About the Macchi

[VonZack]

Hi m8s,

I am new to this board, as you may notice.  sorry if the question I am posting doesn't belong to this board.

Does anyone knows why is the Macchi's cockpit so far behind the geometric center of the plane?  Does it have anything to do with the engine positioning or something like that?

Von Zack - The Lag Master.

[wells]

The cockpit canopy is a good source of drag.  The further back on the airframe it is, the less drag there will be.

[Hans]

I don't beleave you Wells.  That doesn't sound right.

The cannopy will make the same drag no matter where it is.

I would be willing to be that there is some machinery or fuel tank in front of the instrument panel.

Or that it just has a short tail.

Hans.

[Minotaur]

Hans;

 

The cannopy will make the same drag no matter where it is.

What Wells says about canopy drag, seems to make sense to me.  

Ever ride in a convertable car or the back of a pick-up truck?  Once the air is penetraded, it takes a certain amount of time for the air to reform after the vehicle has pasted through it.  There is a area of vacuum formed from the rapid seperation of the air.  

Another good example would be the "Drafting" that is done in high speed automobile racing, particularly NASCAR.  The trailing car is out of the air stream by being shielded by the leading car.  The trailing car is also "Pulled" along by the vacuum created by the leading car.

This is more readily visible by watching the wake of a boat in the water moving rapidly.  Except air wake would have a top, bottom and two sides, while water wake only has the bottom and two sides.  Essentially, the bottom half of the air wake.  The valley of the water wake representing the vacuum area create by an air wake.

By placing the canopy at just the right position on the fuselage, it will could be placed in the seperated portion of air wake.  This position would be located at a position after the air has been seperated by the nose of the A/C and before it reforms near the epinage.  

The canopy would have reduced drag, because it is out of the highest air flow and in the vacuum created by the parting air.  This reduced drag effect would be effective for a specific speed range.  

I also would assume, that a bubble canopy might actually create more drag than a non-bubble canopy.  This drag due to the vacuum created on the canopies rear facing surfaces.  Non-bubble canopies would suffer less from this vacuum effect drag, because they don't have those rear facing surfaces.

I have no clue how propeller thrust air might effect any of this, but I am sure that it does.

I am by no means an expert, but it seems reasonable to me.  Flame me if you like.  I really am curious now and I would like to know.  

Mino

[combat23]

What ever the reason, The French D520, Moraine, and the first US P40 all have rear set cockpits.  In the P40 it was the only place left after engine fuel and turbo charger. The P40 position was changed on later prototypes.

[dolomite]

Related to what Minotaur said:

In the case of the P51, drag was reduced on the air scoop by moving it aft. Wind tunnel analysis proved this. The laminar flow airfoil of the P51 had its area of greatest thickness aft of contemporary airfoils, again with the net result of reduced drag.

In this particular argument placement of the cockpit can have a dramatic impact on drag. A cockpit is not a cockpit is not a cockpit...

[BBGunn]

I think Italians just like long nosed vehicles.  HEHE.

[iculus]

I forget the exact physics behind it, but I do know that the air scoop on the Mustang was put where it was because it actually provides a bit of thrust, by heat shed from the radiator.

Can anyone comment on this?... I'll try some research myself

Thanks,
IC

[sparviero]

I think, you should consider that it isn't the cockpit who is far in the back, it's the engine who is long way in the front  

It sounds a joke, howewer you should consider that the airframe is basically the same as that of the Macchi 200, with radial engine. If you have a look at this bird, you'll see that the cockpit is in the position where it is expected to be, well, maybe a little *above* as you expect to see it   . Well, maybe adding the in line engine led to put it well forward because of centering reasons, but you also should consider that between the engine and the cockpit you have two big cases which were there in order to collect the cartridges fired from the two 12,7 Breda Safat cowling mounted machine guns (Italians were at the point not to efford to throw away such precious brass, so the cartridges were refilled if still useable...) This required a lot of space and made the rearming operations quite long lasting   . I'm not sure if also the 20 mm wing mounted cannons cartridges were saved.

Ciao

Luigi "falco" Pacetti
4° Stormo Caccia

[This message has been edited by sparviero (edited 01-05-2000).]

[juzz]

Probably not. After all, where would they go? The spinner cannon on Bf109's "saves" it's empty shells too - I wonder if they ever escaped and floated all over the cockpit, hehehe.

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When the light was right it was actually possible to see the 30mm(1.18ins) shells in flight. - Heinrich Beauvais(Test Pilots, W.Späte).

[Pyro]

A big consideration in cockpit placement is where to put the fuel.  The fuel needs to be kept near the center of gravity so the CG doesn't shift too much as fuel is burned.  On just about all the planes that have the cockpit position moved aft, you'll find a fuel tank keeping the cockpit from a more forward position.



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Doug "Pyro" Balmos
HiTech Creations

"The side with the fanciest uniforms loses."

[scout]

>I forget the exact physics behind it, but I do know that the air scoop on the Mustang was put where it was because it actually provides a bit of thrust, by heat shed from the radiator.
Can anyone comment on this?... I'll try some research myself

Thanks,
IC


The air scoop on P51 was meticulously researched by the help of wind tunnels because its a potential source of great drag.

It was placed behind the wing to not disturb wing airflow, another important point was to lower it a bit and not let the inlet be flush with the empennage.

On starting testflights with the P51 it was discovered to be faster than windtunnel predictions.
The explanation was the heat discharge through the radiator air scoop that had the effect of emitting a heated 'jet' of air adding equivalence of 200 hp.
(havent got the book here, but I believe it was 200)

[iculus]

Thanks Scout!

IC