Idea for next update - stall physics fade

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rfoshaug
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Idea for next update - stall physics fade

Post by rfoshaug »

I do a lot of aerobatic flying (especially love those few aircraft that have simulated propwash effect). When I go vertical and do a hammerhead with full rudder, for a short while the aircraft can go through some pretty violent transients in AOA. This causes the Accu-feel stall physics to jolt the aircraft around even though airspeed is very close to 0 at the top of the hammerhead.

What I'd love is to have the stall physics fade away at, say, below 20 knots absolute airspeed (and I mean airspeed in any direction, not necessarily along the aircraft nose line, as 100 knots and 90° AOA gives 0 indicated airspeed but should introduce a very noticable stall instability whereas 1 knot and 90° AOA should give almost no buffeting). So if the aircraft is moving in any direction at below that threshold speed, the movements on the airframe caused by stall should diminish or fade away as the forces acting on the wings and airframe at for example 1 knot should be very small regardless of the angle of attack.

Hope I managed to explain what I mean on my less-than-perfect and more-tedious-than-necessary English. :-)

BTW thanks for this great product. If a version 3.0 comes and is another paid upgrade, I'll gladly pay for it again! Worth every penny! ...or cent... ...or øre... :)

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DHenriques_
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Re: Idea for next update - stall physics fade

Post by DHenriques_ »

rfoshaug wrote:I do a lot of aerobatic flying (especially love those few aircraft that have simulated propwash effect). When I go vertical and do a hammerhead with full rudder, for a short while the aircraft can go through some pretty violent transients in AOA. This causes the Accu-feel stall physics to jolt the aircraft around even though airspeed is very close to 0 at the top of the hammerhead.

What I'd love is to have the stall physics fade away at, say, below 20 knots absolute airspeed (and I mean airspeed in any direction, not necessarily along the aircraft nose line, as 100 knots and 90° AOA gives 0 indicated airspeed but should introduce a very noticable stall instability whereas 1 knot and 90° AOA should give almost no buffeting). So if the aircraft is moving in any direction at below that threshold speed, the movements on the airframe caused by stall should diminish or fade away as the forces acting on the wings and airframe at for example 1 knot should be very small regardless of the angle of attack.

Hope I managed to explain what I mean on my less-than-perfect and more-tedious-than-necessary English. :-)

BTW thanks for this great product. If a version 3.0 comes and is another paid upgrade, I'll gladly pay for it again! Worth every penny! ...or cent... ...or øre... :)
I'm not sure I'm reading you correctly. At NO time during a Hammer Head Turn will you either have the wing stalled OR have an AOA of 90 degrees ?????


Dudley Henriques

rfoshaug
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Re: Idea for next update - stall physics fade

Post by rfoshaug »

Take a look at this video:

https://www.youtube.com/watch?v=Eybrx7lILPc

At 10 seconds into the video, the aircraft is more or less stationary in the air as the pilot gives full rudder to turn it around. If the aircraft is drifting slightly down (relative to the aircraft, ie moving slowly in the direction of the aircraft's landing gear), which in fact it seems that the aircraft in the video is, as it comes out of the maneuver behind the smoke from the way up, it can and will have rather large fluctuations in AOA, although at very low speed.

What I've found is that during maneuvers such as this, with Accu-feel's stall physics enabled, the aircraft much more easily gets out of control in a violent way at the top of the maneuvre.

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DHenriques_
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Re: Idea for next update - stall physics fade

Post by DHenriques_ »

rfoshaug wrote:Take a look at this video:

https://www.youtube.com/watch?v=Eybrx7lILPc

At 10 seconds into the video, the aircraft is more or less stationary in the air as the pilot gives full rudder to turn it around. If the aircraft is drifting slightly down (relative to the aircraft, ie moving slowly in the direction of the aircraft's landing gear), which in fact it seems that the aircraft in the video is, as it comes out of the maneuver behind the smoke from the way up, it can and will have rather large fluctuations in AOA, although at very low speed.

What I've found is that during maneuvers such as this, with Accu-feel's stall physics enabled, the aircraft much more easily gets out of control in a violent way at the top of the maneuvre.
The first maneuver isn't a Hammerhead. It's a tumble off the apex of the vertical line. Hard to tell if it was a botched torque roll through the smoke. In that tumble you are correct. There would be fluctuations in AOA.
The second maneuver is a Hammerhead. A Hammerhead by definition and to be correctly done requires a 0 AOA established on the upline and held through the pivot.

