ThomasP
Senior Master Sergeant
Hey Reluctant Poster,
Thanks for the info.
Thanks for the info.
Japanese Zero vs Spitfire vs FW 190
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GregP
Major
Hi ThomasP.
The fuel in the Allison V-1710 is introduced right directly into the supercharger impeller intake. In fact, it sprays right onto the small end of the supercharger impeller. I've helped assemble some 20 of them. The supercharger discharges directly into a large intake manifold that goes straight down the Vee between the cylinder banks. About halfway down, it splits into two tubes going up each cylinder bank. When it reaches the top, each of the two up tubes splits into two 3-cylinder intake manifolds, and the fuel sprays directly into the center of each 3-cylinder manifold. Fours manifolds times three cylinders per manifold is 12 cylinders.
The fuel flow would make the two end cylinders rich and the center cylinder lean. The turbulators or venturis, depending on what terminology you like, kept the air-fuel mixture moving around and kept the mixture even for all cylinders. Reputable builders today don't use the older, non-modified intake manifolds. I've seen them referred to in documents as turbulators, but whether it is called a turbulator or a venturi, it keeps the air-fuel mixture moving around and in more or less homogeneous suspension.
I have much less experience with Merlins, but the Merlin intake tract likely isn't nearly as smooth inside, and maybe that helps.
It also didn't help that early P-38 squadron leaders were having their pilots run the Allisons at low rpm and high MAP on British fuel that was not bad in any way, but WAS different from what the Allisons were jetted for in their carburetors from the factory. That meant lower air-fuel mixture velocity, which might have been the difference between the Allison and Merlin issues (yes, the Merlin had issues in British service, but they were addressed quickly, with the factory right there with test cells and fuel to run in them). I do not claim to know for sure if these U.S. practices were the exact reasons that caused the Allison issues.
What I DO know, for sure, is use of the modified intake manifolds, proper jetting for the fuel used (the early Allison were jetted wrong for British fuel), and proper engine operation eliminated the issues and made the P-38 run very well, even in the ETO. It all took about 9 months from reported engine problems until they were more or les corrected. The cockpit heater and the dive recovery flaps took longer.
Cheers.
The fuel in the Allison V-1710 is introduced right directly into the supercharger impeller intake. In fact, it sprays right onto the small end of the supercharger impeller. I've helped assemble some 20 of them. The supercharger discharges directly into a large intake manifold that goes straight down the Vee between the cylinder banks. About halfway down, it splits into two tubes going up each cylinder bank. When it reaches the top, each of the two up tubes splits into two 3-cylinder intake manifolds, and the fuel sprays directly into the center of each 3-cylinder manifold. Fours manifolds times three cylinders per manifold is 12 cylinders.
The fuel flow would make the two end cylinders rich and the center cylinder lean. The turbulators or venturis, depending on what terminology you like, kept the air-fuel mixture moving around and kept the mixture even for all cylinders. Reputable builders today don't use the older, non-modified intake manifolds. I've seen them referred to in documents as turbulators, but whether it is called a turbulator or a venturi, it keeps the air-fuel mixture moving around and in more or less homogeneous suspension.
I have much less experience with Merlins, but the Merlin intake tract likely isn't nearly as smooth inside, and maybe that helps.
It also didn't help that early P-38 squadron leaders were having their pilots run the Allisons at low rpm and high MAP on British fuel that was not bad in any way, but WAS different from what the Allisons were jetted for in their carburetors from the factory. That meant lower air-fuel mixture velocity, which might have been the difference between the Allison and Merlin issues (yes, the Merlin had issues in British service, but they were addressed quickly, with the factory right there with test cells and fuel to run in them). I do not claim to know for sure if these U.S. practices were the exact reasons that caused the Allison issues.
What I DO know, for sure, is use of the modified intake manifolds, proper jetting for the fuel used (the early Allison were jetted wrong for British fuel), and proper engine operation eliminated the issues and made the P-38 run very well, even in the ETO. It all took about 9 months from reported engine problems until they were more or les corrected. The cockpit heater and the dive recovery flaps took longer.
