Can Helicopters fly upside down?

The key has been touched upon a couple times here. When a rotary wing aircraft's attitude exceed 90 degrees from horizonal it must maintain positive G's, allowing only momentary successful flight beyond that 90 degree point. Helicopters such as the UH-1, OH-58, AH-1, etc., with their two bladed, semi-rigid, underslung rotor head (my old friend Rex Reinl used to call it the semi-ridiculous rotor system) will encounter a condition called mast bumping when the rotor disc is unloaded (approaching zero G's). At normal RPM (approx. 320) the hub of the two blades contact the mast approximately 11 times per second, which is about how long it takes the rotor to become a free flying frisbee and the fuselage to achieve the aerodynamic properties of a brick.

A maneuver called return to target will be familiar to gun ship pilots. That maneuver pushes the limits of the above named aircraft when it comes to unloading the rotor system. There are other things that can induce mast bumping, and in fact, I lost a friend in 1980 who lost his rotor right in front of me while he was doing emergency maneuver training in a UH-1H. All four in the aircraft died.

The fully articulated rotor system, as used in the UH-60, AH-64, etc., etc. are not subject to mast bumping and therefore can unload the system without catastrophic results. However, rolling a UH-60 in CONTROLLED flight does require maintaining positive G forces throughout the maneuver, which, of course, requires quite a lot of spare altitude, because some power must be applied throughout.

I never rolled a Blackhawk because that was against regulation AR-95-1.

Lift counters gravity/ thrust counters drag, until you are inverted,

Flight Engineers

Flight engineers, of this thread, have been heartily, discussing, their theories concerning flight. A lot of those statistics, and theories, are fare above some of us folk's knowledge, and Most of us will never see them in practice.

I’d like to offer a more common flight phenomenon, for discussion, one that most of us have seen, the bumblebee. Any engineer, can indisputably prove that it’s impossible for a bumblebee to fly. Since those engineers have no way to convey that information to bumblebees, the bees just fly anyway.

Would any of the engineers on this thread, care to comment on that Phenomena?

I do not doubt several helicopters may be able to fly inverted (for a brief period), but in order to do so they will have to have had the oil system, fuel system, both set up to maintain positive pressure in the correct direction. Most oil systems are not under pressure, and to turn them upside down would allow the oil to run out and cause damage to the engine..

"Would any of the engineers on this thread, care to comment on that Phenomena?"

Bad assumptions!

73,
Rick

H Richard said:

I do not doubt several helicopters may be able to fly inverted (for a brief period), but in order to do so they will have to have had the oil system, fuel system, both set up to maintain positive pressure in the correct direction. Most oil systems are not under pressure, and to turn them upside down would allow the oil to run out and cause damage to the engine..

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For the same reason, older airplanes with engines using traditional carburetors cannot stay inverted longer than a few moments, as the float system of metering fuel isn’t pressurized.

This is why specialized aerobatic aircraft usually have fuel injection.

Not too long, anyway...

1. As for inverted flight in helicopters, note in the video of the AH-64 the rotor disc always has a positive cone to it, indicating that power is applied throughout those maneuvers beyond 90 degrees to horizonal.
2. It's correct that many aerobatic aircraft must maintain positive G's because most of their systems rely on gravity for proper function. Some, like the Citabria, in which I have a few hours, can maintain negative G flight for short periods without oil starvation. I don't remember the time limit.
3. I'm no flight engineer (just an amateur aerodynamicist), but when it comes to bees and humming birds, it all comes down to the basics. Lift over Gravity, and thrust over Drag. They are some of nature's finest hovering aviators, but they do comport with the laws of physics.

Some of my favorite topics are Gyroscopic Procession and Rotational Velocity, both of which are extremely important in R/W flight.

Bumblbee flight?

The flight engineers, still, haven't commented on the flight of bumblebees.

Chubbo said:

The flight engineers, still, haven't commented on the flight of bumblebees.

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How about this??? [ame]https://www.youtube.com/watch?v=M93qXQWaBdE[/ame]

Chubbo said:

The flight engineers, still, haven't commented on the flight of bumblebees.

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As has been stated before, the basic laws of aerodynamics apply: Lift over Gravity, Thrust over Drag - Lift greater then Gravity, you go up; Thrust greater then Drag , you go forward. Bumblebees beat their wings at >200 times/second. That’s power (read Thrust) and with enough power you overcome Drag and Gravity. The power of their beating wings cause a density and pressure change in the localized air around them. With the increase in localized air density, lift forces increase.

So, bumblebee fly, - and ballistically bullets shoot from barrel and rockets reach the Moon.

It’s all about Power.

I give up! Anything that's observed happening, can be declared possible, That's a no-brainer.

