0824
This could serve as a manifesto for the SynchroLite, or any new light helicopter for that matter.
In Search of the VolksCopter
The new/proposed Sport Pilot Certification and endorsements opens the door for more people to own and fly recreational helicopters. To achieve this, manufacturers will start producing helicopters that are safer and easier to fly. They then can obtain from the FAA a lower cost pilot's license category for flying this craft. At this point more people will be willing to train and subsequently more people will buy.
The helicopter and the car have many things in common. One is that at some point they will probably be sold and a portion of their initial costs will be recovered. The licenses for both have something in common also; you never get your money back. For the helicopter to gain in popularity the high cost of learning to fly it must come down. This can only happen when helicopters are developed that are easier and safer to fly.
A large percentage of a student pilot's time is spent practicing:
Anything that minimizes the required learning time in these two areas will eventually help to lessen the cost of the license.
The following is an attempt to address and reduce the above limitations. It is not written as a definitive answer but as a means to provoke thought.
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The helicopter pilot's license will be a lot more economical when a light helicopter is produced that is:
1. Easier to Fly
Symmetry of Flight:
The closer the function of flying a helicopter can come to that of flying a plane then the shorter the learning curve. The pilot of a light plane can quite satisfactorily fly and never have to touch the pedals (unless he felt like putting the brakes on). His turns might not look the best and he may have problems with X-wind landings, but he could still fly. The pilot of a conventional helicopter, with a tail rotor, must be extremely competent at mastering the coordination of pedals, collective and cyclic. To over come this limitation the helicopter must be aerodynamically symmetrical about the longitudinal-vertical plane.
Twin rotor configurations meet much this requirement in that the torque imparted to the craft by one rotor is offset by the torque imparted by the second rotor. This eliminates the need for a tail rotor. There is a multitude of arrangements that have been applied, namely vertically separated rotors such as the Kamov coaxials, horizontal separated rotors such as the Kaman intermeshing Synchropter, plus the Boeing tandem Vertol where the rotors are separated both vertically and horizontally.
The coaxials and tandems both eliminate the need for a tail rotor but they do not have absolute symmetry about the longitudinal-vertical plane. Helicopters with laterally separated rotor disks do.
Three such disk configurations are:
* Separated (disk center-to-center greater than disk diameter)
* Interleaved (disk center-to-center greater than disk radius)
* Intermeshing (disk center-to-center less than disk radius)
Quad and possibly ducted rotors (that include reverse direction stationary airfoils) should also give true symmetry.
There is another advantage in not having a tail rotor. All current helicopters, to my knowledge, have their overrunning clutch located between the engine and transmission or in the early stages of the transmission. This is necessitated by the need to drive the tail rotor from the main rotor during auto-rotations. The speed differential between the two rotors also dictates that a portion of the transmission be located in this segment of the drive train to drive the tail rotor at a higher speed than the main rotor. The elimination of the tail rotor allows the overrunning clutch to be located after both the engine and the transmission. Removing the transmission from the rotors during autorotation has an advantage in that the frictional drag of the transmission is removed and the efficiency of the autorotation is improved slightly.
Constant Speed Rotor
Rotor Governor; which incorporates autorotation capabilities.
See: Constant Speed Rotor. 0786
Maybe also See: Elastomeric Collective.
0575Heavier Tip Weights:
The idea here is to have reasonably heavy tip weights that will soffen inputs to the rotor, from the pilot or from the environment. These weight should not so high so as to significantly reduce the response to control inputs.
Strong Blades:
Strong blade will allow;
2. Safer to Fly
Redundancy
There should be redundancy of as many components as possible. This does not mean that the helicopter must have full flying capabilities when a component breaks down. It means the craft is still capable of being controlled and that it has a much larger "foot-print" in which to land than that which is available from autorotation.
Two Engines
A number of current medium and large helicopters have two or more engines. Safety is one of the reasons. This argument is even more valid when flying with a 2-stroke air-cooled reciprocating engine; that has a lower degree of reliability. This is a feature that can be incorporated in smaller helicopters. The helicopter does not have to climb or hover on one engine but it should be able to fly horizontally or at least have a very shallow glide slope and thereby a large area in which to find a landing site.
Two Transmissions
The probability of a transmission failure is much less than that of an engine failure, but having a second transmission adds to the reliability. Having a separate overrunning clutch after each engine/transmission combination means that there can be two completely independent power trains.
Two engines with half the power and two transmissions with half the strength can never weigh half that of the single engine or transmission. This "weight penalty" is not all that great though, since the half size engines and transmissions can be constructed with slightly lower safety factors. This is because simultaneous failures in both power trains will be extremely remote. There is another advantage with 2 power trains, if one breaks down the pilot is going to be more alert in respect to looking for landing sites etc. This way, under the remote circumstances that the second power train does go down, much of the preparatory work for landing has already been done. See Duality:
Multiple Function Components
Having a single part serve multiple functions will result it a lower overall weight. This weight saving can then be used for additional redundancy of components or higher safety factors on single components.
Example: Combined, seat / fuel tank / structural member.
Composites and Light Weight Metals
Weight reduction can be achieved by using lightweight materials and this will also allow for additional redundancy or higher safety factors in the components. Enter calculations from Human powered.
Electronics
The advancements in electronics bodes well for its expanded use in helicopters since the electronic equipment can take over many of the navigation and monitoring functions (list potential functions.) that currently require a high level of pilot expertise. The lightweight of electronics is another positive.
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If a safer and easier to fly helicopter were to come about then the Sport Pilot Certification could be modified to accommodate it. For now the only solution is to try and "cram" as much of the above into an ultralight helicopter that complies with FAR 103.
It would appear that the intermeshing rotor configuration (synchropter) is an ideal platform on which to develop this helicopter. In the words of R.W. Prouty 'The synchropter may be an idea whose time has come and gone. On the other hand, it may have been ahead of its time and just the right configuration for some future helicopter requirement'.
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Date: |
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Rotorcraft - Popular Rotorcraft Association |
Sept 2000 |