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JT-5 Autogyro

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These pages have been created to help builders in various countries to complete their JT-5 autogyro project. I shall add new pictures and text every now and then to explain details and answer builder questions. So, the pages are a kind of a FAQ pages.

 General layup information:

For those who have never used epoxies I have included SP Ampreg 20(TM) data sheet, which gives very valuable information to use any epoxy.

Glass/epoxy layup and vacuumbagging involves a myriad of tricks and tips. Most of them, I belive, are explained in good books available from EAA and similar sources. And there sure are many new methods I dont even know.

One essential know how is how to roughen the previous glass layup surfaces before continuing to the next layup or bonding step. This a very important step since the bond between the two layers will be very poor unless the roughening is properly made. Two methods are in general use:

1) You can roughen the surfaces by sanding them. Sanding will remove the glossy epoxy surface and lift tiny glass filament tips up from the surface. However, too much sanding will weaken the fabric by cutting too many threads. This was the method I used in making my JT-5 autogyro fuselage pod, fuel tank, tail surfaces and blades.

2) A new method developed by the glass sailplane industry on the seventies is to layup peel ply, nylon fabric on the free surfaces later to be bonded to another surface. You peel off the nylon fabric after curing. This is a fast and easy method and does not harm the glass fabric below. You can also combine these two methods.

Glass content in hand layup:

The strenght of the final glass layup laminate depends on filament orientation and what is the glass content of the layup. It may vary videly, say 30....60 percent when unidirectional rowing is used. The glass percentage and filament orientation are especially important on highly loaded unidirectional laminates such as rotor blade spar and landing gear legs. However, reaching high glass content by hand layup is difficult. You may try to copy techniques used by the industry, like pulling the unidirectional rowing through a liquid expoxy bath and then through a tight nozzle which removes excess epoxy. Anyway, to reach a glass content of 50 percent should be the goal.
If you are unsure of the final laminate strenght, make samples and specimens and carry them to a test loading facility. I test loaded my rotor blade root design with several samples. The maximum sentrifugal load for the blade roots in my JT-5 would be about 5 metric tons (high speed pull maneuver, 600 rotor rpm) and the roots were strong enough to carry over 15 tons load.
Another testing method I highly recommend to anyone building his first set of rotor blades: Instead of actual flying, test run the blade set on the ground. Tie down your gyro very securely on a truck platform and step into the cockpit while your fellow drives the truck. Start slowly and increase the speed slowly until you have reached, say 600 rotor rpm. You dont need to go very fast, about 60 kmh may be enough. Move the stick aft/forward and watch the rpm gauge. Thisway you can test several things at the same time: Blade strenght, rotor vibrations, rotor tracking and the absence of blade flutter.

More pictures on the fuselage pod construction:
Notice, that aft part of the pod is a separate non load carrying structure attached by screws (not shown) to the main pod part. Although the aft part is shown here as 10 mm thick (due to modeling simplicity) it should be made as a 1 mm thick glass/epoxy laminate. Most of the seat and tank corners and edges were rounded in a real fuselage although shown here as sharp edges.
All the fuel tank side walls were laminated first (both inside and outside for perfect sealing), intake tubing was added as well a drain walve and finally tank cover was laminated on on top of the tank using a aluminium sheet as a template (outside, of course. It was removed after curing).

Notice the two tunnels going through the tank, one for the airframe keel tube and one for the throttle and prerotation cables.

Notice that I have created new Pod and Canopy sections!


Questions and Answers:

Q: How do the landing gear secure into the tubes?
A: Landing gear is secured by drilling a small (5 mm dia) bolt through the tube and gear leg at the upper end near the mast. This prevents the gear leg to rotate or drop.

Q: Would you be able to send me weight and balance info, please???
A: Weight and balance are easy in a gyro. You hang it fully loaded (yourself in the cockpit with full fuel) from the teetering bolt using a lifting tackle. If the mast angle is about 10...12 degrees to vertical (nose down attitude) your balance is OK. You can see this angle on the main drawing showing the medium CG position.If you hang it empty the mast should be vertical or some degrees in nose up attitude. You can weigh the machine in this occasion as well if you have a suitable spring scale. The preferred empty weight is about 170 kg (like my prototype machine) but the other JT-5 gyros in Finland are closer to 200 kg.

Q: What is the gyro performance at higher elevations and temperatures?
A: Autogyros are quite sensitive to density altitude and gross weight. If your location is above 3000 ft MSL and the summer temperatures are very high plus the gross weight of the machine is much over 300 kg I recommend to install 2000 ccm VW engine. I had 1700 ccm VW but Finland is a cool country in summertime and cold on wintertime and my weight is 165 lb.

Q: In vacuum bagging the cockpit, is this the correct sequence? I've done a lot of glass work over the years, mostly with cars and boats and lately a camper roof, but this will be my first entry to the vacuum bagging world.

Generate Male Plug,
Pull Female Mould,
Vacuum in outer skin,
Vacuum in honeycomb,
Vacuum in inner skin,
Add seat and tank.

A: Generally correct except one point, you should vacuumbag the outer skin and honeycomb together to get a good bond. A special type of honeycomb is needed which will bend and adapt to double curvature surfaces. You should prebend the honeycomb to the pod shape. I did not vacuumbag the inner skin but it may a better choice to do. If the corematerial is plastic foam instead of honeycomb the inner skin does not need vacuumbagging.

Q: How do you feel about bronze welding (Sifbronze) instead of regular welding for the airframe?
A: Welding is the safe way to go. I have not yet heard of an airframe made with bronze soldering?

 Technical Photo Gallery:

 JT-5 3D model. To view some construction details, I have modeled the JT-5 autogyro using formZ RenderZone modeling software. The model even includes the Limbach engine and a pilot (me!) and shows details down to the nut and bolt level. Make a visit to my 3D page.

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