Washout built into the wings of the Ta-152H (WWII Aviation Question) 1

[Broncazonk]

I have a question pertaining to the late-war German high altitude fighter, the Ta-152H.

3-view here:

http://www.largescaleplanes.com/reviews/Kits/WW2/PacificCoastModels/32008/images/schemes01.jpg

Here is a description of the washout built into the wings of the Ta-152H written by the National Air and Space Museum:

“Kurt Tank chose the same workhorse Jumo 213 powerplant used in the Fw 190D. For the Ta 152H, he selected an uprated version, the Jumo 213E, equipped with a 2-stage, 3-speed mechanical supercharger and MW 50 engine boost. The MW 50 system used methanol-water mixture to boost engine output from 1,312 kw (1,750 hp) to 1,537 kw (2,050 hp) for short periods. Because of aluminum shortages, Focke-Wulf made the wing spars from steel and built the rear fuselage and empennage. The wing contained two steel spars. The front spar extended slightly beyond the landing gear attachment points but the rear spar spanned the entire wing. The wing twisted 3° from the root to the flap-aileron junction. This 'washout' prevented the ailerons from stalling before the center section. This allowed the pilot to maintain roll control during a stall. Armament consisted of one 30mm MK 108 cannon firing 90 rounds through the propeller hub and one 20mm MG 151 cannon firing 150-175 rounds from each wing root.”

http://airandspace.si.edu/collection...m_A19600317000

And here is another description:

The aircraft had an increased wingspan compared to the previous FW 190 design, as a further accommodation towards better high altitude performance. Due to the war's impact on aluminum availability, the wing was built around two steel spars, the front extending from just past the landing gear attachment points, and the rear spar spanning the entire wing. The wing itself was designed with 3° of washout, from the root to the flap-aileron junction, to prevent the ailerons from stalling before the center section of the wing. This design allowed the pilot to maintain roll control during a stall and extreme flight envelope maneuvers.

http://warthunder.wikia.com/wiki/Ta_152_H-1

Are these descriptions correct? Isn't it more likely that 3° of washout (three degrees of downward twist) was built into the wings beginning at the flap-aileron junction that extended to the wing tips—not and not from the root to the flap-aileron junction?

Would the experts on the list please provide some clarity on this?

Thank you,

Bronc

 

[Broncazonk]

From another discussion on this topic:

"My interpretation of the text is:

a) washout goes from 0 degrees (relative) at the wing root, to -3 degrees at the flap-aileron junction;

b) washout remains at a constant -3 degrees across the outer wing supporting the aileron hinges.

The inner wing washout means it goes from 0 to -3 degrees across the span between root to flap/aileron junction, so not -3 degrees all the way along the inner wing."

So yes, does this make sense? The downward twist of the wing arrived at -3 degrees at flap-aileron junction, and then the twist was maintained at a constant -3 degrees throughout the aileron section to the tips.

Thank you again,

Bronc

 

[FastMouse]

The description of washout sounds responsible to me.

It is no secret that WWII military aircraft were designed quickly, and frequently there was not time to perfect the design from an aero point of view. The priorities were to create an aircraft that was (1) usable, and (2) producible with the constraints on workforce skills, etc. Crew safety was not the overriding objective that it is today and that why these aircraft sometimes had handling qualities that would not be acceptable if designed into a contemporary aircraft.

With the Ta-152H, perhaps it was decided that it would be sufficient to ensure that a limited portion of the center-section stalled first and the ailerons remained effective, at least in the early in the stall, even if the overall stalling behavior was not very friendly. (Additionally, stalling behavior is also governed by planform, change in section, etc. Washout is just part of the story.)

A plausible *guess* is that the wing outboard of the flap-aileron junction was manufactured using a separate jig, and to minimize the required manufacturing effort & skill, that section was built with zero washout, and the washout was restricted to the center section, which would anyway be more complicated, requiring more sophisticated tooling & manufacturing skill. Again, just conjecture.

 

[rb1957]

agree with the above.

makes sense to me (lower incidence outbd = stall at root first).

why quote 2 sources saying the same thing ? i expected them to say different things, and so a source of confusion.

i expect most people reading (or responding) would recognise a Ta152 (as being a WW2 plane); the others I'd expect would google it.

another day in paradise, or is paradise one day closer ?