My question was, according to the laws of physics, it is impossible for a bumblebee to fly, just as it is impossible for a rat dumpling to roll uphill. If you consult the laws of physics, would you agree? This matter was merely friendly bantering.

Hopefully no offense was taken.

I asked Alexa; "how do bumblebees fly?"

Alexa: "Our friendly neighbourhood bumblebee has asynchronous flight muscles (i.e. one nerve impulse for several muscle contractions) that are innervated by tergosternal muscles (upstroke) and dorsal longitudinal muscles (downstroke) i.e. it utilises the second method – indirect flight (King et al., 1996). Bumblebees’ wings may be small and heavily loaded, but they are still able to generate significant lift through several cumulative aerodynamic principles. The most important of these is the production of a ‘leading edge vortex’ on each wing (Dickinson et al., 1999).

As the bee’s wing moves through the air (translation), the air flow separates upon crossing the leading edge, but reattaches before reaching the trailing edge. This leaves a sort of air bubble, stimulating the formation of a vortex (a circulating ‘parcel’ of air) that is situated on the dorsal surface of the wing near the leading edge. This vortex generates lift perpendicular to the plane of the wing (‘normal’ force). It sucks in air, accelerating it downwards at high velocity, however, the area it is being sucked into is at low pressure (Bernoulli’s Principle) and it is this low pressure above the wing that provides the lift."

The girl knows her beeswax.

Rustyt1953 said:

I asked Alexa; "how do bumblebees fly?"

Alexa: "Our friendly neighbourhood bumblebee has asynchronous flight muscles (i.e. one nerve impulse for several muscle contractions) that are innervated by tergosternal muscles (upstroke) and dorsal longitudinal muscles (downstroke) i.e. it utilises the second method – indirect flight (King et al., 1996). Bumblebees’ wings may be small and heavily loaded, but they are still able to generate significant lift through several cumulative aerodynamic principles. The most important of these is the production of a ‘leading edge vortex’ on each wing (Dickinson et al., 1999).

As the bee’s wing moves through the air (translation), the air flow separates upon crossing the leading edge, but reattaches before reaching the trailing edge. This leaves a sort of air bubble, stimulating the formation of a vortex (a circulating ‘parcel’ of air) that is situated on the dorsal surface of the wing near the leading edge. This vortex generates lift perpendicular to the plane of the wing (‘normal’ force). It sucks in air, accelerating it downwards at high velocity, however, the area it is being sucked into is at low pressure (Bernoulli’s Principle) and it is this low pressure above the wing that provides the lift."

The girl knows her beeswax.

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Thanks for mentioning Burnoulli, Rusty. All the other information you brought up is well within our basic understanding of physics as well. The bee and humming bird operate in a different manner than helicopters. Early experimenters of vertical flight tried to imitate those creatures but were wildly unsuccessful because they didn't understand the mechanics (that you pointed out) of that method. It turned out that it was impractical. The rotating airfoil, which of course insects and birds don't use, was the answer.

As for the call for response from flight engineers, I think who you are really looking for are aerodynamic/aeronautical engineers. I am not one, but I have studied the subject for 40 years. That does not make me an expert, by any means.

Chubbo said:

I give up! Anything that's observed happening, can be declared possible, That's a no-brainer.

My question was, according to the laws of physics, it is impossible for a bumblebee to fly, just as it is impossible for a rat dumpling to roll uphill. If you consult the laws of physics, would you agree? This matter was merely friendly bantering.

Hopefully no offense was taken.

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“…….. according to the laws of physics, it is impossible for a bumblebee to fly ………”

I think you are looking for a “yes” or “no” answer.

If so, the short answer is no, they do not “violate “ the laws of physics.
It is a myth that bumblebee, and hummingbirds for that matter, fly beyond the realm of Newtonian physics. They do not fly in the conventional manner of fixed wind or rotary wing aircraft where Wing surface area, relative airflow velocity across an airfoil and payload(weight) are significance parameters. They fly and the laws of physics can explain how, they just do it differently.

Hopefully that answers your question.

A friend that drove helos in the Army says yes they can do loops if needed. He flew mainly Hueys and Apaches.

AJ said:

A friend that drove helos in the Army says yes they can do loops if needed. He flew mainly Hueys and Apaches.

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AH-64, yes.
UH-1A/B/C/D/M/H, no.

Mark8 said:

As others have said, current production helicopters can only do it as part of a roll, but it's only a matter of design of the aircraft. RC helicopters have been doing it to the extreme for years.
Alan Szabo Jr. ALIGN Trex 650X 7/16/2021 - YouTube

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You sure that is real? Looks pretty CGI to me...

BC38 said:

You sure that is real? Looks pretty CGI to me...

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There are major international competitions (US included), and Alan Szabo Jr. is quite a celebrity in the sport.