Adour powered concepts

[BB1984]

Dual, dry/reheat engines is a light fighter, e.g, AIDC F-CK-1 Ching-kuo

The question is… why would anyone want 2x small engines when you can have a single F404, RB-199 etc? Even an old Atar was better than 2x Adours in many respects (despite the higher fuel consumption).

2 engines will always be more expensive to buy and maintain, plus have a negative impact on overall aircraft design potential (extra drag etc).

Since the whole point of a lightweight aircraft is to be cheap… design around a single Adour (or F125, or even better the slightly larger M.45G) seems more appropriate… But no one seems to have really pursued this except for the ALR Piranha.

I agree that, in general, that's true, and I also found the Piranha to be a fascinating design approach for a cheap fighter, but the thread was about the Adour, and . . .

• F-CK-1 has twin engines because of political wrangling over what engines Taiwan was allowed to have
• Engine commonality between types is a plus when looking at fleet wide cost/maintenance, so the right call might not be based on just what's optimal for a single plane. A country that already had the Adour (or any other particular engine) in service might find it preferable to standardize rather than introduce a new type of engine.
  • This is particularly true if that engine is domestically manufactured (by the designer or under license) but the alternative is not, since then there are jobs/industrial-base implications for the engine choice.
• As I said, I agree in general, but the Adour powered Jaguar and other designs (F-18 and MB-346 jump to mind currently) made design decisions to go with two engines even when single engines of comparable thrust were available so it seems like there must be at least some advantages to the dual engine approach

 

[iverson]

Dual, dry/reheat engines is a light fighter, e.g, AIDC F-CK-1 Ching-kuo

The question is… why would anyone want 2x small engines when you can have a single F404, RB-199 etc? Even an old Atar was better than 2x Adours in many respects (despite the higher fuel consumption).

2 engines will always be more expensive to buy and maintain, plus have a negative impact on overall aircraft design potential (extra drag etc).

Since the whole point of a lightweight aircraft is to be cheap… design around a single Adour (or F125, or even better the slightly larger M.45G) seems more appropriate… But no one seems to have really pursued this except for the ALR Piranha.

I agree that, in general, that's true, and I also found the Piranha to be a fascinating design approach for a cheap fighter, but the thread was about the Adour, and . . .

• F-CK-1 has twin engines because of political wrangling over what engines Taiwan was allowed to have
• Engine commonality between types is a plus when looking at fleet wide cost/maintenance, so the right call might not be based on just what's optimal for a single plane. A country that already had the Adour (or any other particular engine) in service might find it preferable to standardize rather than introduce a new type of engine.
  • This is particularly true if that engine is domestically manufactured (by the designer or under license) but the alternative is not, since then there are jobs/industrial-base implications for the engine choice.
• As I said, I agree in general, but the Adour powered Jaguar and other designs (F-18 and MB-346 jump to mind currently) made design decisions to go with two engines even when single engines of comparable thrust were available so it seems like there must be at least some advantages to the dual engine approach

If one engine in the pair can keep the aircraft in the air with the other out of commission, then twin engines will always be more reliable than a single engine of equivalent thrust. So if the extra cost of the extra engine is less than the cost of losing the airframe, equipment, and crew/passengers, air forces and airlines alike tend to prefer twins.

 

[BullpupRafale]

If one engine in the pair can keep the aircraft in the air with the other out of commission, then twin engines will always be more reliable than a single engine of equivalent thrust. So if the extra cost of the extra engine is less than the cost of losing the airframe, equipment, and crew/passengers, air forces and airlines alike tend to prefer twins.

Sure, yet what are chances of such occuring? Especially with modern day jet engines?

Losing few airframes is still cheaper than having few hundred aircraft with 2 engines when single engine with comparable thrust would be lower cost overall even if one large engine itself cost same as two of small ones.

Primary reason why fighter jets have two engines is due to limitations in production capacity to produce huge jet engines with up to date technologies that are possible with older yet more expensive due to inherent complexities such as quantity of parts.

Nowadays a single F135 has enough thrust as two F100 on F-15C.

 

[Arjen]

Military aircraft sometimes operate in an environment that eats engines. Flying low. Dust. Heat. Getting shot at.

 

[iverson]

Military aircraft sometimes operate in an environment that eats engines. Flying low. Dust. Heat. Getting shot at.

And don't forget bird strikes.

Bird strikes are a significant enough hazard around airfields and in low-level flight to warrant a lot of effort and expense aimed at countering the danger. When I was in college, an occasional climbing partner of mine operated something called the "chicken-gun lab". As he described it, this was a large area with room for airframe sections, windscreens, and engine sections that was equipped with a pneumatic cannon that fired chickens. It was not a job he enjoyed, apparently.

