Greg of Auto and Airplanes has asked for a Debate

[drgondog]

I don't think the document listing the 1942 200 gallon tank shows anything really. We have bo idea what that tank is or it's specifications. It could be a ferry tank that was made of metal. Or otherwise unpressurized.

Could it not also just be the 205 gallon tanks of the later war but still in development?

The assertion that there was some high altitude capable 200 gallon tank before now never discovered by historians remains without evidence.

The top 200gal tak was the plastic/paper composite rated to 7psi and deemed 'not suitable' for pressurization. I supplied Greg all those tank and related source docs - ut as usual n mention of the help. That said, they DO form the source pool for Boylon's Study 136, which is how I found them at USAFHRC.

I seriously doubt that Greg understands that for an external tank mounted below the engine fuel pump, either a submerged/wind driven pump be installed in the auxiliary tank, or a second connection from tank to say exhaust outlet of engine vacuum pump to force pressure into the tank, is a requirement. The limit for a blow job scheme is in the 18-22K range for highly voltile avgas.

The 'slave' system devised for field mod of the P-47 vacuum pump was not to create a vacuum - but to force pressurization of the auxiliary tank to 'force evacuation of the avgas contained therein'.

My theory is that the prototype experienced sway brace design issues for which Republic scaled down the 200gal version to 150gal flat tank, then solved the sway brace issue to accomodate both the B-10 rack and the larger tank.

The B-7 'std' as used on P-47 and P-51 early, was rated at 600# AFAIK. The B-10 std was 2000#

 

[wuzak]

Another question regarding Greg's range calculations.

He says that when the external tank(s) is in use, the overflow from the carburetor is returned to the main tank, thus topping up the main tank.

He used, IIRC, this fuel to add range in his calcultions.

Is this a legitimate method?

 

[wuzak]

The B-7 'std' as used on P-47 and P-51 early, was rated at 600# AFAIK.

That would allow carrying the 75/84 gallon tank?

 

[ThomasP]

re the 200 gallon steel belly tank or auxiliary tank referred to in the above document

My understanding is that the 200 gallon steel belly tank referred to in the document above is the prototype for what became the 205 gallon 'paper' ferry tank as we are referring to it. Republic made the aerodynamic shape and mechanical function testing prototype(s) out of steel because they worked with steel on a regular basis, and steel was cheap and easy to work with. When the production RFQs were sent out the respondents came up with a couple of different designs - including what became what we (and others) are calling the 205 gallon 'paper' ferry tank, although it was sometimes called a 'fiber' tank. One of the respondents also offered what was referred to as a 'composite' tank made of steel, wood, and plastic. For whatever reason the 'paper' aka 'fiber' tank design was chosen over a steel design - I suspect for weight reasons but do not know.


re the term auxiliary tank

In the pre-war and early-war period the USAAC/AAF often referred to the ferry tanks and DT as auxiliary tanks. The terminology bounced around a bit, and started to use modifiers like droppable, and belly or underwing.

The Australians seemed to use the term belly tank for all drop tanks and ferry tanks if they were not carried in the bomb bays, at least in their contracts.


re the term assemblies

The USAAC/AAF used the term assemblies to denote what are sometimes referred to as knockdown kits by the UK & Australians - ie the parts are shipped to wherever they are going in disassembled or partially disassembled kit form for ease of shipment and reduced space required. It takes a lot less space to package the drop tank half shells when they are packed like spoons and the baffles are still flat pressed stampings. I do not know how many were shipped like this to the ETO but there were a lot of them shipped as knockdown kits to Australia, where the factories would then solder, weld, or braze the appropriate half-shells, baffles, fuel tight fittings, etc. Also, shipping the tanks with all the bits already in place would allow greater chance of damage to the more fragile pieces.

I have also seen the term assemblies used in other military equipment literature to mean assembly kits or knockdown kits.


I do not know if this helps with the discussion, but it provides part of the timeline for the initial use of the British made 108 USgal paper and the US made 205 USgal paper ferry tank relative to the P-47. I think this has already been posted on the forum somewhere (maybe even by me?) in one form or another, but I do not remember for sure.

