New 109's

[Crumpp]

Just pointing out that it is hard to tell what is photo finish and what is aircraft finish in that picture.  It is an awfully green light/hue to that picture.

The report says the aircraft was coated with a smooth matt finish.

All the best,

Crumpp

[LRRP22]

Originally posted by Crumpp
Just pointing out that it is hard to tell what is photo finish and what is aircraft finish in that picture.  

Not all that tough, really.  It's pretty obvious that the aircraft finish is very scuffed and worn.  The picture itself has a green tinge, but other than that it is very clear.  


.

[Debonair]

Just was reading on of my Jeppessen books & it mentioned that parasite drag increases with the square of airspeed, so it is probably not too hard to estimate the drag penalty of a bomb shackle at any speed if you know the penalty at a particular airspeed

[Kurfürst]

Originally posted by Angus
Anyway, when the discussion goes about 1% differences between PS and HP and 2 mph top speeds, - then IMHO somebody is grabbing a straw,- while at the same time nobody mentions weight difference of what, - 1000 - 2000 lbs maybe (?). [/B]

Yeah, I agree.

The paint is another issue. AFAIK the Germans were ahead in their finishing, so their paint weight is not a penalty. Crumpp has the numbers I belive, if I remember correctly, a good finish could make some 10 mph. [/B]

Some good friend of mine - an aviation author - a good while had some info (though a bit general) about WW2 camo paints. He said that the camo paint the jerries used was of smaller grain size than allied one, so the surface would be smoother. But paint weight is definietely a penalty, think about how much paint you would need to cover about 8-900 sq. feet area - a fighter's surface!

The doc I have also notes some 12 kph gain for the 109G if some care like polishing was done to the surface, though it would vary from plane to plane, and how much work and how many types of improvements were used.

This doc also notes this about gondolas, so I guess we can move to the next subject...

[MiloMorai]

One can draw their own conclusions about the Mtt data, but on the 190G, the 3 different Ruckflug being mounted resulted in a 15kph, 30kph and 18kph loss of speed.

The first Ruckflug was a small little thing used on the G-2, smaller, and with no no stabilizer arms, than what is seen in the pic of the P-51D posted earlier. The second 2 Ruckflugs had 4 small stabilizer arms.

A 4th Ruckflug was used on the G-1 resulted in a 40kph loss of speed.

Data and drawings in Wagner's bio of K Tank, pg. 149, 150

Mounting the MK103 gondolas on the 190 resulted in a 27kph loss of speed.

[Crumpp]

Some good friend of mine - an aviation author - a good while had some info (though a bit general) about WW2 camo paints. He said that the camo paint the jerries used was of smaller grain size than allied one, so the surface would be smoother. But paint weight is definietely a penalty, think about how much paint you would need to cover about 8-900 sq. feet area - a fighter's surface!

I am being somewhat misquoted.  The RLM finishes are of much smaller grain than the allied paints.  They are much more resistant to chipping and seem almost chaulky when cured.  They wear smooth rather than chip or flake.  

Weight is still a penalty but much less than the allied finishes as the RLM paints cover the surface in a much thinner coat and do not require a second coat.

All of these properties are dependant upon proper application.  It took help from ex-Luftwaffe maintenance personnel to get our paint to apply correctly.  It is very finicky paint requiring the proper ratio of reducer, etc...
In the field, especially in Russia, it was not always possible to get the correct components.  The paint could still be applied but was then rubbed down with fuel to improve the finish.

All the best,

Crumpp

[Crumpp]

Ruckflug

Is a condition of the aircraft Milo, not a piece of equipment.  Rückflug is after the stores have been dropped.

It literally means "return flight".

The equipment is the Junkers, Mtt, Focke Wulf, and finally the ETC 503 träger.

Milo says:
One can draw their own conclusions about the Mtt data, but on the 190G, the 3 different Ruckflug being mounted resulted in a 15kph, 30kph and 18kph loss of speed.

The first Ruckflug was a small little thing used on the G-2, smaller, and with no no stabilizer arms, than what is seen in the pic of the P-51D posted earlier. The second 2 Ruckflugs had 4 small stabilizer arms.

A 4th Ruckflug was used on the G-1 resulted in a 40kph loss of speed.

