Suggestions to Preston Briggs
This site was last updated on February 15, 2008.
Tony Huber, Jeffrey Rein, and friends have been working on a new shutoff. These are pictures of a couple of their prototypes. (The lastest information is at the bottom of the page.) Jeffrey writes:
I had a flyaway in Houston with a string-over-the-wing shutoff last year, dragging a full set of lines. I gave many of my friends quite a scare, and I don't want to repeat it again. I started working on a shutoff that had a lot more tension than the one I was currently using. The string over the wing was already at its limits, without loosing its ability to land the plane with control to the bellcrank. This meant a design change.
Ken and I worked on a pivot concept that showed good promise, but I wanted to explore all ideas before making a commitment. I borrowed a sliding bellcrank from Steve Stewart and, after evaluating it, I decided that for simplicity, weight, and functionality, it was the way to go. Working on the design with me were a machinist and friends with backgrounds in small parts and model making, engineering, NC control, and a combined 160 years of modeling experience. The shutoff that we have now is configurable for Fast and Speed Limit with a 4-pound torsion bar, F2D (which is shown below) with a 2-pound torsion bar, and a 1/2A version in the works that will have a torsion bar between 12-16 ounces. I am installing them internally to show that it can easily be done.
The goal is to supply an extremely reliable shutoff to anybody that wants one at a reasonable price. As more test data comes in, I will update this information.
An update: Two dynamic tests have been successfully completed. The handle was released on an 80MPH plane in Arlington Wa, and another in Southern Cal. In both cases dragging 60'x.018" lines and a handle, the shutoff stopped the motor almost immediately. We have decided to start production and they should be ready to market before the end of March (see below).
The shutoff is configured with Sig small surgical tubing, on the high-pressure side of the needle valve.
These views show it cocked and ready for launch.
These views show it armed.
Here's one installed with internal controls. There's a flap of clear plastic across the hatch. The fuel line runs internally from the bladder to the shutoff.
Here are some recent pictures of the H&R shutoff. The three shutoffs shown are the 3" Fast/SL version which has a 4 pound, 2 ounce torsion bar, the 2" F2D version with a 2 pound, 6 ounce torsion bar, and the 2" 1/2A version with a 1 pound, 6 ounce torsion bar. We will also make a 2" Fast version on request.
This picture shows the shutoff completely disassembled. There are 13 parts in all. The two features that make this shutoff unique is the floating torsion bar and the double bushing. With the floating torsion bar, the shutoff is able to be configured for anything from 1/2A to Fast combat simply by changing the diameter and the orientation of the wire.
After several months of R&D we came up with the double bushing. As the pictures show, the outer bushing is installed then the ring is fit and soldered on the bottom of the bushing. This bushing both slides and rotates in the slot of the bellcrank. Then the inner bushing is installed and capped with about .005" clearance. We decided not to produce the shutoff with the original single bushing because when it was latched for launch, the friction of the wire against the bushing caused the controls to be very stiff at launch, and somewhat stiff during flight. With the double bushing the friction was completely eliminated.
The bellcrank is CNC milled out of 7075 aluminum that has been anodized and hard coated to eliminate wear. It is harder than the bushing. The bushing and line buttons are turned out of brass on a turret lathe. For consistency, we made a wire bending tool for both wires.
These shutoffs are for sale now, $20 each, plus $2 for shipping. For more info, contact Jeffrey Rein.
Here are pictures of the latest (Mark III) version of the H&R shutoffs. Compared with the Mark II (just above), we can see that the 1/2A and F2D have been slightly redesigned and reduced in size. Other improvements are harder to see.
The 1/2A shutoff
The F2D shutoff (competition proven at the Team Trials)
The Fast/Speed-Limit shutoff