 

[Shortround6]

Another question regarding Greg's range calculations.

He says that when the external tank(s) is in use, the overflow from the carburetor is returned to the main tank, thus topping up the main tank.

He used, IIRC, this fuel to add range in his calcultions.

Is this a legitimate method?

It was a standard method of handling the fuel, ALL US fighters routed the fuel back to one of the main tanks, the tank that also the "reserve" tank.

As to using the fuel for figuring/calculating the range?
This may more doubtful. A lot more doubtful.

1. Fuel is being returned most of the time when the engine is running, regardless of which tank it is drawn from. This is one reason (but NOT the the most important) that starting, warm up and take-off are done on the main tank that is designated the reserve tank, it gives the fuel somewhere to go instead of dribbling out all over the cowl/engine compartment/fuselage.
2. rate of fuel return depends on the fuel flow and depends on the fuel pump pressure, this varies from plane to plane and varies depending on the throttle settings. You know it is going to happen, But predicting the amount of return is very hard. A few long range special missions may have done this. Most of the time they just figured it gave a few extra gallons to find the field in bad weather or to circle the field if there was a landing mishap that had to be cleared. Some planes returned just a few gallons per hour (smaller engines than a P-47).

 

[wuzak]

I imagine that a pilot who used a higher engine power, whether through mistake, avoiding enemy contact before rendezvousing with the bombers, or other, would use more fuel and return less fuel to the tank.

 

[Shortround6]

I really don't know, Some/most of the fuel pumps were mechanical pumps and pump RPM (fuel delivered) depended on engine rpm. There was a spring loaded valve (calibrated how?) that governed the pressure, and excess fuel/pressure went back to the tank.
High cruise RPM but low boost might return more fuel than low rpm and high boost?

 

[pbehn]

Another question regarding Greg's range calculations.

He says that when the external tank(s) is in use, the overflow from the carburetor is returned to the main tank, thus topping up the main tank.

He used, IIRC, this fuel to add range in his calcultions.

Is this a legitimate method?

The first question I would ask there is how was the fuel consumption data collected in the first place? Was it from a bench test of fuel flow and calculation of cruise speeds etc. Or was it from actual data on planes, taking the actual fuel used on actual flights where the fuel is returned to the tank and therefore inclusive of it. The first thing I would say is that if your calculations use such margins of safety as normal then you risk your whole force dropping in the sea off the English coast when things go even slightly fubar.

 

[DarrenW]

Later for P-47, P-38 Dec 1941 prototype flight and kits for wing pylons and 165/330gal steel ferry tanks, A-36 prototype flight Aug 1942 for both bombs and auxiliary 60gal fuel tanks. P-39/P-40 centerline racks B-7 type for bombs and aux. fuel tamks.

The reference to the P-47B crash skid is also applicable to P-47C-2 thru P-47D-4.

This is the genesis for the future 150gal Flat tank, and possibly the 215gal flat tank mounted on B-7/B-10 type rack in serial production from P-47D-5.

The four point attach scheme is the reason that the D-2 & D-4 headed for PTO did Not receive B-7/lower cowl kits as the Brisbane tank was schemed for the four point attach scheme of earlier models.

I'll see if Aero Library has the drawing numbers cited above, but believe a.) above is the 205 gal composite tank used briefly for about 30 days before B-7 kits installed and 75 (84actual)gal tank was first used.

The telex indeed proves that Republic was at advanced stage to test and then deliver a 200gal steel tank, so Greg was correct in that assertion. I wonder why it was not delivered until 1944.

re the 200 gallon steel belly tank or auxiliary tank referred to in the above document

My understanding is that the 200 gallon steel belly tank referred to in the document above is the prototype for what became the 205 gallon 'paper' ferry tank as we are referring to it. Republic made the aerodynamic shape and mechanical function testing prototype(s) out of steel because they worked with steel on a regular basis, and steel was cheap and easy to work with. When the production RFQs were sent out the respondents came up with a couple of different designs - including what became what we (and others) are calling the 205 gallon 'paper' ferry tank, although it was sometimes called a 'fiber' tank. One of the respondents also offered what was referred to as a 'composite' tank made of steel, wood, and plastic. For whatever reason the 'paper' aka 'fiber' tank design was chosen over a steel design - I suspect for weight reasons but do not know.


re the term auxiliary tank

In the pre-war and early-war period the USAAC/AAF often referred to the ferry tanks and DT as auxiliary tanks. The terminology bounced around a bit, and started to use modifiers like droppable, and belly or underwing.