 

[Arjen]

I am reminded of a story where cockpit windscreens survived Brit pneumatic firings of chickens, but not the US replication of that test. At the same weight/speed. One bright spark asked if US supermarket chickens had been used? Check. Frozen ones? Ahh...
.

 

[iverson]

[Sure, yet what are chances of such occuring? Especially with modern day jet engines?

Losing few airframes is still cheaper than having few hundred aircraft with 2 engines when single engine with comparable thrust would be lower cost overall even if one large engine itself cost same as two of small ones.

Primary reason why fighter jets have two engines is due to limitations in production capacity to produce huge jet engines with up to date technologies that are possible with older yet more expensive due to inherent complexities such as quantity of parts.

Nowadays a single F135 has enough thrust as two F100 on F-15C.

The chances of engine failure remain high enough. There are no single-engined commercial airliners that I've heard of, because engine failures on airliners are common enough to make the risk too high.

Besides, airframes aren't the only potential cost or even the most significant. An aircraft that can fly home on a second engine can bring home the airframe, the damaged engine (which may be repairable) , and the electronics. But I suspect that even these costs pale in comparison with the cost of losing a trained pilot and, possibly, a flight crew and/or passengers. Even if there are no passengers and bailout is possible, the danger of losing the aircrew is still higher than it would be when flying home. Ejections do kill aviators, and even when they don't, ejecting over open water, wilderness, or hostile territory may result in death or long imprisonment.

Accepting single points of failure on economic grounds seldom proves wise when redundancy is possible at anything less than prohibitive cost. The high reliability of modern technologies does nothing to negate this principle. Even in the semiconductor/computer industry, where reliability is very much greater than anything you can get with a highly stressed mechanical system like a turbine, engineers seldom accept single-points of failure, and when they do, they often regret it.

We have a perfect example of the dangers of depending on reliability in the absence of redundancy: the 737 MAX. Boeing made a penny-pinching decision to eliminate redundant angle-of-attack vanes based on their reliability and the presumed reliability of software and microprocessors. The decision to cut back on these relatively simple and inexpensive, electro-mechanical sensors directly contributed to the loss of multiple aircraft, crews, and passengers, lawsuits, criminal investigations, withdrawal of certification, loss of business, and huge financial and reputational losses for the manufacturer. Turbine engines are a good deal more complex than these vanes.

 

[BullpupRafale]

On subject on two versus one engine is about military aircraft and not commercial airlines that you grasp straws by mentioning those when mentioning sensors which is different off-topic from subject involving jet engines and side-topic of 1 versus 2 engines in military aircraft.

J-37 is single engine.
F-16 is single engine.
F-20 based on two engine F-5 series is single engine.
Mirage-2000 is single engine.
J-39 is single engine.
J-10 is single engine.
F-35 is single engine.
Tejas is single engine.
JF-17 is single engine.
J-39 NG is single engine.
Su-75 is single engine.

Cost of two engines to output as much as single engine at best is comparable while inferior fuel efficiency and thrust to weight ratio along more demanding to maintain, greater dead weight as too drag and more complexity for airframe of the aircraft hence more parts to fail.

 

[iverson]

I am reminded of a story where cockpit windscreens survived Brit pneumatic firings of chickens, but not the US replication of that test. At the same weight/speed. One bright spark asked if US supermarket chickens had been used? Check. Frozen ones? Ahh...
.

They were thawed US chickens according to my acquaintance. But at some point, the customeer decided that there just might be a difference between thawed and fresh-killed. When he told me about all this, he had just finished spending four hours or so pursuing the revised protocol, which involved inserting the two wires of a live circuit into the fore and aft orifices of a less-than-cooperative bird, at which point he got a baseball bat from his car and applied an out-of-protocol but, in his view, more humane solution and called it good.

 

[iverson]

On subject on two versus one engine is about military aircraft and not commercial airlines that you grasp straws by mentioning those when mentioning sensors which is different off-topic from subject involving jet engines and side-topic of 1 versus 2 engines in military aircraft.

J-37 is single engine.
F-16 is single engine.
F-20 based on two engine F-5 series is single engine.
Mirage-2000 is single engine.
J-39 is single engine.
J-10 is single engine.
F-35 is single engine.
Tejas is single engine.
JF-17 is single engine.
J-39 NG is single engine.
Su-75 is single engine.

Cost of two engines to output as much as single engine at best is comparable while inferior fuel efficiency and thrust to weight ratio along more demanding to maintain, greater dead weight as too drag and more complexity for airframe of the aircraft hence more parts to fail.

