If recips were made nowadays

[razor1uk]

Fair enough FBJ, I did preload my statement to suggest that they might not as much as the Finns FAF due to them being a customer nation and not a creating nation of its air power assets, I apologise.

Yes, I can quite easily image the FOD program is huge, you'd (the US I'd imagine) have not far off 100 or more Airbases in country, and not the inferred joke of having a problem with huge FOD - that's the navy when occasionally sucks an unfortunate deck hand in to an intake.

It was a little poking of fun between the services the civvies; you know ships are full of seamen seawomen too (sorry, to/for political correct UKers along the lines of our 'excellent' police force(s) PC-ness, I should say sea-persons or sea-personnel). Mmm just noticed I keep returning to navy jokes, which are generally(or should be more fitting being 'admirally') so old its running out of interpretations and newer versions,....

 

[Shortround6]

reciprocating engines just have a lot less air going through the "engine". Although a 1000hp turbine probably doesn't suck much more air than a 1000hp recip. The fans replace the prop so what ever the term for foreign objects striking propeller ( or propeller driven objects striking air frame) might have to be figured into which "engine" is more sensitive. Throwing a handful of sand, gravel or 1/4in nuts into the intake of a large reciprocating engine isn't going to do it much good.

Some people think that Allison engines in P-40s lasted longer in North Africa because the air intake was on top of the nose instead of underneath so it swallowed less dirt. Neither engine in a P-40 had "tropical" filters although their may have been some sort of trap in the ducting at the curve. Some radials did.

Don't know if it is a fact or just a good rumor.

 

[swampyankee]

To a first approximation, gas turbines need three times the air per unit power as do steam or internal combustion engines, as spark ignition engines need to operate very close to stoichiometric conditions, and diesels can operate there. Gas turbines need to operate with a lot of excess air because they're at their peak temperatures all the time. As an aside, the turbine inlet temperature for modern gas turbine engines is frequently above the melting point of the turbine blades and vanes.

 

[swampyankee]

By pampering I mean that e.g. when sand was used to combat slipping due to ice, this sand had to be cleared away when turbine engined Fouga Crapsters (aka Magisters) operated on these runways as their turbine engines had to be pampered. When erecting temporary shelters for FAF Hornets, special care has to be taken by using self-locking nuts on any shelter structures as, again, Hornets' turbine engines have to be pampered. When I served at an FAF airbase operating turbine engined aircraft, walking across the runways was forbidden as "sand or small stones may be transferred to runways". This is what I mean by pampering.

One of the tests I remember as required for civil engines was the "mechanic's hand tool ingestion test," which is just what it sounds like: chuck a torque wrench or something like it into the front of the engine. A former coworker worked at Pratt: his anecdote was that JT9D's were run without bellmouth screens (at Lycoming, we almost always used them, and they were SOP at Pratt before the JT9D), and in one test a poorly-secured aluminum stepladder was sucked through the engine. The engine survived; the stepladder was turned into metallic confetti. As an aside, it's normal practice in engine testing to make sure that test cells are clean to minimize the chance of FOD, even if we're going to be deliberately doing an ingestion test.

 

[PWR4360-59B]

Good old thread resurrection since I have not come to this site in a long time. Out of all this posted here no mentions of economy, at least someone mentioned diesel and turbo compounding. Jet engines suck fuel like a vacuum cleaner, only time there is efficiency is when the plane they are powering is going fast. Jet engines are not cheaper to overhaul than even an old 18 cylinder radial recip, the materials they (turbines) are made from and the manufacturing process makes them very expensive, and like someone mentioned they have a certain life, turbines may look easy and simple but the design is much more complicated than a recip. Working on one? Balance is ultra critical at the speeds they run at, just search out "agent jayz" on you tube and see how difficult it is to work on them. With the blade vibrations etc. I don't see how they get the life they do from them. I know that after take off the pilots back way off the throttles almost making those planes as fast or as slow as an old constellation. If there was a modern recip, why does everyone think it has to look or be like an old radial? A proper designed recip will always be more economical than a turbine and could burn the same fuel. Power density? they claim 10K HP from the average nitro burning dragster engine that probably doesn't weigh more than an average auto engine, that is way less than say the XR7755, and yeah I know the responses here will be about how its torn down every run etc. but does prove what can be possible.

 

[tyrodtom]

Torn down after every run, etc.
I guess that etc. also covers that it's burning pure nitromethane, only about $55.00 a gallon.
It just shows what's possible when you barely contain a explosion for a few seconds.