The Australians seemed to use the term belly tank for all drop tanks and ferry tanks if they were not carried in the bomb bays, at least in their contracts.


re the term assemblies

The USAAC/AAF used the term assemblies to denote what are sometimes referred to as knockdown kits by the UK & Australians - ie the parts are shipped to wherever they are going in disassembled or partially disassembled kit form for ease of shipment and reduced space required. It takes a lot less space to package the drop tank half shells when they are packed like spoons and the baffles are still flat pressed stampings. I do not know how many were shipped like this to the ETO but there were a lot of them shipped as knockdown kits to Australia, where the factories would then solder, weld, or braze the appropriate half-shells, baffles, fuel tight fittings, etc. Also, shipping the tanks with all the bits already in place would allow greater chance of damage to the more fragile pieces.

I have also seen the term assemblies used in other military equipment literature to mean assembly kits or knockdown kits.


I do not know if this helps with the discussion, but it provides part of the timeline for the initial use of the British made 108 USgal paper and the US made 205 USgal paper ferry tank relative to the P-47. I think this has already been posted on the forum somewhere (maybe even by me?) in one form or another, but I do not remember for sure.

Thank you both for your invaluable information.

 

[Engineman]

Another question regarding Greg's range calculations.

He says that when the external tank(s) is in use, the overflow from the carburetor is returned to the main tank, thus topping up the main tank.

He used, IIRC, this fuel to add range in his calcultions.

Is this a legitimate method?

This would depend entirely on the fuel pump and the carburettor system. Many P-47 R-2800 engines used the Bendix Stromberg PT13 Pressure Carburettor. This carburettor did not feature a fixed rate of fuel return to the tanks. What it did have was a vapour separator operated by a float valve. This vapour separator released trapped air that had been entrained in the fuel flow, back to the (vented) fuel tank. In steady flight, the return of vapour with some fuel would be minimal. In aerobatics or manoeuvring flight it is likely that some fuel would recycle to the tank. However, this returned fuel was not metered and did not effect the fuel consumption, it was just recycled in the process of keeping the carb fuel air-free.

Eng

 

[DarrenW]

This question is for Bill or anyone else who can clarify bomber escort tactics used by the 5th Air Force in the Pacific. Did the fighters normally join up with bombers at the initial start of a mission and stay with them the entire trip, or would this most likely occur X amount of miles from the target area? The reason why I ask this is that the longer the escorts were required to fly along side the bombers their combat range would likely suffer as a result. This would be due to the various speed adjustments and weaving required in order to stay close to the bomber formations, such as what often occurred in the ETO.

Greg's video seemed to focus more on straight-line range and most of his calculations are based on this, which would obviously increase combat range accordingly. He often quotes flight manual range calculations which are straight line in nature as well. He then tries to apply this to the ETO and forgets that you can't compare the two theaters that easily.

 

[drgondog]

Another question regarding Greg's range calculations.

He says that when the external tank(s) is in use, the overflow from the carburetor is returned to the main tank, thus topping up the main tank.

He used, IIRC, this fuel to add range in his calcultions.

Is this a legitimate method?

LOL - I called him on that and quoted E=mC^2, reminding him that a.) carb overflow returns were small in cruise, more common while starting engine and taxiing, while avancing and retarding throttle, and b.) was not a filling station in the sky adding to internal fuel.

At best, break even.

 

[MiTasol]

Another question regarding Greg's range calculations.

He says that when the external tank(s) is in use, the overflow from the carburetor is returned to the main tank, thus topping up the main tank.

He used, IIRC, this fuel to add range in his calcultions.

Is this a legitimate method?