 

[FastMouse]

Oops, in my prev post "...sounds responsible to me." should read "...sounds reasonable to me." I prefer to blame the spellchecker, rather than my failure to check the spelling changes it makes.

 

[Broncazonk]

If the Ta-152H was being built today would the designer utilize structural washout or are there more modern alternatives?

 

[btrueblood]

Given that the majority of planes/gliders built today use some type of structural washout, I'd say not. Unless you can elaborate on the "modern alternatives"?

 

[Broncazonk]

btrueblood wrote, "Given that the majority of planes/gliders built today use some type of structural washout, I'd say not. Unless you can elaborate on the "modern alternatives"?"

Nope, don't have any. (I'm in way over my head as it is.) I was just wondering if changing/modifying the airfoil to a different NACA 4 or 5 or whatever along the span of the ailerons would be an alternative to washout, because that's kind of what washout already is.

Bronc

 

[Broncazonk]

Another question: is the part of the wing with a -3 degree washout constantly creating negative lift in horizontal flight?

Thanks again..

 

[rb1957]

not necessarily ... certainly it is creating less lift (due to lower incidence) but it doesn't have to be negative

another day in paradise, or is paradise one day closer ?

 

[FastMouse]

Without a doubt. Washout works. (Even if stall strips are routinely added.)


With -3° washout, there will not be negative lift. The important thing is the local angle of attack measured from the zero lift angle, not the washout. Even with -3° washout, the local angle of attack can still be positive. Say the AoA at the root is +7°. Out at the tip, the local AoA will still be ~+4° (The tip flow effects will affect the local AoA, but the principle is unchanged.)

Without a fuselage, a typical, conventional wing design has a spanwise lift distribution that is more-or-less elliptical-ish; approx zero, as rb1957 highlighted, at the extreme tip and maximum at the center. Adding the fuselage usually reduces the lift in the root region, but the point is that the lift distribution is not less than zero at the tip. "Patterns in the Sky" is an out-of-print NASA book, but the PDF is available on the NASA TRS. Amongst other things, it dwells at length on using condensation above the wing of an in-flight aircraft to make a qualitative judgement of lift distribution. 90% of the text is devoted to high speed aircraft, but the concepts are applicable to light aircraft. I think that it's an illuminating book with some really interesting photographs. Might be worth a click.

 

[rb1957]

agreed, the wing incidence is set so that in 1g flight, lift = weight, by design. some parts of the wing can have -ve CL ... it's not like "it's the law, all CL is +ve". then there's practice, flight test, wich can carefully measure the airplane incidence for 1g flight and it is usually close to the design value (too different and they'll redesign).

but sometimes tips do have -ve lift. i know one case where's it's happened, it wasn't by design, it was due to the aeroelastic flexibility of the wing; but it wasn't so bad that they couldn't live with it.

another day in paradise, or is paradise one day closer ?

 

[Broncazonk]

FastMouse wrote, “Say the AoA at the root is +7°. Out at the tip, the local AoA will still be ~+4° (The tip flow effects will affect the local AoA, but the principle is unchanged.)

The above corresponds exactly to what was going on with the FW 190D-9 and FW 190A. From a post by drgondog (a WWII aviation expert) on TOCH:

“The FW 190D-9 and FW 190A had a Positive angle of 2 degrees at the root with constant wash out to the 80% semi span point at which point the angle was zero, thence no further twist to the tip. I don't have access to the Ta 152 data. (reference - P. Gross "Die Entwicklung der Tragwerkkonstruction Fw 190", Bericht 176, der lillenthal Gesellschaft, 2 Teil, January 1944.)

So with the Ta-152H, is it reasonable to assume that Kurt Tank incorporated a +3 degree angle at the root with a constant washout to the flap-aileron junction, at which point the AoA was zero, with no further twist in the span along the ailerons?

Bronc

 

[FastMouse]

rb1957: Agreed; it is possible to have local cl < 0 in 1g flight, but it sure is nice to avoid it! The Horton flying wings are non-typical, and I believe that some of those intentionally had negative cl in the tip region. And I've seen aircraft flying with full-flap, nose-down, where the tips were clearly at a negative cl.

