Recent content by helisphere

Here is a small stable coax heli that has been modified to fly inverted. Looks pretty stable. https://www.youtube.com/watch?v=l1azqZhWsrU

Possibly it is slightly below his feet but this would still be well above the thrust plane. The empty weight is about 370 lb and the engines are above the rotors.

Yes, it's obviously an issue not easily understood. I don't have all the answers either. Also, if you are talking about semi-rigid, teetering type rotor then the pendelum effect is valid because the thrust vector does not remain coincident to the CG. But still the aerodynamic forces are the...

Here is another example of CG above thrust and it is stable enough for a pilot to control simply by shifting his weight. https://www.youtube.com/watch?v=XJARrc40imk

A pendelum rights itself because gravity generates a moment about a hanging attachment point. That is not the case here, the thrust and weight forces do not generate a moment about the CG and therefore there will be no pendelum or righting effect. The imbalance of forces indicated below will...

if you break it down to just the lift force and the force of gravity, there is not much difference between the CG above or CG below scenarios. That is if you make the assumption that the rotor is rigid enough so that it's thrust vector is always coincident with the CG. Since there are only...

here is a coaxial rotor with CG above, looks pretty stable to me... Listen to the last 30 seconds and see what it says about its stability https://www.youtube.com/watch?v=C_UtPmb3Z-o

PedalPower, Don't let me or anyone else discourage you. If this is something you really want to do then do your homework, find the answers and go for it! I'm not trying to smash anyone's dream, reality has a way of doing that on its own. I'm not your enemy, Love us, hate us, learn from us...

Ok, many of you are asking for more details concerning the real problem. I posted it here, simplified, just to see if I might get a few ideas about solutions. Anyway, the real problem I am trying to solve is: can you make a rigid (helicopter) rotor blade out of wood, rigid hub, all bending...

535 rotor RPM? You don't say what your rotor diameter is but let's say that it's only 25 ft in diameter. That would give you a tip velocity of 535*2*pi*12.5/60 = 700 feet/sec. Typical helicopters don't use tip speeds any faster than this because of sonic compressibility effects and if your...

Simply combining bending and axial loads only works when using the the small deflection assumption. This is obviously not the case here. In this case, the free end of the beam, outboard of some unknown point, is not bending at all and therefore will develop no internal bending moment and no...

Here is a link to a little bit different way of looking at how lift is produced: http://www.aviation-history.com/theory/lift.htm

mheslep, My point was that the model in the video was also unstable but they made it stable and they didn't do it by lowering the lock number. They took a stable reference and made the blades fly to it. Phrak, Yes I think that is probably the best way to go. The problem with big slow...

And if you want helicopter knowledge try this one: buy the printed copy: http://www.esscoaircraft.com/p-30250-bell-helicopter-army-fundamentals-of-flight-1988-field-manual.aspx or here is a pdf copy: http://www.fas.org/irp/doddir/army/fm3-04-203.pdf

Aerodynamics for Naval Aviators is more advanced and uses more math than most of the other pilot training books but is still kept in the realm of understandability for pilots. https://www.amazon.com/dp/156027140X/?tag=pfamazon01-20 Here is a navy training manual...