Spin characteristic prop planes in DCS or rather spin proof.

[Echo38]

All prop aircraft still appeared ( last time I used DCS ) to overdo the P-Factor effect. This is particularly notorious in the K4, where from level or climbing situation, if you hit the right rudder to center the ball, the aircraft pitches noticeably up!

 

That sounds like gyroscopic effect, not P-factor. Pitch motion resulting from a yawing motion would be gyroscopic effect, right? As I understand it, gyro effect means that a change of pitch while under power (single-engine prop plane, of course) will cause a change of yaw. P-factor isn't about pitch/yaw change but rather about pitch/yaw amount. Gyro effect is proportionate to the rate of pitch/yaw change, while P-factor is proportionate to the amount of pitch/yaw angle. Isn't this so?

Edited February 20, 2015 by Echo38

[Crumpp]

P-factor isn't about pitch/yaw change but rather about pitch/yaw amount. Gyro effect is proportionate to the rate of pitch/yaw change, while P-factor is proportionate to the amount of pitch/yaw angle. Isn't this so?

 

Looks like you got it. P-factor is about the angle of the relative wind on the propeller disc while gyro effect is where the resultant force applied to the disc is felt.

 

Of all the propeller effects, P-factor, torque, and spiral slipstream....

 

It is the spiral slipstream that accounts for the majority of the "propeller effects" observed.

 

http://www.qmfc.org/school/asym.htm

Edited February 20, 2015 by Crumpp

[Anatoli-Kagari9]

Guys, I know what p-factor is, as well as gyroscopic effect, but it was Yo-Yo who explained some of these effects were due to it.

 

Actually, on a CW rotating prop, hitting the right rudder would, by gyroscopic effect, create a pitching down moment, and not a pitching up... but, if you believe it is p-factor causing it then you can try to imagine the loading of the prop disk in the 3D space ...

 

Say the aircraft is flying level. As you hit the right rudder pedal, the relative wind will asymmetrically load your prop in what sector? Exactly! On the bottom one ( because it's CW rotating ), thus, being it p-factor, it'll create additional lift from that sector, and hence the pitching up moment!

 

This was how I tried to make sense of Yo-Yo's justification. Since it was Yo-Yo who said it was due to P-Factor that we could observe that nose rotation when diving in the p51d with the prop stopped, but I really don't have the aerodynamics background to figure out if indeed P-factor could account for these pitching up effect when you apply rudder in the K4 ( or any other prop aircraft in DCS, but is't more evident in this one! ).

Edited February 20, 2015 by jcomm

[TAGERT]

The problem with pilot accounts is that memories change and are lost or become inaccurate over a period of time. And like someone telling a how big fish story, they tend to embellish the facts, which is just human nature found in us all...just look at Brian Williams

Agreed 100%

 

While we are on the subject, IMHO until the game provides a way to log data during flight, as 1C did in IL-2 with DeviceLink, or as 1C did in CoD with C#, no one can say with any certainty how well the planes are matching the real world data. Just too many potential sim pilot errors can be made during testing that can corrupt the results.

 

This statement is based on the hundreds of test logs I have reviewed over the past 10+ from several different flight sim. I found that most of the errors were in the way the user performed the in-game test, and not an actual error in the FM. For example, not taking into account the difference in the in-game atmosphere and the real world data, which is typically corrected/converted to standard atmosphere, but not always! Another example, in WWII some countries the beginning of a rate of climb test started from a dead stop on the runway, where as others the beginning of a rate of climb test started with the plane air born at a low altitude. Not a big impact on the rate of climb data, but it does affect the time to climb results. Little difference like that can have a big effect on the results.

 

So, until we have a way to log the in-game data, any and all in-game testing should be taken with a grain of salt. As a bare minimum a video should be recorded during the test so others can review the methods used during testing.

 

On a related note, Combat Pilot Accounts..

 

Combat Pilot Accounts are great source for information on the planes flying qualities of a plane, like ground handling, the sounds it makes when you do this, the vibrations you feel when you do that..