 

[Shortround6]

I know that after take off the pilots back way off the throttles almost making those planes as fast or as slow as an old constellation. If there was a modern recip, why does everyone think it has to look or be like an old radial? A proper designed recip will always be more economical than a turbine and could burn the same fuel. Power density? they claim 10K HP from the average nitro burning dragster engine that probably doesn't weigh more than an average auto engine, that is way less than say the XR7755, and yeah I know the responses here will be about how its torn down every run etc. but does prove what can be possible.

Power needed follows the cube rule for starters (until you get to around mach 0.6 or so?) 450mph requires a LOT more power than 350mph. Like about a 212 % increase in power assuming there is no increase in drag coefficient as the plane goes from 350 to 450mph.

Comparing engines using unlike fuels gets really strange real quick. from wiki so.......
"The amount of air required to burn 1 kg (2.2 lb) of gasoline is 14.7 kg (32 lb), but only 1.7 kg (3.7 lb) of air is required for 1 kg of nitromethane. Since an engine's cylinder can only contain a limited amount of air on each stroke, 8.7 times more nitromethane than gasoline can be burned in one stroke. Nitromethane, however, has a lower specific energy: gasoline provides about 42–44 MJ/kg, whereas nitromethane provides only 11.3 MJ/kg. This analysis indicates that nitromethane generates about 2.3 times the power of gasoline when combined with a given amount of oxygen."

But please note the weight of the fuel required to make that power.
going to diesel fuel (essentially jet fuel) requires a radically different calculation as to the amount of air needed to burn the the fuel, the BTUs per pound of fuel (or MJ/kg) and so on.
Diesels use a much higher compression ratio than gasoline engines and while their average cylinder pressure may be close their peak pressure is much higher which calls for heavier construction to stand up to the pressures in the cylinder, so power to weight ratio of the engine is usually worse than a spark ignition (gasoline engine).

I would also note that "modern" jet engines (or turbofans) are much more efficient than many people think. "Modern" being from the late 50s on.

for example when P & W stuck a two stage fan on the JT3C engine to create the JT3D not only did take-off thrust go from 12,000lbs to 18,000lbs the specific fuel consumption at max continuous dropped from 0.76lbs fuel per pound of thrust per hour to 0.53 LB/LBT/hr. Please note they were using about 13.0 compression ratio in the compressor sections before the burner section. This may be test stand data and not real world.
However in real world the jets/turbo fans operate at altitudes that require superchargers on reciprocating engines. Trying to fly reciprocating engines at over 20,000ft (to get out of weather/turbulence in addition to lower drag) requires a large part of the power in the cylinders to be used to drive the superchargers which puts a real dent in the fuel economy. To get 1000 hp to the prop of a reciprocating engine at 30,000ft may require using around 300hp to drive the supercharger/s (if not turboed) as opposed to a sea level engine.

Jet engines began exceeding the overhaul life of reciprocating engines back in the 50s. Airline managers are a hard headed bunch. If the Jets didn't offer better operating economics they would not have replaced reciprocating engines.

 

[PWR4360-59B]

What helped the jets in the old days was the fuel was pennys a gallon (very likely some government subsidies), it had to be that way as it was guzzled by turbines. That was the economics for those hard headed ones, I've always wondered if there was also subsidies for jet engine use in aircraft designed with them. And since this is likely a non political area I'll end there.

 

[Shortround6]

Conspiracies are always much more fun than reality.

Jet fuel is fancy Kerosene.
The Big Piston engines in the late 40s early 50s airliners were using 115/145 gas or 108/135. This was not cheap stuff. It either needs a different base stock than 100/130 or it needs extra refining steps and additives (lead alone doesn't do it, commercial fuel wasn't allowed the same amount of lead as military fuel in some cases, like 100/130)

Operating economics included fuel used per seat mile and also the number of seat miles that could be flown in a week or month. You not only have to pay for the fuel/flight crew and maintenance. You have to pay for the airplane itself in a timely fashion.
The Boeing 707 could carry more passengers than the Boeing Stratocruiser and flew at around 550mph cruise vs the 350mph Cruise of the Stratocruiser, The Stratocruiser's 28 cylinder R-4360 engines were notorious maintenance hogs.
And fuel has to be looked at in passenger seat miles per hour.
A 1500 mile trip takes roughly 3 hours in the 707 compared to around 4 1/2 hours for the Stratocruiser, so it is not just the fuel burn per hour.