Cheers.
Reluctant Poster
Tech Sergeant
- 1,635
- Dec 6, 2006
According to Allison it was a a venturi
As you can see the there is a main venturi and an auxiliary venturi. The auxiliary venturi has a induction tube reaching down to the bottom of the manifold to suck up any condensed fuel. Some time ago I posted a paper written by the SAE before WWI showing that the vaporized fuel, being heavier than air, would not follow the path of the air through the sharp elbow and would hit the wall and condense. Allison should have know better than to design a manifold like this. There are no examples of any other engine having a manifold like this and with good reason.
A turbulator is a completely different device used in heat exchangers to enhance heat transfer, See the following link:
Turbulators in Heat Exchangers: Types and Purposes | The Super Blog
Learn how turbulators help create turbulent flow, which contributes to improved system efficiency and smaller footprint without compromising performance.
Venturis actually don't create much turbulence. This is why we use as flow measuring devices since they regain most of their pressure loss down stream. Here's is a CFD analysis showing the flow field through a venturi . The flow is very laminar indeed. Of course if the venturi is operating in conditions it is not suited for the picture can be very different.
As I stated previously the venturi acted as a second carburetor, in fact the manifold looks very much like a classic weber carburetor.
Finally, some time ago, I wrote a lengthy essay in this forum debunking the British flue myth. 85% of all avgas used in the UK in WWII was produced in the continental USA. Al avgas produced in the US was to the same specifications regardless of it destination. The problems of the Allison lie within.
Shortround6
Major General
However the specification/s allowed quite a bit of latitude in the actual fuel composition.
Late war (like 1943 on) was allowed up to 4.6 cc lead per US gallon for 100/130 fuel. Not all batches needed the full 4.6cc to meet the specification. Not all batches got the same percentages of other additives, like the heavy aromatics.
The specifications were a performance specification. Not a recipe.
Performance also included BTUs per pound of fuel, vapor pressure, residual gum, and a number of other things that had no bearing on power output but a lot to do with keeping fuel filters and other small fuel passages clear, getting proper vaporization at altitude (cold temperatures) while avoiding vapor lock at high temperatures.
As long as the fuel met these performance specifications it would be purchased and used almost regardless of actual chemical composition.
There were practical limits. Too much lead fouled spark plugs. The Heavy aromatics had less BTUs per pound than the fuel specs called for so going past 20% aromatics in the blend made it hard to meet the BTUs per pound requirement. The different aromatics had different vaporization temperatures and other properties. A lot of "blends" depended on what a particular refinery had for base stocks and for additives available at a given time.
GregP
Major
Well, there IS a venturi, but the venturi is held in with angled fin and that is only one Allison illustration. The angled fins form a turbulator, so I suppose you can call it whichever you want and be technically correct since it is a combination of both. The effect was to prevent the fuel from separating. It worked. The industry that builds Allisons today calls it a turbulator. I don't really care myself as long as the manifold in the airplane has one inside it. My generic term is a late intake manifold (as opposed to an early manifold). Likewise, there are "early" and "late" wrist pins, rocker arm assemblies, and various other parts. If someone is making a flying engine today, they generally want to use -100 series parts, not early parts.
The older, unmodified intakes are OK for run-stand engines, boat engines or tractor engines that don't ever really get to altitude.
The older, unmodified intakes are OK for run-stand engines, boat engines or tractor engines that don't ever really get to altitude.
