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

[Hornbein]

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.

 

[Motore]

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

 

[jrmichler]

And a real small version, AKA jet pack: https://en.wikipedia.org/wiki/Jet_pack.

 

[FactChecker]

A simple jet engine pointing down requires a lot more power than the blades do. The way to understand this is to see how each would fall with no power. Each design requires only the amount of power to counteract the descent at the "zero power" speed. With a jet engine and no power, the helicopter would fall like a stone. It takes a lot of power to counteract that. A regular helicopter would fall a lot slower because the blades slow it like a (bad) parachute (see autorotation). It takes a lot less power to counteract that.

Another problem is that the aircraft would be harder to control. The act of keeping upright with a jet engine pointing down requires very fast vectoring. Modern controls can do that, but it makes the stability of the aircraft completely dependent on the control system. Helicopter blades can be above the vehicle, which is stable. The blades pull it up and keep it upright. A jet engine can not be above the vehicle because of the hot exhaust and the disturbed airflow. With the jet engine below, the vehicle is balanced on top of the jet thrust and is unstable.
EDIT: The crossed-out part is the "Pendulum Rocket Fallacy". It is not true. Thanks, @hutchphd .

 

[Lnewqban]

You also need to consider the complexity and expense of one (or more) vertical jet engine capable of way above 1.0 thrust to weight ratio.
Please, see:
https://en.m.wikipedia.org/wiki/Thrust-to-weight_ratio

 

[FactChecker]

Once you put that much power in a "helicopter", it is a shame to not add some wings and get a much faster vehicle. Examples are the Harrier jet and the F-35B.

CORRECTION: The F-35B also uses a large jet-driven internal fan for its takeoffs and landings. It is STOVL (Short TakeOff Vertical Landing). I think it may have some limited vertical takeoff capability if it is light enough.

 

[jrmichler]

Or you can look at batteries and electric power. These people are getting over 250 mile range, vertical takeoff, and vertical landing with battery power: https://www.beta.team/aircraft/. It's larger than you are interested in, but gives an idea of what can be done with batteries and electric motors. They claim a useful load of 1400 lbs or six people. And it has a wing, so could glide to a landing on a total power loss.

If you search the N number (N250UT), it has flown several 1.5 to 2.0 hour flights recently.

 

[berkeman]

These people are getting over 250 mile range, vertical takeoff, and vertical landing with battery power: https://www.beta.team/aircraft/.

WITW? They do indeed claim VTO on their website, but how? I don't see any pics of the configuration for VTO on their website, and don't see any way to either tilt that aircraft onto its tail (plus the tail rotor is way too small for a balanced VTO), or to tilt the rotor.

How does it take off vertically?

 

[FactChecker]

How does it take off vertically?

It looks like it is actually a quad-copter. It doesn't sit on its tail. In the photos, you can see 4 rotors aligned with the two front-to-back braces on the sides. The rotor on the tail is for forward motion after the vertical takeoff.

 

[pbuk]

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

 

[Vanadium 50]

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

Ask and ye shall receive:


The V-22 Osprey, One of the most maligned aircraft in history.

 

[Vanadium 50]

And the AV-8B Harrier:



Vectored thrust engine.

 

[phinds]

In the photos, you can see 4 rotors aligned with the two front-to-back braces on the sides.

You must have X-ray vision or something --- I can't see anything like that

 

[pbuk]

Ask and ye shall receive:

No, not the V22 or Harrier: I have seen at least one of those in VTOL mode with my own eyes. 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.

 

[FactChecker]

You must have X-ray vision or something --- I can't see anything like that

The first photo on their website is clearer. You can see the 4 rotors, but they blend in well.

 

[pbuk]

The first photo on their website is clearer.

Yes, funny how CGI always looks clearer.

 

[berkeman]

It looks like it is actually a quad-copter. It doesn't sit on its tail. In the photos, you can see 4 rotors aligned with the two front-to-back braces on the sides.

Weird. I see that now in the line drawing and overhead pic with the rotors aligned front-to-back for aero flight forward, but the pictures on their website show only bumps in those two braces, not rotors in the test flights.

 

[FactChecker]

Weird. I see that now in the line drawing and overhead pic with the rotors aligned front-to-back for aero flight forward, but the pictures on their website show only bumps in those two braces, not rotors in the test flights.

It's not clear how far along they are in development. It looks like they have a flying plane without the rotors and the final goal is to get vertical takeoff with rotors. But It looks to me as though they still have work to do.