 

But..

 

Combat Pilot Accounts are worthless sources for information on the planes performance!

 

Reason being combat pilot accounts are typically one sided stories that says more about the pilot vs pilot skill than plane v.s. plane performance.. That and the combat pilot accounts typically do not contain enough information to recreate the scenario in-game to see if you can obtain the same results, let alone the other planes state..

 

For example, for every German pilot combat account of his Bf109 being able to out turn a Spitfire, their is a British pilot combat account of his Spitfire being able to out turn a Bf109..

 

Yet to this day people still think some sort of statistical average can be gleamed from pilot accounts.. But that is a pipe dream IMHO, for so many reasons, but probably the most important reason being, you never get a chance to read the after action report from the pilots that were killed in action! ;)

[Crumpp]

Guys, I know what p-factor is, as well as gyroscopic effect, but it was Yo-Yo who explained some of these effects were due to it.

 

Actually, on a CW rotating prop, hitting the right rudder would, by gyroscopic effect, create a pitching down moment, and not a pitching up... but, if you believe it is p-factor causing it then you can try to imagine the loading of the prop disk in the 3D space ...

 

Say the aircraft is flying level. As you hit the right rudder pedal, the relative wind will asymmetrically load your prop in what sector? Exactly! On the bottom one ( because it's CW rotating ), thus, being it p-factor, it'll create additional lift from that sector, and hence the pitching up moment!

 

This was how I tried to make sense of Yo-Yo's justification. Since it was Yo-Yo who said it was due to P-Factor that we could observe that nose rotation when diving in the p51d with the prop stopped, but I really don't have the aerodynamics background to figure out if indeed P-factor could account for these pitching up effect when you apply rudder in the K4 ( or any other prop aircraft in DCS, but is't more evident in this one! ).

 

Keep in mind Jcomm, P-factor is asymmetrical disc loading. The blades are at different angles of attack and therefore producing different amounts of lift.

 

Gyroscopic effect is when the relative wind pushes on the blade, the resultant force is felt 90 degrees in the plane of rotation.

 

They sound really similar but they are not.

 

Torque, P-factor, and gyro effect are all actually pretty minor in effect. The airplane just has a lot of natural dampening working against them such that they do not influence it all that much.

 

The major effect on stability is the spiral slipstream. That is a function of the helix angle formed by the aerodynamic pitch of the blade. The difference between the zero lift blade angle and the angle of attack is the slippage of the propeller.

 

The distance on the helix path of the blade is called the pitch length and varies with velocity and power in a Constant Speed Propeller.

 

How it strikes the fuselage and surfaces of the aircraft determine its effects. There are several mathematical models that attempt to replicate it's effect.

[Anatoli-Kagari9]

Keep in mind Jcomm, P-factor is asymmetrical disc loading. The blades are at different angles of attack and therefore producing different amounts of lift.

 

Gyroscopic effect is when the relative wind pushes on the blade, the resultant force is felt 90 degrees in the plane of rotation.

 

They sound really similar but they are not.

 

Torque, P-factor, and gyro effect are all actually pretty minor in effect. The airplane just has a lot of natural dampening working against them such that they do not influence it all that much.

 

The major effect on stability is the spiral slipstream. That is a function of the helix angle formed by the aerodynamic pitch of the blade. The difference between the zero lift blade angle and the angle of attack is the slippage of the propeller.

 

The distance on the helix path of the blade is called the pitch length and varies with velocity and power in a Constant Speed Propeller.

 

How it strikes the fuselage and surfaces of the aircraft determine its effects. There are several mathematical models that attempt to replicate it's effect.

 

Exactly, and that's why I say, p-factor is overdone in DCS as it is right now, because it has been mentioned as being in the origin of those effects...

 

Anyway, when I was given the justification based on P-factor, I tried to understand how it could work... If you imagine the effect, on the prop disk of a CW rotating prop, of application of right rudder, you can find there a possible justification for the pitching up moment ( the low sector of the prop disk becomes loaded ) - again, by gyroscopic effect it should be a pitching down moment...

