Can a Vertical Jet Engine Replace Helicopter Blades for Hovering Crafts?

[FactChecker]

Here's one. https://second.wiki/wiki/falacia_del_cohete_pc3a9ndulo
And a video
The crux here is that the thrust vector for a rocket is rigidly attached to the rocket. If you could always pull the nose up then you would stabilize but that is not easy to do. Goddard figured this out pretty quickly as I recall. (I read his biography 60 years ago! )

A first thought:
If the thrust is stabilized to always point in the desired direction of travel, the "puller" position would have some stability. A "pusher" position would require the vectoring to point even farther from the desired direction than the rocket is pointing.
Of course, if the steering is done with fins, then vectored thrust is not an issue. It might not take much velocity for the aerodynamic forces to be more powerful than thrust vectoring.

 

[berkeman]

Here's one. https://second.wiki/wiki/falacia_del_cohete_pc3a9ndulo
And a video
The crux here is that the thrust vector for a rocket is rigidly attached to the rocket. If you could always pull the nose up then you would stabilize but that is not easy to do. Goddard figured this out pretty quickly as I recall. (I read his biography 60 years ago! )

I didn't click into the video yet (late work night here at home), but why is the rocket engine so high in the structure? Is it above or below the COM of the structure, and why is that position important (trick question...)?

 

[hutchphd]

Assume the force from the rocket is "applied" (by the fuel) at roughly the nozzle throat and along the motor axis. Then the torque will depend upon the closest approach of that line to the Center of Mass for a given gimbal angle. Meaning how far is the throat from the CoM. I think the bottom mounted engine will usually give more control authority. In an active control situatiuon that might be desirable...(?)

 

[berkeman]

I think the bottom mounted engine will usually give more control authority. In an active control situatiuon that might be desirable...(?)

Yeah, but what happens when your electronic systems fail and you want to switch to manual control...?

https://en.wikipedia.org/wiki/Grumman_X-29

Spoiler

You yell bad words and pull the Eject handles...!

 

[hutchphd]

didn't click into the video yet (late work night here at home), but why is the rocket engine so high in the structure? Is it above or below the COM of the structure, and why is that position important (trick question...)?

It is definitely above the CoM of this rocket (much of the structure is launch tower. That position matters only to determine the sign and magnitude of the active control parameters. If your alignment is sloppy you want that distance large and big aero fins.

I was going to make a (Boeing) comment about whether the X29 came with a software description manual but I won't because in fact Grumman built it ! I'll bet that thing would just uncork...but the F117 is unconditionally unstable too I believe

 

[FactChecker]

Given that a pulling engine is shooting hot exhaust at the payload, I assume that the original experimenters really were fooled about the stability, or they would have put the engine at the bottom.

 

[FactChecker]

I was going to make a (Boeing) comment about whether the X29 came with a software description manual but I won't because in fact Grumman built it ! I'll bet that thing would just uncork...but the F117 is unconditionally unstable too I believe

Instability is not uncommon in a modern fighter. In certain flight conditions, the F-16 is unstable. The flight control system is necessary to keep it flying. There are a lot of redundancies and safety checks built into its flight control.

 

[russ_watters]

If it works, why isn't there a video of it working?

However I was referring to the scam design presented in #7: I don't see any evidence that the fraudsters engineers have produced a working model that can VTOL, and there is no evidence of rotors on the images of N250UT.

About as far as I am with my warp drive - look, here's a picture

Yes, I have a flying plane without the warp drive.

No s**t.

+1 on this. What I see in the photos is a funny-looking plane that looks like it was built on a helicopter body, and that's it. At first I was thinking the rotors might retract into the booms, but, as you say, if it works, just show a video of it working. So I would conclude as well that what we are seeing here is just marketing BS designed to hook investors. Right now it appears they are testing a short-range battery powered plane and that's it. Will they succeed in their ambitious plan of making it VTOL? Nobody has succeeded yet at either goal, but maybe they will be the first not to fail at both simultaneously?

As always the main issue with battery-powered aircraft is the weight of the batteries. For this 7,000 lb craft, more than half will need to be batteries. One wonders whether they'd be better off trying to prove the VTOL part can work by making an all gas or gas-electric version first.

 

[256bits]

Source? It takes no effort for me to hold a stick in a vertical position with my fingertips. It takes constant concentration and feedback control for me to balance that same stick in the palm of my hand and keep it vertical...

The force vector from the hand points up, and not along the axis of the broomstick.
If the broomstick does tilt due to whatever reason ( try to place and balance of a stick on its end on a table and it will tilt and fall over ), the hand force vector still points up, providing a torque to the stick and the stick rotates more, To compensate you move the hand sideways in the direction of the tilt.

The rocket engine has its force vector 'always' pointing along the rocket axis and can never provides a torque to the rocket. Gravity cannot provide a torque since all parts of the rocket fall at the same rate ( ie are attracted to the Earth ) , including the engine.

Top or bottom engine amounts to the same thing.

try visualizing a rocket in space without air currents or air drag to see the effects of top-bottom engine behavior and determine if either would give different results.

 

[russ_watters]

Source? It takes no effort for me to hold a stick in a vertical position with my fingertips. It takes constant concentration and feedback control for me to balance that same stick in the palm of my hand and keep it vertical...

You are either embracing or dangerously flirting with the Rocket Pendulum Fallacy. The pendulum rocket fallacy is the incorrect idea that a top mounted rocket will make the vehicle more stable than a bottom mounted rocket. Robert Goddard's early "puller" rockets were not more stable than the later "pusher" ones. In either case it is the misaligned rocket that supplies unwanted torque, not gravity. Goddard clearly figured this out early.

