USN/USMC Superprops

[jcf]

BTW in regards to the R-4360, no 4,300hp version was ever actually built.
The single VDT engine that was ever flight-tested, those were limited tests
and the engine was never tested to that supposed output. This was due to
a number of factors outside of Pratt & Whitney's control, specifically GE
delays with the turbosupercharger system and the necessary B-50 test
aircraft conversion not being a priority for Boeing. The 4,300hp was always
just a paper number.

Anyhow a VDT version would be of no use to a "super-mudmover", it was
designed, like all turbosupercharger systems, to maintain the engine's base
power output as the altitude increases. One of P&W's intents for the VDT
system was dramatically improved fuel efficiency, down to. 37 lbs. per hp
per hour as a baseline, .45 lbs. at standard cruise with a full load.
A VDT system would actually be of little use at low altitude which is why
the turbosupercharger system of the P-47 was rarely used at low altitude,
ditto the second/auxiliary stage of mechanically supercharged engines.
The Spitfires that were biased towards low-level operations had their
superchargers locked in the middle speed setting and they had cropped
impellers. This was also done on Bristol Hercules and Napier Sabre engines
and it's why the R-4360 in the F2G had a single-stage supercharger.

The mechanical supercharger and turbosupercharger systems on aircraft
engines are not used in the same way that they are on automobiles, nor
are they used for the same purpose. Aircraft engines use them to maintain
power output as the air thins with an increase in altitude, automobiles use
them to increase power at +- sea-level. You'll also note the relationship
between engine displacement and supercharging in automobiles, the smaller
that number, the more likely that supercharging will be involved. The big
exception is, of course, in large displacement dragsters, but those are basically
bombs with a TBO of seconds. Those are actually a good analogy in reference
to piston engined aircraft using full-boost for maximum output, at low or high
level, as soon as you kick it into that mode you've turned the aircraft into a
dragster and it can only be maintained for a handful of minutes before you slag
the engine. Also the lower your altitude, the thicker the air, the less time you
have before catastrophic failure.

Another issue is that an airframe designed for a maximum of 2,500 horsepower
for very brief periods of time at a given load factor can be easily overpowered
and won't actually perform better, but it is more likely to fail. Doubling the
power doesn't equate to doubling the performance or load carrying ability. Also
doubling the engine power means that fuel consumption would increase by more
than double, probably threefold at a minimum, add in an increased payload and
you've probably cut the range, on existing internal fuel, by 75 to 80%. Okay you
add more external tanks but that just reduces the amount of external ordnance
you can carry, but wasn't an increase in that the original point?

Yeah, I can already hear the predictable "but it's Whiffverse" blah, blah, blah.
The ever welcoming, big tent of anything goes whiffery, unless, of course, one
likes to look at things from the standpoint of how could you make it work
within the parameters of actual physics, engineering and technology rather than
hand-wavium and magic. Somehow that's not acceptable in the Church of What-If.

[kerick]

I get what you mean but if we stick to reality then we end up with RW subjects. And that's no fun.
I do like to keep things somewhat plausible at least. But  if others choose to go the more fanciful route that's OK with me. It's all about the fun.
I would like to do a turbo Corsair or Skyraider. But it's hard to find a reasonable engine for that time frame.

[PR19_Kit]

Yeah, I can already hear the predictable "but it's Whiffverse" blah, blah, blah.
The ever welcoming, big tent of anything goes whiffery, unless, of course, one
likes to look at things from the standpoint of how could you make it work
within the parameters of actual physics, engineering and technology rather than
hand-wavium and magic. Somehow that's not acceptable in the Church of What-If.

Not true at all.

This is a broad church, and any and ALL opinions are acceptable and available. This Forum itself is an example of that, covering a whole range of Whiffs from the 'paint and decal only' operator type change to something totally radical like Kilnoizer's Tupolev Landpseeder posted today.

[NARSES2]

This is a broad church, and any and ALL opinions are acceptable and available. This Forum itself is an example of that, covering a whole range of Whiffs from the 'paint and decal only' operator type change to something totally radical like Kilnoizer's Tupolev Landpseeder posted today.

Absolutely, and long may it remain so as long as I'm a moderator. All I ask for is basic politeness when it comes to commenting on peoples work and ideas.

Chris

[zenrat]

Jon, what does TBO mean? I know TBF - Time Between Failure but not TBO.
All I can come up with is Time Between Orgasm but I doubt that is what you mean...
 

[Gondor]

Time Between Overhauls

[Old Wombat]

Jon, what does TBO mean? I know TBF - Time Between Failure but not TBO.
All I can come up with is Time Between Orgasm but I doubt that is what you mean...
 

Gondor beat me to it by seconds but;

Fairly sure it's Time Between Overhauls (ie: re-builds).

[zenrat]

Thanks.  That makes more sense.
 

[sandiego89]

BTW in regards to the R-4360, no 4,300hp version was ever actually built.
The single VDT engine that was ever flight-tested, those were limited tests
and the engine was never tested to that supposed output. This was due to
a number of factors outside of Pratt & Whitney's control, specifically GE
delays with the turbosupercharger system and the necessary B-50 test
aircraft conversion not being a priority for Boeing. The 4,300hp was always
just a paper number.

