FM-sideslips and drag

The lack of people on mulitplayer suggests many of us feel the same way.

haha what a load of horseradish

See the previous posts from birdstrike.

Well, I see a speed loss if I, say, crab the plane on a crosswind landing. But if what Birdstrike says is true, something's definitely off-kilter there too. Just thought I'd ask is all...

But the thing is, if you want this problem to be looked at, you've got to be able to quantify it. Hunches are not enough, unless something's so badly off that it's kind of obvious; but I just checked this with the Yak and at least she bled off speed when put into a slip / crab. Comes to the nitty gritty however? No idea, but at least the basic physical phenomenon is there.

Mind you that I'm not saying this cannot be broken, I'm just saying you guys need quantifiable data. Out ;)

But the thing is, if you want this problem to be looked at, you've got to be able to quantify it. Hunches are not enough, unless something's so badly off that it's kind of obvious; but I just checked this with the Yak and at least she bled off speed when put into a slip / crab. Comes to the nitty gritty however? No idea, but at least the basic physical phenomenon is there.

 

Mind you that I'm not saying this cannot be broken, I'm just saying you guys need quantifiable data. Out ;)

Msalama, what data are you asking for? In birdstrike's original post, he clearly specifies the conditions he is testing it in, and gives a data point, i.e. 0 knots lost in uncoordinated flight in those level flight conditions. I'm not saying that's wrong, but it certainly seems counterintuitive. Kwiatek added a link to his post which was expressing a similar concern. While there wasn't specific data in his, his experience as a pilot should count for something. Thus it seems that there is nothing wrong with them bringing their concerns to the forums for discussion.

Perhaps if there is specific data that you think is necessary to make the case, you could let us know what that is, rather than a generic call for data that doesn't enlighten the conversation.

I think the real question is, how much slip should induce how much drag? Half a ball out of center? Full? How much airspeed SHOULD be lost under those conditions for the Mustang?

My initial testing DOES show speed loss starting to be noticeable at a full ball out of center and increases greatly from there. Will try to have a video up soon showing the test parameters for evaluation of the situation.

EDIT: Oh, and flaps? yes, they induce a good amount of drag. I have mine on an axis, and even minimal setting you will see speed degradation, which I will also show in the video.

Here it is, flying a straight, 6 mile course at around 200 ft agl, code shows the airspeed as the a/c passes each mile marker. I input rudder trim to cause uncoordinated flight, ailerons to keep it straight. All other controls were set and untouched. As you will see, half a ball out of trim seems to do nothing. There was some variances in speeds as I struggled a bit to maintain the course on a level flight.

Once the ball was a full width out of trim, then you can start to see the speed degradation, but it isnt much, and some might say within the variances of the altitude changes. Full, out of trim conditions showed larger degradations of speed as expected.

https://www.twitch.tv/videos/335549700

Msalama, what data are you asking for?

Well Shahdoh formulated it correctly, i.e. how much slip should induce how much drag.

thats an interesting question indeed.

but my concern is, why should the ball half off center or a little more not cause any drag?

shadoh's test confirm my/our tests. while i cant say how much of a speed loss u should have in the various types at certain slip angles, ultimately there should be drag by any slip in any aircraft except when flying perfectly coordinated.

Here it is, flying a straight, 6 mile course at around 200 ft agl, code shows the airspeed as the a/c passes each mile marker. I input rudder trim to cause uncoordinated flight, ailerons to keep it straight. All other controls were set and untouched. As you will see, half a ball out of trim seems to do nothing. There was some variances in speeds as I struggled a bit to maintain the course on a level flight.

 

Once the ball was a full width out of trim, then you can start to see the speed degradation, but it isnt much, and some might say within the variances of the altitude changes. Full, out of trim conditions showed larger degradations of speed as expected.

 

Thanks for posting this.

It's great so see someone do tests with a solid methodology, explaining with their voice what they are doing and seeing all the time.

Far too often I see people posting crappy 30 second long context-free nonsense without proper explanation of what they are doing, what they are controlling for and the results they are seeing.

THIS is how FM testing should be done and shared.

but my concern is, why should the ball half off center or a little more not cause any drag?

Interesting observation. Half a ball off isn't a great deal out of trim though, especially when the engine is producing enough power to travel at 370mph.

I'd like to see the tests conducted at 200mph to see if the lower engine power setting shows a difference.

The fully-off centre ball showed a 9mph speed degradation. And Shahdoh asks the right question, how much should we expect to see?

How sensitive is the slip indicator in the mustang for a start?I notice that in the spit a very small amount of slip results in quite a lot of nose-movement form the aircraft. But in Shahdoh's video it seems the Mustang is not that responsive to being un-balanced. This could just mean that the P51 has a low range in the slip indicator.

What about other aircraft with vastly different wing design like the spitfire? Do we see a different response to slip?

Thanks for posting this.

It's great so see someone do tests with a solid methodology, explaining with their voice what they are doing and seeing all the time.

Far too often I see people posting crappy 30 second long context-free nonsense without proper explanation of what they are doing, what they are controlling for and the results they are seeing.

