
Aviation’s Largest Piston Engine (2016) - PretzelFisch
https://www.tested.com/tech/564279-story-aviations-largest-piston-engine/
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nimbius
>At full power, the XR-7755 generated a tremendous amount of heat.

Speaking as a full time engine mechanic for a small chain of midwestern repair
stores, this is the death-knell of every heavily customized car. Heck, 3/4ths
of the engineering for a Dodge Hellcat or Mustang cobra is just to keep the
thing cool enough that the driver isnt chased out of the cockpit. You cant
idle them the same way you idle a Toyota...they'll burn up.

the Dodge Viper is another perfect example of engine displacement gone wild.
The intercooler and radiator are massive, but the additional cylinders and
their size means the V-10 motor has 10 cylinders firing onto a 90-degree
crankshaft, which means it has an uneven firing interval for two of the ten
cylinders. it makes the idle rougher than a garbage truck, and very prone to
overheat with a 220 degree camshaft.

~~~
dsfyu404ed
I'm not seeing how crank and cam specs significantly affect cooling at idle
all else being equal. Any cooling system that can work under load will be fine
at idle.

Edit:

For something like a race-car that's trying to minimize weight/power loss by
running the minimum radiator/fan necessary and depending on airflow from
movement (or rely on the fact that you're only running 1/4mi at a time) I can
understand. Still, that's a cooling system sizing issue, not a cam or crank
issue. A street going vehicle isn't going to have a cooling system that's
sized within a hair of inadequate like that. Power output (and heat generated)
at/near idle should be fairly constant regardless of cam and if it's not the
higher power output cam profiles will probably have lower power output at/near
idle (this depends a lot on the engine, some engines force you to choose where
you want your power, some are hard to throw "too much cam" at). No matter how
you cut it only so much air can get passed a closed throttle and that amount
of air only corresponds to a certain amount of fuel, that puts an upper bound
on heat generated at idle. I can see how adding forced induction could
significantly affect heat generated at idle but even then, if everything is
sized properly it shouldn't be much of an issue.

This place is really turning into Reddit where you get down-voted for
questioning anyone who sounds knowledgeable.

~~~
maxxxxx
Cars depend on air moving through the cooling system under load which means
it's at speed. Cooling at idle can be a big problem for high performance cars.
Going to the extreme, F1 cars have to be super careful not to overheat when
stopped.

~~~
justin66
> Cooling at idle can be a big problem for high performance cars.

Or any air cooled car ever made. But the reality is that in a lot of designs,
idling will test the effectiveness of the cooling system more than driving the
car at speed. (Adding power only exacerbates such a problem. The OP completely
fails to understand this)

It's much less of a problem than it used to be, with lots of cars including
electric fans to help out the radiator, but it used to be standard to see a
warning in the owner's manual about temperatures increasing in slow traffic or
at idle.

~~~
maxxxxx
"Or any air cooled car ever made."

Are there still any being built? I thought the 911 was the last holdout until
they also switched to water cooling.

"with lots of cars including electric fans to help out the radiator,"

I had that fan breaking once in my Miata and temperatures went into the red
really quickly in LA rush hour.

~~~
justin66
They switched the 911 over to water-cooled in the late nineties, yes. Prior to
that, Porsche got the idle temp problem somewhat under control using powerful
electric fans positioned in front of some of the oil coolers, but there's
essentially no reliable way to cool four-valve cylinder heads with a purely
air-cooled engine (the 959 used separate water cooling just for the heads), so
they decided the whole thing was a performance dead end. The air-cooled 911
Turbo _did_ get up above 400hp with two-valve heads before the change, though.

> I had that fan breaking once in my Miata and temperatures went into the red
> really quickly in LA rush hour.

No doubt. Once you train yourself to hear that fan, you realize how much the
car depends on it.

~~~
maxxxxx
The problem is that they lost the air cooler sound. A long time ago I drove an
air cooled 911 on track. It wasn't that crazy powerful (300hp) but the sound
was just fantastic.

~~~
justin66
They got big and fat, too. The air-cooled cars had wheelbases similar to your
Miata, but they were really pretty small compared to the modern Porsche stuff.

The new stuff is technologically stunning, of course.

~~~
maxxxxx
True. The old 911s were really small. Now everything is way too big, including
the Miata. Mine was a 2000 which was already much bigger than the original but
the current ones are just way too big. That's not the point of a Miata.

~~~
justin66
It's funny, I actually admire the extent to which Mazda have managed to keep
the Miata small. They're still very easy to pick out in a parking lot when
viewed from above, even amidst other sports cars.

Is the extra width and weight the Miata has gained over the years down to
changing safety standards? I guess on the bright side, in 2019 they're adding
a little power.

