Hacker News Board Hacker News, browsed like a classic message board
Live data from Hacker News

Boom (YC W16) – Supersonic Passenger Airplanes

boom.aero

Post reply on HN
Print view View original

441–450 of 488 posts

Re: Boom (YC W16) – Supersonic Passenger Airplanes

#441

Post by diskcat »

ungerik wrote: post #437
diskcat wrote: post #387

Earlier quoted context omitted.

Yeah but you are getting 50:1 difference in energy density between hydrocarbon fuel and battery. Also, vertical takeoff is extremely inefficient because a wing can generate a lot of lift compared to drag. this in addition to the fact that a vertical lift system is only used during take off and landing while being dead weight the rest of the trip. even elon can't override physics

The big power requirement of VTOL is not the problem in the overall energy budget because the hovering time is very short compared to the total flight time. Main problem is the additional weight of the more powerful engines. BUT: If you want to fly supersonic, you need very powerful engines anyways, so if you can re-use them for VTOL it's a win win.

To fly supersonic you need an engine that is very powerful at supersonic speed.

VTOL requires an engine that is powerful at low speed.

The harrier jump jet, a most famous VTOL aircraft, didn't have supersonic capability when all its contemporaries did and can only take off vertically with reduced payload or it would burn all its fuel just taking off.

While I don't have the numbers I think VTOL supersonic aircraft would be VERY hard indeed and it would be something that has to be seen to be believed.

Re: Boom (YC W16) – Supersonic Passenger Airplanes

#442

Post by xgbi »

lmm wrote: post #430
schwarrrtz wrote: post #309

Earlier quoted context omitted.

A 70% battery mass fraction seems like a huge engineering challenge for an aircraft. I did a quick calculation of fuel mass fraction for the various Boeing 777 models [0] which ranged from ~13% to ~36%. Not saying it's impossible. Just hard. [0] https://en.wikipedia.org/wiki/Boeing_777#Specifications

I don't see that the engineering is hard. You could just take an existing design and replace most of the cabin with batteries. Building an economically viable mass-market aircraft with a 70% mass fraction might be another question, but if we're just talking about the engineering challenge of building it at all I don't think that's hard?

And on top of that, "refueling" wouldn't cost the 250k figure that usually gets thrown in comments. I imagine it being more in the space of a 1-2k$ ; in which case the reduced passenger capacity might still be worth the premium in batteries.

Re: Boom (YC W16) – Supersonic Passenger Airplanes

#443

Post by Retric »

robotresearcher wrote: post #295
Retric wrote: post #232

Earlier quoted context omitted.

Yes, but if the Concorde slows from Mach 2 to 0 over 45 mins then it's average may be ~mach 1. Which is faster than the average velocity of a normal 747. Granted, if the Concorde shows up and needs to circle the airport for 20 minutes then that's the same delay.

Those data show slowdown to subsonic over the first 10-15 mins of that period.

It also shows fairly linear acceleration to Mach 2 over the first 30 minutes of flight and very rapid deceleration from Mach 2 to Mach 1. Which IMO suggests they could use a different decent profile.

Re: Boom (YC W16) – Supersonic Passenger Airplanes

#444

Post by TheOtherHobbes »

bscholl wrote: post #219
JoshTriplett wrote: post #212

Earlier quoted context omitted.

What's the regulatory situation in countries other than the US? Europe, Asia, Canada, Mexico, South America?

It's complicated and unclear, unfortunately. We'll have to see how things unfold when the airplanes are flying.

Might be an idea to spend a little more time on that.

The engineering is not the hard part here.

Without regulatory support and approval you don't have a product or a market, so "Let's worry about that after we get the prototype working" may not be a fully viable strategy.

Re: Boom (YC W16) – Supersonic Passenger Airplanes

#445

Post by TheOtherHobbes »

sjm-lbm wrote: post #220
jessaustin wrote: post #188

Earlier quoted context omitted.

You're right, it has been awhile since the mid-60s. If we were talking about flying F-104s and B-58s, that would be very relevant information. As I understand it, Boom are developing a new aircraft. They're probably aware of that test and indeed lots of other information about supersonic flight. This whole "engineering vs physics" question reminds me of the misunderstandings people have of modern radio technology. Ye…

I do generally agree with you, but I'm not really talking about engineering or physics, I'm talking about social acceptance. If - via engineering, physics, magic or whatever - sonic booms can be minimized to the point of being indistinguishable from general background noise (or even only as intrusive as current subsonic airliners), I could be convinced that an SST project has a bright future. Until then, I don't thin…

I used to live near an army training area. There were regular artillery exercises, and the bigger shells would literally shake the walls of the house. The smaller shells just made things fall off shelves.

I think any design that literally goes "boom" over land, even a little, isn't going to work. It's too much of an open legal target.

The design really does need to be damn near silent, or at least closer to a mild and unobjectionable "whomp", to have any hope of commercial success.

Re: Boom (YC W16) – Supersonic Passenger Airplanes

#447

Post by john61 »

briandear wrote: post #428
john61 wrote: post #421

Earlier quoted context omitted.

What about CO2 emissions?

Are CO2 emissions really a concern? If 5000 of these planes were flying, as a proportion of global CO2, it would be undetectable if they reduced the plane's emissions by 50%. Then you'd have the argument of how much of that CO2 had any measurable effect on climate -- and that would assume that effect was deleterious. A lot of assumptions to bet a revolutionary aircraft design upon. Adding CO2 reduction engineering to…

If 1969 the planet would have been at stake because of CO2, it would have been better to not fly to the moon but rather use the resources to save the planet.

Re: Boom (YC W16) – Supersonic Passenger Airplanes

#449

Post by Xixi »

diskcat wrote: post #441
ungerik wrote: post #437

Earlier quoted context omitted.

The big power requirement of VTOL is not the problem in the overall energy budget because the hovering time is very short compared to the total flight time. Main problem is the additional weight of the more powerful engines. BUT: If you want to fly supersonic, you need very powerful engines anyways, so if you can re-use them for VTOL it's a win win.

To fly supersonic you need an engine that is very powerful at supersonic speed. VTOL requires an engine that is powerful at low speed. The harrier jump jet, a most famous VTOL aircraft, didn't have supersonic capability when all its contemporaries did and can only take off vertically with reduced payload or it would burn all its fuel just taking off. While I don't have the numbers I think VTOL supersonic aircraft wou…

The F35-B is both supersonic and VSTOL [1]: very hard indeed, but done. Just like the Harrier, the F35-B probably doesn't take off vertically with any significant payload though.

[1] https://en.wikipedia.org/wiki/Lockheed_Martin_F-35_Lightning...

Re: Boom (YC W16) – Supersonic Passenger Airplanes

#450

Post by mathattack »

mark-r wrote: post #401
mathattack wrote: post #328

Earlier quoted context omitted.

Great idea. The airline industry needs innovation around product and service to get out of it's current race to mediocrity. 2 questions: 1) Why 2.2 times the speed of sound? (Why not aim higher?) 2) Where will you get the capital? Seems like a very big ask compared to the typical company coming out of YC. Again - good luck! I would love to clip 4 hours from the SF to NYC flight.

SF to NYC seems unlikely; the sonic booms from the transition between subsonic and supersonic are disruptive enough that they're essentially banned over land areas. Edit: I'm informed by other comments that the boom occurs the entire time you're supersonic, not just during the transition. That makes it even worse.

Interesting. I assumed there could be an engineering way around the boom, but it's not my specialty. I'll have to settle for easier access to Honolulu and Tokyo. :-)
Post reply on HN