The only issue with Flight Model

First of all i must say, that, while obviously i am not a real Spit pilot i must say this must be the closest to a real deal i've experienced.

 

There is only one thing that, in my mind seems unreal. When i ease the throttle there's hardly any reaction to the plane's pitch attitude. I admit that due to the changing twisting and turning reactions of the propeller (which are awesome) it is a bit hard to diagnose what the plane is doing but i've even seen nose up reaction after significant power reduction.

 

Now, since this is a prop plane and the horizontal stabilator is where they usually are - behind the prop, reducing thrust should ~immediately weaken the airstream over the stabilazer making the nose go down, and the plane should climb when adding thrust. This only happens after the speed reduction of reduced thrust which is not right in my mind.

 

What'ya think?

The spitfire is tail heavy, and the elevator is pointed down slightly in cruise to compensate for this and reduce drag in hard turns. This leads to some rather fiddly pitch handling when you're not in a dogfight.

First of all i must say, that, while obviously i am not a real Spit pilot i must say this must be the closest to a real deal i've experienced.

 

There is only one thing that, in my mind seems unreal. When i ease the throttle there's hardly any reaction to the plane's pitch attitude. I admit that due to the changing twisting and turning reactions of the propeller (which are awesome) it is a bit hard to diagnose what the plane is doing but i've even seen nose up reaction after significant power reduction.

 

Now, since this is a prop plane and the horizontal stabilator is where they usually are - behind the prop, reducing thrust should ~immediately weaken the airstream over the stabilazer making the nose go down, and the plane should climb when adding thrust. This only happens after the speed reduction of reduced thrust which is not right in my mind.

 

What'ya think?

 

Was the Spit perfectly trimmed for a given airspeed and level flight when you performed this test?

Edited April 13, 2017 by OnlyforDCS

Was the Spit perfectly trimmed for a given airspeed and level flight when you performed this test?

 

Absolutely. But as i said, the test is not very easy to perform accurately, since the power reduction causes torque changes etc and you need to keep the plane level, so a hands off test is quite impossible but anyway no pulling back is necessary and it indeed might climb.

 

The P51 mustang however, starts to dip nose if you retard the throttle.

The P51 mustang however, starts to dip nose if you retard the throttle.

 

Because of its differently configured center of gravity and horizontal stabilizer.

I look forward for stiffness to be added ( with dynamic pressure ) to the rudder axis, to better balance the feel of the three controls.

Edited April 14, 2017 by jcomm
My rubish in the original post...

Because of its differently configured center of gravity and horizontal stabilizer.

 

Well you might be right. I just do not figure this out. If the plane is "tail heavy", or the CoG is more aft than usual, ok they slightly increased the AoA of the stabilazer, but shouldn't it still react to airflow preetty much normally...? Tailheaviness would sound really bad. The Airacobra was tail heavy in some situations and it could end up in fatal accidents for that, but its engine was mounted behind the pilot...

Only airspeed is going to change the lift when you reduce the throttle, if nothing else is changed. One thing my group has noticed is that when you reduced the throttle, the plane wants to yaw to the left, the same as when you add throttle. That's fine and correct when adding power due to torque and other factors, but definitely shouldn't be happening when reducing power.

Based on what?

 

Based on my more than 40 hrs in DCS's Spitfire :-)

 

Well, jokes apart, and while you should always filter my exclamations .. I believe it was even mentioned by developer on some thread I can't find right now.

 

Of course it's not impeditive or a show stopper. It can somehow be tamed down using, for instance, 25 % curve for rudder axis - that's what I am using...

 

Anyway, post amended ;-)

 

Here's that interesting "NACA" report: http://jsbsim.sourceforge.net/spit_flying.pdf

Edited April 14, 2017 by jcomm

Only airspeed is going to change the lift when you reduce the throttle, if nothing else is changed. One thing my group has noticed is that when you reduced the throttle, the plane wants to yaw to the left, the same as when you add throttle. That's fine and correct when adding power due to torque and other factors, but definitely shouldn't be happening when reducing power.

 

That sounds like a pretty obvious FM bug. (I haven't flown the Spit in a few weeks, going to try and reproduce that today)

I did a quick research, and i found that in some airplanes the horizontal stabilator can create a positive lift (up-force). (Conventionally it creates a downforce, and when you reduce the throttle, the slipstream of the propeller over the downforcing elevator is reduced, so the nose dives).

 

IF the spitfire's horizontal stabilator creates a positive lift, when i reduce the throttle, the force pushing the tail UP is reduced and it should indeed result in nose up situation (because the force that used to lift tail up has now decreased). But because reducing throttle causes airspeed to drop too, the plane will lose lift too so that could be the simplified reason why it is either ~stable or even noses up.

 

Is this what "Pocked Sized" tried to explain? am i on a right track here?

I did a quick research, and i found that in some airplanes the horizontal stabilator can create a positive lift (up-force). (Conventionally it creates a downforce, and when you reduce the throttle, the slipstream of the propeller over the downforcing elevator is reduced, so the nose dives).

 

IF the spitfire's horizontal stabilator creates a positive lift, when i reduce the throttle, the force pushing the tail UP is reduced and it should indeed result in nose up situation (because the force that used to lift tail up has now decreased). But because reducing throttle causes airspeed to drop too, the plane will lose lift too so that could be the simplified reason why it is either ~stable or even noses up.

 

Is this what "Pocked Sized" tried to explain? am i on a right track here?

 

Yes, sounds about right.

