SB-00036 hor stab aft spar inspection at hinge

[A2022]

received notice of SB-00036 and completed the inspection. a lot of paint overspray but no cracks. looks OK.

it makes sense that the outer hinges receive an increased loading. during a hard pull up maneuver, the hor stab wants to flex upward while the elevator is applying downward load. the outboard hinges absorb the loading. hey, these planes are experimental, don't pull too hard.

low cycle fatigue cracks are primarily driven by the max load cycles, such as would be experienced in aerobatics. I don't do aerobatics because this is a -9. the -9 has a taller aft spar compared to a -7 and will carry the load by a wider rivet distance that should also be a benefit. so far, this -9 airframe has been completely trouble free. I could not be happier. whoops, now I said it! I should vacuum this area.

designing and building aircraft is hard and my hat is off for Van's. may Van's Aircraft live long and prosper!

https://www.vansaircraft.com/service-in ... /sb-00036/

the areas in RED should be the rivets with the first indications of cracking.

[A2022]

to answer the email. these photos were taken using a cell phone thru the outer rib lightening holes. I used a standard flashlight for lighting. the inspection took about two minutes. you don't want to be flying around with a cracked horizontal stab spar. if you are going to be doing aerobatics, I would bite the bullet and strengthen this area instead of always wondering about it. upon resale, it will be worth more.

[A2022]

perhaps the new hinge bracket could look something like this for the bracket ears. not sure how the existing rivets line up but could always add a hole if needed. need precision bends and may require 3 hands to install. not sure if there is enough room to squeeze this into the space but this bracket shape should be the goal. now we wait and see what Van's solution is. get the young pups working on it to correct sins of the past.

when you have sinned in aviation you must ask for forgiveness and then do your work as unto God. then you will receive the blessing and know you have done your job to the best of your abilities.... Round the Bend is a 1951 novel by Nevil Shute. It tells the story of Constantine "Connie" Shaklin, an aircraft engineer who founds a new religion transcending existing religions based on the merit of good work. a cracked spar is a sin and the existing design should not have been allowed, a poor design. a loss of that hinge in-flight and it's all over. free your mind and reach into the metaphysical to understand the true nature of stress but also have the stress numbers to confirm.

that's my 30 minutes' worth, you get what you pay for.

now back to the music
Go Back Now (feat. Beacon)
https://youtu.be/3YX-PLIqcZU

[bruceh]

I was able to get my Vivida borescope through the outer lightening hole on the rear HS spar (my HS side rib holes are filled). No cracks on my RV-9A!

[rockwoodrv9a]

It was so easy to check mine I wasnt sure I was doing it correct. The lightning holes give a nice view. I guess the other horz stab on the other models does not have the holes. No cracks on mine.

[A2022]

I also checked with Vlad, the RV9 flight leader, he has 5 or 6 thousand hours on his aircraft. no hor stab spar cracks on his aircraft. I fly mine easy, I don't expect to need to have a hinge replacement, but I wish they would offer one and put some rivets in shear loading to strengthen this hinge. the hinge attachment they have now is a poor design. I don't want to be in any thunderstorms with it. Vans should take a look at Cessna elevator hinges. simple lightweight and strong. note: it's hard to design retrofit parts to fit an existing design, it's never optimum, better to have done it from the beginning. the retrofit process alone adds some risk for damage; such as misdrilled holes, bent sheet metal skins, disassembly, reassembly, etc.

[A2022]

cessna 140 from the 1940's carrying the elevator hinge load with rivets in shear. hey, maybe they knew back then, that rivets are best when they are in shear. a lightweight and strong design.

seems that Van's is working hard to catch up with the 1940's. what about the vertical stab and rudder? my recommendation is to fly RV's easy and avoid thunderstorms and take care of them in ground winds. they are delicate machines and did not have rigorous engineering of previous designs. inspect them often. to be honest: a simple oversight such as the hinges makes me wonder about other aspects. .... but they sure are fun to fly and relatively simple to build! that's the beauty of Van's Aircraft, live long and prosper.

if you subjected an RV to the flight cycles and abuse of a flight school, they would deteriorate quickly.

JUST SAY NO TO CRACK

[A2022]

do you really want elevator hinges to be installed with pop rivets in tension? cherry max are still pop rivets, and they are not in the correct shear configuration. Van's needs to rethink the elevator hinge arrangement in total. the current hor stab and elevator design and SB has doublers everywhere, becoming a mess. put the rivets in the correct configuration like an old Cessna 140, shear.