Space and Science BS Thread

They had a pretty significant budget so I think hardware issues were more “can we make it?” rather than “can we afford it?” and they did a good job of managing what they could make vs what they would like to have if only…

 

I think the different amounts of satellites has to do with the different delta V requirements for inserting the satellites into their orbit.\

@Pixeltim If you watch the RGV Aerial stream, or the 20 minute recap this coming weekend, you should see some good shots of the launch site after the SF.

 

https://twitter.com/space_jim1/status/1689267125494353920?s=46

 

Any official word on why they went back to the old method of ship lifts?
https://m.youtube.com/watch?v=QNDpY8FTnbI
I assume it’s because the under flap cradle was damaging tiles.

 

https://m.youtube.com/watch?v=xUjcHW7SHaI
Interesting video. I’ll admit going in that I believe their test was a special case that only applies when the propulsion is capable of moving enough air past the wing(s) and not just the fuselage (i.e. enough excess P/W). It’s still the airspeed at the wing(s) that lifts the plane otherwise you could just VTOL any plane, anytime with the brakes set and we wouldn’t need runways. Yes, the prop, jet, or whatever moves more than just a horizontal column of air but the effect on surrounding air diminishes rapidly. Propelling air past the fuselage could allow the plane to keep pace with the conveyor but doesn’t guarantee the air along the entire wing(s) gets moved enough since true airspeed drops to zero near the wingtips. As was often the case on the show they used an exception to prove a rule. Still a fun and entertaining show.

 

Not sure what you're saying. Are you trying to argue that the conveyor impacts the take off in some way?

 

No, I’m saying it doesn’t. If you were able to match the acceleration of the conveyor in one direction to the speed over the conveyor by the plane in the other direction effect would be the same as if the wheels were chocked or the brakes set on a tarmac. The plane only has whatever airspeed can be generated by the engine thrust in the immediate vicinity of the engines which goes to zero elsewhere. It works for an ultralight which is basically all wing and no fuselage along with an absurdly low takeoff speed but I’d bet it takes more throttle than if allowed to accelerate so the airflow over the wings is uniform from tip to tip. They picked a special case with unique parameters and use it to generalize to ANY plane. What matters is airflow over the entire wing Sure you can use thrust to balance the movement of the fuselage to zero net ground speed but that’s not the same thing as moving the entire wing through the air at takeoff velocity. We already have VTOL(lift off with zero ground speed) and this isn’t how it’s done so I can’t imagine this is a more efficient way to accomplish it.
I like your videos explanation much better since in the second case it allows the plane to move relative to the ground outside the conveyor belt to achieve takeoff velocity. It changes the parameters of the riddle in a way that allows the wing to generate lift.

 

If you assume the wheel bearings are frictionless then from a kinematics standpoint the plane is not affected by the runway at all. However since the moving runway will actually drag air with it via air viscosity, this would create a headwind that would slightly reduce the required forward takeoff speed relative to a stationary observer not moving with the runway.

 

Exactly, the trick is when they insist that the conveyor matches the plane’s acceleration resulting in net zero ground speed. Otherwise the plane will ignore the conveyor other than increased drag from more rapidly spinning wheels or possibly experience tire failure from the excessive wheel speed.

 

https://twitter.com/nasaspaceflight/status/1689661538884313089?s=46
https://twitter.com/thejackbeyer/status/1689708879960227844?s=46

 

@Pixeltim
https://twitter.com/colewzy/status/1689683325886124032?s=46

 

Not a regular here but I'll toss this in. One key element is that the airplane has a lot of mass and therefore momentum and kinetic energy. In order for the plane to start moving backwards on the tarmac, the energy to move the plane backwards must be transmitted through the bearings in the wheels. Since the bearings are designed to not do this, there is not significant nor rapid energy transfer from the moving runway to the airplane. The momentum and kinetic energy maintain the plane on its course before the tarmac started moving and the wheels just spin to match the energy reqirements, namely that it takes a lot of energy to move the plane and instead the wheels spin.

A very similar analogy is when KITT (1982 Trans Am on Knight Rider) would be driving highway speed behind the semi it pulls into while moving. In the show you see the car driving full speed, then hit the ramp into the back of a moving truck also going full speed. The car transitions from driving on the highway to being in the back of the truck, with wheels not moving and this seemed strange to kids watching the show. What is happening is the momentum of the moving car is maintained and keeps going essentially the same speed, but the wheels need to rapidly change speed to a quick full stop in order to satisfy the momentum and kinetic energy of the car irrespective of what the wheels are doing. That is, the wheels just need to match the requirements of the rest of the system and are the first thing to give with respect to satisfying all the necessary relationships.

 

I think y'all making this airplane on a conveyor way harder than it actually is. Airplane wheels, skis, floats, skids, etc only have one job, hold up the plane until it gets into the air. You could do the same test in a float plane with moving water taking the place of the conveyor. I've watched float planes take off and they seem to ignore the current and take off in prescribed pathways. That means the current could be toward, with, or across the direction of travel. The plane is going to get into the air regardless of how the water is moving. Wheel bearings, momentum, kinetic energy have nothing to do with the plane's ability to move on a moving surface.

And here is The Myth Busters confirming KITT can drive into the back of a truck.

 

Hi Def from Mars:
https://twitter.com/mastronomers/status/1689745709799514113?s=46

 

The amount of access these days is remarkable:
https://twitter.com/europaclipper/status/1689751105809666053?s=46

 

https://twitter.com/pogue/status/1689771764434227200?s=46

 

This isn't my thread but I think this speaks to me.

In my experience this is flat out wrong. We obviously have very different experience up to this point, so I'll leave it at that. I'm happy to elucidate the details but doubt most people want to see this continue.

Specifically, your primary sentence is based around "kinetic energy have nothing to do with the plane's ability to move" with some extra stuff in there.

Cheers.

 

A float plane could actually take off without the engine running if in a body of water with enough current.

 

Yep, because floats provide a lot more friction than wheels, which are designed to minimize friction. Of course once the plane left the water, it would fall back down and repeat.

 

Set a wheeled plane on a long enough conveyer belt and it would do the same takeoff and fall right after getting airborne as well. All that matters is the relative airflow over the wings imparted by the aircraft being moved across the ground.