Stumbled Onto This Doing Something Else

[Stoney]

I was doing some math for another post and saw something I didn't know.

at 75% fuel, 267 rds per gun (8 guns)"

P-47N wingloading = 46.4 lbs/ft^2  (15,500 lbs / 334 ft^2)

P-47D25 wingload = 46.7 lbs/ft^2  (14,000 lbs / 300 ft^2)


Thought that was interesting given most of the anecdotal opinions are and Gonzo's test results show that the November can't outturn a D25.  I know wingloading isn't everything, but everything else being equal, they should turn almost identically, with a slight edge to the N even though its 1500 lbs heavier.  Can the induced drag as a result of the N's slightly lower aspect ratio or clipped wings be the difference?

[Wolfala]

My experience has been the N uses its extra power to more or less plow through the turns - regardless of wing loading. I've never had trouble out turning a D-11, 25, or 40. Maybe thats just my experience and I ended up in back of some not so bright sticks.

But also, the wing type of the N, I believe had more square footage then either the -11, 25 or 40.

[Pannono]

the N has fuel tanks in wings, earlier jugs didnt

[E25280]

I know nothing of aerodynamics, so this could be waaaaaay off base . . .

But thinking of a large, heavy car vs. a smaller, lighter car on a slick surface, with roughly equal PSI on the tires (traction), trying to make a turn . . . the heavier car has more inertia working against it, so it will "slide" a little more, and therefore tend to turn "wider" than the smaller car. 

Not sure if that makes sense.

[Stoney]

I know nothing of aerodynamics, so this could be waaaaaay off base . . .

But thinking of a large, heavy car vs. a smaller, lighter car on a slick surface, with roughly equal PSI on the tires (traction), trying to make a turn . . . the heavier car has more inertia working against it, so it will "slide" a little more, and therefore tend to turn "wider" than the smaller car. 

Not sure if that makes sense.

Fuel in the wing tanks would impact roll rate, but wingloading is merely a function of weight and wing area only.  The wingloading isn't impacted by what type of weight, or the location of weight.  The location of the weight would merely impact the center of gravity and contribute to structural characteristics.

Its the aerodynamic portion of this that I'm curious about.  The wingloading merely indicates that the P-47N does not have to create as high a lift coefficient in order to make the same maneuver as the P-47D.  Typically, this can result in a lower resulting drag coefficient, i.e. the wing is working more efficiently handling the weight of the aircraft, or more accurately, creating the lift required to equal the weight.  The only variables would be that the increased wing area creates more friction drag than the smaller wing of the D models, and the aspect ratio of the N's wing would also create a lower aspect ratio than the D, which can indicate an increase in induced drag on the N wing.  I was just curious if anyone could make a comparison of which would be more conspicuous in the performance comparison, the lower wing loading or the potential of higher induced and friction drag.

[Stoney]

But also, the wing type of the N, I believe had more square footage then either the -11, 25 or 40.

It did.  I hid the difference in the parenthesis in the first post:  300 ft^2 in the D models versus 334 ft^2 in the N.

[dtango]

Stoney,

I believe the differences have to do primarily with the differences in weight.  Checking E6B weights, for 75% fuel clean here's what's listed:

P-47D-25: 14,399 lbs
P-47N: 15,882 lbs

That's a difference of 1483 lbs.

Keep in mind that wingloading gives you a rough measure of instantaneous turn performance, not sustained turn performance.  Sustained turn performance like what the gonzoville charts show is a lot more tricky with excess Power-to-Weight ratio being one of several key variables.

Look at the climb performance charts for the D-25 and N. You'll see the impact the weight has with the D-25 having much better climb performance vs. the N.  Dean's AHT also show's similar climb performance differences due to the weight between the D-25 and the N.  RoC gives us a measure of specific-excess-power (Ps) available at 1g which tells us that the P-47N has a lower Ps overall compared to the P-47D-25 (at 1g).

Being that we're talking about generally the same evolved airframe this Ps margin most likely also exists in a sustained turn and hurts the P-47N sustained turn performance compared to the P-47D-25.

Hope that's useful!

Tango, XO
412th FS Braunco Mustangs

[Stoney]

Stoney,

I believe the differences have to do primarily with the differences in weight.  Checking E6B weights, for 75% fuel clean here's what's listed:

P-47D-25: 14,399 lbs
P-47N: 15,882 lbs

That's a difference of 1483 lbs.

Keep in mind that wingloading gives you a rough measure of instantaneous turn performance, not sustained turn performance.  Sustained turn performance like what the gonzoville charts show is a lot more tricky with excess Power-to-Weight ratio being one of several key variables.

Look at the climb performance charts for the D-25 and N. You'll see the impact the weight has with the D-25 having much better climb performance vs. the N.  Dean's AHT also show's similar climb performance differences due to the weight between the D-25 and the N.  RoC gives us a measure of specific-excess-power (Ps) available at 1g which tells us that the P-47N has a lower Ps overall compared to the P-47D-25 (at 1g).

Being that we're talking about generally the same evolved airframe this Ps margin most likely also exists in a sustained turn and hurts the P-47N sustained turn performance compared to the P-47D-25.

Hope that's useful!

Tango, XO
412th FS Braunco Mustangs

Thank you sir.  That was the insight I was looking for.  I suppose it also applies to my comparisons of dynamic pressure on lift coefficients as well.

[bozon]

Keep in mind that wingloading gives you a rough measure of instantaneous turn performance, not sustained turn performance.  Sustained turn performance like what the gonzoville charts show is a lot more tricky with excess Power-to-Weight ratio being one of several key variables.

Do gonzoville charts consider sustained turn with WEP on or off? The N has better power loading with WEP on, worse with WEP off.

Also, I think N's aspect ratio is higher. The wing tips were squared off but the wing are extended to include the inner wet section.

[Stoney]

Also, I think N's aspect ratio is higher. The wing tips were squared off but the wing are extended to include the inner wet section.

Hmmm.  I made an error above.  Wing area on the P-47N is 322 versus 334.  Using the same weights gives me a wingloading of 48.1 lbs/ft^2 for the N.

Adjusting the aspect ratios for the correct wing area, you're correct, the N has an A of 5.6 versus the D's 5.5