Reluctant Poster
Tech Sergeant
- 1,635
- Dec 6, 2006
Agreed. The point I am trying to make is that it wasn't some eccentric British specification, it was the varying nature of the avgas production process that all engines had to account for. The feedstock made a difference as did the method of octane boosting such as Alkylation vs Houdry catalytic cracking vs Thermofor cat cracking vs Fluid Cat cracking vs adding Cumene, etc. all of which could be added in various combinations
Hi
'Turbulator' is not a term I have found in 1940s 'technical' books on aviation ICEs, the closest I have come is the 'Ricardo Comet Mark III', not an aviation product, which had a 'Turbulence Chamber', page 102, Fig. 21, of 'Internal Combustion Engines Illustrated' Odhams Press 1947 reprint:
'Venturi tubes' are everywhere, in the same publication is the Rolls-Royce Bendix-Stromberg carburettor with large and small Venturi tubes:
A more colourful illustration of this is found on page 111 of 'Rolls-Royce Piston Aero Engines - a designer remembers' by A A Rubbra (Rolls-Royce Heritage Trust, Historical Series No. 16):
Mike
'Turbulator' is not a term I have found in 1940s 'technical' books on aviation ICEs, the closest I have come is the 'Ricardo Comet Mark III', not an aviation product, which had a 'Turbulence Chamber', page 102, Fig. 21, of 'Internal Combustion Engines Illustrated' Odhams Press 1947 reprint:
'Venturi tubes' are everywhere, in the same publication is the Rolls-Royce Bendix-Stromberg carburettor with large and small Venturi tubes:
A more colourful illustration of this is found on page 111 of 'Rolls-Royce Piston Aero Engines - a designer remembers' by A A Rubbra (Rolls-Royce Heritage Trust, Historical Series No. 16):
Mike
SaparotRob
Unter Gemeine Geschwader Murmeltier XIII
Turbolizers were briefly mentioned in an episode of Battlestar Galactica. The original series.
For two years I had the dizzying job description of inspection, expediting, shipping coordinator for a Japanese engineering company. I frequently was given purchase orders for stuff I and no one else in the company really knew anything about. Some stick in the memory like a "steam sparger" WTF is that. Another was for some rotary airlock valves (also known as star valves). I had no idea what they were or what makes a good or bad one or even any problems you may encounter, so when I arrived at the factory in a beautiful place by a lake near the Alps in South Germany I just asked" these rotary valves, WTF are they". Then there was a complete fibre glass heated pipeline for Hong Kong, who in the world knows anything about fibre glass pipelines apart from the people who make them? At times it was a hoot, the blind leading the blind, with all sorts of words made up like "turbulator".
ThomasP
Senior Master Sergeant
Although I must confess that I learned what a 'steam sparger' is in engineering classes, the only place I have ever knowingly run across it in use is at the various coffee houses like Starbuck's and Caribou Coffee - where they inject steam into some of the different mixes to heat them and/or create foam (without cooling the mixture down). 
SaparotRob
Unter Gemeine Geschwader Murmeltier XIII
Honest, I thought you guys made up turbulator.
Reluctant Poster
Tech Sergeant
- 1,635
- Dec 6, 2006
FLYBOYJ
"THE GREAT GAZOO"
Classic!
Reluctant Poster
Tech Sergeant
- 1,635
- Dec 6, 2006
Actually some were
Secrets of a P-38 Ace. John Tilley's electrifying story
One of the enduring P-38 myths is that Lockheed was suddenly blindsided by heating issues when P-38s started flying escort missions out of the UK. In fact, the P-38 heating system was known to be inadequate long before that. The following test report on the "Tactical Suitability of the P-38F Type Airplane" (from Mike Williams marvelous site) makes this crystal clear:
P-38F Tactical Trials
Note that the tests were completed a year before any long-range escort missions were flown. As I have pointed out previously escorted deep penetrations raids didn't start until Big Week in February 1944. In fact, the tests were completed even before the 8th AF had dropped a single bomb on Germany. While the tests were going on the P-38 was just beginning to enter service. At that time bomber escort missions of any sort weren't even being contemplated.
Note that contrary to the claims that the problems were related to the English winter the tests were done in balmy Florida. Also note the unfavorable comparison to the P-39 which was certainly was not flying great distances at high altitudes.