As it happens, I visited the Smithsonian Air and Space Museum annex at Dulles, viewed a re-creation of his first rocket, explained why he designed it that way and explained fallacy to my friend this afternoon. Here it is:
https://en.wikipedia.org/wiki/Robert_H._Goddard#First_liquid-fueled_flight
https://en-academic.com/dic.nsf/enwiki/1272265

 

[Borek]

How does it take off vertically?

After watching some videos: they are testing flight efficiency, VTOL configuration "will be tested later". Whatever it means.

 

[anorlunda]

What a coincidence. Beta Technologies is a local story for me. I'm posting right now 400m away from Beta's office/factory. They have certification for the aircraft, the factory, and the inspection techniques. My daughter tends the gardens of the Beta executives, and she promised to introduce me to them real soon now.

Like SpaceX, like Edison's power company, Beta's plans include the entire infrastructure, not just the aircraft. Infrastructure include recharging, maintenance and service facilities, and simulator training, manufacture of the body, batteries and control electronics. They are starting with local package delivery, and organ transplant delivery, but eventually their target it urban taxis.

This picture if from July 3. They did a flyby before the fireworks show in Burlington, VT.

This video let's you see more details of this very unique design. It is not easily comparable to anything else.

 

[FactChecker]

What a coincidence. Beta Technologies is a local story for me. I'm posting right now 400m away from Beta's office/factory. They have certification for the aircraft, the factory, and the inspection techniques. My daughter tends the gardens of the Beta executives, and she promised to introduce me to them real soon now.

Like SpaceX, like Edison's power company, Beta's plans include the entire infrastructure, not just the aircraft. Infrastructure include recharging, maintenance and service facilities, and simulator training, manufacture of the body, batteries and control electronics. They are starting with local package delivery, and organ transplant delivery, but eventually their target it urban taxis.

This picture if from July 3. They did a flyby before the fireworks show in Burlington, VT.

View attachment 303855

This video let's you see more details of this very unique design. It is not easily comparable to anything else.

I think that battery technology will make giant strides in the next couple of decades and battery-powered flight will benefit. The VTOL aspect has been actively pursued for a while.

 

[DennisN]

Have a hovering craft powered by a jet engine.

https://en.wikipedia.org/wiki/V/STOL

The British RAF Hawker Siddeley Harrier (1969-) is a legendary design.

And here's a video demonstrating the impressive STOVL capability of
the US Lockheed Martin F-35 Lightning II:

US F-35 Showing Its Insane Capability During Vertical Take-Off

 

[camerart]

Summary: Have a hovering craft powered by a jet engine.

Instead of helicopter blades have a vertical jet engine embedded in the craft. Steer via thrust vectoring.

The angular momentum of the jet engine might not provide enough stability but surely there is some way to get that.

Hi H,
There are jet engined helicopters, if that suits.
Camerart

 

[Hornbein]

It seems to me that because of the Goddard paradox the stability of would be the same if the blades were below the body. The stability of the rotor is due to its angular momentum, not from being above the body.

We can call this My Even Nuttier Helicopter Idea.

 

[Jonathan Scott]

It seems to me that because of the Goddard paradox the stability of would be the same if the blades were below the body. The stability of the rotor is due to its angular momentum, not from being above the body.

We can call this My Even Nuttier Helicopter Idea.

Sounds more like a novel lawn mower.

 

[tsmspace]

Summary: Have a hovering craft powered by a jet engine.

Instead of helicopter blades have a vertical jet engine embedded in the craft. Steer via thrust vectoring.

The angular momentum of the jet engine might not provide enough stability but surely there is some way to get that.

it would work. it's just not better for now.

 

[tsmspace]

It seems to me that because of the Goddard paradox the stability of would be the same if the blades were below the body. The stability of the rotor is due to its angular momentum, not from being above the body.

We can call this My Even Nuttier Helicopter Idea.

the reason that vehicles are more stable with the "foot" above the mass of the vehicle, is that when hanging, as long as upright is the most natural attitude, then the vehicle will default to upright, so stabilization can come in the form of "let gravity work". Whereas, with the thrust below the craft, the weight is going to droop from gravity, which will cause it to accelerate towards instead of away from the ground. So, helicopters can zero out from lots of positions, and then end up stable, because they hang from the thrust. But, rockets must actively posture no matter what, which is more difficult, and requires more accurate and precise control .

 

[pbuk]

the reason that vehicles are more stable with the "foot" above the mass of the vehicle, is that when hanging, as long as upright is the most natural attitude, then the vehicle will default to upright, so stabilization can come in the form of "let gravity work".

This is wrong: you have fallen victim of the pendulum fallacy.

 

[Office_Shredder]

The highest voted answer here

https://aviation.stackexchange.com/...e-blades-on-the-bottom-fly-the-same-if-at-allActually says this would be a superior aviation design, except for all the obvious ways it's inferior (accidental blade damage from ground contact, cutting people in half by accident etc)

 

[phinds]

the reason that vehicles are more stable with the "foot" above the mass of the vehicle

@tsmspace, perhaps you should read a thread in its entirety before responding. You are promoting an idea that has already been debunked in the thread.

 

[DennisN]

Sounds more like a novel lawn mower.

Bring it up a bit and it becomes a haircutting machine that can service 2 to 3 persons at the same time. Bring it down a bit and it becomes a decapitator. A versatile tool for various types of occasions.

 

[anorlunda]

Bring it down a bit and it becomes a decapitator. A versatile tool for various types of occasions.

It would be marvelous for crowd control.

Snow blowing might be another great application.

 

[renormalize]

Bring it up a bit and it becomes a haircutting machine that can service 2 to 3 persons at the same time.

The US Army played with this concept in the 1950s. Maybe they gave up because of too many close shaves?

 

[Office_Shredder]

The VZ-1 easy target? Looks legit to me