If every thing except the overall form of the fuselage is changed it is a new plane.

I don't think that's unusual at all for any jet aircraft that's around for decades. They almost all get new engines, avionics, etc. That the B-52 still has 8 engines is somewhat surprising...that's not terribly desirable.

The Air Force considered replacing the 8 engines with 4 more powerful ones. However, they determined that the loss of one of those engines on take-off would cause a dangerous thrust asymmetry. Dealing with that would have required more extensive changes like moving the engine mounts, so they dropped the idea. But they are going to replace the engines with newer models.

https://www.thedrive.com/the-war-zone/42517/rolls-royce-will...

I had seen/heard/read that the thrust asymmetry was a design feature to help with yaw, and that fewer engines would overpower the design limits of other parts of the airplane, to the extent that everything else would need to be redesigned to handle them (mounts, tail, rudder, etc.)

edit: I believe this is the original video where I saw the above https://www.youtube.com/watch?v=02_geGISTLg

You can use thrust asymmetry to help with yaw, yes.

But here we're talking about unplanned sudden thrust asymmetry, causing a massive yaw force at a critical phase of flight, takeoff, where you're engines are likely to be near their full power and you're close to/on the ground.

If you go from 8 engines to 4, loosing one engine goes from causing 25% thrust loss on the wing to 50%.

Makes sense, but must be also tied to something else unique about the B-52. There are certainly much larger aircraft with 4 engines.

What if most major structural elements of the plane, the skin, the control surfaces, etc. are ~1960 original? Multiple rounds of upgrading avionics, weapons, engines, etc. are extremely common in military planes.

..for certain definitions of "new" (last built 60 years ago)

Only if the new plane is not Tu-144 or Buran. Then it's not a new plane, but a stolen one.

/s

Buran was made to look like Shuttle (despite opposition of engineers on the project), but was completely local design.

I’ve not read too much on the Soviet space program, but whenever I read about Buran (a wonderful accomplishment per se) my thought process goes something like this: “The Soviets must have seen the Americans working on the shuttle thing -> the Soviets must have thought that that shuttle thing was great mostly on account of the Americans working on it -> the Soviets built a shuttle system for themselves -> the Soviets threw away lots of resources for almost nothing”.

Also, as it became apparent in the meantime, even the Americans didn’t get it right when it came to the reasons behind building the shuttle system. As far as I understood there were other, less expensive ways, that they could have taken in order to “improve” their space program.

Buran system was very, very different from US' STS, and honestly multiple groups combined under one umbrella to get what they wanted in Buran project. Some bits of Buran were a "me too" (the visual look of the orbiter, for political reasons), but Soviet space program has combined multiple previous tracks that existed independent of what Americans were doing.

Among various tracks that combined together, there was

1. Super Heavy Launcher - a long term dream since the failure of N1, realised in Energia

2. Reusable crewed orbiter - Buran orbiter

3. Mir-2, the successor to Mir space station - was supposed to use (1) for construction and (2) for crew

4. Fully reusable launch vehicle - was proposed continuation of Energia project

5. various missions requiring super heavy launchers (either Energia, or prospective Vulkan which added extra energia core stage on top) - including mars missions that were on slow boil since end of moon program

6. Soviet Space Forces - anti-SDI systems, orbital warfare unmanned cruisers (Polyot) etc. - dependant on (1).

7. Reduction of space construction and launch costs - nuclear-powered orbital tug launched by Energia which would be responsible for moving objects from low LEO to target orbit, including GEO

1,2,4, and 7 were all included directly in the scope of Buran, with Polyot (6) being in progress as well (the other Energia launch was launch of Polyot test unit).

Note that Buran orbiter, the one part that resembled Shuttle, is independent of other tasks though considered beneficial for the space station goals - if the orbiter project failed, it would still provide data for Reusable Energia variant, and Energia would still mean a working 100t-to-LEO system they could use for whatever - unlike Shuttle which was one specific vehicle. This also meant that Buran's orbiter had much lower cargo capacity - because it didn't need to have higher one as space station modules and the like could just use Energia.

Thanks a lot for the detailed response, that cleared up things for me.

How does one separate the outer mold line of the spacecraft from its performance?

Isn't Buran's appearance driven by similar requirements vs. aesthetics? What else would it have looked like — if you want lots of crossrange capability, you're not going to get something that looked like Faget's designs, would you?

Buran had different design requirements (once you discard the political), because unlike STS the orbiter wasn't sole launcher of the system - Energia took care of shipping heavy cargo to whatever orbit you wanted. So they had different set of constraints including size & prospective contents of the cargo bay.

They have also flirted with the idea of just putting two jet engines into orbiter for extra cross range, which was probably not an option on STS given the huge dead weight of engines

It wasn't needed because the STS wing area achieved the goal of not overflying the Soviets after dropping off a military satellite (once-around mission out of Vandenberg SLC-6), and the US had many politically friendly potential landing areas, while USSR did not.

Catering to NRO and USAF wartime requirements doomed the STS to cost overruns. Sticking with Faget's designs and the NASA requirements may have salvaged the program's cost goals, but I'm no expert.

The two stage design from IIRC phase II of Shuttle project was a marvel

> despite opposition of engineers on the project

Huh? Despite 'opposition'? Can you elaborate?

(also make sure not to miss /s in my previous comment)

I didn't miss the /s, but I feared others might think different ;)

From what I've read, the decisions to make Buran look externally like STS orbiter was a political one, and the engineers at MiG OKB weren't happy about it - they have been working on a bunch of space planes for some time, including the infamous suborbital fighter. However the similarity was found to have political benefits in the weird opposite of kremlinology and the decision stood.

Not having USAF's annoying requirements though, they were able to design a better system anyway. (Pre-USAF involvement STS was also better, but congress cost cutting made a necessity of begging DoD for funds)

I checked the Wiki article on it, just to be sure.

I just don't understand how it could look any way different (at least significantly), this is a classical case of the function dictating the form.

Essentially, the Buran orbiter had different function, and thus different forces on its form.

US' STS shape was ultimately dictated by its cross range requirements combined with cargo capacity. Explicit case of function leading to specific form.

Buran didn't require the same huge cargo capacity in the orbiter, because Soviets had already tested and verified self-assembly of space station in orbit from multiple launched modules (technology that they would later employ in ISS). For huge capacity it had Energia, which once proven could be also launched on Polar orbits (the specific requirements from USAF for STS involved heavy cargo on polar orbits from Vandenberg).

This meant that Buran orbiter had wider design space to explore, and previous experiments in crewed reusable spacecraft were centered around lifting body shape, to extent much higher than STS was. However, the command to make it look like US STS came pretty early in the project, in addition to general lack of documents, so we don't really know how they would go.

Ah, that clears some things for me, I thought more about the aerodynamic form.

> the command to make it look like US STS came pretty early in the projec

I never heard anything about that, AFAIR.

Any ideas where to look abou that?

I wish I was more diligent in noting back then, but essentially I went on a long walk on google, encyclopedia astronautica, checking russian pages with google translate etc. trying to read as much about the project - at the time it was still running we had more information published in Poland about Shuttle (including accurate drawings and system descriptions) than about Buran, and thus I was always left fascinated about this space plane that, compared to STS, I had only a blurry photo and maybe A4 page of description.

> Buran

> 27. Alternative projects considered at the stages of the preliminary design and preliminary design: attempts to create OK "Buran" on the basis of OK "Spiral" - what was proposed (options and technical solutions) and what was accepted, what was not accepted, how and why.

> Orbital vehicle "Buran" in landing configuration

> Answer: We (NPO Molniya) worked on an alternative variant in a guise that mimics that of the Spiral orbital plane, but General Designer Glushko considered that by that time there were few materials that would confirm and guarantee success at a time when Shuttle flights proved that the Shuttle-like configuration works successfully and there is less risk when choosing a configuration, therefore, despite the larger useful volume of the Spiral configuration, it was decided to carry out the Buran in a configuration similar to the Shuttle configuration. Although the absence of sustainer engines on the Buran noticeably changed the centering, the position of the wings, the configuration of the influx, and a number of other differences.

> 28. Was the copying of "Space Shuttle" in a larger or smaller volume during the creation of Buran deliberate or were there "directive instructions"?

> Answer: Copying, as indicated in the previous answer, was, of course, completely conscious and justified in the process of those design developments that were carried out and during which, as already indicated above, many changes were made to both the configuration and the design. The main political requirement was to ensure that the dimensions of the payload compartment were the same as the payload compartment of the Shuttle.

https://www-buran-ru.translate.goog/htm/archivl.htm?_x_tr_sc...

> Shuttle flights proved that the Shuttle-like configuration works successfully and there is less risk when choosing a configuration

Classic Soviet risk-averse behavior. See also: copying every single detail from the B-29 because they knew it worked and it would be their heads (perhaps literally) if the Tu-4 didn't. They did the same thing with Joe-1, their first atomic bomb test. Do what you know works so you can go home at the end of the day. Innovation is a luxury.

This is what happens when employees fear management. Lessons to be learned.

> This is what happens when employees fear management. Lessons to be learned.

You just listed the things what management decided to do, so risk aversion was on management side, not employees.

Just like the idea to copy S/360.

Thank you for finding more!

I guess I was wrong on that part. Interesting that Spiral had greater capacity, I thought the opposite based in some of the sketches - possibly I mixed up sketches of another MiG space plane.

Wish someone manages to one day do a definitive history translated into English

It's worth noting that the C-130 Hercules has been in continuous service since 1956, and new aircraft were still being produced at least as recently as 2015 (and perhaps longer). That aircraft really is a flying truck!