 

[berkeman]

Agreed, but it is an active area of development, so hopefully there will be some systems online in the next 5-10 years. A couple of other links:

https://aerospace.honeywell.com/us/...wjg6GxqYHbrh0va0Pxv51Vv33ZmB1z_kaAjnREALw_wcB

https://supernal.aero/?gclid=Cj0KCQ...JCugFV1reNoKk7j0GAlW4eDLAonyw-ScaAu5xEALw_wcB

 

[pbuk]

They are showing you two pictures, one of an aircraft with little bumps on its wings that can fly, and one of a model (or CGI mockup) of something with 4 "rotors" for which there is no evidence, or indeed direct claim, of its ability to fly. The association of the picture with the thing that flies is deliberately deceptive, and this deception clearly fools at least some of the people at least some of the time.

 

[pbuk]

It's not clear how far along they are in development.

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

It looks like they have a flying plane without the rotors

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

and the final goal is to get vertical takeoff with rotors. But It looks to me as though they still have work to do.

No s**t.

 

[FactChecker]

I do not fault them for proceeding in a cautious, step-by-step development. They are just showing some of their work and ideas. I think the first photo is of a model. It's a concept that definitely can work eventually, but the devil is in the details.

 

[berkeman]

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

Woo-hoo! I'll buy a ride on that baby! How much, and what star date should I put on my calendar? Will I be able to meet Scotty?

 

[pbuk]

I do not fault them for proceeding in a cautious, step-by-step development.

It seems to me that they have skipped straight from blue sky thinking to marketing, without even bothering with a proof of concept.

They are just showing some of their work and ideas. I think the first photo is of a model.

Then why aren't they saying that?

It's a concept that definitely can work eventually.

As is my dilithium crystal warp drive.

but the devil is in the details.

Yeah, those damn details. Evidence is another thing that I find troublesome. Oh and regulators who insist on not deceiving potential investors (of course I don't live in the land of the free to defraud).

 

[jrmichler]

It's not clear how far along they are in development. It looks like they have a flying plane without the rotors and the final goal is to get vertical takeoff with rotors. But It looks to me as though they still have work to do.

On closer examination, that's exactly where they are right now. They are currently flying it in airplane mode. Flightaware shows a 2 hour 5 minute flight on June 26, 2022. That's impressive for a battery powered airplane.

The concept is vertical takeoff in a quadcopter configuration, then use a fifth motor to move it horizontally. The horizontal velocity generates enough lift from the wing to unload the lift rotors, after which the lift rotors are stopped and stowed. The idea of rotors for vertical takeoff and a separate propeller and wing for horizontal flight appears to have originated with Jay Carter. He built a gyrocopter with a wing to demonstrate the concept, and was able to show proof of concept: http://carteraero.com/home2/ and https://en.wikipedia.org/wiki/CarterCopter.

On the other hand, Joby Aviation has a more conventional quadcopter design with tilting motors: https://evtol.com/news/joby-evtol-aircraft-surpasses-150-miles-flight-test/. Since then, it crashed due to a "component failure". But it was flying that day: https://globe.adsbexchange.com/?icao=a6df63&lat=35.882&lon=-121.198&zoom=12.5&showTrace=2022-02-16. Search the N-number N542AJ for more information.

 

[hutchphd]

Helicopter blades can be above the vehicle, which is stable. The blades pull it up and keep it upright. A jet engine can not be above the vehicle because of the hot exhaust and the disturbed airflow. With the jet engine below, the vehicle is balanced on top of the jet thrust and is unstable.

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.

 

[berkeman]

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.

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...

 

[FactChecker]

It seems to me that they have skipped straight from blue sky thinking to marketing, without even bothering with a proof of concept.

I see it as just a webpage to represent their company. They are a small company. Apparently, they have a military contract to develop a quad-copter that converts to regular airplane flight. This is not unusual.

Then why aren't they saying that?

They are just showing where it is heading. They are not asking you for $, so it's not a con job.

As is my dilithium crystal warp drive.

A gross exaggeration. This concept is very realistic. There have been several similar efforts. When battery technology improves, it might be a real winner.

Yeah, those damn details. Evidence is another thing that I find troublesome. Oh and regulators who insist on not deceiving potential investors (of course I don't live in the land of the free to defraud).

I assume that a serious investor can get a lot more information. (Their current effort has military funding.)

 

[FactChecker]

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.

I stand corrected. It is more complicated than I indicated.
Still, it seems to me that the vectoring required to correct a lateral disturbance is better if it points in the desired direction of motion. That seems true in a "puller" position but false in a "pusher" position.

 

[hutchphd]

Source?

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! )

 

[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