~~~
maxxxxx
" I actually admire the extent to which Mazda have managed to keep the Miata
small."

To me the new model has lost all of its appeal. It's way too mainstream. The
only interesting thing left is the rear wheel drive.

~~~
justin66
You can still reach over your shoulder and pull the top up. To me that's kind
of magical.

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dsfyu404ed
>What was truly unique about the cams was that there were two sets of lobes
for each cylinder. One set of lobes optimized the operation of the engine
valves at high power settings

VTEC, yo. In in the 1940s no less.

There's tons of tech that was well understood for WW2 aviation that finds its
way back into land transportation given enough time. Adding water and alcohol
blends to the intake charge to reduce temperature and prevent detonation, ABS,
Fuel injection, probably other stuff as well.

~~~
mkarr
A large part of these technologies making their way into consumer automobile
engines was advances in material science, lubrication, manufacturing, etc,
that allowed for them to exist economically and reliably. Those WW2 era piston
engines were horrifically expensive, and required dozens to hundreds of hours
of maintenance per hour of flight time.

~~~
Gravityloss
Sleeve valves could enable higher compression ratios without detonation, for
higher efficiency? I guess there is the NOx to consider nowadays though.

------
Gravityloss
120 liter displacement. 4x9 = 36 cylinders and many valves and sparks plugs in
each.

As comparison an early generation single spool turbojet has pretty much one
moving part.

Nowadays there might be two or three spools and moving vanes and a thrust
reverser.

But aviation would never have been possible for the masses with piston
engines.

~~~
NeedMoreTea
Avro Lancaster, one of the two most successful heavy bombers of WW2 had 4
27litre V12 merlins, with proven reliability.

The Avro Lancastrian was a passenger variant of the Lanc and developed into
the large bodied Avro York that had the range to replace a few of the old
flying boat routes. Some lasted into the 60s on commercial routes.

The Lockheed Constellation had four 18 cyl radials, and being pressurised
survived in commercial service even longer.

Neither had a turboprop variant.

Mass aviation was going to happen anyway whether the DH Comet arrived or not.
It would have looked rather different, and perhaps not quite as endemic as
now, but definitely mass aviation as we know it. Jets just hastened the
process, and came at just the right time.

~~~
dingaling
Mass aviation could not have happened without the turbine. The big propliners
of the 50s were notorious for having engines fail in flight and had
insufficient power reserves to do anything but struggle to the crash site,
even with the tiny payloads they carried.

64 years ago today a KLM Constellation crashed at Shannon in Ireland, it was
carrying 56 people. That's miniscule and was only sustainable with fares that
the 1%ers of the era could afford. A Norwegian 737Max on a thin Atlantic route
today carries 186 and that is considered borderline small.

Incidentally the Constellation did have a turboprop variant but Lockheed and
GE had a disagreement and it went ahead with pistons instead as the Starliner.
Few people even remember that aircraft now because of the 707.

~~~
NeedMoreTea
I disagree. The desire for aviation came in thanks in part to the war, and was
there with or without jets in amongst post-war growth.

Jets _certainly_ helped the growth in size, and grew the market faster than it
could have without. The market was already there and growing. Prop aircraft
would have grown too had there been no jet engines, though I doubt we'd have
got to 300+ capacity - but who knows?

On seating. The DH Comet had a smaller passenger capacity than the Super
Constellation, which was upto 110 depending on seating configuration, though
usually a bit less. The 707 had 140 when first introduced. For the 1.5% -
2%ers then?

A turboprop constellation variant was prototyped but never produced
commercially. The were none in service. I think the US Navy might have ended
up with a couple for trials too.

~~~
Gravityloss
Even the 707 didn't really make it cheap yet.

At least over here, the last significant price drop was after 2000 or so with
Ryanair etc. with 737:s and A320:s. Probably a new business model in other
ways as well. Single aisle, two reliable high bypass engines. There were still
DC-9 derivatives flying around but no more really.

I bet you could calculate maintenance man hour per kilowatt hour for all sorts
of engines.

Even the old manual flight control operations without computers meant the
amount of work hours per flight was big - meaning for an ordinary worker it
would not be possible.

------
nabla9
Even if you ignore the heat and the power/weight ratio, reliability starts to
become a problem. Adding more smaller piston engines improves reliability and
safety in long flights.

The number of moving parts and the complexity of the piston engine compared to
a gas turbine is significant.

------
funAtParties
Sometimes I think about aerial bombardment, and what that really meant during
that period of conflict.

When you think about the effort to concoct the compounds for the air war, and
drop them on cities, with no guidance like lasers or anything, and then you
look at the sheer tonnage dropped, and how indiscriminate it really was, you
wonder how aerial bombardment is at all distinguishable from chemical weapons.

It really is chemical warfare by another name. The only real difference being
the explosive burning. Clean up was still a similar problem, since, as with
shells, munitions would hit but not detonate. Couple this with such
indiscriminate bombings that cities were engulfed in fire storms, and I think
it's splitting hairs, for the most part.

