Greg of Auto and Airplanes has asked for a Debate (1 Viewer)

[Peter Gunn]

That is perfectly correct, small is a great word, on a gas guzzling hog like a P-47 a 200 gallon tank only produces a "small" increase in range, I have no idea why Greg bangs on about it so much. To match the P-38 and P-51 the P-47 needed around 500 gallons internal and 400 gallons external fuel, since that was impossible, lets talk about pressurisation of fuel in modern airliners.

Couldn't agree more, I was never impressed (even with the P-47N) with the Thunderbolt in that regard. I prefer something like the Mustang that can go further on a gallon of gas, for the P-47 to match the Mustang they just filled it with even more fuel but it was still a gas hog, and if it was such a great plane, why did the Mustang out perform it on the kill scoreboard in the toughest aerial theater of WWII?

Certainly the P-51 could get to the areas where the LW was more prevalent and so had more opportunities (I suppose) but it isn't like the Thunderbolt wasn't getting into combat.

Reminds me of two vehicles I used to own, bought a brand new 1989 Chevy Suburban with a 454 cu. in. (7.4L) V8, pulled a large Airstream trailer with it, thing was a powerhouse. On the highway with no trailer, on 40 gallons of fuel, ~14mpg @ 70mph (sometimes less).

Traded it for a 1996 Chevy Suburban with a 350 cu. in. (5.7L) V8 with fuel injection and an overdrive transmission, on the same 40 gallon tank I could eke out 25mpg @ 70mph.

Apropos of nothing I admit but that's kinda' how I see the fuel issue between the Mustang and the Thunderbolt, and I always lean on the side that gets more performance for less fuel.

 

[Reluctant Poster]

You've missed a possibility: Bomber Command had been steadily increasing its ability to fly in poor weather.

Bad weather was a double-edged sword. It helped as German night-fighters were sometimes grounded by bad weather even though the bombers were flying, and made it harder to find and intercept the incoming attackers. It hindered by making it more difficult to navigate to and mark the target. Flying in bad weather was much more challenging and raised the risk of accidents. Icing was a significant concern in winter months.

That's sort of my second point. The RAF was the best bad weather air force in the world
Bad weather also helped the 8AF reduce combat losses on occasion. If the target is clear while the fighter fields are socked its a win for the bombers. If the target is obscured as well its just a waste of fuel and sometimes aircraft.

 

[drgondog]

Finally watching his video "P-47 Pacific Theater Missions".

One of his examples is from Februry 1944, and he isn't sure whether the aircraft was configured with the "Brisbane" tank built in Geelong by Ford, or later standard tanks.

He also cites the small amount of performance lost by the P-47 when carrying drop tanks, and concluded that the tanks don't add much drag.

He didn't seem to make the connection that the P-47 could also be draggy, and that the extra drag of the tanks was proptionally smaller than for other aircraft.

There is something fishy about the Pilot Manual Tables he presented, I'm going to look at my own.

Only 10mph drop in airspeed between 'clean' and lugging 2x150 tanks at Max Continuous is impossible.

The very well documented P-51D Range testing in June 1945

P 51D Performance Test

At Max Continuous @25000ft - Clean 404mph (with 2xbomb racks)
At Max Continuous @25000ft - 2x110gal 357mph------> 47mph

The drag of the tanks is mostly form/pressure drag and independent of RN. That also holds as the delta at 5000feet ---------->45mph at Max Continuous (342mph vs 297mph).

The main component is Induced drag increase of full tanks due to 1400# of fuel/tank wt combo.

The Lift Coefficient at 25000 feet increases 18.6% due to increase of 1400# fuel/tank over clean GW, and V reduces 45mph. Therefore Induced Drag = k*CL^2 > (1.186)^2, which increases 40% due to the combined pressure drag and extra weight. That however is worst case at Take Off condition and fuel burning from externals takes the increase down to zero when tanks are dropped.

Until tanks are dropped the pressure drag component remains.

 

[Peter Gunn]

*SNIP*

The very well documented P-51D Range testing in June 1945

P 51D Performance Test

*SNIP*

Am I mistaken or wasn't the Merlin cleared for more than 67" of manifold pressure using 150 octane? Or am I hallucinating again?

 

[drgondog]

Am I mistaken or wasn't the Merlin cleared for more than 67" of manifold pressure using 150 octane? Or am I hallucinating again?

yes. IIRC the June tests were all about Pacific Range demands and 150 octane fuel wasn't available outside ETO

 

[Engineman]

Am I mistaken or wasn't the Merlin cleared for more than 67" of manifold pressure using 150 octane? Or am I hallucinating again?

Yes, there was the Service use of 25lb Boost with some engines on "150 Octane", around 80" Hg abs.