The P-39 and the other Allison powered fighters used a different heating system than the P-38. They simply tapped hot air from the radiator discharge. This would have been impractical for the P-38 due to the location of the radiators. The P-38 used the same system Lockheed used on their pre-war radial powered airliners. I am curious as to why the USAAC didn't use the glycol cockpit heater they developed in the early 1930s which would have yielded better results. From Air Corps News February 18, 1932:
The following Test Report delineates the extensive modifications finally undertaken to the heating system to get satisfactory performance:
http://www.wwiiaircraftperformance.org/p-38/P-38J_performance_11march44.pdf
The amount of heat was more than doubled and a plug for a heated flight suit was added. Even in this test it was noted that the cockpit was poorly sealed.
The P-38 flight manual gives the history of the heating system
The right emitter heated the cockpit and the left heated the armament (camera in the PR versions) The heat previously used for the armament was diverted to the cockpit and an electric heater was substituted for the armament.
Also of note was the cockpit sealing was extremely poor. Considering that Lockheed built the high altitude XC-35 research aircraft before WWII this is inexcusable.
Lockheed XC-35 Electra | National Air and Space Museum
The Lockheed XC-35 and the Evolution of the Pressurized Cabin
FLYBOYJ
"THE GREAT GAZOO"
I am well aware of all the data you posted and the way twin engine aircraft are heated, either via engine exhaust or by a separate heater unit. Using an engine exhaust heat exchanger on a twin engine aircraft is obviously inadequate because of the distance between the engine nacelle and the cockpit. Many twin engine aircraft, both commercial and military aircraft will use an independent heating unit because of this. As mentioned many times before, the heating system on the P-38 was ACCEPTED BY THE AAC early in the program. It wasn't until feedback from the field, where the P-38 was being operated as a high altitude escort (something that the aircraft was never designed for) where Lockheed was given the go-ahead BY THE AAF to fix the heating system!!!!
Understand that during WW2 (and in today's world) a manufacturer cannot implement a modification without government (or customer) approval!
Lockheed gave "the customer" what they asked for with regards to Circular Proposal X-608. If you want to hold someone accountable for the poor heating system, start with Lt. Benjamin S. Kelsey!!!
Oh - in that March 1943 report, you left out one thing:
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GrauGeist
Generalfeldmarschall zur Luftschiff Abteilung
Regarding the "Prestone Heater" found in civil aircraft:
In a combat aircraft, a bullet or shrapnel passing through the line or heat-exchanger will send that all over the cockpit interior.
In a combat aircraft, a bullet or shrapnel passing through the line or heat-exchanger will send that all over the cockpit interior.
GregP
Major
I'm not much into period terminology except when discussing that period, so I'll call it a turbulator like the people who build them today. Your selection of terms is a choice and venturi is likely as good as any. It's at least mostly accurate. If I want a car today with an exhaust-driven compressor, I generally ask for a turbocharged car, not one that is turbo-supercharged.
But hey, you call it whatever you want. The net result was elimination of the fuel separation issues, which was the entire point of the effort. Whatever it is properly called, it worked and still does. So, it's all good.
Cheers.
But hey, you call it whatever you want. The net result was elimination of the fuel separation issues, which was the entire point of the effort. Whatever it is properly called, it worked and still does. So, it's all good.
Cheers.
wuzak
Captain
A kludge?
Reluctant Poster
Tech Sergeant
- 1,635
- Dec 6, 2006
The test in question was concluded on January 26, 1943. That's almost a year before the P-38 starting flying long range escort missions over Germany. In fact the tests were being conducted in the same time frame that the time the P-38 was entering combat in the Pacific and North Africa. Regardless of who decided not to improve the heating there was plenty of time to implement a fix before the P-38J began having issues over Germany.
I would certainly agree that the P-38F was superior to its American contemporaries.
FLYBOYJ
"THE GREAT GAZOO"
Yes, there was plenty of time to implement a fix, just as there was plenty of time to fix other issues on the P-38 as well as other aircraft. Again, the contractor (Lockheed) can't and won't implement any major design change (as it's a modification to the contract) unless government approved. My guess is someone at Wright Patterson decided the heating issue wasn't important enough to order an aircraft modification through a contract change or didn't want to halt the production line to implement this modification.
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