Dora roll rate and turning rate, true to real-life data?

[Aluminum Donkey]

Greetings everyone,

 

I've been in the virtual seats of the P-51D, BF-109 and FW-190 for a while now and can say that while they are great simulations, a little quirk has been bugging me...

 

The 190 seems to easily out-turn the Mustang and keep up with the 109 above about 250 km/h or so. It also has a low roll rate from what I expected. From what I've heard, a major strength of the 190 was it's extremely high rate of roll, and it seems little faster than the P-51's. Also, the 190 had a high wing loading, giving it mediocre turning ability compared to most other fighters. In the sim, it appears to out-turn the Mustang and keep up with the BF-109 easily in the turning department.

 

I always got the impression that the real-life FW-190 had a very high roll rate but a greater minimum turning radius than most other fighters of WW2, both characteristics attributed to it's high wing loading. In DCS World it seems that the 190 feels sluggish in roll and turns too tightly. The BF-109 should effortlessly out-turn the FW-190, and the P-51 should slightly out-turn it, but the FW-190 should easily roll much faster than either the 109 or P-51. This is not the case.

 

Can anyone elaborate?

 

A D

[Crumpp]

Unfortunately the math shows that at or below 1st Gear Supercharger FTH, the Mustang is on the short end of the stick for sustained turn performance vs the FW-190D9.

[SkyCaptain109]

When flying the P-51 against the Dora I feel that it can easily outroll me and get out of my gunsight at any speed.

Turn performance is close and I think that it depends on pilot ability. Once I turned with a Dora down on the deck at the edge of a stall, had 20° of flaps and he couldn't get his guns on me instead he spun out and crashed.

When I was in the Dora I couldn't outturn the Mustang and it seemed easy for him to stay on my tail. He got some strikes and finally after heavy turning and scissoring I spun out.....:joystick:

 

The Dora can climb like a rocket and can easily outclimb the Mustang the best tactic would probably be doing vertical maneuvers.

Edited December 29, 2014 by SkyCaptain109

[Crumpp]

Turn performance is close and I think that it depends on pilot ability.

 

I agree, the performance is not so far apart and pilot skill makes the difference. Whoever blinks first is going to lose.

[fastfreddie]

Roll rate of the Dora is better than both the Mustang and 109 ... the earlier versions of the 190 may of had a higher roll rate but I'd have to look that up in my books. Different engines, armor, armament, airframe etc changed the 190 over time. Turn rate on the deck for the Mustang and Dora is very similar (flaps etc) with pilot ability like some of the others said being a deciding factor. Once you start get off the deck it starts to lean the Mustangs direction vs the Dora. I haven't done any real testing on the 109 but it also changed alot from the early E models to the K4 so you'd have to look at that also when determining turn radius while comparing it to other planes.

[Aluminum Donkey]

Interesting... I'd be inclined to think the 109 would be the best turner because of its leading edge slats (highest CL Max.)

 

Thanks guys!

A D

[arthuro12]

The Dora can climb like a rocket and can easily outclimb the Mustang the best tactic would probably be doing vertical maneuvers.

 

Not really.

 

Vertical manoeuvres are nice to handle in the Dora but climbing isn't that impressive.

Unless the Mustang pilot is turning and burning and the 190 retains some of it's energy it might look like a superior aircraft.. but most of it's speed can be held in the horizontals.

[Nooch]

From the experience I've had with the Fw 190 and P-51, the mustang generally turns better than the Dora but at very low speed, the Dora is more controllable.

The FW 190 controlls feel lighter than the Mustang's, giving the impression it's much more agile overall but after dogfighting you realize it's just an impression, the Dora can't turn that well.

Concerning the roll rate, I haven't paid much attention to it so I can't relate.

[Chappie]

Greetings everyone,

 

I've been in the virtual seats of the P-51D, BF-109 and FW-190 for a while now and can say that while they are great simulations, a little quirk has been bugging me...

 

The 190 seems to easily out-turn the Mustang and keep up with the 109 above about 250 km/h or so. It also has a low roll rate from what I expected. From what I've heard, a major strength of the 190 was it's extremely high rate of roll, and it seems little faster than the P-51's. Also, the 190 had a high wing loading, giving it mediocre turning ability compared to most other fighters. In the sim, it appears to out-turn the Mustang and keep up with the BF-109 easily in the turning department.

 

I always got the impression that the real-life FW-190 had a very high roll rate but a greater minimum turning radius than most other fighters of WW2, both characteristics attributed to it's high wing loading. In DCS World it seems that the 190 feels sluggish in roll and turns too tightly. The BF-109 should effortlessly out-turn the FW-190, and the P-51 should slightly out-turn it, but the FW-190 should easily roll much faster than either the 109 or P-51. This is not the case.

 

Can anyone elaborate?

 

A D

 

 

The 190 does have a high rate of roll. I can out-scissor the P-51 because of this very fact. To achieve such a high rate of roll you need to use rudder.

