Why aren't there more manned quad copter designs?

[larkin]

The quad copter design has become synonymous with the current era generation of consumer drones; however, when you look at military designs, even at a small scale, they are almost all single prop. When it comes to manned aerial vehicles you also don't see much (if any?) quad copter designs. The quad works so well for the consumer market due to its stability. Why is this not a similarly desirable design for manned aircraft and any military UAV applications?

 

[LuvMyTJ]

When you refer to military or the helicopters at first glance you may see only one rotor but looking closer you will see a tail rotor also. The big plus with a traditional heli is that if it loses power it can "auto rotate" to the ground safely (will luck). I believe to get your helicopters airman license you must preform this to pass the test. Better have your leak proof underwear on for that test!

A quad has a major problem should even one of the four motors were to stop. It is like kicking the leg out from under a table, it will fall over.
That hasn't stopped some creative inventors, in fact Ehang plans on taxi service in Dubai coming soon, Jetsons here we come!

 

[larkin]

The pilot safety issue makes sense for why we don't see them in manned forms, much. When I said military I was mostly thinking about stuff like this

I know fixed wing buys you both distance and payload over copter design. It's just funny that consumer drones are predominantly quads but drones everywhere else refers to a different design.

I guess it's a linguistic thing I'm curious about. The term "UAV" use to, and mostly still does, refer to the Predator. Now the term "drone" pretty well refers to quads.

 

[BorisTheSpider]

Yeah it's a pilot and people on the ground safety thing - a quadcopter has zero redundancy and if it loses a prop, motor, ESC, motherboard, battery or any one of the many other completely non-redundant things essential to continued controlled flight is immediately an uncontrollable brick which is why they are unsuitable for flying over people or with people aboard.

Also, despite the inherent mechanical simplicity they are not really efficient when you scale them up to a size that can carry significant loads - once a rotorcraft gets big enough it makes sense to have the complication of a swash plate and tail rotor for the added efficiency but that stuff is not terribly practical when we're talking about lifting a kilo or two.

 

[Wombat55]

I read an article on quadcopter design issues awhile back. Quadcopters don't scale up to larger and heavier sizes very well. One problem is that, unlike helicopters, quadcopters are inherently very unstable and are only saved from immediately crashing into the ground by some pretty sophisticated electronics combined with motion sensors. A hovering quadcopter may look fairly peaceful and stable, but in actuality its little electronic brain is constantly and frantically monitoring its motion sensors, making complicated calculations, and adjusting the speeds of its motors in order to keep itself in the air. The propellers are constantly being sped up and slowed down in order to keep the drone stable. It's a nice trick but constantly speeding up and slowing down the propellers is not very energy efficient. Moreover, the strategy doesn't scale up to larger and heavier propeller sizes very well because the energy efficiency problem becomes larger and larger.

Another problem is that to achieve flight it's more energy efficient for a propeller or propellers to move a lot of air relatively slowly (like a helicopter does) than to move a small amount of air relatively fast (like a drone does). But for quadcopters fast moving propellers are important because for electrionic stabilization to work the propeller thrusts have to respond instantly to commands from the electronic stabilization system. So quadcopters sacrifice considerable flight efficiency in order to have electronic stabilization. That's OK when the quadcopter is a small one like a Mavic. But for a drone large enough to carry a human, the energy inefficiency becomes a really big problem.

 

[Robbyg]

Also using electrical power for a larger aircraft is not efficient and Gas engine speeds are very hard to control precisely enough in order to make it work reliably.

As for swarming unmanned drones and unmanned drones in general I know that the military is very hesitant to get into it too much. Anything that is unmanned can be hacked. Not that much of a problem when your at war with a third world country but it can overnight become useless against a more advanced country. Just look at how Iran tricked the most sophisticated drone in the world to land in their own airspace and be captured.

 

[Wombat55]

Just look at how Iran tricked the most sophisticated drone in the world to land in their own airspace and be captured.

Well, of course, that's their story. These are the same guys who are claiming that their new stealth fighter is ready to enter serial production. I'll leave it to you to judge the validity of their claim and their general truthfulness:

Why Iran's New Stealth Fighter Might Be the Ultimate Paper Tiger

 

[Robbyg]

Well, of course, that's their story. These are the same guys who are claiming that their new stealth fighter is ready to enter serial production. I'll leave it to you to judge the validity of their claim and their general truthfulness:

Why Iran's New Stealth Fighter Might Be the Ultimate Paper Tiger

Since political talk is not allowed on the forum. I will only point out that they do have a perfectly intact latest Gen American stealth drone in their possession. That's not something that they could have done with a manned craft.

