WHAT'S SO DIFFERENT ABOUT THE HELICYCLE?
IN ONE WORD:
P R E C I S I O N
P R E C I S I O N
P R E C I S I O N
P R E C I S I O N
P R E C I S I O N
P R E C I S I O N
It's quite easy to claim this word, however it takes a bit longer to defend it.
My friend Tom Stuelpnagel, President of Howard Hughes helicopter company for many years and who is also the father of the U. S. Army Apache, once said to me that he thought the most difficult business anyone could be in was the helicopter manufacturing business. He came to this conclusion after many years of engineering and management experience. Tom was a member of the Conquistadors and knew many of the key players in U. S. big business. Tom is a kind and unassuming "type A," (but with a mind like a steel trap.) I don't believe he based his feelings solely on pride of accomplishment, but rather on the fact that Hughes Helicopters was able to maintain a good safety record and hold it's own in a community of much better funded players. (i.e.: Bell Helicopter, Sikorsky, Boeing & Aero Spatiale.)
To put the word precision into better perspective, we'll first make a list of things that relate to it.
1. The sheer volume of parts it takes to defy gravity vertically. In the HELICYCLE(c) main transmission alone there are 32 parts we make from raw materials and castings. 78 operations are performed on these pieces with varying degrees of difficulty and precision. There are 196 hardware items and 25 bearings, snap rings, o-rings and seals
2. The difficulty of making all these parts light enough to fly, but strong enough to last.
3. The level of quality of machine tools required to form each part to perfection. Each component has it's sequence of manufacture, many operations on some, fewer on others. Each specification and tolerance must be precisely held on every step.
4. Precision assembly of transmissions, rotor blades and rotor Hubs must be completed with the mind set of a Swiss watchmaker and the tenacity of a Wolverine. Supporting documentation must be filled out and placed on file.
Okay you say, enough puffery, give us some examples.
WE'LL BE HAPPY TO!
The next time you're close enough to get your hands on someone's kit helicopter, do this....ask the owner/builder to grasp the cyclic and collective sticks and hold them rigidly. With his permission walk out to the tip of the rotor blade and grasp it with both hands, one at the leading edge and one at the trailing edge. Pitch the blade up and down, i.e. around it's feathering axis. In the process, feel the end play generated. Next, oscillate the blade "in plane" (horizontally) and note the freedom of movement you feel between the two blades.
If you perform these tests on a HELICYCLE(c), you will find virtually no end play movement. Why is this so important and why is it so hard to achieve?
As the rotor system rotates, it follows the path defined by the cyclic control. The rotor system needs to be smooth and free of unwanted vibration. For this to be the case, each blade must pass through almost the same slot of air. We say "the blades are in track" when this is the case. When the cyclic pitch is displaced off 90º to the main shaft centerline, one blade climbs and the other dives. The amount of climb must precisely equal the amount of dive. If there is any end play, a disparity of pitch will result, sending the blades out of track and causing undesirable vibration. We're talking very close tolerances here. Less than 1/4 of a degree is going to cause problems. In the HELICYCLE we hover at 5-1/4º so 1/4 of a degree is up to 40 lbs. of lift differential at each blade tip. 90% of the lift is created on the outboard 10% of the rotor diameter. It's imperative that pitch differential be held to a minimum. To achieve this, the inter-connections throughout the cyclic and collective mixing system and the swash plate must be virtually free from end play. Check out the control system in most any certified, 2 bladed helicopter and you'll see why the gulf between kits and certified machines is so wide.
Next, we'll address the in-plane condition. To operate smoothly, the rotor has to be dynamically balanced and once adjusted we want it to stay that way. Certified 2-bladed helo's all have what is called pitch bearing spindles and "blade grips". These units have high quality alignment bearings and are very precisely machined. The result is a near zero amount of "in-plane" play.
In flight the dynamic imbalance forces from a slight amount of play can be magnified by enough maneuvering or gusts, so that a shift in adjustment could take place. As soon as the machine is back on the ground, more balancing adjustments must then be made. In helicopter parlance, this is called "fine tuning". It really should be called "a big headache".
