LaGG-3/La5 ailerons

[Bilbo_Baggins]

Gents,

 

Hoping to learn a little something about control surface design of some of the machines in the game. The La5/LaGG-3 airframe stands out as an interesting example in that the ailerons are just huge, like big paddles, in comparison to some of the slowest roll rate machines like the Migg-3 or the Messerschmitts. Large deflection angles too.

 

Obviously the La5/LaGG is very maneuverable on the longitudinal axis, so my question is what are the reasons for this design discrepancy and why weren't other machines designed with these large ailerons and big deflection angles for quick roll rates?

Edited April 15, 2021 by Bilbo_Baggins

[Luftschiff]

Some were, but the primary drawbacks to my amateur knowledge is that a larger control surface area also creates more drag, which, esp. at the time , would also mean greater stick force required. More well-read aeronautical engineers can add further points of contention I'm sure, but in design it's always about compromises. Control surfaces also have a detrimental effect on the airflow over the wing and its lift capacity. Obviously there are also cases where you do not WANT your plane to be 'twitchy' in the roll axis, and the advantages in roll rate would decrease as speed goes up.

I'd guess the large control surfaces owe on the La5 and LaGG also owe in some small part to the large wing surface area, but now I'm guessing so I'll step aside and wait for more expert experts.

Edited April 15, 2021 by Luftschiff

[BlitzPig_EL]

The A6M Zero also has very long span ailerons.   This gives very responsive roll control and  high roll rates at low speeds.  The downside is that as speed increases these large ailerons become increasingly difficult for the pilot to move, and hence are less effective at higher speeds.  As air combat occurred at ever faster speeds these "barn door" ailerons simply stopped being a good idea.

 

Today you really only see them on aerobatic aircraft.  

[gimpy117]

im no expert, but yeah more area means more control, if you were Hercules you could roll well at high speeds, but low speeds a mere mortal should perform well, better than a 109 maybe...but, you know the lagg has no slats and the La5 doesn't have magic ones. 

[Bilbo_Baggins]

11 hours ago, gimpy117 said:

im no expert, but yeah more area means more control, if you were Hercules you could roll well at high speeds, but low speeds a mere mortal should perform well, better than a 109 maybe...but, you know the lagg has no slats and the La5 doesn't have magic ones. 

 

This has nothing whatsoever to do with slats. Could you reiterate?

[RyanR]

There's some black magic going on with the wing as a whole. In other words, the aileron design/size isn't independent from the aerodynamics in the design of the wing.

 

I'd love to know more. Planes that seem to roll better at higher speeds also seem to have better pitch authority as well.

 

-Ryan

[Pahec97]

Gennerally, spanwise you make ailerons as large as you can as long as it does't interfere with internal structure and you can keep two hinges. Most planes you see go from flaps to ailerons, so you cant extend in this manner.

Chordwise, larger aileron provides more control, but at much worse efficiency, and of course, you can't really go in front of your aft spar.

Most ailerons you see on older planes are made with these exact dimensions: spanwise from flap to almost end and chordwise they start bit after aft spar.

Flap dimension is determined by required stall speed and aft beam position has many variables, especially inner structure and all around strength, meaning that roll rate isn't something you design for.

[oc2209]

I think there's a large amount of unknown variables in terms of control harmonization and input forces. Things maybe even the engineers themselves can't anticipate (on paper alone) until the aircraft is in prototype stage.

 

One thing we, as mere aviation enthusiasts and not engineers, can understand is that roll rates are not totally dependent on ailerons, but also on wing shape. Squared wing tips seem to offer better roll rates than rounded, if the Fw-190, the low-altitude clipped-wing Spitfire mods, the Hamp Zero, and the pre-F series of 109s are any indication.

 

We also need to differentiate between mechanically assisted/unassisted aileron controls; the P-38 would be a famous example of a plane with an 'artificial' advantage in its roll rate after the addition of power boosted ailerons.

 

In the case of the La-5 in particular, I would say its roll performance is as much to do with its tapered wing shape as its aileron size. But that's just a blind guess on my part.

[gimpy117]

10 hours ago, Bilbo_Baggins said:

 

This has nothing whatsoever to do with slats. Could you reiterate?

i suppose my point is, a lot of things are attributed to their presence on the aircraft, at least as the 109 is concerned. the 109 has slats : it is supposed to have incredible turn with little drag, wo, why is the lagg not a good roller? it just seems counter intuitive 

[oc2209]

Just for fun, I took the following screens.

 

Yak-1b:

 

 

Yak-9 (I've never read an explanation regarding the wingtip change in Yak-9s):

 

 

La-5FN:

 

 

Fw-190 A-3:

 

 

One thing that's striking to me is just how odd the 190's horizontal stabilizer looks compared to most other planes. So narrow from above.

 

Anyway, this isn't meant to be remotely scientific. I just thought it'd be interesting to show planes with decent roll rates (Yaks) versus planes with exceptional rates (La and Fw).

 

At face value, the La-5's wings look stubbier than all the others, relative to its fuselage size. The 190's, by contrast, aren't stubby, but are narrower at the root. Does any of that matter? As I said, this is just my guesswork.

[6./ZG26_Klaus_Mann]

There are a couple of different Factors that influence how your Aircraft Rolls.

