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Comment by mmooss | Hacker News Reader

I don't see that as a valid comparison. SR-71s could operate with a much higher level of risk than commercial passenger planes. IIRC, SR-71s leaked fuel on the ground, and their wings dragged on the ground without special attachments. Pilots needed special pressure suits, etc.

I also expect that they were much less complex than an aircraft that provides a comfortable, pressurized cabin; the high level of safety mentioned above; freight capacity; etc.

Also, despite Boeing's recent problems, I would guess that commerical passenger planes are far more safe than they were decades ago when the SR-71 was developed. Accidents were much more common despite many fewer flights, iirc.

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12/32 SR71s were lost in the 33 years they were flying. 11/200 MD-11s have been hull-lost from 1988-2025. Not to mention that passenger/cargo planes will put on a lot more flight hours than the SR71s did in a given year.

the SR-71 leaking fuel on the ground was not a design flaw. it was designed to be operated at speed where things would expand to fill in. if they were filled in on the ground, they'd have no place to expand at speed/temps. the risk assessment was that it was better to leak fuel on the ground rather than blowing up at speed/temp

Right, it was risk management. I doubt that leaking fuel would be acceptable risk management for a commercial passenger plane at a public airport.

Obviously they could have designed something that could expand and contract if they thought it was worth it.

They designed special fuel that wouldn’t catch on fire under normal circumstances.

Also, this was done because airframe skin temps exceeded 400F during flight due to the high speeds.

The U-2 is the plane that drags the wings on dolly wheels.

Oops, thanks.

Much less complex? I'm not sure about that for a plane that's expected to travel so fast. In terms of features I'm sure modern passenger planes have quite a bit more. I'm sure planes are absolutely safer now, the point I'm trying to make is the SR71 was thought to be almost impossible to make yet they were able to do it with an impressively small team and (rumored) budget. Yet so many years later we struggle to make reliable workhorse planes that have no such expectations of going faster than anything before. I don't think it's a stretch to say that we could and should be making much better planes.

> have no such expectations of going faster than anything before

They have many other unprecedented expectations, such a fuel usage and safety.

The SR-71 is pressurized. Not to sea level pressure, obviously, but it wasn't exactly unpressurized either. The main reason the crew wore pressure suits is for heat retention and oxygen delivery.

Interesting; I wonder why the bothered to pressurize it. It would seem to add a more complexity to many things - every seal, seam, etc - plus the pressurization system. Maybe some equipment ran better with more pressure.

Even commercial passenger flights are not pressurized to sea level; I think it's something like 8,000 ft. IIRC, Boeing's 787 was designed to be pressurized a bit more which, from on-the-ground experience acclimatizing to altitude, I think could make a noticeable difference.

Running stuff in an unpressurized environment at that altitude brings another set of challenges.

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