The solution to pitch differential and fine tuning is neither simple or inexpensive. Taking the high road here requires design expertise and the willingness to add some spendy hard to build, precision parts we'd rather do without. To get a better sight picture of how Eagle R & D approaches this problem, send for the video on the HELICYCLE rotor hub ($10).
Next we'll give an example of the precision that must be achieved to create a long life, light weight helicopter transmission. Manufacturing high quality equipment like the HELICYCLE transmission demands the following:
Accurate assembly, sub-assembly and individual parts drawings.
In-process drawings for each stage of manufacturing on each part requiring more than one process.
2. Computer controlled machine tools of several types. (See photos 2 & 5). For the HELICYCLE we use turning and 4th axis vertical machining centers. These machines have a repeatable accuracy of +/- .0001.
3. Additional stand alone machine tools required for individual tasks such as grinding, honing and sawing, etc.
4. Two types of tooling are required:
The tool holders and cutters used in conjunction with the turning and machining operations. This also includes the cutting inserts used in these tools. (A small drawer full of inserts costs thousands of dollars, $10 apiece for a chip smaller than an M & M.) Example: there are 16 tools used in just one machining operation on the main transmission caseing.
Every operation on each part must have some type of fixturing or method of clamping while it is being worked on. In the turning center we use approximately 50 different sets of chuck jaws each of which is designated by part number. For the vertical machining center, tooling fixtures are needed for many operations which require non-standard clamping. The first operations on castings are a good example of this, see photo 3 & 7.
5. Quality control tools for pre & post process tolerance checks must be made according to each parts processing documentation. The HELICYCLE documentation is now close to a stack of paper work 2' high and growing.
6. Precision assembly tools, including presses & special assembly fixtures.
Now that you know the basics, you're probably asking - How does this process work?
We'll use the main transmission pinion bearing housing (photo #6) as an example. Processing is as follows:
1. Saw cut a 5-1/2" dia. 4" long blank.
2. 1st operation on turning center. 100% dial bore check I.D. and O.D. in machine. +/- .0002 tolerance on both diameters. (To achieve these close tolerances without a high scrap rate requires unique programming techniques and very special handling.)
3. 2nd turning operation on back end.
4. 1st vertical machine center operation on face (drill mounting holes).
5. 2nd fourth axis operation to drill and tap oil drain hole.
6. At this point the Timken bearing cones & a precision spacer are carefully pressed in place. Hydraulic pressure is monitored within limits to confirm accurate sizing.
7. A third 4th axis vertical machining center operation pins the spacer and drills an orifice hole so that pressurized oil is fed properly to the pinion head Timken bearings.
8. The part is final inspected for O.D. size and roundness, final deburred, washed dried, oiled and individually bagged awaiting assembly.
Earlier we mentioned that we produced 32 parts for the HELICYCLE transmission. Each part and sub-assembly receives the TLC of the one just mentioned. We hope by now the meaning of the word precision is starting to make sense. We've said it before, the HELICYCLE is not about performance, looks or handling qualities. It's all about an affordable price. Each part in it has to be built for 50% of what it would cost to have it made outside. The best news for our customers however, is not merely that the price is right, but that the parts are right. Precision is not just another word at Eagle R & D, it's our way of life.
#1 RING GEAR CARRIERS READY FOR ASSEMBLY WITH MAIN SHAFTS.
#2 OUR VERTICAL MACHINING CENTER WITH 4TH AXIS.
#3 DRILLING CASE COVER HOLES
#4 DRILLING AND REAMING RING GEAR CARRIER ATTACHMENT HOLES ON ASSEMBLY WITH RING GEAR.
#5 OUR HAAS TURNING CENTER
#6 PINION BEARING HOUSING WITH BEARING CONES PRESSED IN PLACE.
#7 GREEN MACHINING THE MAIN TRANSMISSION CASING IN A TARGET FIXTURE.
#8 USING AN INSERT DRILL TO PUNCH A 1-3/8" HOLE THROUGH THE RING GEAR CARRIER FORGING.
#9 4TH AXIS OPERATION ON MAIN TRANSMISSION CASING MACHINES ALL DETAILS AROUND PERIPHERY OF CASE.