improving the 109?? (2 Viewers)

[GrauGeist]

Considering that the wheel well fairings were commonly removed in service on FW-190's due to mud getting trapped in them - why put them on in the first place?

They are referring to covering the exposed portion of the maingear tire/wheel when it's retracted into the wing.

The Spitfire, Hurricane, Fw190, KI-43, P-40 and other aircraft that had their roots in the 30's, had a portion (or all) of the maingear wheel/tire exposed when retracted.

 

[Shortround6]

In some cases things actually went backwards a bit.

AS with many things serviceability and real world performance (take-off and landing on crappy airstrips) often trumped the last 1-2% of performance.

 

[GrauGeist]

Don't forget the F4U, F6F, Ju88, He219 and Me210!

 

[CharlesBronson]

It must be remembered that the 109 had the best aerodinamics available in pre-war Germany inside some limited parameters of weight, size and price, the airframe is quite simple compared with a Spitfire, p-39 or P-51, big accent was put by Messerschmitt on easy of manufacturing, that was a big advantage of the 109 above the elliptical wing He-112.

 

[gumbyk]

They are referring to covering the exposed portion of the maingear tire/wheel when it's retracted into the wing.

The Spitfire, Hurricane, Fw190, KI-43, P-40 and other aircraft that had their roots in the 30's, had a portion (or all) of the maingear wheel/tire exposed when retracted.

That's a huge amount of re-engineering required to put that system in - sequencing valves and all that - certainly more than 30 days work.
The easiest way would be to extend the existing fairing to cover most of the wheel.

Either way - the amount of maintenance required is excessive.

 

[Milosh]

Just need a bar that is attached to the cover.

 

[drgondog]

I

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AS far as the slats vs washout thing goes, Drgondog or some of our other engineers may correct me but my understanding is that the slats are activated (by airflow over the area) just before stall, or in other words at an angle of attack just below that at which the airfoil stalls. The slats keep the airflow going over the wing and the higher angle of attack generates more lift in the area of the wing affected and the airflow is effective over the ailerons helping keep control of the aircraft, a double benefit.

Close enough. At very high AoA the adverse pressure gradient causes the boundary layer of the wing aft of the slats to begin separation - destroying lift - while the flow (and lift) remains on the slats - which activates the slats. When the slats deploy they also permit the high energy free stream flow underneath the slats to move across the wing aft of the slat and the higher energy flow temporarily re-engages the boundary layer. "Snatching occurs when the high wing at greater effective AoA activates before the down wing reaches the same relative AoA. The aileron deflections (up and down) change the local chord of the airfoil slightly up and slightly down to the free stream velocity.

Washout means the outer wing is operating at a lower angle of attack than the inner wing, the inner wing stalls before the outer wing and so the airflow over the ailerons is still effective (unless the stall gets really bad) however at any point in time the outer wing area/s will be generating less left due to the shallower angle of attack compared to the inner wing area/s or a similar wing with no washout.

The washout also causes an incremental profile drag component, hence Willy analyzing the balance and choosing slats along with zero twist to the wing.

Total lift from a wing is a complex issue with things like aspect ratio coming into play. It is not quite so simple as picking airfoil XXXX and using YYY sq ft and any wing using both those numbers will generate the same lift at the same speed regardless of shape/planform or washout.
During the design process the designers can "tweak" the wing (change shape and size) to get the desired lift at the drag that is acceptable to them and taking into account other considerations, like landing and taking off. Trying to "re-tweak" an existing wing is a lot harder. Do you make the wing larger (extend the wing tips) as you introduce the washout to maintain the same amount of lift at the same speed for landing? What does the larger wing do to drag at high speed?

As an illustration of 'complexity, consider that the P-38, FW 190, F6F, F8F and F4U all had the NACA 23xxx airfoil with only 1% T/C difference between them - some round tips, some 'square', all trapezoidal plan forms (to minimize departure from optimal Oswald efficiency) - all having aspect ratios less than 6 except P-38 with 8+. All have essentially the same CDo for each wing. The differences were due to 'gaps' (wheelwell, flap, aileron, wing fold joints), guns, surface finish. All 50% greater than P-51 low drag wing with laminar flow airfoil shape, prepared wing surface, including puttying, sanding and painting. The NACA 23015.5 was the alternative to the NACA.NAA 45-100 wing had it 'failed' wind tunnel tests. It was a good airfoil with nice L/D, Max CL.

The P-38 with an Aspect ration >8 had the lowest Relative Induced drag - but still high because it was so damned heavy. This is important when designing to optimize maximum cruise range at middle range speeds where the CDo and CDi 'cross' (i.e. equal to each other) on the drag polar.

Then the hard work of designing for weight considerations (i.e taper from root to tip and the underlying beam structure to support aero loads spanwise), house fuel/weapons, landing gear, etc). The first choice for structural consideration is to place the main spar near the center of pressure at maximum load condition - usually a high AoA dive pullout at Limit G Load.

Back to the 109 - the placement of the gear, desire to easily remove wings for transport/repair dictated a 40% rather than 25% location for the spar - which necessitated a greater than normal secondary bending resistant spar design, including spar caps (thick skin).

