Is it time for Booster Engines?
ENTREPPRUNEUR
Thread Starter
Join Date: Jun 2001
Location: The 60s
Posts: 566
Likes: 0
Received 0 Likes
on
0 Posts
Is it time for Booster Engines?
In the world of automobiles, engine stop/start appeared now and again but didn't catch on. Now fuel is so expensive it's regularly on even upmarket vehicles. For aircraft should we be starting to think about more complex configurations?
Booster engines have appeared now and again but I don't recall anything in the western civil arena since the Trident 3. Is there now a case for having engines used for only part of the flight?
Take-off (particularly with engine failure) is a big deteriminent on what engines you have although it is a tiny portion of the whole flight. The Trident booster was to reduce runway requirements, not for example to sustain/enhance cruising speeds or levels.
I know they didn't install a booster out of choice, but maybe with fuel costs as they are now, it would make sense to have smaller, less powerful main engines supplemented by boosters. Remember the more engines you have for take-off the less power excess you need, and the less rudder moment you have to fly with.
Booster engines have appeared now and again but I don't recall anything in the western civil arena since the Trident 3. Is there now a case for having engines used for only part of the flight?
Take-off (particularly with engine failure) is a big deteriminent on what engines you have although it is a tiny portion of the whole flight. The Trident booster was to reduce runway requirements, not for example to sustain/enhance cruising speeds or levels.
I know they didn't install a booster out of choice, but maybe with fuel costs as they are now, it would make sense to have smaller, less powerful main engines supplemented by boosters. Remember the more engines you have for take-off the less power excess you need, and the less rudder moment you have to fly with.
Join Date: May 2000
Location: Seattle
Posts: 3,197
Likes: 0
Received 0 Likes
on
0 Posts
Where would you put such a booster engine? How would you offset the weight and volume penalty? Note that max cargo or passenger density is what the customer wants...
Early turbojets had a specific fuel consumption of around 1 lb/hr per lb thrust. Current high-bypass turbofans are closer to 0.3.
Early turbojets had a specific fuel consumption of around 1 lb/hr per lb thrust. Current high-bypass turbofans are closer to 0.3.
Join Date: Apr 2008
Location: A tropical island.
Posts: 461
Likes: 0
Received 0 Likes
on
0 Posts
"Booster" engines have actually been applied in the past, JATOs on the 727 for instance, clearly it didn't catch on, for technical, logistical and safety reasons.
For instance... how do you "safely" abort with some rockets at full power attached to the side of your plane?
Sure you can jettison them, but then they pottentially go flying through a terminal full of people.
For instance... how do you "safely" abort with some rockets at full power attached to the side of your plane?
Sure you can jettison them, but then they pottentially go flying through a terminal full of people.
Join Date: Dec 2001
Location: England
Posts: 1,389
Likes: 0
Received 0 Likes
on
0 Posts
I think the penalty of carrying engines that are more powerful than needed for cruise is small, compared to the penalty of carring extra boost engines that are only needed part of the time.
Join Date: Nov 2006
Location: SoCalif
Posts: 896
Likes: 0
Received 0 Likes
on
0 Posts
How about filling the wings with hydrogen, and the plane gets heavier as you burn it? Then you could land heavier than at takeoff.
Swissair reportedly shut down one engine at cruise in their DC-9s. It was not just flight idle, but complete shutdown. Wasn't the center engine shut down at cruise on the 727 with re-engined #1 & #3?
If you want greater efficiency, charge SLF by the pound, like normal cargo.
GB
Swissair reportedly shut down one engine at cruise in their DC-9s. It was not just flight idle, but complete shutdown. Wasn't the center engine shut down at cruise on the 727 with re-engined #1 & #3?
If you want greater efficiency, charge SLF by the pound, like normal cargo.
GB
Join Date: Feb 2005
Location: flyover country USA
Age: 82
Posts: 4,579
Likes: 0
Received 0 Likes
on
0 Posts
In a typical flight cycle of a modern jet, operating from typical runways, the OEI takeoff case is NOT the most demanding operating point. Top of climb calls for more "oomph" than takeoff. This assertion is supported by the fact that a great majority of takeoffs are made either derated, or flex (ATM), or some combination of the two.
But going back to JATO - I once worked around a DC-3 fleet with JATO installed. They weren't fired until after V1.
But going back to JATO - I once worked around a DC-3 fleet with JATO installed. They weren't fired until after V1.
Join Date: Apr 2008
Location: A tropical island.
