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Old 05-14-2018, 11:51 AM
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czechsix czechsix is offline
 
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Location: Spring Hill, KS
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Default Lap belt attachment location in RV-14

As I work through the fuselage floor sections I've been thinking about moving the lap belt attach lugs a few inches further forward. What got my attention was this post from the General Discussion section of the forums a while back:

http://www.vansairforce.com/communit...d.php?t=158840

The OP's concern was hitting his head on the canopy in turbulence. While this is certainly unpleasant (and may also scratch your canopy where the headset makes contact), my bigger concern is what happens if you ever flip the airplane over. I know the nose gear design makes this less likely than the other 2-seaters, but it's still not out of the question especially in a forced landing. If you can hit your head on the canopy in turbulence despite tightening down the lap belt and crotch strap, imagine the full weight of your body hanging from the harness upside down...keep in mind the top of the canopy is well above the rollbar on the tip up design.

I've looked at a number of certified airplane recently, and without exception all of them have lap belt attach points right where the seatback meets the base of the seat pan. Cars seem to use this geometry as well. On the RV-14 the lap belt lugs attach behind the rear spar and protrude through the spar several inches aft of the seatback. On the RV-7, the lap belt lugs attach to the forward face of the rear spar and appear to be closer to the seat. The RV-8 also places the lap belt attach points closer to the seat. The aft placement on the -14 is exacerbated if you are using the middle or forward seatback hinge point...the further forward you move the seat, the less ideal the geometry of the lapbelt to hold you down onto the seat.

Curious if anyone else has had issues with the lap belt geometry in the -14 (especially those who are flying) and if anyone has done mods to move the primary lap belt attach points forward?
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Old 05-14-2018, 02:06 PM
Ron B. Ron B. is offline
 
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I cannot see how the seat belt system would not hold you in place with the five point harness.
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Old 05-14-2018, 08:40 PM
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czechsix czechsix is offline
 
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Quote:
Originally Posted by Ron B. View Post
I cannot see how the seat belt system would not hold you in place with the five point harness.
The OP in the above link states "I found Van's claim that the crotch strap will keep your head from hitting the canopy not to be the case for me. The aft location of the lap belt anchor points still allows one's hips to lift up a few inches." I think if you look at the last picture in his post, you can see how the geometry of the lap belt will allow the occupant to move upward before it restrains him.

This evening I took another look at the RV-8A I built. In addition to the attach points being located closer to the seat back, the lap belt also passes through cutouts in the lower part of the seat back. Those cutouts keep the belt from moving upward and positions it to go up over your hips & waist at about a 45 degree angle (like most other aircraft and cars). I wonder if something similar could be done on the -14 in lieu of or in addition to moving the anchor points to the forward side of the rear spar...
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Old 05-15-2018, 06:43 AM
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Jared_Solomon Jared_Solomon is offline
 
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Location: Powder Springs, GA
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Question No problems here

I have flown my RV-14 in some pretty moderate turbulence with the 5-point restraints. I have not had any problems with the seat belt not holding me in place.
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Old 05-15-2018, 07:46 AM
mturnerb mturnerb is online now
 
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I would be very leery of making changes to a critical, and presumably carefully engineered, component in an aircraft. The most important function of restraints is restraining/protecting occupants in an accident and distributing forces in a way that protects internal organs. While moving anchor points may preserve this, how would one know without doing some serious analysis?
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Old 05-15-2018, 11:30 AM
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czechsix czechsix is offline
 
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Quote:
Originally Posted by mturnerb View Post
I would be very leery of making changes to a critical, and presumably carefully engineered, component in an aircraft. The most important function of restraints is restraining/protecting occupants in an accident and distributing forces in a way that protects internal organs. While moving anchor points may preserve this, how would one know without doing some serious analysis?
Yeah I wasn't even going to get into the structural analysis part in this thread...I've thought about it quite a bit and I'm also familiar with how the lap belt anchors are designed in other RVs, so I think I could create something of equivalent strength. The outboard belt lugs are more straightforward, the inboard lugs more challenging due to the placement of the UHMW flap torque tube support and the fact that the floor ribs don't align fore & aft of the rear spar. Not insurmountable, but it does complicate things.
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