THIS is how FM testing should be done and shared.

 

 

 

 

Interesting observation. Half a ball off isn't a great deal out of trim though, especially when the engine is producing enough power to travel at 370mph.

I'd like to see the tests conducted at 200mph to see if the lower engine power setting shows a difference.

 

The fully-off centre ball showed a 9mph speed degradation. And Shahdoh asks the right question, how much should we expect to see?

How sensitive is the slip indicator in the mustang for a start?I notice that in the spit a very small amount of slip results in quite a lot of nose-movement form the aircraft. But in Shahdoh's video it seems the Mustang is not that responsive to being un-balanced. This could just mean that the P51 has a low range in the slip indicator.

What about other aircraft with vastly different wing design like the spitfire? Do we see a different response to slip?

Thanks. I will try to do more tests at 200mph as well as testing with the 109 and 190. Unfortunately, I do not have the Spitfire yet. Sacrilege I know, I really do like the spit, just not in the budget currently.

For those wanting to test this for themselves under your own conditions, look for the VARS racing server currently on the release version. Look for the SOCHI aircraft and there you will find the dragstrip race course that I flew in the tests. I am using a modified version providing an airstart for faster and more consistent starts.

PS: You will need the VARS Pylon mod by Grinnelli that can be found in the User Downloads: https://www.digitalcombatsimulator.com/en/files/3196986/

Here is the next round of testing with the mustang going slower. I wanted to use some established power settings so I used "Cruise - Max" setting with 20 degrees of flaps (2 notches) that gave me 180 mph instead. I felt those numbers provided a better baseline for stability of the test then a real low manifold pressure setting. I then did the test at the same cruise setting without flaps, getting the mustang to a midrange speed of nearly 280 mph.

Results were similar, though the slower the speed, the more pronounced the induced drag was, but not by much.

I also ran some quick and dirty tests with the 109 and 190. I have not flown those as much so I just used a low to midrange power setting. Even still, could see similar results due to slip drag.

https://www.twitch.tv/videos/335869562

 

Results were similar, though the slower the speed, the more pronounced the induced drag was, but not by much.

 

It's actually more a case of parasite drag here, with the added contribution, among other elements, by the fuselage...

Thanks for the correction. I used the term induced in the manner that I had introduced it by causing the slip with the rudder trim. Research on the term "induced drag" shows that is has a different meaning (that part of the drag on an airfoil that arises from the development of lift) and that I miss used the term. My apologies for any confusion it may have caused.

Thanks for the correction. I used the term induced in the manner that I had introduced it by causing the slip with the rudder trim. Research on the term "induced drag" shows that is has a different meaning (that part of the drag on an airfoil that arises from the development of lift) and that I miss used the term. My apologies for any confusion it may have caused.

No problem at all, alas, being Portuguese I would naturally use "induced" too and we have "induzido" here as something caused by...

But I did know about that "official" definition in the domain of aerodynamics, so, I decided to suggest the correction.

What matters is that your and others posts have been important in bringing this subject to discussion - sideslip effects as modelled in DCS prop aircraft.

Thanks Yo-Yo.

Back to the issue at hand though, how accurate are the effects of drag displayed in the tests for the prop aircraft in DCS.

Interesting that "induced" in your case was not a mistake. Sideslip generates side force or "lift" that generates induced drag giving the main part of resulting drag. This side force gives side acceleration moving the ball.

So, remembering that induced drag is proportional to lift^2...

Touché :-)

Thanks Yo-Yo.

 

Back to the issue at hand though, how accurate are the effects of drag displayed in the tests for the prop aircraft in DCS.

thats the real question here.

thats the real question here.

Right. And the answer is?

Anyway, the L-39 loses a carpton of airspeed and lift when sideslipped / crabbed. Not a prop AC, I know, but the basic physics are definitely there in the sim regardless and seem about right to me at least.

Right. And the answer is?

 

Anyway, the L-39 loses a carpton of airspeed and lift when sideslipped / crabbed. Not a prop AC, I know, but the basic physics are definitely there in the sim regardless and seem about right to me at least.

read the op? nobody is doubting that a general drag effect is existent...

an answer from the devs would be interesting.

and jets are absolutely off topic there

In a way, I believe we have our answer. It is what it is for a $40 piece of entertainment software. I know I have gotten great value for my purchase and am willing to accept it as is. I have flown some combat in it, many hours racing it and flying in virtual airshows. My cost ratio is now in the pennies per hour or even less. Could it be better? Certainly, everything can always be better, but you know what, it will never be the same as flying the real aircraft and I for one am willing to accept that.

In a way, I believe we have our answer. It is what it is for a $40 piece of entertainment software. I know I have gotten great value for my purchase and am willing to accept it as is. I have flown some combat in it, many hours racing it and flying in virtual airshows. My cost ratio is now in the pennies per hour or even less. Could it be better? Certainly, everything can always be better, but you know what, it will never be the same as flying the real aircraft and I for one am willing to accept that.

YEAH...you are right...we have our answer.:noexpression: wish they would make the FMs more detailed tbh.

thx for your input in this thread shadoh