wolfy
Gold Supporter
Great article XXavier.
wolfy
wolfy
On a hot day, with no wind, at high elevation, and with heavy load, the jump is less enthusiastic. In practice, that gives you a jump ceiling that varies with wind and load. If you are above that density altitude, you do a short run before liftoff. You pre-spin with full power while sitting still, disengage the rotor drive clutch, then release the brakes (with a tap on one or the other as necessary to steer), for a quick dash at full throttle and flat collective, position the cyclic stick, then pop in the pitch, and off you go. This all happens very quickly. Unlike conventional gyros, the run is NOT to gain rpm. In flat pitch, you will actually lose a little rpm during the run. Instead, the purpose is just to get some airspeed before adding collective. 30 mph is usually sufficient and that doesn't take long to reach at full throttle (just a few seconds for the whole process from clutch disengagement to lift-off).Is there a noticeable difference in jump capability depending on density altitude? Can you still jump it on a really hot day?
Eric
Cadmium plated depleted U weights used to be pretty common, seen in Boeing civil aircraft and even as boat keel ballast. It wasn't as tightly regulated as you might expect, because if you were evil and wanted to make something nasty out of it, it's a really poor starting point. Being much less radioactive that what you can dig up in nature, it would require significant enrichment just to reach the natural state. Of course, it would still be toxic to ingest, like many other metals, purely as a chemical issue, radioactivity notwithstanding. I think you could easily get a permit from the Feds to use it (perhaps from the NRC?) without many hoops or much fanfare.I am a bit amazed that depleted uranium is (evidently) available to civilians.
I understand that tungsten is actually more dense than DU.
It is not only the centrifugal stress that must be taken into account for the jump takeoff, it is mainly the over-torque applied by the hub to the blade roots: Between two and three times more than that of strong pre-launch of a standard takeoff.You would have to make sure that you stay within the limits of the blade's design load, which used to be 3.5 times the maneuvering load ( as per FAR 27.337, not sure whether this is still the case), i.e. the blade is designed to support 3.5 times the gross weight of the aircraft. From my understanding you would first have to calculate the maximum acceleration during the jump. You could modify the jump takeoff program I mentioned earlier to calculate the acceleration from the jump speed vs time history. Let us assume that the maximum acceleration is 1.25g
Now for the rotor the overspeed load increases with the square of the rotational speed. Assuming that normal flight rrpm is 370 then the overspeed of 430rrpm, which Michel uses, results in an increase of the load by (430/370)² = 1.35 or 35%. Combined with jump load this gives (1.25 + 1.35) = 1.6g, which would still give a comfortable margin of safety. These are some general engineering calculations but I am not a rotor designer so additional considerations might be required. I am looking forward to the comments of the experts.
There is no “FAA approval” required for experimental, amateur built aircraft beyond getting an airworthiness certificate.Quote:
In my opinion Far 27.337 is not applicable to the rotor blades of an experimental gyroplane.
According to Jim Vanek the maximum rpm limit for my 30 foot sport rotors is 450.
/Quote
Martin Hollmann has based the HA-28 rotor blade design for his "Sportster" gyro on 27.337 as he explained in his book "Modern Gyroplane Design" Edition 2.1 1992 page 30. Since a couple of "Sportsters" have been built his design seems to have gotten the required (FAA?) approval.
And yet somehow rotor blade failures are extremely rare in the USA.Quote:
There is no “FAA approval” required for experimental, amateur built aircraft beyond getting an airworthiness certificate.
There are no requirements for rotor blade strength on experimental amateur built gyroplanes.
/Quote
So you can get an airworthiness certificate without presenting the tiniest bit of information on how you arrived at the dimensions you used?
The sounds a bit like a 007b, a license to kill yourself...;-)
Quote: It is not only the centrifugal stress that must be taken into account for the jump takeoff, it is mainly the over-torque applied by the hub to the blade roots: Between two and three times more than that of strong pre-launch of a standard takeoff. /Quote
You can calculate the bending stress during pre-rotation from the maximum engine torque but things get a little involved as the rotor acceleration is probably not constant so you will have to find the point where the von Mises equivalent stress from bending and tension (centrifugal force) is a maximum.
Quote:
three times more than that of strong pre-launch of a standard takeoff.
/Quote
How did you arrive at your figure that stresses from overspeed are that much larger? The engine torque is the same for normal pre launch or jump takeoff if we limit the consideration to the same aircraft. You do mean bending stresses at the hub, don't you?
One other point is that the overspeed only begins when the rrpm is already at or beyond normal operation and at that point the centrifugal stresses are already very large.
As I said, I'm talking about constraints of rotation torque on the blade roots.How did you arrive at your figure that stresses from overspeed are that much larger? The engine torque is the same for normal pre launch or jump takeoff if we limit the consideration to the same aircraft. You do mean bending stresses at the hub, don't you?
One other point is that the overspeed only begins when the rrpm is already at or beyond normal operation and at that point the centrifugal stresses are already very large.
In my opinion statistical/scaling problem is a completely false argument.Quote:
As I remember the last big problems with rotor blade cracks were on AutoGyro products that had been engineered and approved in Germany.
What happened?
/Quote
Probably a statistical/scaling problem. If you have sold that many aircraft, chances are that some will develop a problem. How many times more aircraft has AutoGyro sold worldwide than all US companies combined... 5 ... 10 ... 15 ..... 20 ....more.....???