 

Also, if you are really wavy, stall the left wing with rudder application for some really fast snap rolls to the left. Won't work to the right because of that pesky fixed trim tab.

 

The 190 can't out turn the P-51 below 15000 feet without dumping flaps. Same with the 109. These are zoom and boomer aircraft and any good P-51 pilot can out turn them without the use of flaps.

 

Head over to the Dogs of War server and see for yourself. Zoom and boom and high altitude are your friends unless you wanna fight down low but in a 190 you are dumping heavy flaps and loosing lotta speed to do so. Same in the 109 but now you are also breaking your wing tips and spewing flame and smoke out the back.

 

So the only advantage the 190 has is in the scissor horizontal and vertical in addition to climb rate. Never be a P-51 pilot zooming north as it is certain death.

 

Remember to use rudder for faster rolls.

[Crumpp]

Once I turned with a Dora down on the deck at the edge of a stall, had 20° of flaps

 

The analysis is without flaps. Adding the flaps will shift the advantage to the Mustang.

[Crumpp]

Remember to use rudder for faster rolls.

 

That is so important! All roll data assumes coordinated use of rudder. Problem even pilots today do not know what that means because rudder usage is not critical in tricycle gear aircraft.

[Echo38]

It's important to not base one's {impressions of how these airplanes ought to handle} upon shoddy sim/games of the past. {Warbirds, IL-2, Aces High, War Thunder, and the like} did a rather poor job of accurately portraying these aircraft. I suspect that {the assumption that the FW 190 ought to roll faster and turn worse} comes from having played those outdated games, in which the characteristics of the FW 190 were surely exaggerated or otherwise misrepresented (as was proven to be the case with other aircraft in those games).

Edited January 4, 2015 by Echo38

[Crumpp]

It's important to not base one's {impressions of how these airplanes ought to handle} upon shoddy sim/games of the past. {Warbirds, IL-2, Aces High, War Thunder, and the like} did a rather poor job of accurately portraying these aircraft. I suspect that {the assumption that the FW 190 ought to roll faster and turn worse} comes from having played those outdated sim/games, in which the characteristics of the FW 190 were surely exaggerated or otherwise misrepresented (as was proven to be the case with other aircraft in those games).

 

I agree.

 

FastFreddie says:

the earlier versions of the 190 may of had a higher roll rate but I'd have to look that up in my books.

 

 

An important aspect of the Dora 9 vs Antons is the CG range is shifted forward on the Dora series.

 

The stability margin is larger and is reflected in the roll rate. That is why the Antons roll better.

[Bluedog]

An important aspect of the Dora 9 vs Antons is the CG range is shifted forward on the Dora series.

 

The stability margin is larger and is reflected in the roll rate. That is why the Antons roll better.

 

I'm no aerodynamicist, so I don't understand why forward movement of the CG should have an effect on the roll rate. Could you explain, please.

[Crumpp]

I'm no aerodynamicist, so I don't understand why forward movement of the CG should have an effect on the roll rate. Could you explain, please.

 

Sure.

 

Think of a see saw on a playground. If you extend the length of one side of a see saw, you have to move the balance point (fulcrum) toward that side to keep it in balance. That is the basic principle of what happened when Focke Wulf extended the fuselage.

 

Allow me to provide a basic explanation and cover some terms.

 

The point all the aerodynamic forces (lift and drag) acts is called the Aerodynamic Center (AC).

 

http://www.grc.nasa.gov/WWW/k-12/airplane/ac.html

 

 

The entire aircraft's AC is also called the Neutral Point (NP) and it is a function of the distance between the wings AC and horizontal and vertical stabilizer AC. Think of the AC as the fulcrum where all of the aerodynamic forces balance much like our playground see saw. Most horizontal stabilizers produce a down force to balance the CG and NP, btw.

 

This distance between the point the gravitational forces (weight) act is called the Center of Gravity (CG). The distance between the Center of Gravity and the Neutral Point is called the stability margin.

 

When we move our NP back, we increase the stability margin.

 

That means we have a larger "arm" or distance.

 

Weight X Arm = Moment or Torque

 

What is a moment? It is a measure of force of a bodies tendency to rotate about an axis.

 

2 lbs X 5inches = 10 inch pounds

 

2 lbs X 10 inches = 20 inch pounds

 

So when we increase the arm, we increase the moment required to move it and our roll rate slows down.

 

Understand?

[Bluedog]

Sure, and thank you for the explanation and I can see how that applies to longitudinal stability. However, I still don't see how it applies to roll rate. Surely the aircraft will roll around its roll axis and will therefore be largely (or even totally) unaffected by fore or aft movement of the CG. To my way of thinking the roll rate will be dependent on the degree of aileron deflection and span location of the aileron.

 

Or am I missing something?

[gavagai]

Thanks for the great discussion.

 

I am afraid I don't see it either. After reading the NASA link, the AC and Natural Point seem clear enough, and center of gravity is OK too.

 

But, from this perspective

 

 

I could not tell how far apart the CoG and NP are, or if one or the other had moved.

