A small question on seat belt anchoring cable. I have some stock of 3/32 7x7 cable left over from the rudder cable stock. I am not sure about load rating of the rudder cable, but for similar cables on Ebay I see a load rating of 925 lbs.
I also have 1/8 (7 x 19) galvanized steel cable left over from a previous project with 2000 lbs rating. Plans state to use 3/32 cable.
I was wondering if I could use the 1/8 cable because it is only 14 ft of cable to be used, and so weight-wise, the extra 2 or 3 ounces is acceptable to me.
Just wondering if there are any other issues to keep in mind ? The rudder cable is unused, but old stock. The 1/8 cable is brand new.
Thanks for any suggestions.
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gyrojeffro
March 16, 2018, 2:43am
Guest User
I'm no expert but I think you will be fine unless you plan on crashing extra hard. take my opinion with a grain of salt, wasn't meant to be funny.
Following an accident in the UK, our regulator looked into it and beefed the mounting and, I believe the cable up a bit. I'll dig it out for you. Nobody wants to crash but we all want to survive one!
Shoulder straps/Seat Belts When Francis Donaldson reviewed the HiMax he noted that the shoulder straps were attached to a continuous cable routed around the rear of the fuselage. Given a sharp pull on one strap, it was possible to pull the other. He commented that in a cartwheel type accident, such an even force may be seen on the straps, and such a movement of the straps would allow the pilot’s upper body to twist. He suggested therefore they be linked together to prevent the possibility of this happening.
Issue 205 of the minimax uk club newsletter contains a photograph of the improved mounting. I am not going to even try to reproduce it here as it is weeks since I spent weeks trying to post pictures but somebody else might. The cables are made as two, probably 5/32" and are fitted to a steel plate which has two shackle holes and, set back an inch, a central bolt hole that carries a bolt through the centre of the rear elevator cable mounting bracket.
Issue 205 of the minimax uk club newsletter contains a photograph of the improved mounting. I am not going to even try to reproduce it here as it is weeks since I spent weeks trying to post pictures but somebody else might. The cables are made as two, probably 5/32" and are fitted to a steel plate which has two shackle holes and, set back an inch, a central bolt hole that carries a bolt through the centre of the rear elevator cable mounting bracket.
I guess that means 1/8 steel cable should be OK, because you mention the cable may even be 5/32. Why not continue to use one cable length to loop through the bracket as in the plans, but swag the two cables together about an inch or two ahead of the bracket ? Will that not make it act like two independent cables ? Thanks
I guess I just look at things and concern myself with things differently than a lot of people. If the load rating on the cable you have is 925#, and we double that figure, since there are two cables going forward, that's 1850# of capacity.
#1.....How well do you think you'd survive the G force that would result from an impact that would put 1850# of stress on your shoulders and body?
#2.....How well do you think the MiniMAX fuselage would fare in the case of an impact of that magnitude.
#3.....Don't you think you'd have bigger concerns and problems than the strength of your shoulder belt cables?
OK....get the fire started under the stake in town square.
Further to what Tom said earlier, please see the picture below, which clearly shows the UK mod for the attachment of the shoulder straps to the metal cross piece at the tail of the fuselage.
I agree with Lynn. The cable is much stronger than any accident you could survive, and I don't see how the cable can move the way its attached. Larry
It was 2004 when I crashed G-MYTA Minimax. I allowed the canopy to open after take-off and in trying to sort out the mess basically I chose to stall-in rather than nose-in. Long story.
Must have been coming down like a brick because the axle went under the ground and cut a piece of grass-turf clear out of the runway. It was serious.
Because the seatbelt is mounted by your side and then goes straight back over your shoulder the 'resultant' force when you carry on moving forward after the aircraft has stopped is to press down on your shoulders. While that is happening your torso is still moving forward in the cockpit but your waist is restrained by the lap-strap. The result is that your head is forced to approach a certain part of your anatomy which I'm told only babies can get that close to. As you bow so low forward the fronts of the vertebrae in your spine are compressed very much, and some crumble, but thankfully it is the back and not at the front (anterior?) where all the wiring is. It's likely that your forehead clouting the instrument panel will mitigate this effect (yup, can still feel the scar there).
