The International Cessna 170 Association

I would be changing the nut plates.when you have a bad day you really do not want becoming some thing that you will regret as the threads strip out. Personally it's my own opinion the 10/32 screw is not large enough to take the forces that can occur when things go bad. For example the mod of the rear seat belt shoulder strap and that has a certified drawing with a single screw going through a 63 thou strap and the fuselage frame taking all the loads for shoulder strap. I really question the safety of this mod . Mr Newton had it right . F=MA. The weight of a human torso times 60 mph is the force that is exerted on a 10/32 screw and surrounding metal. These are just my thoughts only .

have you read the install of these BAS harnesses? have you read testimonials of the BAS harnesses?

Me thinks your not thinking this out thoroughly. Have you considered the force on the human body, more specifically the vital organs. They all have mass. Your larger screws may not rip out but you will still die because your heart is ripped out when the screws you installed don't give and your body is stopped cold but your heart and other organs are not.

I no longer have any idea what this thread is about.

I have seen what happens when seat belts and attach fittings give way and if the situation is so bad that your heart and organs are destroyed by a seat belt then the aircraft is often totally destroyed. A 3 g stop you will possibility will survive but a 9 g stop is terminal for you. You do not want a screw breaking away at a 2 g stop. The BAS harnesses is one of the best around but only good as the weakest link .its the aircraft structure and the attach fittings that give way mostly. With the exception of the harness with the hook attachment this has had a number of incidences when this has dislodged /broken when the aircraft has run into a ditch and nosed over.

ghostflyer, I just need a confirmation that you are aware that the BAS harness uses a #10 STRUCTURAL screw in the Cessna provided nut plate and adds TWO additional #10 STRUCTURAL screws as replacements for two rivets that attach the cabin roof skin to the rear spar carry through. These THREE screws attach the STEEL bracket that the shoulder harness reel attaches to to the airframe. Cessna factory harnesses use a single screw in the nut plate. Thank you.

Tim

Me thinks (ouch) get the best protection you can.
The BAS does beef up the roof attach point and I've even done a test trial on them...unintentionally ...and they work!

In one accident that I investigated the screws tore through the surrounding metal and another accident the screw just sheared. The passenger survived ok, which was surprising due what they hit. One area of concern of mine was the hook aggrangement for the back seat passengers where this became distorted allowing the belt to seperate. I am not writing this to scare you but just to think about some of the structure of early aircraft wasn't designed for the modern seat belts .
Just recently have seen the results of the new airbag seat belt . It was 182 that had the nose wheel collapse on landing and the aircraft went over on its back and then slide and rolled on to its side . It was a mess but the pilot (only occupant) crawled from the wreckage with some cuts but no broken bones . It was fitted with the airbag from the factory .

ghostflyer wrote:In one accident that I investigated the screws tore through the surrounding metal and another accident the screw just sheared. The passenger survived ok, which was surprising due what they hit. One area of concern of mine was the hook aggrangement for the back seat passengers where this became distorted allowing the belt to seperate. I am not writing this to scare you but just to think about some of the structure of early aircraft wasn't designed for the modern seat belts . ...

Shearing the screws would absorb a good bit of energy. I'd have to guess that anything has to be better than nothing.

Aryana wrote:I'd imagine it would slow down the speed of your noggin heading towards the panel a significant amount even if it tore out.

Yep, just like vehicles are design to collapse and absorb a lot of the crash energy.

In my simpleton/layman's math, a #10 screw (3/16ths inch dia) of average strength (125,000psi) would require [.1875 X 125K)= 23,475 lbs of effort to break in tension, and about a third of that in shear. (A better injuneer like Miles can do better I'm sure).....

I don't think the screw is the weakest-link in the human-body vs screw chain.

Not an injuneer either George but the strength is based on cross sectional area so here goes .1875/2 x .1875/2 x 3.14159 x 125,000 psi = 3469.9 pounds. Now divide that by 3 (your example) for shear equals 1156.6 pounds to shear. Now we'll divide that by 9 g's (forward loading limit) / 2 (assuming half of the load is on the seat belt and half of the load on the shoulder harness) for each screw supporting 257 pounds total passenger weight. The use of 3 screws gives a safety factor of 3.

Tim

Tim for standby on duty rocket engineer

When designing some thing I always look at what has happen in the past and it's parent product and how it is redesigned today . It's all about compromise.for example look how cessna bolts their front lap sash belts to the center part of the ceiling in the lastest models The structure that the enertia reels are attached to is very interesting design. The old days of attaching it to the door pillar is gone . Why we must ask? Cessna has done a lot of research on survivably . While some 30 year old designs/materials are legal ,there are better and improved concepts around but at a cost.
[ note. I always get a second or a third opinion on a idea /concept before it goes into production as some times my " rose colored glasses get foggy with my enthusiasm.]
This conversation has really gone on a wander into the mist , but basically what I said originally the nut plate that is retapped out because of crossed threads was a bad idea , I would be replacing the the nut plate .

Why stop now? It has been a good read!