"IMPROVING/Changing" the wing was a tantamount to starting from scratch.

 

[GrauGeist]

Just need a bar that is attached to the cover.

What would you attach the "bar" to?

The tire is literally resting against the upper wing surface...

 

[tomo pauk]

Removal of wing wheel covers on the Fw 190 occured once the belly rack was installed, not beacause it was a troublesome thing to install & operate. Let's recall that Soviets, renown for their adherence to KISS principle, were installing fully retractable & covered undercarriages.
Both Spitfire and Bf 109 (new models, but still) received whell well covers from winter of 1944/45 on; the fully retractable and covered U/C was one of main things that made Spitfire III faster by 15+ mph than Spitfire V.

 

[Shortround6]

And in the case of later 109s the upper wing surface got bulges to house the larger tires needed due to increasing weights. This happened twice, very late 109s have some rather large bulges.

Obvious model

poor photo

Granted some sort of linkage might have been arranged to go around the wheel rather than over it but we are back to cost and maintenance vs performance.

given enough wind tunnel time perhaps a small spoiler/fairing could have been devised to "bounce" the airflow over the exposed part of the wheel ( a bit like airflow defectors in front of bombbays ?) but that might only work at certain speeds and cause more drag at other speeds.

 

[gumbyk]

See how that linkage is bent? It will cause one of two things to happen. Either the door won't close fully, or it will close before the gear is fully up, depending in how much it is bent and the geometry, and potentially prevent the gear coming down again.

 

[pbehn]

The Me109 was a very small aircraft which ended up with an engine of over 2000BHP output. It takes a lot of uncovered wheel wells dodgy air inlets and crude joints before it becomes notably disadvantaged when you compare to the size and weight of planes like the P47 and Typhoon.

 

[GrauGeist]

The Me109 was a very small aircraft which ended up with an engine of over 2000BHP output. It takes a lot of uncovered wheel wells dodgy air inlets and crude joints before it becomes notably disadvantaged when you compare to the size and weight of planes like the P47 and Typhoon.

Don't forget the "totally turbulent" Slats, too!

 

[pbehn]

Don't forget the "totally turbulent" Slats, too!

I havnt, as I understand it the 2% washout of the Spitfire guarantees turbulence and drag, ailerons and elevators also cause drag when used. I am not an expert but from what I have read everything in WW2(even present day) aviation was a compromise. The Me109 was a fabulous design which was at the front in combat from the star to the finish of WW2. I have no doubt it could have been improved and if it was then it would have been produced in much bigger numbers than it was and would have achieved a much higher number of kills than it did. 34,000 produced is really pathetic for what was a promising design.

 

[gumbyk]

given enough wind tunnel time perhaps a small spoiler/fairing could have been devised to "bounce" the airflow over the exposed part of the wheel ( a bit like airflow defectors in front of bombbays ?) but that might only work at certain speeds and cause more drag at other speeds.

Like this?
LoPresti make one for Pipers - it gives 4 knots.

 

[GregP]

Gumbyk,

That linkage isn't bent at all. It is articulated, with a joint near the top right of your red circle. It is intended to be that way.

The stop nut allows adjustment of the door travel to ensure proper closing.

Don't think there was room above the main wheel in the Bf 109 for the linkage since the wheel is right against the upper skin. However they COULD have made a mechanical stop that rested against the bottom of the wheel when retracted, and it would have been "out of the way" with respect to the upper skin. I'm thinking the complexity wasn't worth the potential gain. There are several airloners noted for their efficiency that have exposed tires.

Here's a Boeing 737:

The exposed wheels don't keep it from cruising over 500 mph. The drag is what is important, not whether it is exposed or covered flush.

 

[ww2restorer]

Very correct Greg P, the linkage is bent that angle by Herr Tank so the linkage will clear the bottom radius of the tire when the wheel is retracted.

 

[wuzak]

Both Spitfire and Bf 109 (new models, but still) received whell well covers from winter of 1944/45 on; the fully retractable and covered U/C was one of main things that made Spitfire III faster by 15+ mph than Spitfire V.

The Spitfire III had several changes which add up to the 15mph increase over the V, including clipped wings and a new radiator design.

The Prototype Spitfire, K5054, originally had flaps to cover the wheels completely when retracted.

These proved to be a problem, so they were removed and were found to have little effect on speed.

The Hurricane prototype also had these covers which disappeared on production machines

 

[gumbyk]

Gumbyk,

That linkage isn't bent at all. It is articulated, with a joint near the top right of your red circle. It is intended to be that way.

The stop nut allows adjustment of the door travel to ensure proper closing.

Greg,
I was referring to the bend at the top of the "U" part of the fitting, where the threaded portion is (The centre of the circle) not the two articulated joints.

[/QUOTE]

 

[stona]

The boundary layer over almost the entire Bf 109 airframe was turbulent for a variety of reasons,same for most WW2 aircraft.

One aerodynamic analysis I read suggested that a cleaned up Bf 109 G-6 would have been capable, theoretically, of 800kph.
It would not be practical to mass produce such an aircraft under wartime conditions.

Cheers


Steve