see it manifested in at least three obvious ways: (1) Yaw when taking off induced by prop slipstream impingement on the tails v-stab and (2) decrease in stall speed with power on vs. power off, and (3) asymetric wing stall due to prop upwash.

To illustrate #3, here is a single frame from a series of frames that Pyro posted awhile ago where he was doing some power on stall tests.

White indicates when max aoa is exceeded. Note how the left wing stalls first with the prop on. This is because the direction of rotation of the blades creates and upwash on side of the prop disc where the blade is travelling upward. The upwash basically increases the aoa on that side of the wing which causes it to stall before the other side.

Tango, XO
412th FS Braunco Mustangs

Krusty · « **Reply #2 on:** December 21, 2007, 03:00:46 PM »

Well, I asked because you can plug in values for torque and yaw based on power settings, you can "multiply" the stall settings based on power on/off, but that doesn't tell me whether or not they thought to model the thrust of 40+mph wind hitting the rudder at all times plus whatever forward speed it has, etc...

We know propwash itself is not modeled. No wash or atmospheric effects are. There is no air, basically. So any effects that we have now, have to be hard coded into the variables based on throttle settings.

I'm just wondering if they over looked the rudder/elevators on single engine planes and flaps on twin engined planes.

dtango · « **Reply #3 on:** December 21, 2007, 03:37:15 PM »

Quote

Originally posted by Krusty
We know propwash itself is not modeled. No wash or atmospheric effects are. There is no air, basically. So any effects that we have now, have to be hard coded into the variables based on throttle settings.

Wow. Propwash is modelled. Besides the examples I've already given, look at the lift forces on the span nearest the wing root. They are much higher than the other parts of the wing because of propwash with engine on. So it's not only the forward velocity that determines how much lift the wing is producing.

If you're saying they don't model individual air molecules or wakes left by one airplane that effect another airplane then fine.

But the atmosphere and airflow are modelled by definition. Otherwise you wouldn't have any lift or drag forces acting on our virtual airplanes and they wouldn't behave the way the do.

I understand that you're wondering what effects slipstream has on rudder and elevator effectiveness in particular situations and how they have handled this. How the yaw varies at takeoff due to slipstream and how it reduces with increasing airspeed shows you that they have modelled this dynamic relationship at some level and that this isn't some preset thing based purely on where your throttle is set at.

Tango, XO
412th FS Braunco Mustangs

Krusty · « **Reply #4 on:** December 22, 2007, 01:51:26 PM »

dtango, I think you're taking anything I say and purposefully trying to nitpick.

No atmosphere at all is programmed. None. ANY effects that in real life are caused by certain air effects, are in the game hard-coded as behaviors based on other variables.

If, for example, throttle off stall speeds are N at a certain point in the wing, and throttle on stalls are (N * 0.85), that gets the same end result as "prop wash" -- but no propwash itself is modeled.

Basically, the end result is accounted for, but not the means.

The question is, did they think, plan, and code, for certain end results, or did they slip under the proverbial radar?

You can only code for what you can think of. Anything you don't think about slips through the cracks.

moot · « **Reply #5 on:** December 22, 2007, 06:48:54 PM »

Krusty you haven't coded the thing.. how do you know?

Badboy · « **Reply #6 on:** December 22, 2007, 07:32:36 PM »

Quote

Originally posted by Krusty
No atmosphere at all is programmed. None. ANY effects that in real life are caused by certain air effects, are in the game hard-coded as behaviors based on other variables.

Sorry Krusty, that is incorrect. The atmospheric model used in Aces High was posted on 20th Oct 2001 by HiTech and it conforms to a standard
atmospheric model. An atmospheric model has been a fairly normal approach in every flight sim for the last 20 years.

Badboy

Kweassa · « **Reply #7 on:** December 23, 2007, 12:00:13 PM »

What Krusty's saying, is that it ain't real "air" or an "atmosphere" the plane truly flies through in the game, but rather, the various FM equations/calculations just take into account the "atmospheric conditions" as a variable to simulate a plane flying through atmosphere under standard conditions...

... though, I fail to grasp why that is anything important, since if the equation already takes into account how the atmospheric conditions would interact with the FM equation/calculation, then by all means, that's practically no different from having a plane flying through an environment where the "atmosphere" is really modelled in.

leitwolf · « **Reply #8 on:** December 23, 2007, 12:33:44 PM »

It's also the tiny little difference between a realtime mmp sim and full blown CFD sim. You get n frames / second in AH. Your CFD simmer cheers when it's n seconds / frame.

moot · « **Reply #9 on:** December 23, 2007, 12:33:45 PM »

Wasn't there the same argument years ago from an X-plane fanboy, about lookup tables vs real time calc?

leitwolf · « **Reply #10 on:** December 23, 2007, 01:03:31 PM »

Never really tried X-plane so i have no idea about that.

I do know, however, that i get ~60fps in AH and there's no way to keep that up by using CFD instead of lookup tables and simpler equations. (Simpler in the sense of not generating insane amounts of numbers to crunch).

moot · « **Reply #11 on:** December 23, 2007, 01:36:14 PM »

IIRC it made no sensible difference in practice... Not in fps, but in faithfulness to real performance.

leitwolf · « **Reply #12 on:** December 23, 2007, 02:19:08 PM »

Well the beauty of a hypothetical full CFD sim is that it is not only very cool

, you also get the vortices behind the airplane Krusty asked for (which will screw the newbies in a pork&auger mission on the runway after that big B-24 formation took off).

Traditional sims need to get the "lookup tables" with drag values and lift coefficients right in the first place, a CFD sim wont need them.
In fact, you can measure them from your sim - provided that you have a correct highres 3D model of your plane.
But, this is probably not easier than to get the other variables right for WW2 planes.
If you already know that your Fw190 has a NACA23015 wing you aren't going to see any surprises in a CFD sim because the data is already available.
For X-plane, however, CFD might have been a good idea to get weird stuff modeled better (as in "what if i give it 8 wings - all of different length").

Saxman · « **Reply #13 on:** December 23, 2007, 03:55:05 PM »

I wonder what X-plane would show about the interaction between airflow, prop wash, flaps, and the F4U's wing configuration...?

SgtPappy · « **Reply #14 on:** December 23, 2007, 04:58:10 PM »

Is there going to be hope of the prop wash of say a bomber affecting a Spitfire or even a P-38 for example if they were to fly in close proximity behind the bomber's slipstream?

also,
any news on the new fluid flight-modeling engine supposedly coming out?