Radial Engines vs Inline Engines?

[BuckShot]

Too bad they didn't just go for looks and used the inlines in the 17!

This is my first time seeing one. That thing looks fantastic.

Thanks for posting.

[Volron]

If they went with inline engines for the 17's, I can only imagine how many more would not have made it home.

But I will admit, she has a nice look.

[Zimme83]

A bunch of Griffons instead of the Allisons would have done it. 

[bozon]

Regardless of cooling drag the wider fuselage required for a radial engine application increases form drag considerably.

Wider fuselage does not necessarily means increased drag. It was all about the so called cooling drag. In radiators, designers already knew how to use the heat energy that was transferred to the air to not only reduce the drag, but to end up with thrust in some conditions. Only post war radials had a significant improvement to their cooling drag.

[colmbo]

  I am not sure what the length of travel of the C.G. is on the 17, Columbo could tell us I suppose

CG limit on the B-17G is from 20% MAC to 32% MAC (Mean Aerodynamic Chord).  For the most part I never noticed much difference CG related in the B-17.  When doing rides quite often all 9 pax would end up aft of the bomb bay, never noticed much trim change when flying.  On the B-24 you notice on the ground because the nose would "bounce" more.  Main gear are quite close to the CG, rough brake usage could get the nose bobbing up and down, aft loading just made that worse.

Probably the heaviest I flew the airplanes was the B-24 out of Naples, Fl.  Full fuel, 11 SOB, baggage, fresh load of oil (2 gal cans stowed above wing)…around 56000 for takeoff on a warm, muggy Florida afternoon.  I got my share of the landing fee out of the runway on takeoff.  Video here

You guys are worried about the CG on the airplane with the Allisons, Boeing seems to have worked it out without any noticeable differences in the airplane. 

[WaffenVW]

Wider fuselage does not necessarily means increased drag.

Yes it most certainly does. Two aircraft otherwise identical the one with the wider fuselage will produce more drag.

[bozon]

Yes it most certainly does. Two aircraft otherwise identical the one with the wider fuselage will produce more drag.

Not simply because the fuselage is wider. A bigger plane tends to have more drag because it has a larger wet area overall, not because its front is wider.

[WaffenVW]

The wider the fuselage the more mass of air is displaced when that fuselage moves through the air. That takes energy. Think of it like a boat moving through water and it becomes more obvious. The air needs to be pushed aside and then back again as the aircraft moves through it.

[WaffenVW]

Or think of it like this:



Same approximate wetted area the wider shape produce more drag.

[pembquist]

Doesn't that depend on how you throw it?

I think one of you is arguing about shape and the other about size.

One of you is saying that given the same airplane made bigger the increase in drag that comes from the increase in frontal area is less than the increase that comes from drag due to the increase in wetted area.

The other of you is saying a blunt shaped fuselage has more drag than a pointy shaped one.

I would chime in and say that with WW2 fighters the biggest drag reduction benefit available from a liquid cooled inline engine would come from the reduction in cooling drag for the same horsepower, not from benefits in frontal area reduction or wetted surface reduction.

What I would like to know is if this is because of the state of aerodynamics/technology at the time that enabled the design of low or negative drag cooling systems for liquid cooled but was unable to produce the same for aircooled or if it is some kind of theoretical limitation having to do with the air flow requirements of air cooling, especially at higher altitudes.

[earl1937]

CG limit on the B-17G is from 20% MAC to 32% MAC (Mean Aerodynamic Chord).  For the most part I never noticed much difference CG related in the B-17.  When doing rides quite often all 9 pax would end up aft of the bomb bay, never noticed much trim change when flying.  On the B-24 you notice on the ground because the nose would "bounce" more.  Main gear are quite close to the CG, rough brake usage could get the nose bobbing up and down, aft loading just made that worse.

Probably the heaviest I flew the airplanes was the B-24 out of Naples, Fl.  Full fuel, 11 SOB, baggage, fresh load of oil (2 gal cans stowed above wing)…around 56000 for takeoff on a warm, muggy Florida afternoon.  I got my share of the landing fee out of the runway on takeoff.  Video here

You guys are worried about the CG on the airplane with the Allisons, Boeing seems to have worked it out without any noticeable differences in the airplane. 

Great video's!

[WaffenVW]

Premb... I'm simply saying you can't move air molecules without spending energy. That's what drag is: Moving air molecules. The wider the fuselage the more air molecules need to be moved.

[pembquist]

Waaaait....I thought drag was when you put on girlie things.

But seriously, I wasn't saying you were wrong just that it seemed like you two were talking past each other, (something virtually unheard of on this bbs.)

[bozon]

The wider the fuselage the more mass of air is displaced when that fuselage moves through the air. That takes energy. Think of it like a boat moving through water and it becomes more obvious. The air needs to be pushed aside and then back again as the aircraft moves through it.

This is not how drag works. Common misconception, one of great many in hydrodynamics/aerodynamics.
The energy that goes into moving the air out of the way is small. In addition, if the flow is laminar on the large scales, you get this energy back. In order to lose energy, you have to leave something in the flow behind you in the form of vortices (mostly, a turbulent wake). The later is determined by small scales where the Reynolds number is low.

The effect of accelerating a bulk airflow out of the way (large frontal area) is a small resistance to acceleration, but has no effect on steady state flow, that is the drag.

[WaffenVW]

What you are saying is nonsense. We've hijacked this thread long enough and I'm not going to get into a major aerodynamics debate with you. I'll just end by pointing out that if you want something to go fast in air or water you'd better make it slender and pointy. And the less power you have the more important it becomes. There's a reason these guys aren't sitting two abreast.