You continue to miss the point. The extra weight and complexity of an engine compared to an attitude vane reinforces my point. Nor is there any meaningful distinction between military and civilian aircraft in this respect. Nor, for that matter, does it matter whether we are talking about modern gas turbine engines or 1914 Gnome piston engines.

1. "More parts to fail" is true. A gas turbine engine is thus more likely to fail than an electro-mechanical indicator vane. So if redundancy is desirable with indicator vanes, it should be even more desirable in a complex gas turbine, all else being equal.

2. An aircraft with two engines is twice as likely to suffer a breakage in one of the many parts in its two engines than an aircraft with one engine is to suffer in one of the many parts of its single engine.

3. But parts failure is not the issue. Loss of the aircraft, payload, and crew and failure of the mission is.

So assume we have two aircraft with equal total power and engines (of any type) that are equally reliable. Let's call the reliability x. One airplane uses a single engine. The other uses two engines of half the power and twice the parts count.

1. If a single-engined aircraft suffers a breakage in one of its many parts such that the engine fails, the aircraft crashes. There is no redundancy. No matter how much excess ower the engine might provide when healthy, power is now zero. The engine is a single point of failure.

2. An aircraft with two engines has two of every part. If one part breaks, it has another. But this does not on its own provide redundancy and improve flight safety. Assume a twin-engined aircraft loses an engine:

• If the twin-engined aircraft cannot maintain altitude, fly home, and land using only one of its two engines, the aircraft crashes. Each engine is a single point of failure. Neither engine is redundant. So the reliability of this configuration is 1/2x.
• But if the twin-engined aircraft can maintain altitude, fly home, and land using only one of its two engines, the aircraft lands safely. One engine is redundant. There is no single point of failure. The reliability of this configuration is 2x.

The redundant twin-engined aircraft definitely costs more and probably has a lower thrust-to-weight ratio. But it more than makes up for that with survivability and flight safety. The case for twin engines is thus the same as for multiply redundant flight controls, second pilots, multiple radios, extra pitot tubes--and angle-of-attack vanes.

 

[H_K]

The redundant twin-engined aircraft definitely costs more and probably has a lower thrust-to-weight ratio. But it more than makes up for that with survivability and flight safety.

So says logic, but sometimes reality is different.

For example, the single engined Etendard proved to be more survivable to shoulder launched SAMs than the twin engined Jaguar… turns out that having a single long exhaust and high stabilizer is better because the warhead explodes far from vital engine parts and flight controls. Whereas, the Jaguar’s short twin exhausts and low stabilizer were easily peppered with fragments, leading to the engine(s) catching fire and flight controls being damaged. Plus the poor engine separation could lead to an engine fire disabling both engines.

Moral of the story: two engines is not always better than one. And other design factors can sometimes mean than one engine will be more survivable than 2.

P.S. Obviously the above is a rather extreme edge case and most engine problems won’t be combat related but will be due to bird strike, compressor failure, compressor stall etc. Just trying to show that it’s a complex problem and that multiple factors in play that can cause one aircraft to crash where another makes it home.

 

[Arjen]

HawkerI am reminded of a story where cockpit windscreens survived Brit pneumatic firings of chickens, but not the US replication of that test. At the same weight/speed. One bright spark asked if US supermarket chickens had been used? Check. Frozen ones? Ahh...
.

They were thawed US chickens according to my acquaintance. But at some point, the customeer decided that there just might be a difference between thawed and fresh-killed. When he told me about all this, he had just finished spending four hours or so pursuing the revised protocol, which involved inserting the two wires of a live circuit into the fore and aft orifices of a less-than-cooperative bird, at which point he got a baseball bat from his car and applied an out-of-protocol but, in his view, more humane solution and called it good.

I couldn't remember where I had read the story, it appears to be an urban legend - with the nationality of the participants in flux.

The Chicken Cannon

Did British train engineers receive help from the FAA about the proper use of a chicken launcher?

www.snopes.com

The point stands that flying low is risky.
Image from Hawker Tempest and Sea Fury by Robert Jackson, Blandford 1989.

I am sure images exist of more recent mishaps.

 

[iverson]

So says logic, but sometimes reality is different.

For example, the single engined Etendard proved to be more survivable to shoulder launched SAMs than the twin engined Jaguar… turns out that having a single long exhaust and high stabilizer is better because the warhead explodes far from vital engine parts and flight controls. Whereas, the Jaguar’s short twin exhausts and low stabilizer were easily peppered with fragments, leading to the engine(s) catching fire and flight controls being damaged. Plus the poor engine separation could lead to an engine fire disabling both engines.

Moral of the story: two engines is not always better than one. And other design factors can sometimes mean than one engine will be more survivable than 2.

