How fast do propellers need to spin for lift???

Question

I am trying to figure out how fast propellers on a helicopter need to spin for it to lift the helicopter. If it depends on weight, then is there a equation that deals with weight to get the speed it needs for lift? pleaseee help!!!

Answer 1

It depends on the blade angle, The weight to be lifted, The size of the blade, These factors will determine how fast it needs to spin to lift the load!! Yes there is a formula based on these things that will tell you this.

Answer 2

The propellers are like a giant fan...

when they turn off, the pilot starts sweating

Answer 3

That MUST vary from one helicopter to the next. The rotorblade is pretty much a WING that's constantly spinning to create lift.  Different helicopter blades have different sizes, areas and airfoil shapes, and therefore would have different airflow requirements. This speed would also be influenced by the weight of the aircraft.

In some cases there will be a minimum speed dictated by the safe operating RPM for the engine/turbine.

Somewhere about 450mph is an upper 'speed limit' that has NOTHING TO DO WITH the minimum you are asking aout. This 'high speed limit' as roughly the same regardless of the helicopter configuration. The tip speed can go up dramatically (way beyond that presumed 450 design limit) during certain extreme manuevers (rotorspeed + aircraft airspeed). They don't want the tips of the rotorblades to be going 'supersonic' so they set an ideal rotational speed that gives it some room where that is concerned.

The 450mph has nothing to do with the LOWEST speed the blade should spin at.

Answer 4

I just answered a very similar question by anonymous posted just after yours.

the rotor speed is not dependent on the weight of the helicopter.  It is dependent on the length of the blade that will be required to lift the weight of the helicopter.  Ages ago Howard Hughes designed a two-bladed helicopter with blades 75 feet long that had jet engines mounted on the tips.  It never flew, but they did ground run it.  It had a terrible 2-per revolution vertical bounce that almost destroyed the machine and the people working on it. The blades turned at some slow rate of maybe 50rpm, but because of their length, could still provide enough lift to theoretically fly.

As I responded to the other posting, what dictates the rotor speed of a helicopter is the blade tip speed. Designers try to maintain a tip speed of about 450mph.  The shorter the blade, the faster it can be turned.  A Hughes 500, with a 25' rotor disc, can be turned much faster than a SkyCrane, with a 72' disc.  the tip speeds, however, will be amazingly similar.

The trade-off, is that typically, the larger the disc, the more lift that can be achieved.  There is going to be an increase in parasitic drag, which is going to require more power to overcome, which is going to require a larger airframe to contain it, which is going to increase drag and weight, which is going to increase the need for more lift, which is going to require more power....

Answer 5

It depends on numerous other things. How much the helicopter weighs, the size of the blades, the design of the blades, what pitch they are set at, etc. There is no answer to your question unless you get into very specific cases.

Answer 6

A helicopter has NO propeller... it has a rotary wing for lift and a tail rotor to control torque and direction. There are too many variables to consider to give you a correct answer, such as length, pitch and number of wings (blades) of the main rotor.. the weight ( as you mentioned) of the fuselage, etc. that must be defined first.