Posts: 461
Likes: 0
Received 0 Likes
on
0 Posts
Shutting one engine down on a two engine airplane to conserve fuel with revenue on board isn't the most intelligent thing in the world. Though I did once overhear a rather humorous exchange about just such a thing when a Twin Otter was holding over some airport in the bush and wanted to stay overhead for a bit longer than he could have running both engines.
No sane operator would have shut an engine down on a DC-9 to do this and on the 727 we definetly do not do that.
No sane operator would have shut an engine down on a DC-9 to do this and on the 727 we definetly do not do that.
D177
One thing aerial refueling is NOT, is fuel efficient. First, you have to account for the fuel burned by the tanker. Second, the receiver flies the entire segment at a higher average gross weight--it's burn is thus higher. Lastly, their would be the wasted time descending, RV'ing with the tanker burning more fuel than in cruise and wasting time, climbing back up to cruise level.
GF
One thing aerial refueling is NOT, is fuel efficient. First, you have to account for the fuel burned by the tanker. Second, the receiver flies the entire segment at a higher average gross weight--it's burn is thus higher. Lastly, their would be the wasted time descending, RV'ing with the tanker burning more fuel than in cruise and wasting time, climbing back up to cruise level.
GF
How about just using the right aircraft for the job?
Modern engines are more than good enough to provide enough power and also good enough on fuel to give excellent range, far more than you'd ever want to sit in a passenger seat for.
Modern engines are more than good enough to provide enough power and also good enough on fuel to give excellent range, far more than you'd ever want to sit in a passenger seat for.
ENTREPPRUNEUR
Thread Starter
Join Date: Jun 2001
Location: The 60s
Posts: 566
Likes: 0
Received 0 Likes
on
0 Posts
Engines aplenty
You don't need wierd rockets.
An Airbus uses a V2500 - 27,000 lbs thrust for 2,400 Kg. You could have two main engines - CF24s at 20,000 lbs thrust - and two retractable AE3001s (9,400 lbs) for the same weight.
As a simple solution, put them at the back, around the apu (would you still need one?). I'm would guess there's enough room (although you'd have to change the tail surfaces and adjust the fuselage length to maintain CG).
Hybrid cars which use different engines for different phases, were ridiculous once for reasons of cost, weight, complexity, reliablity etc. Now things have changed completely.
An Airbus uses a V2500 - 27,000 lbs thrust for 2,400 Kg. You could have two main engines - CF24s at 20,000 lbs thrust - and two retractable AE3001s (9,400 lbs) for the same weight.
As a simple solution, put them at the back, around the apu (would you still need one?). I'm would guess there's enough room (although you'd have to change the tail surfaces and adjust the fuselage length to maintain CG).
Hybrid cars which use different engines for different phases, were ridiculous once for reasons of cost, weight, complexity, reliablity etc. Now things have changed completely.
Join Date: Apr 2008
Location: A tropical island.
Posts: 461
Likes: 0
Received 0 Likes
on
0 Posts
Planes and cars are different animals (I would hope this goes without saying).
Also, since the topic of cars has been introduced a Prius is rated to carry somewhere around an 840 lb payload, which is incredibly low, for comparison a Mini Cooper can do almost 1000. The whole idea of carrying engines around for the sake of "boosters" is just nonsensical, if there was a way to incorporate one as an APU it MIGHT be worth looking at. Even then, the additional costs associated with an idea like that in civil aviation a) don't make any financial sense, and b) have not made financial or operational sense in the past.
Also, since the topic of cars has been introduced a Prius is rated to carry somewhere around an 840 lb payload, which is incredibly low, for comparison a Mini Cooper can do almost 1000. The whole idea of carrying engines around for the sake of "boosters" is just nonsensical, if there was a way to incorporate one as an APU it MIGHT be worth looking at. Even then, the additional costs associated with an idea like that in civil aviation a) don't make any financial sense, and b) have not made financial or operational sense in the past.
ENTREPPRUNEUR
Thread Starter
Join Date: Jun 2001
Location: The 60s
Posts: 566
Likes: 0
Received 0 Likes
on
0 Posts
aviatorhi
As I explained you are not carrying any extra weight around. The weight of four engines is the same as two for the same thrust.
It probably didn't make financial sense in the past (hence the move from A340 to B777) but my whole question is does it make sense now, with fuel prices much, much higher? Does that change the equation?
barit1
If you don't need full thrust for take-off then just use two engines (lower noise?), and pull your other two out at altitude.
As I explained you are not carrying any extra weight around. The weight of four engines is the same as two for the same thrust.
It probably didn't make financial sense in the past (hence the move from A340 to B777) but my whole question is does it make sense now, with fuel prices much, much higher? Does that change the equation?
barit1
If you don't need full thrust for take-off then just use two engines (lower noise?), and pull your other two out at altitude.