 

I'm going to be thinking about this all day now! Fwiw, I do not have any kind of engineering background, just two semesters of physics in college.

[Crumpp]

However, I still don't see how it applies to roll rate.

 

It is not direct so it is more difficult to spot on the surface. It is easy to see why one would not think the stability margin is important. It changes the forces that oppose the rolling velocity our aileron design can produce.

 

The lateral axis is still dependent upon the point where all the aerodynamic forces act and the point gravitational force acts.

 

The Stability Margin is applicable because only the force of gravity acts through the CG, the aerodynamic forces act through the aircraft's Neutral Point even in lateral dynamics.

 

Since all three lifting surfaces (wing, horizontal tail, and vertical tail) are contributing to

the rolling drag, the yD is in fact, the average of three average distances.

 

Rolling velocity is dependent upon the rolling rate the ailerons/wing can produce. The wing/aileron rolling rate is generally considered independent of CG location except to consider vertical axis distance from the wings AC to the CG.

 

The rolling drag which opposes the rolling rate of the wing/aileron IS a function of CG location.

 

Understand?

Edited January 8, 2015 by Crumpp
added NASA's illustration for clarity and Aircraft Design: A Systems Engineering Approach aileron design chapter

[Crumpp]

Here, maybe this will help! There are also additional contributions to rolling moment from tail design. The larger tail of the Ta-152 would have helped restore the rolling moment lost by the forward movement of the CG limits in the Dora.

 

 

Edited January 8, 2015 by Crumpp

[Crumpp]

Sure, and thank you for the explanation

 

You are welcome!

 

Let me know if you still have questions!

[Crumpp]

I'm going to be thinking about this all day now!

 

:thumbup:

 

Your thinking is correct. It is just not the whole story! :smilewink:

[Yo-Yo]

I agree.

 

 

 

 

An important aspect of the Dora 9 vs Antons is the CG range is shifted forward on the Dora series.

 

The stability margin is larger and is reflected in the roll rate. That is why the Antons roll better.

 

How can longitudinal stability affects roll rate? If you mean directional stability I can agree, but Dora because of the long nose got longer tail section to preserve stability margin. If it was more stable than Anton the stick forces would be higher (the same thing was with Spitfires MkV and MkIX - MkIX had positive stability though MkV was neutral. Then the subsequent resulting mod for MkIX was increasing of the elevator moment compensation) but Dora had the same elevator as Anton.

Edited January 8, 2015 by Yo-Yo

[Crumpp]

Yo-Yo,

 

It is not longitudinal stability, it is lateral stability.

 

The Longitudinal stability diagram is just used to illustrate the concept of the stability margin. Sorry if it caused confusion.

[Crumpp]

Dora because of the long nose got longer tail section to preserve stability margin.

 

I agree and that is what I am saying. It looks like they did more than preserve it and increased the stability margin.

 

As for stick forces, the Antons had pretty light almost too light exhibiting some longitudinal instability in the form of force reversals.

 

 

The ladeplan I have for the Dora shows the whole CG range shifted forward. That represents a widening of the stability margin due to the increase in the distance between the wings AC and tail surface AC.

 

Then the subsequent resulting mod for MkIX was increasing of the elevator moment compensation)

 

Right, In July of 1946 they increased the entire horizontal stabilizer area which shifted the tail AC back eliminating the longitudinal instability which AFAIK, existed from the Spitfire Mk I thru Spitfire Mk IX.

 

They addressed the longitudinal instability by increasing the control through the bob-weights, metal elevator, or new aerodynamic balancing of the elevator. No design changes were made that changed the stability margin until the horizontal stabilizer area was increased after the war.

[Art-J]

Hmmm... I don't know, I'm still with Gavagai on this one.

 

 

So when we increase the arm, we increase the moment required to move it and our roll rate slows down.

 

 

This part is as unclear and confusing as it can get. The preceding description concentrates on location of NP and CG along fuselage longitudinal axis and the way the moved empennage changes the pitching moment. How did the rolling, ie. rotation done around the axis perpendicular to the one noted, end up in here? It's almost as if You explained how putting and balancing kids on see-saw works, and suddenly jumped to conclusion "this is why see-saw cannot turn over to its side" :D. I admire the will to explain flight-dynamics issues in simple manner, but the explanation above might do more harm than good I'd say.

 

I also don't get what the "aileron design" chapter and the two pages above have in common with our problem - difference between Anton and Dora rollrate? In both cases wing, horizontal and vertical stab geometry is the same, so, using symbols from the quoted resources, hv, Sv, bh, bw, Sw and Yd are also the same and so is the rolling moment. CG and NP locations are different, sure, but only along longitudinal axis.

 

I guess I could imagine adverse yaw influencing roll somewhat, with more "stability-margin'ized" Dora being less susceptible to such yaw and resulting changes in effective AoA of left and right wing, which would affect roll... but if we presume adverse yaw is not an issue (because of differential ailerons, or skilled pilot or whatever), then we're back to square one.