In the Hammerheads I've tried to do in FSX I've gotten extremely erratic results. I've been convinced for quite a while now that replication of the physics and aerodynamics involved with some aerobatics are very difficult to code into a flight model. Hammerheads are one of these maneuvers.
The physics involved in a HH are extremely complex. Just the spiraling slipstream dynamics alone would tax a flight model. As you proceed up the vertical line the slipstream from the propeller tightens and closes in toward the tail causing a change in the physics. As you approach the apex you have constantly changing torque, P Factor, and strong gyroscopic precession during the rotation. Add to this that in certain aircraft, misuse of controls during the turn are extremely pro inverted spin.
It's a virtual rat's nest of physics gone wild up there :-)
What the FM programmer usually does is treat all this as a straight rotation in yaw and if you manage to hold the AOA at near 0 through the rotation you just MIGHT get some semblance of a HH.
Our Flight model guys here at A2A are without a doubt some of the best I've ever worked with. A lot of what they do as far as aerobatics are concerned has to end up as a compromise due to control response needed elsewhere. In other words, making something exactly right during maneuver A can really mess up something required for maneuver B :-))
I can say this however. A2A has done wonders in flight modeling and it's getting better every day.
Dudley Henriques
DH

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Pistonpilot
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Re: Idea for next update - stall physics fade

Post by Pistonpilot »

Sorry, Mr. Henriques, but I must say I am VERY happy to learn that you cannot perform a hammerhead in FSX...

...only because I can't, either.

Any time I'm messing around with an A2A fighter, that's one of the first things to try to do, and, while I've never done one in real life, I've done one in many other sims. FSX? Never! Glad to hear it MIGHT not be just me. ;)

-Ian
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DHenriques_
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Re: Idea for next update - stall physics fade

Post by DHenriques_ »

Pistonpilot wrote:Sorry, Mr. Henriques, but I must say I am VERY happy to learn that you cannot perform a hammerhead in FSX...

...only because I can't, either.

Any time I'm messing around with an A2A fighter, that's one of the first things to try to do, and, while I've never done one in real life, I've done one in many other sims. FSX? Never! Glad to hear it MIGHT not be just me. ;)

-Ian
:-))

A visual "approximation" of a Hammerhead is possible on a "sometime" basis by cleverly using what has been coded for pure yaw and VERY carefully finding the sweet spot for the 0 angle of attack, but unless someone has gone to the trouble of coding in the exact physics involved what you should be seeing is simply this "approximation" of the maneuver; yaw rotation in an arc rather than as it should be; rotation on the vertical axis at the exact instant the vertical axis is fixed in space.
Getting a Hammerhead exactly right in the actual airplane is hard enough. Getting one right in FSX using available code is even harder.
But hang in there. A2A's flight modeling team is on the job !
DH

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Re: Idea for next update - stall physics fade

Post by Vaga »

Dudley Henriques wrote:
rfoshaug wrote:Take a look at this video:

https://www.youtube.com/watch?v=Eybrx7lILPc

At 10 seconds into the video, the aircraft is more or less stationary in the air as the pilot gives full rudder to turn it around. If the aircraft is drifting slightly down (relative to the aircraft, ie moving slowly in the direction of the aircraft's landing gear), which in fact it seems that the aircraft in the video is, as it comes out of the maneuver behind the smoke from the way up, it can and will have rather large fluctuations in AOA, although at very low speed.

What I've found is that during maneuvers such as this, with Accu-feel's stall physics enabled, the aircraft much more easily gets out of control in a violent way at the top of the maneuvre.
The first maneuver isn't a Hammerhead. It's a tumble off the apex of the vertical line. Hard to tell if it was a botched torque roll through the smoke. In that tumble you are correct. There would be fluctuations in AOA.
The second maneuver is a Hammerhead. A Hammerhead by definition and to be correctly done requires a 0 AOA established on the upline and held through the pivot.

In the Hammerheads I've tried to do in FSX I've gotten extremely erratic results. I've been convinced for quite a while now that replication of the physics and aerodynamics involved with some aerobatics are very difficult to code into a flight model. Hammerheads are one of these maneuvers.
The physics involved in a HH are extremely complex. Just the spiraling slipstream dynamics alone would tax a flight model. As you proceed up the vertical line the slipstream from the propeller tightens and closes in toward the tail causing a change in the physics. As you approach the apex you have constantly changing torque, P Factor, and strong gyroscopic precession during the rotation. Add to this that in certain aircraft, misuse of controls during the turn are extremely pro inverted spin.
It's a virtual rat's nest of physics gone wild up there :-)
What the FM programmer usually does is treat all this as a straight rotation in yaw and if you manage to hold the AOA at near 0 through the rotation you just MIGHT get some semblance of a HH.
Our Flight model guys here at A2A are without a doubt some of the best I've ever worked with. A lot of what they do as far as aerobatics are concerned has to end up as a compromise due to control response needed elsewhere. In other words, making something exactly right during maneuver A can really mess up something required for maneuver B :-))
I can say this however. A2A has done wonders in flight modeling and it's getting better every day.
Dudley Henriques
DH