Join Date: Jun 2001
Location: UTC +8
Posts: 2,626
Likes: 0
Received 0 Likes
on
0 Posts
twistedenginestarter...
If you don't need full thrust for take-off then just use two engines (lower noise?), and pull your other two out at altitude.
If you fly jets you would know that you're not saving fuel by shutting down engines in flight. Think of the drag generated by huge wind milling fans....like unfeathered, wind milling propellers.
Ever wonder why the British Airways B747-436 with an engine failure after take off at LAX didn't reach destination LHR? . . . Because of excess fuel burn on 3 engines!
Join Date: Apr 2008
Location: A tropical island.
Posts: 461
Likes: 0
Received 0 Likes
on
0 Posts
The reason aircraft had 3+ engines in the past was because it couldn't be done with 2. We're not just talking about fuel efficiency and reliability here, we're talking about engine failure at the most critical phase of flight, taking a 707 or 727 in the air and losing more than one power plant past V1 is a good reason to put it back on the ground and take your chances if you are anywhere near MTOW.
You're talking about adding a lot of complexity to something that should be simple. The only aircraft I know of that are currently in service with the concept of booster engines you put forth are certain models of the C-119 and C-123, which, respectively, have 1 and 2 100LL powered jet engines to assist in short field takeoffs, as well as the AN-24, some of which utilize around 2000 lbs of thrust generated by the APU to assist with takeoffs... why? Because they couldn't meet performance requirements with the engines originally installed in the first place, not because it saved fuel or was easier to operate.
Also, you mention "you are not carrying any extra weight around", you're forgetting about the added weight of systems for running those two additional engines, not to mention additional maintenance, checks, inspections etc.
As far as the V2500 and CF34 (I assume that's what you meant) why would I (or anyone else) want to add the complexities of what you're suggesting when you can re-engine the aircraft with a later V2500 (like the V2533-A5) and have all the gains in power, reduction in fuel consumption and none of the headaches?
Finally, the reason this concept isn't going anywhere isn't because of what I or anyone else do or don't think, it's simply because all the aircraft on the drawing board to those nearing certifications, which are expected to be manufactures for the next 20-40 years are not employing this concept.
You're talking about adding a lot of complexity to something that should be simple. The only aircraft I know of that are currently in service with the concept of booster engines you put forth are certain models of the C-119 and C-123, which, respectively, have 1 and 2 100LL powered jet engines to assist in short field takeoffs, as well as the AN-24, some of which utilize around 2000 lbs of thrust generated by the APU to assist with takeoffs... why? Because they couldn't meet performance requirements with the engines originally installed in the first place, not because it saved fuel or was easier to operate.
Also, you mention "you are not carrying any extra weight around", you're forgetting about the added weight of systems for running those two additional engines, not to mention additional maintenance, checks, inspections etc.
As far as the V2500 and CF34 (I assume that's what you meant) why would I (or anyone else) want to add the complexities of what you're suggesting when you can re-engine the aircraft with a later V2500 (like the V2533-A5) and have all the gains in power, reduction in fuel consumption and none of the headaches?
Finally, the reason this concept isn't going anywhere isn't because of what I or anyone else do or don't think, it's simply because all the aircraft on the drawing board to those nearing certifications, which are expected to be manufactures for the next 20-40 years are not employing this concept.
Join Date: Feb 2005
Location: flyover country USA
Age: 82
Posts: 4,579
Likes: 0
Received 0 Likes
on
0 Posts
If you don't need full thrust for take-off then just use two engines (lower noise?), and pull your other two out at altitude.
ENTREPPRUNEUR
Thread Starter
Join Date: Jun 2001
Location: The 60s
Posts: 566
Likes: 0
Received 0 Likes
on
0 Posts
Keep up
Hi Glueball
I hope you're not a pilot. It would be dangerous commanding a big jet if you hear voices in your ears. I never mentioned having engines windmilling in the airflow. Next time you're on Flight Simulator and you retract the undercarriage, have a look at the external view and you'll notice they're no longer sticking out. (Not my idea by the way - somebody thought of it in 1876. But I'm catching up fast)
You maybe right about the 747 but then again it might also be because it had to fly at a lower altitude than planned.
I hope you're not a pilot. It would be dangerous commanding a big jet if you hear voices in your ears. I never mentioned having engines windmilling in the airflow. Next time you're on Flight Simulator and you retract the undercarriage, have a look at the external view and you'll notice they're no longer sticking out. (Not my idea by the way - somebody thought of it in 1876. But I'm catching up fast)
You maybe right about the 747 but then again it might also be because it had to fly at a lower altitude than planned.