The jets could carry more passengers per day or week using less flight crew personnel and increased the overall capacity of the airline.

 

[wuzak]

What helped the jets in the old days was the fuel was pennys a gallon (very likely some government subsidies), it had to be that way as it was guzzled by turbines. That was the economics for those hard headed ones, I've always wondered if there was also subsidies for jet engine use in aircraft designed with them. And since this is likely a non political area I'll end there.

Firstly, jet fuel was less refined than aviation petrol/gasoline. So it cost less there. And it didn't need additives like Tetraethyllead*, which was needed to help with high compression/highly supercharged engines, in order to provide the desired performance.

Secondly, early jet airliners were more expensive to operate than the piston engine liners. Fuel usage was certainly one factor in this. Another factor was the availability of cheap war surplus transport aircraft, such as DC4 and DC6, which were being converted back to civilian airliners.

Newer piston engine airliners also owed a lot to wartime experience. Such as the Boeing Stratocruiser, which was developed from the B-29, and the Lockheed Constellation, which was developed as a civilian aircraft but first went into production as the C69 military transport.

(It must be noted that the Comet I was developed with the aid of the British government.)

In term of passengers carried, the Comet I carried around half of what the Douglas DC-7 and Lockheed Super Constellation, contemporary competitors, could.

The Comet I had less range, but could cruise around 25%-40% faster and nearly twice the altitude.


*Tetraethyllead was known to be harmful to people before it was introduced in to fuel in the mid 1920s. Political lobbying by GM and associates paved the way for its introduction.

 

[wuzak]

Torn down after every run, etc.
I guess that etc. also covers that it's burning pure nitromethane, only about $55.00 a gallon.
It just shows what's possible when you barely contain a explosion for a few seconds.

Top fuel engines not only burn lots of fuel, they are notoriously unreliable. And when they fail, they usually fail spectacularly.



Fatigue failures of the fuselage basically killed the de Havilland Comet. Wonder what would have happened to an airline whose engines were prone to exploding?

Also:

* Under full throttle, a dragster engine consumes 11.2 gallons of nitro methane per second; a fully loaded 747 consumes jet fuel at the same rate with 25% less energy being produced.

TOP FUEL DRAGSTER FAST FACTS - Super Coupe Club of Iowa

 

[Shortround6]

Military 100/130 could have 4.6cc of lead per US gallon as could military 115/145.
Commercial 100/130 could only have 3.0 cc of lead and the same 3.0cc of lead was the limit on 108/135 fuel (there was no military 108/135) commercial 115/145 was allowed 4.6cc of lead.
Many of these last large piston engined airliners used water injection to boost take-off performance.
The amount of 108/135 or 115/145 fuel you could get per barrel (or ton) of feed stock was less than the amount of of 100/130 let alone lower grades of fuel and not all base stocks were suitable for making these grades of gasoline compared to making the motor fuel (car/truck engine gas) of the day. The refining was much more complicated and different amounts of aromatic compounds were needed in addition to the lead. Please note that the difference in lead between the military fuel and commercial called for different base stocks/ and or refining techniques/blending.

During WW II the change from 3.0 to 4.6 cc of lead per gallon allowed for a large increase in fuel production form the same quantity of base stock.

 

[wuzak]

Good old thread resurrection since I have not come to this site in a long time. Out of all this posted here no mentions of economy, at least someone mentioned diesel and turbo compounding. Jet engines suck fuel like a vacuum cleaner, only time there is efficiency is when the plane they are powering is going fast. Jet engines are not cheaper to overhaul than even an old 18 cylinder radial recip, the materials they (turbines) are made from and the manufacturing process makes them very expensive, and like someone mentioned they have a certain life, turbines may look easy and simple but the design is much more complicated than a recip. Working on one? Balance is ultra critical at the speeds they run at, just search out "agent jayz" on you tube and see how difficult it is to work on them. With the blade vibrations etc. I don't see how they get the life they do from them.

Jet engines may not be as cheap to overhaul as a piston engine, but they need overhauls less often. And they tend to be more reliable.

They get the life from them because they are well engineered and built, and there aren't that many moving pieces.

I know that after take off the pilots back way off the throttles almost making those planes as fast or as slow as an old constellation.

Are you talking jet or turboprop?

The Lockheed Electra carried more passengers than a Super Constellation and cruised 30-40mph faster. Other turboprops, didn't, however.

But jets - forget about it. They cruise way higher and way faster than the old piston aeroliners.

