I think a big piece of it is that the B-52s are big, very long ranged and have a pretty large payload capacity. Plus they have the supply chain for spares, the technical expertise for maintenance and repair, and the rest of the infrastructure to support and sustain the B-52. All that would have to essentially be rebuilt or substantially redone with a new bomber.
The other thing is that for a lot of parts, they have a LOT of various sorts of spares out in the boneyard B-52s at Davis-Monthan AFB. So if they need some kind of structural part, odds are they can go take one off an older B-52 if need be. So there’s a fair amount of cost savings there I suspect.
But not its immediate predecessor, the six-engined B-47.
During the '60s, a B-52 was modified to carry a single turbofan engine on one of its pylons, so it could be tested at altitude. I thought that was the only seven-engined aircraft ever, but I recently learned of another. A B-47 was used as a testbed with an extra engine on one side of the rear fuselage.
Just a bit of aviation trivia for the thread. I’m still not aware of any plane that had nine engines.
Although the definition of “engine” starts getting fuzzier as we move towards electrics. Some ideas have, say, two gas turbine power-creators turning two electrical generators which power a bank of batteries. And said batteries are connected to, say, 14 electric motors turning 14 propellers to move the air to push the vehicle. And, like the X-57, some of the motors and props are big and intended for full time use, and others are small and intended for part time use. Or vice versa.
Quick, how many “engines” does what I described have?
We may find aviation getting into the same sorts of terminology as diesel-electric locomotives: a “prime mover” is the initial source of energy conversion. A typical modern US loco has 1 “prime mover” driving 1 generator powering 4 or 6 “motors” and the whole machine is 1 “engine”. Clear as mud.
The key is understanding that the actual “motors” that propel the vehicle are electric, and that the electrical power comes from another source- batteries, some other ICE, or a combination of both. Just like a Prius, actually. I imagine aircraft will have to have substantial battery capacity, even if it is recharged by an onboard diesel or something.
But electric military aircraft are a long way off, except for possibly drones.
This is very much the design assumption most everybody is using. To a much greater degree than cars, trucks, or locomotives, airplanes have a large peak power output demand and a much lower sustained demand. With a well-understood relationship between the size and duration of each demand.
Sizing the upstream-most source of power for the average demand, and having some way to store and deplete energy to supply the peaks would create a lot of efficiency gains. Offset of course by the various translation losses between types of energy plus any storage losses.
40 years ago the trade was negative. It’s positive now, at least at fairly small scales. It’s getting more positive as e-tech advances. Scalability is also improving.
Certainly there would be high upfront costs for a new bomber but when considering whether the B-52 should fly for another 50 years or we design a new low(ish) tech bomb truck (as someone else called it above) I am not sure keeping B-52s operational would be the most cost effective.
One of the problems with the Aerospace-industrial complex is that they seem to be incapable of designing a low-tech aircraft. No doubt there’s a few exceptions out there, but it seems that every new Air Force plane has to have all the latest gizmos, bells and whistles. Drives the price through the roof, which I suspect is the main reason why they do it, but it also means the plane is more likely to be cancelled due to blowing the budget.
My WAG would be that it’s because such aircraft have to face enemies on the entire range of the spectrum. If you want a bomber, it has to be a bomber that’s capable of dropping a truckload of ordnance on the Taliban in Afghanistan (a piece of cake,) yet also capable of penetrating heavily-defended airspace in a war against China or Russia. The latter is what requires all the bells and whistles. That’s why we end up with the B-21 Raider. Which also ties into the one-platform-does-all trend of late, which is what got us the F-35 Lightning II, meant to perform three separate roles all with one airframe.
Not exactly. The F-111 was supposed to do two things: serve as a basis for a low-altitude penetration attack aircraft for the USAF and the basis for a fleet defense interceptor/fighter for the USN. The F-35 variants are dfferent but are all true multirole aircraft; the F-111 and F-111K would have been different highly specialized aircraft that happened to share a lot of parts and airframes.
Notably, the F-111 itself may have been only good as a fighter-bomber, but its successor, the F-15E Strike Eagle, excels in both air-to-air and air-to-ground (once its air-to-ground ordnance is gone, it fights as well as any other Eagle in the air.)
The original question form the OP reminds me of the old story of the commercial airline pilot who would only fly four-engine jets over the Atlantic or Pacific. When asked why, he responded “Because Boeing doesn’t make any six-engine passenger jets.”
Speaking of B-52s and their 8 Pratt&Whitney engines…
…years ago, I once played an afternoon of tennis matches at a park located near the end of the runway at Barksdale AFB. I think my ears were ringing in the 24 hours that followed. This was back during the Cold War days when there were always B-52 in the air.
But I was still mesmerized by those big flying machines. You could hear and feel the thrust.
That reminds me of this story (with apologies to LSLGuy for not knowing the actual time increments):
A four-engine airliner is over the ocean when one of its engines malfunctions. The pilot got onto the PA and informed the passengers, ‘Ladies and gentlemen, we’ve had a problem with one of our engines and we’ve had to shut it down. There’s nothing to worry about. This aircraft flies very well on three engines. We will, however, be delayed about 20 minutes getting to our destination.’ A pair of passengers share an annoyed look.
Later, an engine on the opposite wing had to be shut down. The pilot informed the passengers, '‘Ladies and gentlemen, we’ve had a problem with another one of our engines and we’ve had to shut it down. There’s nothing to worry about. This aircraft flies very well on two engines. We will, however, be delayed another 20 minutes getting to our destination.’ The pair of passengers share another annoyed look.
Would you believe it? Another engine failed! The pilot informed the passengers, '‘Ladies and gentlemen, we’ve had a problem with another one of our engines and we’ve had to shut it down. There’s nothing to worry about. Believe it or not, this aircraft actuall flies well on a single engine. We will, however, be delayed another 20 minutes getting to our destination.’
One of the annoyed passengers exasperatedly says to the other, ‘If that last engine quits, we’ll be up here all day!’
I can’t think of any 9-engine plane, even as a one-off test bed or other oddity.
All the numbers up to 9 are accounted for. I believe there were some modified B-17s after WWII that replaced the bombardier’s compartment with a fifth engine in the nose.