 

[AnzacJack]

When you refer to military or the helicopters at first glance you may see only one rotor but looking closer you will see a tail rotor also. The big plus with a traditional heli is that if it loses power it can "auto rotate" to the ground safely (will luck). I believe to get your helicopters airman license you must preform this to pass the test. Better have your leak proof underwear on for that test!

A quad has a major problem should even one of the four motors were to stop. It is like kicking the leg out from under a table, it will fall over.
That hasn't stopped some creative inventors, in fact Ehang plans on taxi service in Dubai coming soon, Jetsons here we come!

You need to be able to auto rotate to get your ticket

 

[AnzacJack]

The quad copter design has become synonymous with the current era generation of consumer drones; however, when you look at military designs, even at a small scale, they are almost all single prop. When it comes to manned aerial vehicles you also don't see much (if any?) quad copter designs. The quad works so well for the consumer market due to its stability. Why is this not a similarly desirable design for manned aircraft and any military UAV applications?

Economy is the basic answer here

 

[Wombat55]

Since political talk is not allowed on the forum. I will only point out that they do have a perfectly intact latest Gen American stealth drone in their possession. That's not something that they could have done with a manned craft.

Not sure that it was perfectly intact, but even if it were it proves nothing about the prowess of the Iranian government to capture American drones. It could have malfunctioned and simply fallen into their possession. Or the drone could even have deliberately been allowed to fall into their hands. Think that that's a completely wild and absurd idea? Yeah, as absurd as the idea of surreptitiously programming Iranian process control computers to damage their centrifuge equipment as part of a secret operation.

The bottom line is that you don't know anything about the drone that fell into their hands except for what the Iranian government officials have told you.

 

[pgitug]

This is when you really hope you don't have any bird strikes

 

[voyager]

The quad copter design has become synonymous with the current era generation of consumer drones; however, when you look at military designs, even at a small scale, they are almost all single prop. When it comes to manned aerial vehicles you also don't see much (if any?) quad copter designs. The quad works so well for the consumer market due to its stability. Why is this not a similarly desirable design for manned aircraft and any military UAV applications?

Well, Airbus just introduced a four-rotor design at the Geneva Auto Salon. The 'clever bit' is not carrying the rolling chassis (with batteries) when it becomes airborne. Btw, this is my maiden post here... "Hellooo from Holland".

Airbus Swears This Pod/Car/Drone Concept Is a Serious Idea, Definitely

 

[voyager]

Here's another picture...

 

[Wombat55]

Well, Airbus just introduced a four-rotor design at the Geneva Auto Salon. The 'clever bit' is not carrying the rolling chassis (with batteries) when it becomes airborne. Btw, this is my maiden post here... "Hellooo from Holland".

Airbus Swears This Pod/Car/Drone Concept Is a Serious Idea, Definitely

Uh, huh. How is it at gliding if one of the four motors goes out?

 

[Kilrah]

There are actually quite a few multicopter-based designs in development. Jsut remember that what can be done in a year at the hobby/unmanned level takes 10-15 years when it's going to carry people.

 

[Kilrah]

Uh, huh. How is it at gliding if one of the four motors goes out?

It's an X8 as written in the material just above.

 

[voyager]

There are actually quite a few multicopter-based designs in development. Jsut remember that what can be done in a year at the hobby/unmanned level takes 10-15 years when it's going to carry people.

Are there any drone manufacturers that are in fact considering scaling up to manned vehicles? What works to carry a camera may work carrying people... Which are the biggest names in manufacturing drones at the moment? Anyone seen this one?

 

[voyager]

... Btw, do five rotors (instead of four) not present the more obvious choice? In the picture you can see that there's a more even distribution of lifting power with a 'pentacopter' if one rotor fails. Even when two rotors show failure (as long as they are not adjacent). Hence, one can imagine rotating the assembly itself, so that left and right are balanced...

 

[Wombat55]

... Btw, do five rotors (instead of four) not present the more obvious choice? In the picture you can see that there's a more even distribution of lifting power with a 'pentacopter' if one rotor fails. Even when two rotors show failure (as long as they are not adjacent). Hence, one can imagine rotating the assembly itself, so that left and right are balanced...

You're just thinking of lifting force balance. You also have to consider torque balance.