Anyhow a VDT version would be of no use to a "super-mudmover", it was
designed, like all turbosupercharger systems, to maintain the engine's base
power output as the altitude increases. One of P&W's intents for the VDT
system was dramatically improved fuel efficiency, down to. 37 lbs. per hp
per hour as a baseline, .45 lbs. at standard cruise with a full load.
A VDT system would actually be of little use at low altitude which is why
the turbosupercharger system of the P-47 was rarely used at low altitude,
ditto the second/auxiliary stage of mechanically supercharged engines.
The Spitfires that were biased towards low-level operations had their
superchargers locked in the middle speed setting and they had cropped
impellers. This was also done on Bristol Hercules and Napier Sabre engines
and it's why the R-4360 in the F2G had a single-stage supercharger.

The mechanical supercharger and turbosupercharger systems on aircraft
engines are not used in the same way that they are on automobiles, nor
are they used for the same purpose. Aircraft engines use them to maintain
power output as the air thins with an increase in altitude, automobiles use
them to increase power at +- sea-level. You'll also note the relationship
between engine displacement and supercharging in automobiles, the smaller
that number, the more likely that supercharging will be involved. The big
exception is, of course, in large displacement dragsters, but those are basically
bombs with a TBO of seconds. Those are actually a good analogy in reference
to piston engined aircraft using full-boost for maximum output, at low or high
level, as soon as you kick it into that mode you've turned the aircraft into a
dragster and it can only be maintained for a handful of minutes before you slag
the engine. Also the lower your altitude, the thicker the air, the less time you
have before catastrophic failure.

Another issue is that an airframe designed for a maximum of 2,500 horsepower
for very brief periods of time at a given load factor can be easily overpowered
and won't actually perform better, but it is more likely to fail. Doubling the
power doesn't equate to doubling the performance or load carrying ability. Also
doubling the engine power means that fuel consumption would increase by more
than double, probably threefold at a minimum, add in an increased payload and
you've probably cut the range, on existing internal fuel, by 75 to 80%. Okay you
add more external tanks but that just reduces the amount of external ordnance
you can carry, but wasn't an increase in that the original point?

Yeah, I can already hear the predictable "but it's Whiffverse" blah, blah, blah.
The ever welcoming, big tent of anything goes whiffery, unless, of course, one
likes to look at things from the standpoint of how could you make it work
within the parameters of actual physics, engineering and technology rather than
hand-wavium and magic. Somehow that's not acceptable in the Church of What-If.

Great overview of turbo/supercharging limits.  I do prefer WHIFs that are plausible and comply with physics to a certain degree. 

[Spino]

Phew!  I got unloaded on 

So based on the information that I can find, the R-4360s used in the F2G prototypes/pre-production aircraft were rated for 3,000hp.  Since I am trying to stay somewhere within the realm of possibility, I think a good alternative is the R-4360-53 that powered the B-36J.  Apparently good for 2,800hp continuously, 3,500hp with a 30 minute limit, and 3,800hp with a 5-minute limit (with water/alcohol injection for takeoff).  Minus the two GE turbosuperchargers but with its single-stage supercharger it should fit just fine.  Now I just have to figure out how to explain the extra length in the nose of the AU-2, extra fuel tanks I suppose.  As for the bubble canopy Corsair (which I'm calling F2G-3 for the moment), I think it'll have the -53 engine but with a two-stage supercharger since it's supposed to be a high altitude interceptor instead of a low-altitude ground pounder (ordered as a backup to jets presumably).

As for cramming an Allison T40 into the Bearcat, I don't see any other option since the T56 came later and my backstory is sort of a "ordered as a more efficient alternative to jets".  Course I suppose I could invent a new engine that is a theoretical development of the T40, maybe with redesigned gearbox and shorter power section (with reduced power output obviously).  I'll think about it.

[Spino]

Here's all three as they currently stand:

You cannot view this attachment.

The F8F got a taller vertical tail made from one of its horizontal stabilizers that didn't quite finish printing (a happy accident it turns out :XD:).  The AU-2 and the F2G-3 are both getting taller tails as well, you can just see the newly printed tail attached to its print raft next to the F2G-3.  The AU-2 will be a USMC plane, the other two will be USN.

[Spino]

I suppose an Armstrong-Siddeley Python could be substituted for the T40, it's somewhat shorter and still delivers more power than the Wasp Major.

[PR19_Kit]

I suppose an Armstrong-Siddeley Python could be substituted for the T40, it's somewhat shorter and still delivers more power than the Wasp Major.

Indeed, I suggested that a few days ago.

[sandiego89]

The T-40 ruined every aircraft it was fitted to!  Neat concept, but was a disaster.

[kerick]

Just adjust the story to say the Bearcats were taken out of storage in the boneyard and converted in +- 1964 for service in Vietnam. That should create more options for engines. That would be good research for me to do if I ever do my updated AP-61 Black Widow COIN aircraft.