Broncazonk: "So with the Ta-152H, is it reasonable to assume that Kurt Tank incorporated a +3 degree angle at the root with a constant washout to the flap-aileron junction, at which point the AoA was zero, with no further twist in the span along the ailerons?" Yes. Sounds reasonable. But why assume it? You've got a NASM reference that says so, and while I've not seen the reference, I think that NASM info could be considered valid source data. Recommend keeping the concept of AoA and angle of incidence separate. AoA is variable depending on the flight condition (and there is no reason why it should be zero in 1g flight) and angle of incidence is a design parameter, where the airfoil ref line is measured relative to some aircraft datum.

 

[Broncazonk]

FastMouse wrote, "Recommend keeping the concept of AoA and angle of incidence separate." Roger. I see the importance of that.

I have a question pertaining to the split-flaps on the Ta-152H. On most forums, a change of topic would mandate a new thread. Is that the protocol here?

Thank you again for the incredibly informative replies..

Bronc

 

[KENAT]

Broncazonk, be a little careful not to slip into the aviation enthusiast situation as you may be perceived as violating site posting policies. Might be best to keep these Ta152 questions in this one thread.

Posting guidelines faq731-376

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(probably not aimed specifically at you)
What is Engineering anyway: faq1088-1484​

 

[Broncazonk]

The wingspan of the Ta-152H was 14.44 m (47' 4.5") and split flaps were 8.4 m of that: 4.2 m (13' 9.5") per side. Focke Wulf utilized split flaps on the Fw-190A-G and split flaps were utilized on the Supermarine Spitfire. What were the design/engineering consideration(s)/imperative(s) of choosing split flaps for these aircraft instead of plain or slotted flaps?

As a hypothetical (and calling for speculation): what would plain or slotted flaps have done to the take-off, landing, and flight characteristics of the Ta-152?

Thank you,

Bronc

 

[FastMouse]

Split/plain/slotted flaps. They all do the same job, increase max CL and increase CD to faciliate a steeper, slower approach. And help take-off, of course. So why choose one over another? Sure, slotted flaps will give you the biggest increase in CL, but in practice, sometimes design decisions are made based on the fact that the organisation did something in the past and the concept can be easily recycled on the latest project. Split are probably easiest to manufacture and maintain, and if they worked before, then why not use them again? And if the tooing does not need to be significantly adapted, even better.

There is sometimes a tendancy, when outside of a design organisation, to over-think how a design decision was reached. I am not saying that everything is done a scrap of paper during a coffee. That's nonsense and usually hundreds of hours, or more, go into a single decision. But occaisonally that is not the case. In Roskam's war stories book, he tells a tale about how the Cessna A-37 had a spinning (I think it was) issue. Using "That Looks About Right" methodology, overnight they attached a logitudinally-oriented strip to either side of the fwd fuselage. The next day the issue was found to have vanished. They didn't bother to subsequently investigate in a tunnel *exacly* why the strips worked so well, they just did and that was enough. Issue closed.

 

[Broncazonk]

I am under the impression that split flaps provide very limited amounts of lift, and aerodynamically, they act as spoilers and air brakes more than flaps. Also, historically, split flaps were a very short-lived fad among late 1930's aircraft designers, and they quickly faded out of use. So back to the original questions: What were the design/engineering consideration(s)/imperative(s) that these late 1930's aircraft designers thought that they were solving by choosing split flaps for these aircraft instead of plain or slotted flaps? and, As a hypothetical (and calling for speculation): what would plain or slotted flaps have done to the take-off, landing, and flight characteristics of the Ta-152?

Thank you,

Bronc

 

[KENAT]

Simplistically I'd expect more advanced flaps of the types you mention should have improved the take off & landing properties, possibly trim/handling too.

As alluded to above, split flaps may have been chosen for reasons such as ease of manufacture, structural considerations or what the designer was used to amongst others.

Posting guidelines faq731-376

http://eng-tips.com/market.cfm?

(probably not aimed specifically at you)
What is Engineering anyway: faq1088-1484​