Eng

 

[pbehn]

At Max Continuous @25000ft - Clean 404mph (with 2xbomb racks)
At Max Continuous @25000ft - 2x110gal 357mph------> 47mph

What was the effect of the bomb racks? As I remember it was around 10 MPH maybe slightly less. 10MPH was around the difference made to a Spitfire by putting on a BP windscreen and two cannon. The notion that two filled 150 gal tanks suspended from the wings of a P-47 only cost 10MPH in top speed gets this years Balkenkreuz award for ignoring the rules of physics. If 300 gallons of external fuel just cost 10 MPH why bother putting any inside?

 

[Low Battery]

What was the effect of the bomb racks? As I remember it was around 10 MPH maybe slightly less. 10MPH was around the difference made to a Spitfire by putting on a BP windscreen and two cannon. The notion that two filled 150 gal tanks suspended from the wings of a P-47 only cost 10MPH in top speed gets this years Balkenkreuz award for ignoring the rules of physics. If 300 gallons of external fuel just cost 10 MPH why bother putting any inside?

like 4mph with the later racks and 8mph with early ones. For the P-51.

The P-47 loses like 25mph with wing racks.

 

[DarrenW]

Sorry low battery I hit the wrong reaction to your earlier post. I didn't find it humorous in the least. I agree with you.

 

[Thumpalumpacus]

Sorry low battery I hit the wrong reaction to your earlier post. I didn't find it humorous in the least. I agree with you.

If you go back to his post, you can "remove" your "funny" and then change it to agree.

 

[Low Battery]

I just thought he thought the P-47s terrible performance with wing racks was funny

 

[pbehn]

I just thought he thought the P-47s terrible performance with wing racks was funny

If two 150 gallon tanks with their racks reduce speed by 10MPH and the racks alone reduce speed by 8 MPH then each full tank reduces sped by 1 MPH each. This may seem unlikely, but it was fully explained in the 1960s by a young engineer called "Scottie", it is called warp drive but involves potentially dangerous use of Dilithium crystals which Scottie always had problems holding.

 

[SaparotRob]

That's the Bomber Mafia for you.

 

[pbehn]

That's the Bomber Mafia for you.

They morphed into the klingons or the federation but I grew up before I found out.

 

[tyrodtom]

All this smoke and mirrors about drop tanks that Greg has put up, has he said anything about them increasing internal fuel so they can fight and return?
Or does he just point to missions flown in the Pacific ?

 

[Thumpalumpacus]

It's only a matter of time before he brings in the KB-50.

 

[DarrenW]

If you go back to his post, you can "remove" your "funny" and then change it to agree.

Yeah I did that after about an hour went by, when finally realizing i made the mistake. I was somewhat worried that those of you who saw it would think I was absolutely losing my mind by laughing at a straight up fact

 

[Thumpalumpacus]

Yeah I did that after about an hour went by, when finally realizing i made the mistake. I was somewhat worried that those of you who saw it would think I was absolutely losing my mind by laughing at a straight up fact

If it helps, I laugh a lot more at myself than I do at anyone else here.

 

[DarrenW]

Ok guys I did a brief check on pages 47/48 of the P-47D Pilot's Flight Instructions dated 25 Jan 1945 (-25 model and beyond) and this is what I found:

1) with 300 gallons fuel on board and no external tanks the optimal suggested best speed at 20,000 feet is 330 mph with a maximum range of 485 statute miles.

2) with 300 gallons of fuel on board AND two 165 US gallons drop tanks the optimal suggested best speed attainable at 20,000 feet is 291 mph which provided a maximum range of 455 statute miles.

To me it looks like that at the same altitude and taking into account the optimal range profile there was nearly a 40 mph reduction in maximum level speed and a loss in range of 30 statute miles when drop tanks were carried.

Big difference from the 10 mph Greg quoted in his video. And to lose 30 miles of range with the same fuel load is also a clear indication that those tanks created a lot more drag than what he wants everyone to believe.

By the way, the manual I quoted can be found on-line and can be downloaded for free.

 

[pbehn]

Ok guys I did a brief check on pages 47/48 of the P-47D Pilot's Flight Instructions dated 25 Jan 1945 (-25 model and beyond) and this is what I found:

1) with 300 gallons fuel on board and no external tanks the optimal suggested best speed at 20,000 feet is 330 mph with a maximum range of 485 statute miles.

2) with 300 gallons of fuel on board AND two 165 US gallons drop tanks the optimal suggested best speed attainable at 20,000 feet is 291 mph which provided a maximum range of 455 statute miles.

To me it looks like that at the same altitude and taking into account the optimal range profile there was nearly a 40 mph reduction in maximum level speed and a loss in range of 30 statute miles when drop tanks were carried.

Big difference from the 10 mph Greg quoted in his video. And to lose 30 miles of range with the same fuel load is also a clear indication that those tanks created a lot more drag than what he wants everyone to believe.

By the way, the manual I quoted can be found on-line and can be downloaded for free.

I think it is very easy to get lost in a world of numbers and forget what you are actually talking about. The discussion is about dragging things through the air at speeds of around 300MPH at that speed everything makes a difference.