 

I'm not saying that it's indeed due to P-factor, but rather that, if that's the case, then IMHO P-factor must be overdone.

Edited February 20, 2015 by jcomm

[NineLine]

p-factor is overdone in DCS as it is right now

 

Based on what?

[Anatoli-Kagari9]

Based on what?

 

Based on the fact that,

 

it supposedly accounts for:

 

1) the wobbling of the nose of the p51d when diving, engine out, prop stopped, at a high angle of dive ( near vertical );

 

2) the pitching up moment in the K4 when, inflight, from level flight or climbing, applying right rudder causes pitch up...

 

this all assuming I did not mistakenly understand the explanation that was given for both of the effects.

 

Do I have data ? Nope !

 

But something tells me that probably gyroscopic effect at high power and cruise speed regimes would probably play a more important role, and that a p51d falling from the sky, not stalled, in a high speed dive with its engine and prop stopped, would have enough inertia to overcome the effects of the asymmetric lift of it's 4 blades...

 

Of course it's a wrong assumption if the justification for those effects isn't anywhere related to P-factor ( asymmetric load of the prop disk / blades )...

Edited February 20, 2015 by jcomm

[NineLine]

But how do you know they are over done in DCS?

[sobek]

and that a p51d falling from the sky, not stalled, in a high speed dive with its engine and prop stopped, would have enough inertia to overcome the effects of the asymmetric lift of it's 4 blades...

 

Inertia can't "overcome" force. Only force can counter force.

[Anatoli-Kagari9]

But how do you know they are over done in DCS?

 

Certainly not for sure since I never flew anything close to those aircraft, nor have data or aerodynamics knowledge that would give me the chance to show formulas and numbers, but, I still can use common sense to try to find a plausible justification for it...

 

Of course, if I am wrong, it'll be very easy to show it to me.

 

It feels pretty much like that old discussion about the deflected propwash due to x-wind...

 

I was taught that P-Factor plays it's effects, meaning noticeable effects, in taildraggers, at high power and high AoA, like during the start of the takeoff run, but not once airborne, flying straigh & level or at higher speeds. Of course it'll probably come to play again at the top of high power climb, low speed, high AoA...

Edited February 20, 2015 by jcomm

[NineLine]

Certainly not for sure since I never flew anything close to those aircraft, nor have data or aerodynamics knowledge that would give me the chance to show formulas and numbers, but, I still can use common sense to try to find a plausible justification for it...

 

Of course, if I am wrong, it'll be very easy to show it to me.

 

It feels pretty much like that old discussion about the deflected propwash due to x-wind...

 

No real world experience, no data, no aerodynamic Knowledge...

 

and someone here needs to prove you wrong? ;)

[Anatoli-Kagari9]

Inertia can't "overcome" force. Only force can counter force.

 

Ok, I'd say the other the aerodynamic forces, namely lift from the wings and tail surfaces, will do then in the case of the diving p51d...

 

and as far as the K4 goes, when we kick the right rudder and it pitches up, even from cruise regime, flying S&L or in an even shallow climb, I'd say propwash, and again lift and dynamic pressure would probably overcome p-factor, not to count the gyroscopic effect which would tend to make the aircraft pitch down, although I think that under such conditions gyroscopic effect would also be negligible ...

Edited February 20, 2015 by jcomm

[Yo-Yo]

Keep in mind Jcomm, P-factor is asymmetrical disc loading. The blades are at different angles of attack and therefore producing different amounts of lift.

 

Gyroscopic effect is when the relative wind pushes on the blade, the resultant force is felt 90 degrees in the plane of rotation.

 

They sound really similar but they are not.

 

Torque, P-factor, and gyro effect are all actually pretty minor in effect. The airplane just has a lot of natural dampening working against them such that they do not influence it all that much.

 

The major effect on stability is the spiral slipstream. That is a function of the helix angle formed by the aerodynamic pitch of the blade. The difference between the zero lift blade angle and the angle of attack is the slippage of the propeller.

