Just to hammer even more on the point – no full size helos currently in production can fly inverted other than in a dynamic maneuver.
There are two main problems with trying to fly a life-sized helo inverted.
The first has already been mentioned – When a helo produces lift the area inscribed by the rotor blades (aka the disc) “cones.” In other words, the tips of the blades are higher than the root of the blades forming what looks like a bowl or a martini glass. In inverted flight, this “coning” would be toward the rest of the helo instead of away from it, so the rotors will likely impact some portion of the rest of the helo. Additionally, while the pitch of the rotor blades is adjustable, for most helos it is limited to flat pitch. (i.e. no negative pitch, so no way to create lift while the rotor disc is inverted.) I believe there is a European naval helo (the lynx?) that allows slight negative pitch to help keep the helo on the flight deck of a ship in heavy seas, but I’m not sure about that, and it wouldn’t be enough negative pitch to support the weight of the helo when inverted.)
The second main problem is that putting the weight of the helo above the rotor disc is much less stable than the other way around. Suspending the weight of the helo beneath the rotor acts as an built in stabilizing force – the body of the helo wants to hang directly below the lift area, so if the rotors are turned, the weight of the helo works as a righting moment. With all the weight on top, any disturbance from vertical would feed on itself until the helo flipped back over.
I also think a lot of the knife edge stuff is doable because of gyroscopic effect of the main rotor taking into account the % of rotating weight and diameter as compared to the overall machine size and weight.
Also the quickness of the blades to react to minute changes causing small motions that are not really noticeable might mean that the machine is actually moving and not really stationary and that is totally forgetting normal air movement of it’s flight environment. A fixed wing can appear to hover if the wind is strong enough.
You’re right. I think I must have been a little sleepy last night when I was writing that. Or at least that will be my official excuse.
I don’t know of any helos that do anything resembling sustained inverted flight. And having no military background, I don’t know much about what capabilities they have. I was under the impression that there were one or two that the military had designed that could handle some negative g’s with blades that could go to negative pitch. I was certain I saw something about that a while back. Now you have me second-guessing my memory.
I must have spoken presumptuously, and I bow to your credentials.
Also, would´t sustained inverted flight also require an inverted fuel and oil pressurization system? It would not seem to be worth the effort to install that in a helicopter, military or not. In a jet engine, the fuel problem probably doesn´t exist but aeorbatic piston engine planes need an inverted fuel system.
I am not a pilot or anything, but I believe military fixed wing aircraft are also not capable of true sustained inverted flight; their jet engines will have problems with oil pressure rather quickly, I would think.
There also seems to be litte practical use of sustained inverted flight, aside from aerobatics.
All full size modern helicopters use a Turbo Jet engine. There is a good thread on turbojets in GQ. Even the old army Chinook uses turbo jets, and 5 transmissions to get the power to the rotors (at least that’s what the flight engineer told me, what a ride).
I’m glad we got that up-side down flying thing cleared up, it was bugging me.
Jet engines don’t have an oil sump like the typ internal combustion engine does. I’m not sure how and how much lubrication is needed, but a jet engine will need much less because there are so few moving parts.
Lubrication likely comes in high pressure lines and is recirculated from a cooled oil tank. There is no air in that system, so the attitude/angle of the engine is a none issue.
I know almost nothing about internal combustion engines, but many jet engines most definitely have gravity sump type lubrication systems. (For helicopters, you also need to move around quite a bit of transmission lubricant as well.)
And while jet engines may have comparatively fewer moving parts, them parts is moving pretty quick – tens of thousands of rpm for the gas generator and power turbines, anyway. Loosing oil pressure in a jet engine means you will be loosing the engine very soon after.
Bojangles, thanks for the response. As soon as I saw “15mb”, I knew it was over my company’s e-mail limit. I kept on trying various searches on the pilot’s name and found a Quicktime version.
