UFO Helithruster

[birdy]

Mite want to study ina bit more detail the forces that balance rrpm M&M, coz its obvious its not real clear.

[MadMuz]

Well, I am happy to learn Birdy. Are you saying that it is perfectly ok to unload the rotors of a 2 blade teetering gyro in flight? Is it ok to have your rotors slow below the normal flying speed because something else is carrying the weight of the frame, instead of the rotors carrying the machine? I will eagerly await your explanation

[birdy]

You seem to be pretty handy on this net thingy muz, and you spend alota time onit, so as i suggested, get a deeper understandn of autorotation, and you mite even find you could safely drive your alternater off the rotor ( not that thered be any gain in anythn but complexity).No point in me tryn, i know how thatd work out.

[MadMuz]

I have a pretty good understanding of autorotation, I just want to see if you are willing put in writing that it is perfectly ok to unload the rotors on one of our 2 blade teetering rotor systems in flight using some sort of lifting surfaces on our frame or canopy.... which will result in the rotors slowing whilst the machine is in cruise, as the lifting surfaces will be carrying weight, instead of the rotors carrying the weight....

[bones]

I have a pretty good understanding of autorotation, I just want to see if you are willing put in writing that it is perfectly ok to unload the rotors on one of our 2 blade teetering rotor systems in flight using some sort of lifting surfaces on our frame or canopy.... which will result in the rotors slowing whilst the machine is in cruise, as the lifting surfaces will be carrying weight, instead of the rotors carrying the weight....

[gyroo]

I might as well be the circuit breaker here!We all know that rotor speed is dependent on the load it is being required to lift - a 2 seat gyro carrying 2 heavy dudes and full fuel will have a noticeably higher rotor rpm than the same machine flying one-up with a lightweight pilot and only a small amount of fuel. Muz argues that taken to it"s logical conclusion, if you are not asking a rotor to generate any lift, then it won"t be capable of generating any rotational effect by autorotation. Certainly with our existing rotor configurations, that statement would be true.Birdy argues that the self-regulating process of autorotation is quite robust and capable of developing high torques (ie rotation that is difficult to stop), and that statement is also true. There are a number of ASRA members whom I won"t name who have personal experience of how - if autorotation is present and established - that a bearing that is practically smoking and squealing still won"t lock up while airborne but will seize up after landing in only a few rotor revolutions.I"ll play King Solomon here and express my belief - I can"t see any great harm or hazard in potentially relieving a rotor of say, 10, 15, or 20% of the weight load it would normally be required to carry. Of course, as I wrote the other day, the very fact of putting supplementary wings on a gyro is gonna naturally increase both the weight and the parasite and induced drag, so whatever potential reduction in disk loading you could get is gonna be gobbled up anyway because the machine is now heavier and draggier. Whatever reduction in rotor loading is achieved is naturally gonna slow the rotor, but by what percentage I can"t be bothered to calculate. Perhaps the US Army"s prohibition of flight at less than 0.5g in 2 bladed teetering-rotor helicopters might give us useful yardstick. Does this translate to a rule of thumb that cruising-steady-state disk loading could be reduced likewise up to 50% without being overly hazardous? I don"t know, and I"m not asking anyone to slow their rotors to try to find out either. As I also wrote the other day, the Carter Copter has a significantly reduced rotor in faster forward flight, but it also has extremely heavily tip weighted blades. Remember that Carter video from 2009 that showed the astonishing vertical ascents by that modified Butterfly? Never once in that video was the gyro shown doing tight turning maneuvers - most likely because it simply wasn"t capable of doing them with such a heavily tip weighted rotor.I don"t agree with Muz"s concern about "blowback" in a steady-state reduced-disk-loading situation, because that"s conceptually putting the cart before the horse. Blowback (as it is often known in gyro circles) is more routinely called "flapback" in rotary-wing textbooks and is simply a description of the tendency of any rotor in translational accelerating flight to tilt the front of the disk up because of dissymmetry of lift unless the pilot deliberately or subconsciously cancels the effect out by forward stick inputs. If there"s no further acceleration, there"ll be no further blowback or flapback. Like autorotation itself, the blowback or flapback is a self-regulating and amazingly stable phenomenon.Muz may perhaps be concerned with what rotary aerodynamicists call "weave", which is sort of like flutter contained within a rotating system. I don"t share his concern that a modestly reduced disk loading will necessarily lead to the onset of weave.That"s why I"m siding more with Birdy than Muz in this discussion!Cheers,Mark R

[Tim]

"Unloading" the rotors is a very complicated subject, with many variables coming into play.I have seen many different and varied machines with 26 ft blades (for example) ranging from a lightweight Rotax 2 stroke machine to a two seat Subaru. The Rotax turned 290 rrpm and the Subaru 390 rrpm. Both seemed to perform safely. If the Subaru machine had a small wing to supply enough lift to reduce the rrpm to 290 then it"s safety margin would be no less than the 2 stroker (given the same conditions). One disadvantage of the wing would be that as speed increases, so too does the lift, and higher speeds is one instance where you don"t want rotors further slowing. Rotors are really quite fragile and gain the largest percentage of their structural integrity from centrifugal force. Hence the use of heavy tip weights on higher performance machines (amongst a few other reasons). Personally I would not advocate the use of auxiliary lifting devices without full understanding of the rotor system (which very few have) and its requirements for operations under a wider range of rotor speed limitations.