 

First to Consider is Adverse Yaw, which is simply: If you Create more lift on one side, you also create more drag on that side, if you kill lift on one side, you also have less Drag on that Side. So when you put the Stick to the right you create more lift on the left wing and less drag on the right wing --> The Wings bank to the Right, Nose Yaws to the Left.

When the Nose is yawed out of the Direction of Travel, the outside Wing is aerodynamically shadowed by the Fuselage, and thus some Lift is killed on the inner left Wing Section, while on the Right the Fuselage energizes the Airflow over the inner Wing Section.

With enough Yaw, this can mean that despite full Stick Deflection in one Direction, your Aircraft simply stops banking, or even banks in the opposite Direction, this is called a Forward or Side-Slip.

Spoiler

 

This Manouver is not entered by using Rudder, it is only used to maintain this Slip steadily.

 

Conclusion 1: Your Rate of Roll depends on how well you and your Rudder can counteract adverse Yaw.

 

 

Secondly: Your Wingtips are very important, and traditionally Straight/Clipped Wing Tips make for cleaner Roll Characteristics, while rounded Tips make for less snappy Stall Characteristics.

The Spitfire is an interesting Example of this, where the clipped Tips made for better Roll Characteristics, but snappier Stall.

 

Conclusion 2: Your Rate of Roll depends on the shape of your Wingtip.

 

Thirdly: Ailerons sit behind the main Spar, and thus also impart a twisting Force on the Wing. A Light, but Soft Wing cannot resist that twisting very effectively, and thus a lot of Work at High Speed goes into deforming the Wing, which actively counteracts the Aileron Work, up to the Point of Aileron Reversal, where your Stick Movement actually has the opposite Effect, a Problem for many very early Spitfires in High Speed Dives.

 

Conclusion 3: A Stiff, heavy Wing Rolls better at High Speeds than a Soft Light Wing.

[6./ZG26_Klaus_Mann]

Also: The Reason why the Russian Aircraft have those Pyramid shaped Wings instead of the much straighter Western Designs is their Construction from Wood, which in order to be as strong as the Metal Wings need to be a lot thicker near the Fuselage.

[Bremspropeller]

19 minutes ago, 6./ZG26_Klaus_Mann said:

Also: The Reason why the Russian Aircraft have those Pyramid shaped Wings instead of the much straighter Western Designs is their Construction from Wood, which in order to be as strong as the Metal Wings need to be a lot thicker near the Fuselage.

 

Nah, I think it's rather going the easy way of optimising lift-distribution.

The other part might be an additional benefit.

[oc2209]

1 hour ago, 6./ZG26_Klaus_Mann said:

Also: The Reason why the Russian Aircraft have those Pyramid shaped Wings instead of the much straighter Western Designs is their Construction from Wood, which in order to be as strong as the Metal Wings need to be a lot thicker near the Fuselage.

 

I always thought the stubby Russian wings were designed solely to be super-cute for propaganda posters.

 

The I-16, coincidentally, would make for a great plushie toy. Stalin really dropped the ball when he didn't try to sell international Communism via plushie.

[AEthelraedUnraed]

On 4/18/2021 at 11:21 PM, Pahec97 said:

Gennerally, spanwise you make ailerons as large as you can as long as it does't interfere with internal structure and you can keep two hinges.

Just wondering, why is it bad to have more than two hinges?

[CUJO_1970]

I have yet to see any measured roll rate test from WW2 for a Lavochkin fighter, or any Russian fighter for that matter., like we do with the German, RAF and US fighters.

 

The roll rates in the sim make the La-5 series the fastest rolling aircraft, at least up until higher speeds are reached. I believe it was said that they are calculated using the wing/aileron geometry. 

[[CPT]Crunch]

What part does distance from the roll axis play?  Is wing span a factor?  Say the same shape and size ailerons.

[AEthelraedUnraed]

2 hours ago, [CPT]Crunch said:

What part does distance from the roll axis play?  Is wing span a factor?  Say the same shape and size ailerons.

Well classical physics say that a force twice the distance from the center results in twice the torque. So ailerons further from the center result in a larger roll rate (proportional to the wingspan).

 

On the other hand, a larger wing span results in more mass further away from the center and hence a larger rotational inertia. It therefore requires more torque for the same result (proportional to the square of the wingspan).

 

Also there's drag. Not only will a larger wingspan result in a larger wing surface (=more drag), the speed of the wingtip is also much larger with a larger wingspan resulting in, again, more torque required for the same roll rate (I suspect this is quadratic as well, but I don't feel like calculating it).

 

In short, you want your ailerons to be as far away from the center as possible, but at the same time your wing span as small as possible. It's obvious that this creates a conflict, so the aircraft designer will have to compromise.

 

I'm sure there are many more subtleties from an aerodynamics point of view, but this is what classical mechanics has to say.

Edited April 20, 2021 by AEthelraedUnraed

[Pahec97]

22 hours ago, AEthelraedUnraed said:

Just wondering, why is it bad to have more than two hinges?

There are troubles with deformation, and you have to calculate it with the more difficult way

[Voyager]

58 minutes ago, Pahec97 said:

There are troubles with deformation, and you have to calculate it with the more difficult way

 

I recall, if you have an ideal line, it cannot be supported in more than two point. In order to have more than two points in contact, the line is required to be deformed in some degree.