Me110G-2, Me410 and Mosquito Mk.VI maximum speeds.

[Wmaker]

From Generalluftzeugmeister meeting notes, dated 6/15/43

"In the area of the Angriffsfuhrer England [Generalmajor Dietrich Peltz?], an Me 410 is said to have increased its speed by 40 kph [25 mph] through the use of filler paste, something which possibly indicates the potential of this measure, or the poor build quality."

Very interesting, thanks!

Here's some Cds calculated based on these speeds:


The exhaust thrust values are extrapolated from table values of a DB605A-1 for the DB603. For the Merlin I don't remember if I used those those DB605 values as basis or if I based them on one reference on Griffon's values I've seen on the literature. I'll double check them later. Prop efficiency is based on the 109G prop eff charts and Mossie's is based on the doc Scherf kindly posted for me. The Cd value includes both parasitic and induced drag at the speed mentioned to simplify the calculation as I didn't have accurate Cl or Oswald's effiency for these aircraft. Of course some fairly good estimates could be made but it really won't change things much considering the general accuracy of the calculation and for the purposes of this thread.

P.S. Sorry Moot, I'll try to reply to your PM soon.

EDIT/Prop eff for the faster Me410 would change a bit aswell, forgot to change that value but it won't change much anyway./EDIT

[moot]

No hurry on PMs, I'll be burried in research and studying till Wednesday.

[RTHolmes]

Here's some Cds calculated based on these speeds:
(Image removed from quote.)

wow thats an even bigger difference than my back-of-envelope calc earlier

[Scherf]

Shouldn't the power and the Cd for the Mossie both be a touch higher? The data card for the M25 FB.VI says the Merlin we have was making 1635 hp at 2,250 feet. Or am I dreaming again.

[Wmaker]

Shouldn't the power and the Cd for the Mossie both be a touch higher? The data card for the M25 FB.VI says the Merlin we have was making 1635 hp at 2,250 feet. Or am I dreaming again.

My comparison is at sea level (air density 1,25kg/m3). The power output of the Merlin is based on this chart:



Brits usually gave the power output value figures at the first FTH where as Germans for example gave the figures at sea level.

[dtango]

Nice find moot.

I mentioned in another thread I've suspected what we see in the Me410's max level speed performance is mainly due to parasite drag increases due to the shape of it's fuselage.  If you look at the 410 the fuselage shape looks to me like it would promote a longer adverse pressure gradient along the fuselage resulting in more drag due the degree of thickness and curvature in the front 1/4-1/3 of the airplane. 

What does all that mean?  Pressure distribution follows the curvature (camber) of the shape in the air-flow.  Where camber increases pressure tends to increase.  Where camber decreases pressure decreases.    Peak pressure occurs where fluid flow velocity is the highest.  Pressure increases up to the point of peak pressure (following the increase in camber of the shape).  But after the peak pressure point pressure decreases until it reaches the pressure of free-stream airflow at the trailing edge of the shape. 

The area of decrease is known as the adverse pressure gradient.  Viscous forces cause back pressure against the boundary layer in the adverse pressure gradient which eventually leads to separation.  The more forward the pressure peak is on the shape, the longer the adverse pressure gradient is, the more turbulent the flow & the easier separation occurs.  All this conspires to increase parasite drag.  Essentially the similar principle was being applied for laminar airfoils vs. conventional and that is to reduce drag by moving the pressure peak further back along the chord of the airfoil.   

Alas I have no desire to crack out some CFD or computing using DATCOM to estimate the effects on the 410 so don't ask .

[Wmaker]

(Image removed from quote.)

Nice find moot.

I mentioned in another thread I've suspected what we see in the Me410's max level speed performance is mainly due to parasite drag increases due to the shape of it's fuselage.  If you look at the 410 the fuselage shape looks to me like it would promote a longer adverse pressure gradient along the fuselage resulting in more drag due the degree of thickness and curvature in the front 1/4-1/3 of the airplane.  

What does all that mean?  Pressure distribution follows the curvature (camber) of the shape in the air-flow.  Where camber increases pressure tends to increase.  Where camber decreases pressure decreases.    Peak pressure occurs where fluid flow velocity is the highest.  Pressure increases up to the point of peak pressure (following the increase in camber of the shape).  But after the peak pressure point pressure decreases until it reaches the pressure of free-stream airflow at the trailing edge of the shape.  