If there was a modern recip, why does everyone think it has to look or be like an old radial? A proper designed recip will always be more economical than a turbine and could burn the same fuel.

But it will be heavier and will be limited to using props, ducted or otherwise, which limits performance, especially at altitude.

 

[Shortround6]

Modern take-off profiles often call for a steep climb to get the aircraft as high as possible as soon as possible to reduce the area affected by noise on the ground.
This requires a lot more power than is needed for cruise. Likewise modern safety standards require a certain minimum performance level with one engine out so modern twin jets actually have an abundance of power. A Boeing 767 twin may use two engines of such power than one engine has more thrust than all four engines on the early 707s. In fact a late 737 may have more total power than the first 707s. and use only about 1/4 of take-off power when cruising.

 

[wuzak]

Modern take-off profiles often call for a steep climb to get the aircraft as high as possible as soon as possible to reduce the area affected by noise on the ground.

The benefit is gained on long routes by the higher efficiency of the high altitude cruise.

Shorter routes they don't climb as high.

When I caught planes from Launceston to Melbourne the aircraft didn't have time to reach altitude. Basically they climbed half the way, then they went into descent.

Even from Hobart, I don't believe they reach the typical cruise altitudes for the aircraft types.

 

[swampyankee]

Piston airliners took a very long time to turn around, frequently 12 hours or more, so they were much less productive than even the early jets, which could be turned around in less than half the time. Modern jets turn around in an hour from a trans-Atlantic flight.

 

[pbehn]

Piston airliners took a very long time to turn around, frequently 12 hours or more, so they were much less productive than even the early jets, which could be turned around in less than half the time. Modern jets turn around in an hour from a trans-Atlantic flight.

I don't think the turn around time on a modern passenger liner has much to do with the engines, in 1986 the plane to Japan via Anchorage stopped for an hour, basically how long it takes to get all the "stuff" out and put new "stuff" in. Modern jets with budget airlines spend much of their time in the air, then they have an overhaul.

 

[PWR4360-59B]

Conspiracies are always much more fun than reality.

Jet fuel is fancy Kerosene.
The Big Piston engines in the late 40s early 50s airliners were using 115/145 gas or 108/135. This was not cheap stuff. It either needs a different base stock than 100/130 or it needs extra refining steps and additives (lead alone doesn't do it, commercial fuel wasn't allowed the same amount of lead as military fuel in some cases, like 100/130)

Operating economics included fuel used per seat mile and also the number of seat miles that could be flown in a week or month. You not only have to pay for the fuel/flight crew and maintenance. You have to pay for the airplane itself in a timely fashion.
The Boeing 707 could carry more passengers than the Boeing Stratocruiser and flew at around 550mph cruise vs the 350mph Cruise of the Stratocruiser, The Stratocruiser's 28 cylinder R-4360 engines were notorious maintenance hogs.
And fuel has to be looked at in passenger seat miles per hour.
A 1500 mile trip takes roughly 3 hours in the 707 compared to around 4 1/2 hours for the Stratocruiser, so it is not just the fuel burn per hour.

The jets could carry more passengers per day or week using less flight crew personnel and increased the overall capacity of the airline.

So those 4360's where drinking what? 150 gallons each per hour if that? And the jets about a gallon per minute per engine that is 3600 per hour each. Maybe they weren't drinking quite that much and maybe more like 1800 per engine per hour, that still makes that 1.5 extra hour nothing. The catch is with a recip that uses jet fuel and an efficient airframe that comes close to 737 speeds, why not? The recip will always be way better at fuel economy than a turbine.

 

[wuzak]

So those 4360's where drinking what? 150 gallons each per hour if that? And the jets about a gallon per minute per engine that is 3600 per hour each. Maybe they weren't drinking quite that much and maybe more like 1800 per engine per hour, that still makes that 1.5 extra hour nothing. The catch is with a recip that uses jet fuel and an efficient airframe that comes close to 737 speeds, why not? The recip will always be way better at fuel economy than a turbine.

How big and powerful would they need to be?

A 737 at cruise speed would need ~20,000kW/27,000hp! That's at around 520mph cruise.

 

[swampyankee]

Back when I worked on prop design at Hamilton Standard, the issues that killed the propfan were maintenance costs and noise, both external noise and cabin noise. While fuel costs were significant — they were about 10% of the cost of operation for most airlines — the net economics favored turbofans.

Reciprocating engines would be heavier for similar power, have greater vibration and have tose vibrations at lower frequencies, and would probably be less reliable and require more maintenance than turbines.