[gyroo]

Bravo Professor McClure,Well put. For the record, lest it be thought I am advocating supplementary lifting devices (stub wings) on our gyros - my contribution to this fairly interesting discussion should be interpreted as firstly, injecting a bit of textbook knowledge into the discussion, and secondly, making it fairly clear (I thought) that such devices would be impractical on our gyros.Mark R

[MadMuz]

I guess carter copter concept should never have worked huh

[GraemeMonro]

Muz, you made one point a couple of times in the above post that I will support you 100% in.Graeme.

[bones]

What I find sad, is that novices will read thread like this and they will see that sill me, is trying to tell the guru"s that gyro rotors should never be loaded any less than .5 G and should never be totally unloaded in flight, and you guys are arguing that I am stupid, of course wings can help a gyro go faster.... This is almost on par with when Bird said that he is happy to land his machine, lock the stick forward, walk away from his machine with the rotors still spinning, get in the ute and drive to town, while the rotors are still spinning (but its ok, the machine is parked behind trees) the machine doesn"t have to be behind tressSo, Birdies followers (worshippers) "get from that thread that stupid Murray reckons you have to stop your rotors once you have parked your machine.... what an idiot.... and he reckons you have to tie them to Pfffftttt... Birdy would never tie his rotors, he has a stick lock.... if you have a stick lock, you don"t need tie them...."If it set up right you can, I do it all the time also, would have thought that with ALL your years of knowledge and flying experience you would have worked this out also, or just google it

[birdy]

See, i havent said a damn thing, and M&M is already pissed at me.

[gyroo]

Alright disciples,This thread and discussion has just about run its course. If anyone is going to draw any conclusion out of this discussion either in the present day or if an electronic archaeologist is trawling through sometime in the future, I reckon that the "consensus" that can probably be extracted from all this is that OUR GYROS just don"t need supplementary lifting surfaces and that the fitting of any such devices (stub wings, etc) with our present either un-tip-weighted or only moderately-tip-weighted rotors is probably not advisable because of the raft of uncertainties that have been enthusiastically and robustly discussed.I"ll close off by re-iterating that if the US Army prohibits manoeuvring that will expose a 2-bladed teetering rotor system to 0.5 g or less, then that"s good enough for me. They are the experts from many millions of operational hours over many decades. ASRA should also perhaps promote the idea that any manoeuvring that tends to expose our autorotating teetering rotors to between 0.9 g and 0.5g should be avoided, and enthusiastically promote that operations should always be conducted at 1 g or slightly above 1 g (during turns) or even into the 1.1 g, 1.2 g or transiently even a bit higher (in quick stops at altitude or during landing flares). This is not to say that people should shudder with fright or jam up on the controls in terror when they sense their gyro is going slightly negative due to transient turbulence and thermals - there"s no need to panic - one just needs to be aware that in such reduced g situations your rotor won"t generate the same amount of mast tilting moment

[asra]

I think Mark what should be explained is that the low "G" situation is not so much the killer but what the pilot does during low G and how the dynamics of the gyro i.e. how the thrust line, vertical and horizontal surfaces, dictate what happens next.Its the large cyclic inputs during low G that are the problem, especially with tail heavy blades, and its the propeller thrust line that dictates where the airframe will go when rotor thrust is diminished. I tend to think people still believe the rotor bends down and chops the tail off during low G,not the other way round.Tip weighted blades don"t hold on as well in a flare I have found. They take to long to speed up when the stick is pulled back. On the other hand once they have been sped up they do hold on.And Birdy is right, some people still don"t get it.

[RickE]

Just as a matter of interest i got in touch with a bloke in the US that flies an Arrowcopter which Im sure everyone knows has a small "stub" wing style undercarriage. He says that the "wing" design gives him 200lbs or 90 kg of lift which in turn gives him a higher cruise speed and he describes a much greater ground effect on landing.It would obviously depend on the conditions but he believes during cruise he has a rotor rpm of around 350.My Cavalon which would be a fairly similar weight cruises with a rotor rpm of around 360.It seems to me that if i could negate the weight of a passenger with a device that gave extra lift that would be a good thing.Or maybe i should just shutup and go flying!