Bloodhound LSR - the 1,000mph car project

This is the discussion thread for a recent post on GTPlanet:

This article was published by Joe Donaldson (@Joey D) on October 31st, 2017 in the Automotive News category.

 

That's not a car, that's a rocket on wheels.

Must be an amazing feeling to drive that fast on solid ground. Also very scary, I believe.

 

Craaazzzy!!!

I wish them luck though

 

The FIA website is sending me in circles. Does anyone know the rules for how the wheels have to work? It strikes me that the way to win this thing would be to actually just fly a jet low enough to drag something along the ground.

 

Now I know what my next project in Kerbal Space Program is going to be!

 

That's essentially what's happening. I believe once the car hits 600 mph the wheels can no longer turn as quickly as the car is moving, so they are more or less just a rudder for the vehicle. They are still kind of spinning though.

From what I was told by some folks at Bonneville is that in order to meet the land speed record criteria the vehicle needs only have wheels touching the ground.

 

So one could fly a jet and just drag a wheel on the ground? Like.. on a tether or extended rod? Or does the wheel have to support the weight of the vehicle? Does it have to maintain constant contact or could it skip? How far can it skip? Can it just bounce on a cable, touching once every, say, mile or 2? Does the craft have to be piloted or can we do this with a drone? I imagine there's a separate category for rocket sleds on rails.

I'm imagining a "wheel" with its own control surfaces that can be independently piloted behind a towing jet to go down and bounce off the surface periodically. I'm also imagining a jet that touches down every few miles and lifts back off. Not sure if the speed in between touches counts for the record.

 

So a military jet with 4 wheels (tucked inside during the run) flying within ground-effect would count? I'm guessing if someone tried to qualify that they'd change the rules or ban it some other way. The jet in my photograph is probably outside of what one would call "ground effect" but not by a lot. You can make ground effect bigger by adding long thin wings, but that shape is not great for super-sonic flight.

I would expect that the maximum speed achievable would be to fly within ground effect if that's permitted by the rules. You'd start by rolling, transition to hovering, and end by rolling - basically a purpose-built aircraft.

 

They better use very large wheels.

 

In addition to @Famine comments, you can also check out the team's write up here: http://www.bloodhoundssc.com/project/car/wheels/desert-wheels

There's also this:

 

Interesting.

Well if it can hover, even a tiny amount, that's got to be optimal. Maybe it's impactical because it would require too much control, or entail too much risk to the driver, but rolling on the ground is a loss. If you have aerodynamic surfaces that you can use to control hovering flight, that would be the way to do it. Forcing it to the ground increases drag from the aerodynamic surfaces and wheels. Maybe it's just too dangerous (for now).

Edit:

I've never really contemplated the compression wave from supersonic flight hitting the ground before the entire body of the craft had passed. I wonder how they handle the effects of that on this car. I would think that might be pretty damaging on a loose surface. One more reason to stick with paved surfaces.

 

If the South African Pans are anything like the Bonneville Salt Flats, they're incredibly well packed. Even before Speed Week they spend weeks preparing the surface by packing it tighter, making it smoother, and removing anything remotely loose. I'm guessing they'll prep the hell out of the 12 mile course before they attempt to hit 650, 800, or 1000 mph.

 

This is a really nasty problem. Shock waves reflecting off the ground, launching debris, creating unstable lift on different parts of the vehicle as you transition past the sound barrier, it's a lot more to deal with than a supersonic jet. Very cool work.

 

Yea, I'm not too surprised they called that time period out. From what I read briefly, that seemed like it was the most problematic. The compression wave characteristics change rapidly as you go past the speed of sound, so different parts of the vehicle will be hit with rapidly changing pressure. My head is exploding a little.

 

I think it would be hard to design a 1000 mph hovercraft. It would be difficult to maintain a steady attitude and gap to the ground and the skirt would have the potential to pick up a ton of aerodynamic forces and send the craft flying in all sorts of directions.

It would also have to be at least as aerodynamic as the car, or else the increased drag would cost more than what's gained by losing the wheels.

 

I dunno, keeping it on the ground and going straight seems like a similar challenge to me. You'd need a computer to fly it for sure, and a lot of sensors. The pilot would be there for coarse directional inputs only.

But the bottom line, regardless of the technical challenge of making it hover, is that there is no way that it is drag-optimal to roll on the ground. Ground effect is pushing you up off the ground, you're either wasting energy (top speed) pushing against it, or you let it float you. If ground-effect is permitted as being in contact with the ground, flight has to be the answer ultimately. Maybe it's still out of reach right now.

 

I'm glad this project is still alive. I've been looking forward to it for years .

 

This meets my criteria for an Olympic sport.

 

There are a few aircraft that were designed with these conditions in mind. Low altitude deep penetration bombers like the B-1B, F-111, and Tornado. I'm unsure exactly how low and fast they would typically fly, but on paper they were to hug the ground at super/transonic speed to avoid radar. NASA might have some papers relating to test flights or scale model testing. Probably more on the F-111 since it's American and older.

There have also been waveriders like the XB-70, though it was intended for high altitude flight. I wonder how adaptable it would be to low altitudes. The B-70 high altitude mission was changed to low altitude after Soviet SAM technology evolved, but it was no longer capable of supersonic flight with the new profiles.

 

Still, at a minimum, you'd have to get low enough that the shockwave hits the ground within the length of the aircraft. I don't think it's possible to fly supersonic that low with those aircraft.

 

Yeah, I don't know how feasible it is, I just figured that those aircraft might give some ideas on the limits of low level flight.

I did a quick search and apparently an F-4 got down to 85 feet, though that's still a ways off the ground.

http://www.dtic.mil/docs/citations/AD0680800

 

They have to use a V8 from Jaguar just to pump the rocket fuel.

Holy .