P.S. Obviously the above is a rather extreme edge case and most engine problems won’t be combat related but will be due to bird strike, compressor failure, compressor stall etc. Just trying to show that it’s a complex problem and that multiple factors in play that can cause one aircraft to crash where another makes it home.

I have no argument with you on this point, except possibly with the suggestion that logic and reality are different. We are not talking about reality vs something else, but two independant measures of reality, one based on specific, individual cases and another based on statistics. As you note in your P.S., there are always specific corner cases that diverge fro the averages that logic calculates. But the averages are still the way to bet, even if they do not guarantee an outcome in any given case.

Your Jaguar example is an interesting one. Seen from a slightly different perspective, it actually confirms my overall point. Jaguar engines are very close together. I suspect that an explosion or fire that knocks out one is likely to knock out both, whether the cause is a missile warhead, an uncontained turbine or compressor blade loss, or a fractured fuel line. If so, the Jaguar's engines would not be redundant in this failure mode, and reliability/survivability would, at best be no better than that of a single-engined type like the Etendard. On the other hand, compare the Etendard to an A-10 in this regard. The widely spaced, separately podded twin engines and twin vertical tails provide enough redundancy to make loss of the airplane relatively unlikely in this kind of situation, as combat experience has repeatedly shown. A very high level of systems redundancy is key to the A-10's survivability.

The overall point is that redundancy, not number of engines, is what makes for increased reliability and survivability. BullpupRafale is correct to assert the superiority of a single-engined airplane over a twin- or even multi-engined type that can't fly on its remaining engines after a failure.

The fact that some designs continue to be single-engined is nothing more than a matter of engineering tradeoffs. The A-10 goes all-in for redundancy at considerable cost in weight and altitude/speed performance. It would be a poor interceptor. But it survives missile attack, gunfire, and bird strikes. Single-engined design no doubt provided the best balance between competing requirements when the Gripen and the F-16 were designed. But redundant, twin-engined configurations looked like better bets for F-18s operating over the ocean and for MiG-29s and Su-27s operating over vast tracts of uninhabited land with engines that had comparatively short lifespans.

 

[Archibald]

I am reminded of a story where cockpit windscreens survived Brit pneumatic firings of chickens, but not the US replication of that test. At the same weight/speed. One bright spark asked if US supermarket chickens had been used? Check. Frozen ones? Ahh...
.

During the Algerian war one French Navy F-4U Corsair screwed an eagle... it hit right into one of the guns in the wing.
...
The pilot then bragged he had shot an eagle with his gun.

 

[red admiral]

Although we test engines for birdstrike vs chickens, its really difficult to mitigate against encountering a flock of "chickens" or a "big chicken"

Some things will be common mode failures between single and twin engined aircraft, and some won't.

For more mitigatable failures (e.g. engine components) then its normal to design your single engine to have lower probability of encountering these than on equivalent twin in order to get an overall similar failure rate. But its not possible to mitigate everything away

 

[Archibald]

Although we test engines for birdstrike vs chickens, its really difficult to mitigate against encountering a flock of "chickens" or a "big chicken"

Some things will be common mode failures between single and twin engined aircraft, and some won't.

For more mitigatable failures (e.g. engine components) then its normal to design your single engine to have lower probability of encountering these than on equivalent twin in order to get an overall similar failure rate. But its not possible to mitigate everything away

30 years ago one expensive E-3 Sentry and its entire crew went down because of freakkin' gooses. The Boeing in the Hudson was a bit luckier.
There is no easy solution against the damn things...

 

[robunos]

There is no easy solution against the damn things...

"

 

[VictorXL188]

In regards to a single Adour concept, back in 1976, Flight Systems Inc (FSI) proposed the replacement of the J33 engine in T-33 aircraft with the Adour 861, which is the variant used on the T-45 Goshawk. The short article in Air International's August 1986 issue said that the Adour 861 was smaller and lighter than the J33 but with lower fuel consumption, thus giving longer flight times/range. It was expected by FSI that the project would be of particular interest to Third World countries with an estimated 700 T-33s flying at that time.

 

[Foo Fighter]

Following on with the updated t33 trend. https://en.wikipedia.org/wiki/Boeing_Skyfox

 

[Archibald]

In regards to a single Adour concept, back in 1976, Flight Systems Inc (FSI) proposed the replacement of the J33 engine in T-33 aircraft with the Adour 861, which is the variant used on the T-45 Goshawk. The short article in Air International's August 1986 issue said that the Adour 861 was smaller and lighter than the J33 but with lower fuel consumption, thus giving longer flight times/range. It was expected by FSI that the project would be of particular interest to Third World countries with an estimated 700 T-33s flying at that time.

View: https://www.youtube.com/watch?v=momI9XSV3kM