First jump takeoff in France

The Cartercopter jump-takeoff Butterfly achieved dramatic vertical takeoffs (Butterfly footage begins at 1:57):


It did so by adding over 20 lb. of depleted-uranium tip weights to the blade tips. This amount of extra mass, as reported by Rusty Nance (gyro test-pilot extraordinaire), made the rotor very sluggish in its response to control inputs.

This makes sense. The amount of force it takes to make a rotor change its orbit (respond to cyclic control inputs a/k/a precess) is determined by the blades' mass, among other things. The force to accomplish this comes from the lift of whichever blade's pitch is increased by the cyclic control input. A blade of given dimensions and RPM is going to make X pounds of extra lift when pitched up by Y degrees of cyclic input. If the rotor is unusually heavy for its size, this Y pounds of force will be inadequate to tilt the rotor disk promptly. Cyclic response will be sluggish and control forces will be high.

The way out of this trap is to make the blades wider or to add blades. Most jump-takeoff gyro builders have done so, e.g. the Boyette-Degraw LFINO used, IIR, double tip weights and three Dragon Wings blades instead of two.
 
I am a bit amazed that depleted uranium is (evidently) available to civilians.
I understand that tungsten is actually more dense than DU.
Sabot tank round "darts" are mainly DU, but tipped with (super hard) tungsten.
 
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Is there a noticeable difference in jump capability depending on density altitude? Can you still jump it on a really hot day?

Eric
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).
 
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I am a bit amazed that depleted uranium is (evidently) available to civilians.
I understand that tungsten is actually more dense than DU.
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.
 
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Evidently DU still has 60% of the radioactivity of natural U.
But heck, it's almost impossible to get even mercury these days. I have an antique clock that uses that in the pendulum (it changes the moment arm with the temperature), and my clock expert tells me there's no way for him to obtain any, should it break.
 
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.
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:
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.

The value of 3.5g also seems to have been an accepted one since it also appears in table 4-2 to the "Engineering Handbook. Helicopter Engineering" (full title below).

There may be newer design codes and requirements but my experience is that these kind of values only very rarely change radically.

It would be interesting to learn how Jim Vanek arrived at his figure for max rrpm.



ENGINEERING DESIGN HANDBOOK.
HELICOPTER ENGINEERING.
PART ONE.
PRELIMINARY DESIGN

Army Materiel Command
Alexandria, Virginia
30 August 1974 table4-2.png
 
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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.
 
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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.
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.

I realize you were just looking for a place to start.

I would not want people to imagine that experimental aircraft are held to the same standards as standard category aircraft by the FAA.

I am required to explain that every time I give someone a ride in an experimental, amateur built aircraft so they understand the risk.

Speaking of Martin Hollmann’s book “Modern Gyroplane Design” there is all the information needed to calculate what is required for a jump takeoff gyroplane.
 
Quote: Is there a noticeable difference in jump capability depending on density altitude? Can you still jump it on a really hot day? /Quote

Below is the plot (velocity and height) for a jump at sea level (rho=0.002344 slugs/cuft) and at a (density) altitude of 4000ft (rho= 0.001676).
Your jump height is less than half for 4000ft. Note that this is a pure jump, no forward speed.
JS_sea_level.jpgJS_12000ft.jpg
 
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:
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...;-)
And yet somehow rotor blade failures are extremely rare in the USA.

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?
 
Kolibri:

Our FAA does not look at all at design calculations. The airworthiness certificate that we obtain for homebuilt aircraft is, in effect, a license to conduct an experiment. At the time my very first Bensen gyro was inspected, the FAA man said "My job is to protect the public from you. I am not here to protect you. If you want to strap yourself to a rocket and set it off way out in the desert, I will give a certificate to do that."

He did complain about the scribe marks on my rotor hub (Bensen put them there to mark the standard pitch setting). I said "The factory puts them there on purpose." He said (Yoda-like) "There is no factory. YOU are the factory."
 
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.

Kolibri
In the US Experimental AB do not have to give any engineering data. The builder is conducting an Experiment. We have this freedom in the US with Experimental Amateur Built aircraft and we REALLY cherish this freedom. The largest growth sector in light aviation is Experimental Amateur Built in the US. The biggest problems in Experimental AB aircraft here is engine failure in initial flight hours according to NTSB because a lot of engine conversions are used in many of these aircraft. The kit manufacturers do have calculations for design and have generally tested their products due to market forces not due to a government mandate. Examples are Vans Aircraft, Zenith Aircraft, Lance Air, Mosquito helicopters, Safari helicopters and many many others. I can build a 6 seat small jet aircraft as an Experimental Amateur Built technically and get the rating to fly it.
 
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.
I'm not even sure that gyrocopter blades are tested in the rotation plane, since a gyrocopter rotor is not supposed to receive the torque from its hub
The pre-launch of usual gyrocopters is not limited by the motor power but by the strength of the mechanical transmission to the hub
200 rpm on ELA 07 requires about 220 Nm
450 rpm with 0° pitch setting requires 440 Nm
500 rpm with 0° pitch setting requires 540 Nm
 
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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.....???
 
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.....???
In my opinion statistical/scaling problem is a completely false argument.

AutoGyro had not made that many gyroplanes when the problem was discovered.

In my opinion it was a poor design of the blade grips and a few people just made some mistakes.

The success of the newer grips and rotor head appears to me to demonstrate how flawed the earlier design was.

The DULV makes mistakes just as the FAA does.

Get over it Jurgen.
 
Mercury was used in gold mining to capture small gold. A lot of it ended up in the waterways of gold areas. To remove the mercury a retort is necessary and it is recovered. I dont eat the local fish for that reason. Mercury is found in nature and the ore is called cinnabar. The silver fillings a dentist has used was a silver copper mercury amalgam. Mercury has been used in vaccines as a preservative and is called thimerasol. Mercury is usually sold in 60lb flasks. The old expression "mad as a hatter" was from the california gold rush days. The chinese would take the felt out of the sluice boxes and chew it to soften it to make hats and injest the mercury. Some old timers would take a potato cut it in half, scoop out a depression, place the mercury coated gold in it close it back up and bake the potato in the fire. the potato absorbed the mercury and the miner would eat the potato.
 
But that clearly is a statistical question, Vance. If you have a flaw in your design it is much more likely to show up if you sell 3000 aircraft instead of, let's say, 30. Or, in the same context, if Boeing had sold just three 737MAX aircraft these would probably still be flying.

Quote: AutoGyro had not made that many gyroplanes when the problem was discovered. /Quote
What time are we talking here, ten years ago or fifteen?

Perhaps you might want to try and get over the fact that currently the world wide market leader in autogyros is a German company...;-)
 
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