The area of decrease is known as the adverse pressure gradient.  Viscous forces cause back pressure against the boundary layer in the adverse pressure gradient which eventually leads to separation.  The more forward the pressure peak is on the shape, the longer the adverse pressure gradient is, the more turbulent the flow & the easier separation occurs.  All this conspires to increase parasite drag.  Essentially the similar principle was being applied for laminar airfoils vs. conventional and that is to reduce drag by moving the pressure peak further back along the chord of the airfoil.  

Alas I have no desire to crack out some CFD or computing using DATCOM to estimate the effects on the 410 so don't ask .

Awesome and very interesting photo!

Thanks for you input Tango! Very much appriciated.

Yeh, I've been thinking that tadpoles look like they do for many other reasons than low water resistance. (Well, tadpole is slightly slower than Me410 and it moves ina fluid that's almost 100 times denser so the flow stays attached better.) Anyway, I *still* thought that it wouldn't be as big of a difference. The production quality and therefore poor fit of the panels, bombay doors, panel seams etc. For example looking at the Me410 that's preserved in England those things are pretty evident. Obviously do cause that extra bit of drag in reducing the speed according to the account Moot posted. Ie. reducing the speed from ~340mph to 315mph. Considering the power outputs even 340mph is low compared to the Mosquito and that can be largely due to the overall geometry of the airplane. Looking at the test flight data that 356mph figure for the Mosquito also seems to be pretty much the "best performance that was achieved".

[Scherf]

My comparison is at sea level (air density 1,25kg/m3). The power output of the Merlin is based on this chart:

(Image removed from quote.)

Brits usually gave the power output value figures at the first FTH where as Germans for example gave the figures at sea level.

I thought you'd be using that chart. That one confuses me, as the peak power output is lower, and the altitude at which it develops it higher, than what I've read otherwise.

Try your calculation with this one:

.jpg" class="bbc_link" target="_blank">http://bbs.hitechcreations.com/wiki/index.php/Image:Merlin_25_and_23_Power_Curves .jpg

Shows 1610 or 1615 or so for the Merlin 25 at sea level.

You should also have a look at this document:

_Book_AVIA_28-3030_.jpg" class="bbc_link" target="_blank">http://bbs.hitechcreations.com/wiki/index.php/Image:The_Aircraft_Performance_Data _Book_AVIA_28-3030_.jpg

Shows a Coefficient of drag for the Mosquito F.II (outwardly identical to the FB.VI) of 0.0224.

(Tosses head, bats eyes, "Honestly, I don't know why I upload these things if people aren't going to use theh.")

My little daughter would like to say  " and  from Daddy."

[Karnak]

Looking at the test flight data that 356mph figure for the Mosquito also seems to be pretty much the "best performance that was achieved".

This is true, at least for 100 octane fuel, which is the relevant fuel to this discussion and to the AH Mosquito performance.

[icepac]

You can't mention CD without factoring in frontal area to arrive at CX.

[Scherf]

pah, links above to AH wiki no workie. Will do the photobucket thing.

[moot]

(Image removed from quote.)

Nice find moot.

I mentioned in another thread I've suspected what we see in the Me410's max level speed performance is mainly due to parasite drag increases due to the shape of it's fuselage.  If you look at the 410 the fuselage shape looks to me like it would promote a longer adverse pressure gradient along the fuselage resulting in more drag due the degree of thickness and curvature in the front 1/4-1/3 of the airplane.

So because of how blunt is the front-most part of the fuselage, IOW the nose surface and what's down-wind of it a bit, you've got something like



Where the boundary layer is somewhere along those green lines, and somewhere in the yellow area you've got some kind of turbulence... Where the yellow area grows (from the wind current's POV) much quicker than a less blunt shape would cause?  And the parasite drag is much stronger in that yellow area, or due to it being so much larger?

This is the shape of the planned revised 410 front fuselage:
 
So this shape would better "coax" the airflow around it, rather than bluntly deflecting it and then abruptly cambering back like the "forehead" part of the canopy does in the original fuze shape?  Kind of like a motorcycle is "cleaner" when it's got a rider tucked in behind the windscreen, rather than an unmanned motorcycle?

.. And ideally you'd want the pressure peak as far back, so does that mean a pressure peak right at the trailing edge (just speaking hypothetically, dunno if it's possible) would be ideal?

It's really curious that back in WWII they hadn't (had they?) thought of wind tunnel with colored plumes fed into the air flow.

[RTHolmes]

the mossie is alot closer to the sears-haack shape than the 410 ...





(iirc the germans had some excellent wind tunnels)

[moot]

That looks a lot like Skylon/LAPCAT's shape.

[Scherf]

Notes at the bottom of the "drag" file may be of some use: