RE: Jap "Heavy" bombers

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RE: Jap "Heavy" bombers - 8/6/2014 10:24:29 PM

Dili
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quote:

Before Symon again shoots down half the forum, it should be noted that aircraft mass does indeed have a lot to do with range at any wanted airspeed(and thus also effects the maximum range). When the mass is increased, the increased need for lift due to higher mass needs either higher AoA and/or airspeed. Both increase drag and thus more engine thrust and fuel consumption is needed.

Erkki an aircraft will always have more range from more fuel than more range from a better lift except in eventually extreme wing loading situations.

In typical bombers (without external stores) and within the normal parameters - not overload - a bomber can only increase the range with more fuel, taking out : bombs, guns, crew, radios etc. to mantain all up weight.

More range implies not only more fuel but also more engine oil for lubrification. So that needs to be taken in consideration. It is not just increasing fuel. Engines will work longer.

It is true that an aircraft with external stores taking some out even without increasing the fuel will increase the range due to less drag. And an higher altitude also might be more economical. But that are seldom the typical bomber circumstances. As you correctly said the Ju-88 is a case of a bomber that seldom had bombs in bomb bay since they could only take 50kg bombs there. In WITP G3M Nell is a bomber that didn't even had a bomb bay.

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RE: Jap "Heavy" bombers - 8/7/2014 12:22:09 AM

wdolson
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No need to throw personal attacks around. If you don't agree with someone, just take on their argument, not them personally.

Bill

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RE: Jap "Heavy" bombers - 8/7/2014 5:03:03 AM

PaxMondo
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quote:

ORIGINAL: wdolson
Palembang may have been able to produce some higher octane fuels, but the US pioneered a new higher octane refining method that was just coming into use when the war started and the technology was not available to anyone else (though I believe it was shared with the UK soon after US entry). I don't know specifically what any of the Dutch refineries were producing, though I believe the US methods probably became pretty common worldwide in the years just after the war.

Bill

Correct. Post-war the technology was broadly licensed outside of the US. Not that it really made a difference as the construction materials and time requirements were such that effectively they could only have been built in the US during the war. Even if IJ and Germany had the plans (they very well might have), we are talking ~2 years construction and having to use a lot of very rare steels and then a very dangerous process (high temp, acids, and moderate pressures) requiring a lot of infrastructure to support. Tough to do with a war overhead. They chose (correctly in my opinion) to go with wet Meth. much easier to manufacture and can get you the same performance outcome. Logisitically you have doubled your fuels, but the manufacturing savings would be worth it.

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RE: Jap "Heavy" bombers - 8/7/2014 8:44:19 AM

Erkki
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quote:

ORIGINAL: Dili

quote:

Before Symon again shoots down half the forum, it should be noted that aircraft mass does indeed have a lot to do with range at any wanted airspeed(and thus also effects the maximum range). When the mass is increased, the increased need for lift due to higher mass needs either higher AoA and/or airspeed. Both increase drag and thus more engine thrust and fuel consumption is needed.

Erkki an aircraft will always have more range from more fuel than more range from a better lift except in eventually extreme wing loading situations.

In typical bombers (without external stores) and within the normal parameters - not overload - a bomber can only increase the range with more fuel, taking out : bombs, guns, crew, radios etc. to mantain all up weight.

More range implies not only more fuel but also more engine oil for lubrification. So that needs to be taken in consideration. It is not just increasing fuel. Engines will work longer.

It is true that an aircraft with external stores taking some out even without increasing the fuel will increase the range due to less drag. And an higher altitude also might be more economical. But that are seldom the typical bomber circumstances. As you correctly said the Ju-88 is a case of a bomber that seldom had bombs in bomb bay since they could only take 50kg bombs there. In WITP G3M Nell is a bomber that didn't even had a bomb bay.

You did not even read what I wrote! Symon said that " The only way to increase range is with added fuel." which is what I replied to, as its plain wrong. Increasing fuel mass(even if it took no extra volume) does not even increase range linearly as the plane has to carry unused fuel. Where the efficiency is lost is in drag: parasitic for the traditional drag and inductive in wing AoA whirl. Each aircraft has an optimal speed and altitude for best range. Add mass, be that bombs or crew, and it drops. There were few bombers that could bring extra fuel instead of bombs(an extra fuel tank in the bomb bay) and none of those afaik were Japanese, and it wasn't done on daily basis anywhere else either.

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RE: Jap "Heavy" bombers - 8/7/2014 1:43:16 PM

Symon
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So here’s mistress Sally. Range vs speed; statute miles and mph. The solid line is with normal fuel; 691 gal, 4146 lbs and normal internal bomb load 1000 kg (220 lbs). The dashed line is the max fuel curve. To get an extended range for a recce mission (fx), Ms Sally loses her bombs and gets a 131 gallon bomb-bay tank; total of 822 gals, 4932 lbs. The dotted line is what happens with max fuel and the drag of 4x 50 kg bombs hanging off external hardpoints. The take-off weights are all substantially similar varying by only 900 lbs.

The dots are the speed/range marks. ‘Absolute maximum’ range (the far left) requires flying at 133 mph (115 knots). Often this works out to 60% Vmax at most efficient altitude. In this case about 5000 feet. ‘Most efficient’ range is where the second derivative changes sign. Often noted simply as 75% Vmax. In the case of Ms Sally, this is about 175 mph (152 knots).

If one wants to fly far, one flies low and slow. If one wants to fly high and fast, one takes a significant range hit; with or without bombs. Mistress Sally is a space limited airframe. Capacity is 2200 lbs, because that’s all that will fit in the bomb-bay, giving a gross take-off weight of 23500 lbs..

One can do the same analysis for Lilly, Helen, and Peggy.

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RE: Jap "Heavy" bombers - 8/7/2014 3:28:33 PM

Symon
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And here’s Miss Helen, model 2, in red, superposed over the curves for Mistress Sally. Helen is also a space limited airframe. It’s max capacity was 2x 500kg or 4x 250kg, for 2200lbs. In the normal configuration (lower solid red line) it carried 3962lbs (661 gals) fuel and a 2200lb bomb load. This gave a 23520lb take-off weight.

For extended range (the upper dotted line), she adds a removable bomb-bay tank (1582lbs, 263 gals, for a total of 5544lbs fuel). Unlike Ms Sally, whose removable internal tank precluded any use of the bomb-bay, Ms Helen’s tank only took away a “portion” of the bomb-bay space, but left room for a 1650lb bomb load (3x 250kg bombs). Somebody started thinking at the design bureau. This gave a 24400lb take-off weight.

Notably, it’s the heavier plane that has significantly greater range. 28% more fuel gives roughly 28% greater range, at 75% Vmax, as one would expect, but roughly 33% greater range at 200 mph. Taking weight into account, the heavier plane (Ms Helen in Overload configuration) should only exhibit a 23% range advantage. This is clearly not the case. So weight is clearly not a linear function (it follows the square law, actually, all other things being equal).

The smart modders will be plotting furiously and will soon see where the Air Team were coming from. The game data is a snapshot of a single point on a complex curve. And before I forget, and somebody goes off, the data is from Wright/Pat flight and engine tests, March 1945, at normal power settings, using 87 octane fuel.

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< Message edited by Symon -- 8/7/2014 4:31:39 PM >

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RE: Jap "Heavy" bombers - 8/7/2014 6:39:18 PM

Symon
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And then, bringing it aallll home, there’s Miss Piggy .. er .. Peggy. Peggy is different. She has the second category of airframes – performance limited. That means she can load fuel and bombs beyond her max take-off weight. Full fuel, max bomb capacity = a burning bush just beyond the end of the runway.

Nominal load, with full fuel (6150lbs, 1025 gals) is 1765lbs of bombs. She had the bay capacity to carry 2x 800kg bombs (2526lbs), but needed to bleed fuel to get off the ground with that load. So Peggy has a nominal bomb load of 800 kg (1760lbs) with her max fuel load of 6150lbs (1025 gals); for a 30900 TO wt. More bombs, less fuel, lower range.

Now, if you are looking closely, you know how/why the Japanese got such big loads on their kamikazes. They just struck the men shooting downward and packed the space with explosives. Same/same, just a bigger boom. And you will now understand how/why Allied airframes were so ubiquitous in the post war years. They were designed to be performance limited, so anything that would give additional lift to an Overload condition, would be good. Perhaps some prop RPM ratings, and a skoosh of SL turbo, but the Japanese didn’t have any of that. Theoretically, yes (it’s nothing but math, after all), but practically, they were so far behind the power curve, and nobody listened to them anyway, so what the hey

Do you really want to see the same analysis done on Allied bombers? Guarantee you will be running to your little wikipoedia sites, because they will be way different than you expect.

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< Message edited by Symon -- 8/7/2014 7:44:57 PM >

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RE: Jap "Heavy" bombers - 8/7/2014 11:14:33 PM

PaxMondo
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quote:

ORIGINAL: Symon
...they will be way different than you expect.

If I am interpreting your data and discussion correctly, this is why the allies could do "special" missions when necessary; like Doolittle's Raid, Yamamoto's intercept, etc. But they didn't plan daily ops on that basis, they stayed in bounds for normal ops. And the Air team modeled everything "in bounds" so that players weren't abusing "special missions" every day ....

Also, if I am reading your curves correctly, it would appear that the Air Team was a bit "generous" to some of the IJA plane range/load combinations ... I'm guessing that was for play balance considerations ...

< Message edited by PaxMondo -- 8/8/2014 12:15:20 AM >

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RE: Jap "Heavy" bombers - 8/8/2014 1:01:29 AM

Big B
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quote:

ORIGINAL: Erkki
Because higher octane level allows for higher compression and temperature(and power) without premature detonation.

This is correct, but hi octane actually burns cooler - so the temperature does not increase.

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quote:

ORIGINAL: wdolson

Direct no, but indirectly yes. An engine has to be built and tuned for high octane fuel to get the benefit of it. Higher octane fuel allows higher compression ratios, which in turn produce more power out of the same fuel. More of the fuel's energy goes into mechanical force and less into wasted heat. Just putting higher octane fuel into an engine that is built for lower octane fuel is just a waste of money.

This is substantially true, but I will submit from experience in the old days - running higher octane fuel in an engine than it is designed for - does in fact do some damage...though nothing permanent.
What will happen is you will foul your plugs really fast and load up the engine....aside from getting no gain in horse power...
In other words - engine performance actually will suffer.

my 2c.

< Message edited by Big B -- 8/8/2014 2:25:11 AM >

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RE: Jap "Heavy" bombers - 8/8/2014 2:45:29 AM

Dili
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quote:

ORIGINAL: Erkki

You did not even read what I wrote! Symon said that " The only way to increase range is with added fuel." which is what I replied to, as its plain wrong. Increasing fuel mass(even if it took no extra volume) does not even increase range linearly as the plane has to carry unused fuel. Where the efficiency is lost is in drag: parasitic for the traditional drag and inductive in wing AoA whirl. Each aircraft has an optimal speed and altitude for best range. Add mass, be that bombs or crew, and it drops. There were few bombers that could bring extra fuel instead of bombs(an extra fuel tank in the bomb bay) and none of those afaik were Japanese, and it wasn't done on daily basis anywhere else either.

I read what you wrote.
The engine cruise altitude of a bomber is optimized for its max weight.

There is no sense in taking bombs and going higher because replacing that weight with fuel always give more range than increasing the cruise altitude a couple hundred of meters.

Most bombers could take extra fuel(while cutting in typical bomb load) because the designers project the fuel capacity to have wide margin. So in typical load missions they never go with full tanks and full bomb load because pushing both to the maximum would be way over the maximum weight.

So the bomber weight never changes.

< Message edited by Dili -- 8/8/2014 3:46:24 AM >

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RE: Jap "Heavy" bombers - 8/8/2014 2:47:31 AM

PaxMondo
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quote:

ORIGINAL: Big B
This is substantially true, but I will submit from experience in the old days - running higher octane fuel in an engine than it is designed for - does in fact do some damage...though nothing permanent.
What will happen is you will foul your plugs really fast and load up the engine....aside from getting no gain in horse power...
In other words - engine performance actually will suffer.

my 2c.

That is true.

But;

If I am designing an engine for 100 RON vs 142 RON, for the same displacement I can get more power out of the design for the same engine lifetime. That is what the US engineers were able to do. I can add a bit more compression (either via piston chamber and/or boost), a bit more aggressive valve timing, a bit more spark advance for the 142 RON over the 100 RON because the 142 will burn cooler (slower) than the 100 and has more energy contained within it.

Now, I can achieve very similar results by using wet Meth with my 100 RON. Again, if I know during the engine design that I am going to use wet Meth injection, I can do similar things and get very similar results.

IJ and Germany couldn't get 142 RON, so they went with wet Meth injection.

Some will immediately ask: how much more power? The answer to that lies in engine lifetime. If I am building a NHRA engine with a lifetime measured in seconds literally (like 100 secs or so) I can get 60 - 70% more power. If I am talking about a NASCAR motor with a lifetime in hours (~10), then maybe only ~30%. If I am talking about wanting 100K miles (+2000 hours), maybe ~10-15%.

I haven't built radial engines and I'm not an ex-Wright engineer. But I did read somewhere that TBolts were built for the cylinders (or sleaves?) to be replaced every 50 hours of flight time .... that would suggest when the pilot pulled the "tit" for over-boost (combat power) that they were getting very aggressive. Prolly +40% power with the 142 RON ....

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