Data and drawings in Wagner's bio of K Tank, pg. 149, 150

Mounting the MK103 gondolas on the 190 resulted in a 27kph loss of speed.

Say something else funny, Milo...

All the best,

Crumpp

[TDeacon]

The following may be useful when considering Kurfurst's description of the wing treatment on the P-51 test aircraft, above.  This is from the  Osprey "Production Line to Frontline" book, page 16 and other pages:

"At the factory, the wings were primered and finished with airfoil smoother.  The first 40 per cent of the wing chord was shot with one coat of zinc chromate primer.  This was then followed by enough coats of Acme Gray Surfacer No 53N5 to cover all irregularities.  Skin butt joints were then filled with Acme Red Vellunite glazing putty no 58485.  The entire area was then sanded down and sprayed with one coat of camouflage enamel (when camouflage was deleted, the forward portion of the wing was sprayed silver).  This was a simple and quick way to create a nearly perfect laminar flow surface, but one has to wonder just what effect all those size 12 GI boots (warn by both air- and groundcrew) in the field had on the carefully-applied laminar flow finish!."

 To clarify, the book indicates that this procedure was used on all production P-51s.

[Angus]

Lol, good point!
Anyway, I spent some 3 weeks recently wearing U.S.M.C. boots (as well as socks, leggings, trousers, T-Shirt, Shirt, jacket, ammo-belt, helmet, and Thompson or M1), and even with full load those boots don't have such a brutal step at all. Todays military boots are much harder on the sole.
Anyway, as espected, Crumpp brought a complete input aboput the paint. We just need some good info on the allied paint.
Am I right that in the end the U.S. used a transparent glossy paint of epoxy kind? (Those silver birds)
I mean, epoxy is really smooth and strong. Doesn't get any better, even today.
BTW what do they use today?

[Crumpp]

I mean, epoxy is really smooth and strong.

The USAAF paints were developed by a company out of California.  They are smooth and thick.  The bad thing is that flexing causes them to crack around rivets and seems.  These cracks then chip or peel, quickly degrading the finish.  The thickness of the paint combined with the multiple coats required to completely cover the aircraft means the finish is heavy.  IIRC, it adds around 250lbs to the P51.

You can see original RLM finishes here:

http://www.white1foundation.org/parts/droptank.jpg

That Kraftstoffbehälter has paint that was applied in WWII.  Even after being released in flight, landing in a ploughed field and sitting in a barn, the finish is remarkably intact.  Notice the bare metal spots are worn smooth around the edges and not sharp.

This is typical of RLM finishes.

Here is another part with severe wear on the finish.  It is down to the primer/bare metal for much of the part.  However you can see how thin the finish is and how the edges tend to feather:

http://www.white1foundation.org/parts/leadingedge2.jpg

The seat has a new finish painted with RLM paints:

http://www.white1foundation.org/parts/pilotseat2.jpg

It is generally agreed that the P51's in the field never achieved laminar flow.  This is backed up by German wind tunnel test's of the wing even after it was cleaned up.  Laminar flow wings were developed for the Bf-109 and the FW-190.  However, given the technology of the day, it was decided that the "laminar" flow simply did not occur at speeds propeller aircraft could fly nor could surface conditions required be maintained in the field.  

Unless you were flying a jet with significantly more thrust than they could develop in 1945, it was not worth the expense to produce for little to no practical gain.

The P51 came close though when cleaned up.


All the best,

Crumpp

[Angus]

Thanks. Nice info.
So in the paint-war the Germans were ahead. And the effect to top speed is noticable. And the weight penalty is then not equal, - or at least not on the German side.
Laminar flow was not achieved in WW2 with any considerable effect AFAIK, although perhaps with the todays Reno race Mustangs, - I remember seeing something about that. Several coatings I belive.
But what about rivets? All flushed by the 109? 190? Just really thought of this. Spitfires? P47's?

[Crumpp]

But what about rivets?

Most fighters in WWII had flush riveting construction.  The riveting still leaves a surface impression at the seam.  It is this seam that causes the cracking when the frame is flexed in flight with the allied epoxy paints.  This cracking leads to chips and peeling.

All the best,

Crumpp