No

Saying that fuel is extra is a fallacy. Every gallon returned to the main tank is a single gallon that was loaded, not an additional gallon to be used. That is like saying the wing fuel returned to the main tank is additional fuel.

 

[Thumpalumpacus]

It's double-counting the returned fuel -- once when loaded in, and then again when it's returned.

I'd think a pilot would have better math skills than this. I hope it's someone else doing the fuel calculations on his aircraft.

 

[wuzak]

It's double-counting the returned fuel -- once when loaded in, and then again when it's returned.

I'd think a pilot would have better math skills than this. I hope it's someone else doing the fuel calculations on his aircraft.

I think he is using it to claim that there is more fuel in the internal yanks for the return journey, rather than it being additional to the overall fuel.

But wouldn't that amount of fuel be dwarfed by the required fuel reserve?

 

[Shortround6]

it is a way of transferring some of the drop tank fuel into the main tank fuel to be available on the way home.

However there were limits. It can't add more than was used for starting, warm up, take-off and climb to altitude where the drop tanks are selected.
The big assumption is that the overflow return (or vapor return) is enough to refill the replace the fuel used in the first 10-20 minutes of ground operation and climb to a few thousand ft. You used 30 gallons until you changed to drop tank/s. Did you get back 15 gallons or 30 gallons before punching off the drop tanks and entering combat?
P-47 could burn 50-55 gal an hour at low altitude at a few thousand feet just looking for the right air field in Britain. 15 -30 gallons over the "planned" reserve might be the difference between landing and doing a wheels up in a field.
30 gallons cruising at 315-325mph at 25,000ft is worth about 13 minutes. Less than 30 gallons is worth??
If you are figuring things that close you are going to loose a lot of pilots with a wind shift.

 

[wuzak]

Would having P-47s escort to target or the Schweinfurt raids made much difference to the losses on those raids?

We know that in early 1944 the Eighth Air Force bomber losses remained high, even though raids were escorted.

In other words, there was little short term gain, but big long term gains.

 

[Thumpalumpacus]

I think he is using it to claim that there is more fuel in the internal yanks for the return journey, rather than it being additional to the overall fuel.

But wouldn't that amount of fuel be dwarfed by the required fuel reserve?

You're likely right on both counts. Are there any numbers on fuel returned to the internal tanks from unburnt external fuel, in gph? I don't see the recovered fuel being so voluminous that it adds too much to internal range for return. Even five gph returned unburnt equates to one gallon going from drop tanks, not burning, and returning to main tank every twelve minutes -- and a three-hour outbound flight only gives 15 gallons back, which is not very far for an R-2800.

And that ain't getting you to Schweinfurt and back.

 

[Thumpalumpacus]

Would having P-47s escort to target or the Schweinfurt raids made much difference to the losses on those raids?

We know that in early 1944 the Eighth Air Force bomber losses remained high, even though raids were escorted.

In other words, there was little short term gain, but big long term gains.

The thing is that by 1944 losses in 8th AF had largely shifted from losses to fighters to losses from flak.

I'm willing to bet that USAAF fighters over Schweinfurt for that raid would've reduced B-17 losses. How much is obvs uncertain, but the inbound track would likely have suffered less.

 

[Low Battery]

I am not an expert on fuel systems so someone help me out here:

Greg's document from General Kenney claims 16lbs of pressure at 35k, but he also states the Brisbanes were unpressurized which I think everyone here already knew.

My understanding is that vapor lock happens because the fuel boils off due to low pressure at high altitudes. This both filles the fuel line and subsequently the carburetor with vapor bubbles making the fuel useless. It also separates out additives in the fuel further making it useless.

So for one, how does it help if the pump can draw said pressure if the fuel has already boiled and there is vapor in the lines not to mention the additives are separated?

Also how could just sticking more or bigger fuel pumps anywhere but the drop tank itself solve the high altidue issue? If this actually worked, would it notnhave been far for airplane manufacturers everywhere to just put mega pumps on all planes? This would, if it actually worked, be far simpler than having to plumbing for supercharging the tank and also having to have drop tanks that could handle the pressurization.