~~~
mikeash
The taboo against chemical warfare developed after a war that involved mass
bombardment with both chemical weapons and explosives. I’m not qualified to
discuss the reasons, but the people on the pointy end of the stick seem to
have come away thinking that there’s a significant difference.

~~~
funAtParties
I'll argue that the surviving people on the pointy end of the stick haven't
thoroughly considered how pointy conventional aerial bombardment gets.

~~~
mikeash
People who ended up on the pointy end of _that_ stick in the next war still
didn't make it taboo, even though they did with the weapon of mass destruction
made famous by that war.

I see the argument that it ultimately doesn't make much difference how a vast
bunch of civilians end up indiscriminately dead, but the people who actually
experienced it seem to think differently.

~~~
funAtParties

      There's obviously a 
      difference because 
      people differentiate.
    

Sorry, but I'm not buying it. In exactly the same way I don't differentiate
between being maimed by a flamethrower, versus being maimed by battery acid.
The presumptive idea of innate wisdom of the crowd doesn't sway me.

Ask most people choose between burning their face off with a chemical or fire,
and they'll likely choose fire, but getting your face burned off is
categorically bad. Why distinguish.

~~~
mikeash
I’m not saying they _must_ be right. But they were there, they experienced it,
and we did not. They may be wrong, but it would take a really strong argument
to convince me of that. I’m going to start from the assumption that the people
who experienced these weapons and came away with the belief that they should
never be used again had some good reason for that.

~~~
funAtParties
What I really come away from the impression veterans and civilians of the time
give of, is simply that it was unsporting, undignified, and unfair.

That, much more than it was punishingly cruel, in excess of death and
dismemberment by other means.

They say, yeah, it's okay to zip a supersonic bullet through soft tissue such
that it shreds with cavitation, and smash it through bone that splinters and
explodes, so people lose whole limbs. And that's okay. It's like a deer hunt.

But hey, you don't hunt animals by mutilating their lings with bug spray.
That's no fair. You wouldn't consume an elk carcass tainted with persistent
organic pollutants. No fair. We can't even bury our dead.

But, you know what? You aren't going to bury your dead, when they're
incinerated by high explosives.

And hey, what's fair about war at all? What's fair about several hundred
planes unloading kilotons of conventional munitions, indiscriminately, to
break an apparatus of geopolitics.

Gee, unfair, undignified, unsportsmanlike, in the pain, injury and slow death
(leaving a contaminated corpse) department.

When you piece those explicit details together, the real problem is that it
deals a degree of harm to the perception of gallantry, duty and honor of
service. It's pretty much impossible to pat a chemical burn on the back, and
say " _there, there, thanks for defending the country_ " but, you can still
pull that off, when sharing the room with an amputee that lost a limb to
ballistics.

Exchanging chemical weapons for aerial bombardment exhibits "differences" but
nothing that makes me say " _wow, one is okay, and the other isn 't._"

Both are essentially equally bad, and neither is remotely good, or an
improvement over the other.

People have their preferences, but in the same way that they rationalize the
side effect of rampant smog and pollution as bad, but millions of fatal car
accidents as normal, and a calculated risk.

The real choice being put on the table though, is: Would you choose between an
air war that includes both regular explosions and chemical attacks, or just a
regular air war only?

At that point, the choice becomes more rational. We say: "Hmmm, well, at least
I can take some of the destruction out of the equation. I get to make one kind
of misery go away. I can choose _X = A_ as an alternative to _X = (A + B +
C)_. _A_ never goes away, and nothing can be done about that, but at least I
don't have to think about _B_ and _C_ anymore."

So, it's not about incediaries and high explosives being okay. Or aerial
bombardment being different, and better. It's just that they can't be taken
off the table, under any circumstances, no matter whatever else gets
negotiated. I guess it's just a fundamental characteristic of destruction,
that if destroying things is on the table, the basics of destruction get to
keep their scalar qualities. You can limit the method of destruction but not
the quantity.