 

The distance on the helix path of the blade is called the pitch length and varies with velocity and power in a Constant Speed Propeller.

 

How it strikes the fuselage and surfaces of the aircraft determine its effects. There are several mathematical models that attempt to replicate it's effect.

 

P-factor isn't a minor effect especially at high speed where slipstream added velocities is very low in comparison to incoming air velocity, but yes, at high speed the total pitch/yaw is less because of high dynamic pressure creating strong stabilising moments from the empennage.

[Crumpp]

P-factor isn't a minor effect especially at high speed where slipstream added velocities is very low in comparison to incoming air velocity, but yes, at high speed the total pitch/yaw is less because of high dynamic pressure creating strong stabilising moments from the empennage.

 

Absolutely. As you point out, the stabilizing moments tend to "hide" the effect leaving the most dramatic effects as the slipstream.

 

Propeller instability effects tend to manifest themselves as a steady build up of force as the aircraft enters slowflight slowing down to reach the stall point in the air.

 

Does DCS use momentum or blade theory?

 

I included a report from the NACA.

 

"Notes on Propeller and Slipstream in relation to stability" uses blade element theory. So you might find it convenient to use provided DCS uses blade theory, LOL.

[Crumpp]

Yo-Yo, thank you for taking the time to address the players and the answer you gave on page 2 was good enough! :thumbup:

 

Here is another report dealing with propeller effects on stability and control. This time the influence on static longitudinal stability.

 

Again, it uses blade theory and notes the static longitudinal stability effects are minimal except at very low velocities.

[Friedrich-4B]

There are lots of wartime NACA reports on how propellers affected flight characteristics; here's a 1943 vintage report, plus a shorter version, published in 1945:

[Crumpp]

There are lots of wartime NACA reports on how propellers affected flight characteristics;

 

Quantity is not really the point. :music_whistling:

 

Thanks for sharing! :thumbup:

[GrapeJam]

Quantity is not really the point. :music_whistling:

 

Thanks for sharing! :thumbup:

So what makes your report more valid than his?

[MiloMorai]

So what makes your report more valid than his?

 

Depends on who posted the links.

[NineLine]

Can we all see where this is drifting? So knock it off before it goes there... please.

[Solty]

There is a P-51 guncamera footage of Bf109 beeing in a nasty stall.

http://youtu.be/MCiHa0h-6Rs?t=23m48s

[Crumpp]

There is a P-51 guncamera footage of Bf109 beeing in a nasty stall.

 

Good footage. Notice the airplane is tumbling and not spinning....

 

So what makes your report more valid than his?

 

It is not that it more valid, the question is what do you want to do with the information?

 

The first report I posted is a mathmatical description of propeller effects on stability. It provides the big picture using a very common and accepted propeller theory. It is not a adoption of helicopter theory either, it is made to model the behaviors of a Constant Speed Propeller on a single engined aircraft.

 

The second report I posted is a mathmatical microscope looking at a very specific and narrow portion of the aircraft behaviors. It simply illustrates the fact propeller effects on the longitudinal axis are not really a factor except for very low velocity just above the stall.

 

It is a mathmatical microscope like the next reports posted in the thread.

 

Unlike the first reports, the preceding reports are not a simple system that describes the propellers effect on the overall aircraft behaviors nor do they even present complete information on propeller effects on stability.

 

All of the reports accurately describe aircraft behavior within the intended scope. The question becomes how much time and computing power one wants to use to get the same result.

 

Of course, that is not even considering the fact only two small areas of effect are described in the other reports given. In otherwords, we need a few more reports and a lot more information!!

 

Make sense now?

[msalama]

Depends on who posted the links.

So how would my links rank? I'm a complete bozo as it comes to aerodynamics.

* runs away, but remembers to grab his coat regardless, although almost tearing it in 2 in his panicky retreat *

[Crumpp]

Very Good..excellent links!! Best post yet....just show a little more "Aero" in your "dynamics" and it will be spot on target!!

 

:lol: