All the comments about getting out of your education what you put into it are spot on. Things are not taught at MIT; resources are made available, whether that's projects to glom onto, professor's time, the general atmosphere of extracurriculars, etc. The difference is who these companies come recruiting to, and the network of contacts available. I did CMU -> MIT -> JPL, and I wouldn't have made it despite perfect numbers and a host of paper projects without the support of my advisor at MIT, who along with another one of my SE professors pretty much provided a litany of filial academic connection lining the way past those couple days of interviews with golden, personal touches. As an aside, the advisor of my advisor of my advisor was von Karman.
I'll also mention that I got an offer at Orbital, and they revealed they have the directive only to accept students from a short list of some of the better thought of schools people have mentioned. SpaceX is a bit more egalitarian. They will call you up and do the Google 20 questions to suss out your technical acumen. JPL has a wide mix too, though three out of four of my bosses are fellow MIT alum.
I heard the design lead, Mark Drela, resident sage in the Aero/Astro Dept, give his explanation of the design. Been a while, but he addressed some of your points:
I'm disappointed in both of the linked articles. Some real substance about the design would have been nice, but as it is, I'm left with a lot of questions:
-70% less fuel? How much of that is aerodynamic savings and how much of that is engine efficiency savings?
It's a combination. The higher aspect ratio gives you better L/D, that's straightforward. The turbines ingest the boundary layer over the top of the fuselage, which usually goes turbulent given the length of the fuselage. The underside of the fuselage augments lift.
-Did they do any wind tunnel testing of their model? How close were their CFD and tunnel test results?
Nothing has been built. The biggest wind tunnel at MIT doesn't even fit our 11ft UAV. Testing will follow because it is a damn fine design. CFD has already started and will progress this summer.
-Are they using engines based closely off existing ones, or are they projecting fuel savings 25 years into the future (the 2035 time frame from the article)?
No, Drela spent an entire summer (read years of a group of skilled engineers) writing the code that optimized an entire host of operating parameters, including T4, bypass ratio, fan size, compression ratio, the usual suspects (and then some, dozens if not hundreds of primary and derived parameters for airframe, engine, and conops). IIRC, interestingly, he found an optimal T4 that was lower than current designs, which is nice if you don't have to look for that exotic superalloy to buy you a few extra degrees.
-What sort of structural weight-saving advances are they assuming, or projecting from?
I'm not sure, but this is not the primary focus. The double bubble is efficiently pressurized, and that's the reason it's there, along with being wide enough to fit the three turbines along the top of the boundary layer. Drela did specifically mention NOT using industry "rules of thumb" for sizing, such as are so often found in Raymer (not to say anything bad about Raymer), except for things like seats, lavatories, galley, etc. that aren't going to be messed with. So he may have used marginally lighter weight, but I do remember that he did NOT use carbon or any other such stand-in to without qualification lower the weight by X percent.
-So they made the tail smaller, what makes up for the reduction in control authority there?
Tail sizing is pretty straightforward. Drela wrote code for the first order inviscid calculation of tail sizing way back when, called AVL, don't know what he used here, but he knows how to size a tail.
-Plus other more detailed questions based on the answers to those questions. Would it have been so hard for MIT to link a design document pdf or something? I guess not being a public university, they don't have to if they don't want to. Too bad.
This is a classic PR release. There was next to no technical information. I don't think Drela planned to make his code public, I meant to ask him about it. But the work is ongoing and incomplete. There will be public reports in time to augment the internal ones. It's an amazing project.
Slashdot Mirror
All the comments about getting out of your education what you put into it are spot on. Things are not taught at MIT; resources are made available, whether that's projects to glom onto, professor's time, the general atmosphere of extracurriculars, etc. The difference is who these companies come recruiting to, and the network of contacts available. I did CMU -> MIT -> JPL, and I wouldn't have made it despite perfect numbers and a host of paper projects without the support of my advisor at MIT, who along with another one of my SE professors pretty much provided a litany of filial academic connection lining the way past those couple days of interviews with golden, personal touches. As an aside, the advisor of my advisor of my advisor was von Karman. I'll also mention that I got an offer at Orbital, and they revealed they have the directive only to accept students from a short list of some of the better thought of schools people have mentioned. SpaceX is a bit more egalitarian. They will call you up and do the Google 20 questions to suss out your technical acumen. JPL has a wide mix too, though three out of four of my bosses are fellow MIT alum.
I'm disappointed in both of the linked articles. Some real substance about the design would have been nice, but as it is, I'm left with a lot of questions: -70% less fuel? How much of that is aerodynamic savings and how much of that is engine efficiency savings?
It's a combination. The higher aspect ratio gives you better L/D, that's straightforward. The turbines ingest the boundary layer over the top of the fuselage, which usually goes turbulent given the length of the fuselage. The underside of the fuselage augments lift.
-Did they do any wind tunnel testing of their model? How close were their CFD and tunnel test results?
Nothing has been built. The biggest wind tunnel at MIT doesn't even fit our 11ft UAV. Testing will follow because it is a damn fine design. CFD has already started and will progress this summer.
-Are they using engines based closely off existing ones, or are they projecting fuel savings 25 years into the future (the 2035 time frame from the article)?
No, Drela spent an entire summer (read years of a group of skilled engineers) writing the code that optimized an entire host of operating parameters, including T4, bypass ratio, fan size, compression ratio, the usual suspects (and then some, dozens if not hundreds of primary and derived parameters for airframe, engine, and conops). IIRC, interestingly, he found an optimal T4 that was lower than current designs, which is nice if you don't have to look for that exotic superalloy to buy you a few extra degrees.
-What sort of structural weight-saving advances are they assuming, or projecting from?
I'm not sure, but this is not the primary focus. The double bubble is efficiently pressurized, and that's the reason it's there, along with being wide enough to fit the three turbines along the top of the boundary layer. Drela did specifically mention NOT using industry "rules of thumb" for sizing, such as are so often found in Raymer (not to say anything bad about Raymer), except for things like seats, lavatories, galley, etc. that aren't going to be messed with. So he may have used marginally lighter weight, but I do remember that he did NOT use carbon or any other such stand-in to without qualification lower the weight by X percent.
-So they made the tail smaller, what makes up for the reduction in control authority there?
Tail sizing is pretty straightforward. Drela wrote code for the first order inviscid calculation of tail sizing way back when, called AVL, don't know what he used here, but he knows how to size a tail.
-Plus other more detailed questions based on the answers to those questions. Would it have been so hard for MIT to link a design document pdf or something? I guess not being a public university, they don't have to if they don't want to. Too bad.
This is a classic PR release. There was next to no technical information. I don't think Drela planned to make his code public, I meant to ask him about it. But the work is ongoing and incomplete. There will be public reports in time to augment the internal ones. It's an amazing project.