Only airspeed is going to change the lift when you reduce the throttle, if nothing else is changed. One thing my group has noticed is that when you reduced the throttle, the plane wants to yaw to the left, the same as when you add throttle. That's fine and correct when adding power due to torque and other factors, but definitely shouldn't be happening when reducing power.

 

Well I've tested this, and tried to reproduce it. In a prefectly trimmed out level flight, after pulling back on the throttle the plane yaws, to the right. Which is exactly what you would expect to happen with the drop in torque forces, and considering the rudder is trimmed slightly to the right to begin with to negate the torque force from powered flight.

Edited April 15, 2017 by OnlyforDCS

and raise you Nick Grey

 

I couldn't tell if that picture was a screenshot or a photograph. Even after full-screening the picture in my browser, it took me a few seconds to decide that it's a photo. Really, if it weren't for the dents in the fuselage, I still wouldn't want to put money on it.

 

It makes me happy that flight simulators have come this far, even graphically. : )

 

It makes me happy that flight simulators have come this far, even graphically. : )

 

Sure flight sims have come far, especially in fidelity and flight modeling, but IMO graphics are still a some ways behind. Sure the 3d models are very advanced, likewise for texturing very lifelike. However the most important part is still missing. The sky. :)

 

The weather effects, clouds and sky need a lot of love, especially in DCS. It's probably the most difficult part to simulate properly though, or at least reproduce with close to lifelike graphical fidelity.

That said i really love the Spitfire's behaviour in the turbulence. how the altimeter fluctuates and your wing might drop all the sudden, very lively, very cool very nice.

Sure flight sims have come far, especially in fidelity and flight modeling, but IMO graphics are still a some ways behind.

 

Well, yes, they'll always be behind shooters. Flying in Arma 3 will quickly demonstrate why this has to be, until there's a quantum leap in PC power.

First of all i must say, that, while obviously i am not a real Spit pilot i must say this must be the closest to a real deal i've experienced.

 

There is only one thing that, in my mind seems unreal. When i ease the throttle there's hardly any reaction to the plane's pitch attitude. I admit that due to the changing twisting and turning reactions of the propeller (which are awesome) it is a bit hard to diagnose what the plane is doing but i've even seen nose up reaction after significant power reduction.

 

Now, since this is a prop plane and the horizontal stabilator is where they usually are - behind the prop, reducing thrust should ~immediately weaken the airstream over the stabilazer making the nose go down, and the plane should climb when adding thrust. This only happens after the speed reduction of reduced thrust which is not right in my mind.

 

What'ya think?

Well, "should" is the word. What you describe is what well behaved aeroplanes usually do, you're right. Anyway, you are missing a point there, Spitfire is not a Cessna or trainer aircraft, nor is her an american design, as well as she was designed before that behaviour was actively seek among desingers as something likely to happen whenever one flies an aircraft. An aeroplanes has to be designed like that in order to that behaviour happen, otherwise it just and plainly don't. Nowadays most aicraft, specially GA, behave like that unless they are designed in any other way (aerobatics, for instance), well they do usually since a lot of time indeed, but there was a time when that didn't happen widely. Of course in the 30's it didn't, and even in the 40's. Regarding our current modules, 109 definitely don't behave like that, or not completely, Dora may be better, P-51 definitely does, do you wonder why? :smilewink: And Spitfire, no, she doesn't behave like that, definitely. In that kind of "old fashion" aeroplanes one has to intentionally look for the nose down attitude in order to hold a certain airspeed whenever throttle is cut down. So, IMHO, it's just stunning how well captured those quirks are in a PC simulator…

 

 

For further reading, if you are interested in the subject as well as many other related to aeroplane behaviour, "Stick & Rudder" by Wolfgang Langewiesche. Well, it's not like he explains exactly that, it was written in 1944, so he explains "there are" aircraft behaving one and another way :D :thumbup: .

 

 

 

 

Only airspeed is going to change the lift when you reduce the throttle, if nothing else is changed. One thing my group has noticed is that when you reduced the throttle, the plane wants to yaw to the left, the same as when you add throttle. That's fine and correct when adding power due to torque and other factors, but definitely shouldn't be happening when reducing power.

You cannot say that being a pilot yourself. Of course torque affects you either adding as cutting throttle… Or may be I didn't catch what you mean there :huh:.

 

 

S!

Well I've tested this, and tried to reproduce it. In a prefectly trimmed out level flight, after pulling back on the throttle the plane yaws, to the right. Which is exactly what you would expect to happen with the drop in torque forces, and considering the rudder is trimmed slightly to the right to begin with to negate the torque force from powered flight.

Agreed. Need to cut back on right rudder trim as throttle is pulled back.

So, Spit is yawing to the right as throttle is closed.

I did a quick research, and i found that in some airplanes the horizontal stabilator can create a positive lift (up-force). (Conventionally it creates a downforce, and when you reduce the throttle, the slipstream of the propeller over the downforcing elevator is reduced, so the nose dives).

 

IF the spitfire's horizontal stabilator creates a positive lift, when i reduce the throttle, the force pushing the tail UP is reduced and it should indeed result in nose up situation (because the force that used to lift tail up has now decreased). But because reducing throttle causes airspeed to drop too, the plane will lose lift too so that could be the simplified reason why it is either ~stable or even noses up.

 

Is this what "Pocked Sized" tried to explain? am i on a right track here?

 

Precisely. The low mounted wing and radiators probably add to it as well.