Even though this was an arrival with no sideways movement that I was aware of, within a few miilliseconds, the steel cable going through the aluminium plate at the end of the fuselage had sawn a slot in the hole system there by differential movement - pull-through.
WOW that was a very hard hit. How did the gear legs fair and did the bottom of the fuselage hit hard enough to buckle any of the uprights on the inside of the fuselage? That must have been a monster of an experience.Would a helmet have helped or did you have one on?
Thanks for sharing your thoughts. Yes I too thought of the absolute lack of protection and consequent vulnerability in the nose section of the Max. The whole of the forward fuselage is one big crumple zone. The four corner RS-8 sticks and the 1/8 ply on all sides cannot be of much help if you crash, even at a modest speed.
However, since we are anyway installing a cable, we might as well put some thought into it and do it right. It may not be of much use, or might be of use in a particular type of crash, who knows ?
This is how I finally did it. I used 1/8 cable. I pre-bent the cable a little bit to fit the contours of the layout. I am yet to swag the sleeve. Will do that as a last step when everything else is rigged up, just before covering with fabric.
Just for reference, in automobile crashes, it is is not unusual to see seat belt loads in the 9 KN range (x1000/4.45 to get pounds); however, the geometry is such that for the shoulder belt the spine compression is minimized. Generally speaking, the lap belt takes the highest loads and the shoulder belt takes about 1/2 of that (~ 4KN). Those belt systems are also designed to hold the force at a certain level, therefore, once the load is reached, the belt is allowed to pay out (ie spool out and get longer). Given the geometry of the belts in the MiniMax it is unlikely that you could have a geometry which would not result in spinal compression on a hard crash. From what I have seen, the modification proposed by the British PFA is probably a reasonable modification to make. When you fly, make sure that you lap belt is resting on the bony part of your pelvis (ie Iliac wings) and that the shoulder belt will not slip off your shoulders when you lean forward. A snug fit is also a good thing.
WOW that was a very hard hit. How did the gear legs fair and did the bottom of the fuselage hit hard enough to buckle any of the uprights on the inside of the fuselage? That must have been a monster of an experience.Would a helmet have helped or did you have one on?
I can't remember too much about the damage now. The aircraft came to a stop about 10 feet from where it first made contact with the runway. The front cowl, engine and motor-board were 10 feet away from the aircraft, all 4 wing struts were buckled with negative G, the wings looked OKish repairable, the tail feathers were undamaged. The axle tube was bowed. Can't remember the axle uprights' condition. The special aluminium 35 litre tank became detached and possibly contributed to the pelon fracture of my left ankle. The aircraft was repairable but someone stored it in a leaky shipping container, and when I came back to it the aircraft was sodden, with wings were 'full' of water, therefore scrap.
Was not wearing a helmet, fully enclosed cockpit. A leather helmet would have helped but even with hindsight I don't regret my decision never to wear one.
I remember being impressed by what I saw after the accident and later, how the aircraft made very quick decisions about where to distribute the shock load and how to absorb the energy - sort-of equally around itself. If you see what I mean. Good design.
Had two microlights at the time of the accident. Flew in my weightshift before I could walk properly. Stuffed my crutches under the Hornet's seat. But I never said that. My knees were shaking.
The UK modded rear attachment and the addition of Keith's ferrule to the cables, both pictured above, would not have allowed exactly what happened to me in that accident to happen.
I remember that one or both of the holes that the seat-belt cable went through was/were torn into slots by movement of the cable through them. Imagine the power and force needed to do that!
That power and force was absorbed by the aluminium plate, and therefore not by my body. I'm grateful for that.
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