I've seen this video before. If I remember that is the pitts S2S doing what they call a double hammerhead. However If you watch near the top he kicks the rudder left then right while extreemly close to stall speed. I have to agree this is more of a torq spin or something than a hammerhead. I have the Pitts S2S from Albeo and can do hammer heads all day in the thing however at no time does the plane ever stall. Then again I did look the Accusim B-17 the other day and did a loop then went inverted for a low pass over an airfield. (Mostly to see if I could do it and to see how long before an engine fails from no oil.) If you plane stalls when doing a hammer head then it's a type of stall not a hammerhead. The aircraft Factory Albatros D.III is a great plane to do hammer heads and loops at low altitude also.

Also the stall physics of FSX are not able to mimic real life correctly to make the move he used. You would have to be able to do good knife edge that has always been impossible to maintain in FSX.
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Scott - A2A
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Re: Idea for next update - stall physics fade

Post by Scott - A2A »

rfoshaug,

I just wanted to inject here that we may add some more control over the intensity and control of the stall buffet effect in an update. Not 100% sure, but something we've thought about.

Thanks for the post,
Scott.
A2A Simulations Inc.

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Pistonpilot
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Re: Idea for next update - stall physics fade

Post by Pistonpilot »

@Scott

Is there any chance that reducing the 'duration' of a stall might help? I notice that, in FSX, an aircraft stalls..and stalls...and stalls...with the default flight modeling. This is what I experience when attempting a hammerhead in, say, the military version of A2A's mustang; it's like the stall never ends, and I'm stuck wallowing about in it until FSX decides that my random pitch/roll oscillations have resulted in an end to the stall.

Granted, I haven't got much experience with proper departed flight characteristics, but I feel like a real airplane recovers much faster than what FSX simulates, especially when the nose is pointed at the ground!

Also, I haven't had much of a chance to play with stalls/aerobatics since A2A's Accu-Feel V2 has released. Please excuse me if I'm talking about stuff that's already been thought about/implemented. ;)

-Ian
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DHenriques_
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Re: Idea for next update - stall physics fade

Post by DHenriques_ »

Pistonpilot wrote:@Scott

Is there any chance that reducing the 'duration' of a stall might help? I notice that, in FSX, an aircraft stalls..and stalls...and stalls...with the default flight modeling. This is what I experience when attempting a hammerhead in, say, the military version of A2A's mustang; it's like the stall never ends, and I'm stuck wallowing about in it until FSX decides that my random pitch/roll oscillations have resulted in an end to the stall.

Granted, I haven't got much experience with proper departed flight characteristics, but I feel like a real airplane recovers much faster than what FSX simulates, especially when the nose is pointed at the ground!

Also, I haven't had much of a chance to play with stalls/aerobatics since A2A's Accu-Feel V2 has released. Please excuse me if I'm talking about stuff that's already been thought about/implemented. ;)
-Ian
Ian , just to rehash a data point here;

I notice in asking about hammerheads you seem interested in the flight model's stall behavior. The term "Hammerhead Stall" is actually a misnomer and something we in the aerobatic community have to "correct" every once in a while, as the wing is at no time stalled in a hammerhead. If stall behavior is your concern involving hammerheads, that behavior in a properly coded hammerhead shouldn't even be present.
Dudley Henriques

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Pistonpilot
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Re: Idea for next update - stall physics fade

Post by Pistonpilot »

Makes sense, Mr. Henriques!

Like I mentioned, I have no 'real world' aerobatic experience beyond taking a Cessna 172R up and trying to see how many turns in a spin I could get before becoming queasy/the aircraft recovered by itself (3, maximum! Never could manage more!).

My exposure to hammerheads has been in the sim only, and also just my own take on the issue. I am very likely not performing them correctly, which is compounded by FSX's "you stalled, okay, here's some random wobbling!" approach to aerobatics. ;)

-Ian
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DHenriques_
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Re: Idea for next update - stall physics fade

Post by DHenriques_ »

Pistonpilot wrote:Makes sense, Mr. Henriques!

Like I mentioned, I have no 'real world' aerobatic experience beyond taking a Cessna 172R up and trying to see how many turns in a spin I could get before becoming queasy/the aircraft recovered by itself (3, maximum! Never could manage more!).

My exposure to hammerheads has been in the sim only, and also just my own take on the issue. I am very likely not performing them correctly, which is compounded by FSX's "you stalled, okay, here's some random wobbling!" approach to aerobatics. ;)

-Ian
No sweat at all Ian. By all means never worry about lack of experience on these forums. Any and all questions AND observations are always welcome. By all means keep um coming. In this way everybody gets a shot at the questions and the answers and everybody benefits from the exchanges.

DH

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