Hey Jered, I've loved reading through your thread and as someone considering the S-21 it is a huge help! In fact I've enjoyed it so much this is my first post. Any updates on how the build is going?

tomhall1776 wrote:Hey Jered, I've loved reading through your thread and as someone considering the S-21 it is a huge help! In fact I've enjoyed it so much this is my first post. Any updates on how the build is going?

Glad you’re enjoying the posts! We have not touched the airplane since the end of July do to pear harvest and other work. With the seasons changing, we will be back at it shortly. We have everything ‘framed up’ with the exception of the elevator. Next steps will be finishing the interior panels and paint, then fuel tanks, wing and empennage tips, etc. hope to make some major progress this winter and be in the air next summer. I’ll do my best to keep this thread up to date as we go.

Here’s some of the last progress pictures:

She looks great! Really coming along nicely. Thanks for sharing, and keep it up!

Sent from my Pixel 2 using Tapatalk

AMRE2ME2 wrote:What happened? Such an informative thread and all of a sudden, nothing.

Did you fall behind in your subscription?

OK here goes - and maybe this is a different thread.... is a half-spring landing gear design like that common?
I would have expected to see the spring go right through.

In a rough off-airport landing, that design concentrates all the force on those two little bolts in the middle of the belly, particularly shearing forces. The design multiplies the force on those bolts by a factor of 3 or 4 times what the wheel sees. In a situation were the plane hits an unexpected object (oversized rock, driftwood, gopher hole, etc) the design would probably only be 30% of the impact strength compared to most every other design I have seen (Zenith, Savage Cub, Kitfox, etc).

This is about 900 lb airplane. An An-5 has an ultimate tensile strength of about 125,000 psi. The airplane was engineered by proffesionals and drop tested with an excessive amount of weight. Cant tell from the picture, but it’s actually sandwiched with three bolts to the structue. The two bolts in the middle aren’t taking all the load. The last thing on my mind when flying is going to be those bolts. Randy and team have a pretty proven track record. Not saying mistakes can’t be made but I think they hit the mark on this one. Great products and support!

Yes, I am sure it's very well engineered for normal use and I don't want to question their design engineering. It's always amazing how small the bolts are.

My question was about surviving an impact with an unexpected obstacle, typical of backcountry flying. This is nothing to do with the design for normal use, more about crash survivability.

Yes ultimate tensile strength is 125kpsi, but they start to yield much lower, their shear strength is what matters in this case and that is only 76kpsi with a long arm attached to the other end.

Let's say the gear leg gives an advantage over the bolt of 4x. I calculate an impulsive force of about 620kg will shear the bolt off.

My rough working on the back on an envelope came to the conclusion, if the plane weighs 1,200lbs (540kg) when landing, and one gear leg it hits an obstacle big enough to slow the plane by 21 knots (in 1 second), then your gear leg is shearing that AN5 bolt.

(Edit to fix mathematical error)

Not an uncommon system on the landing gear. The spring gear on the murphy rebel with a setup like that does exert the load on that single bolt, in almost pure tension. Sure, there is some shear load associated, but it’s negligible in regards to what the bolt can handle. The most common failure mode is the bolt stretching from a hard landing. It’s pretty easy to spot by noting a loose bolt during the resulting inspection. I’m only familiar with 1 bolt failure event, it it was concluded that this was the result of repeated hard landings. Bottom line, don’t tighten a loose landing gear bolt on this kind of gear; replace it.

http://wrayt.ca/rebel%20site/test_results.html

There is no issue with the bolts holding I assure you. The gear leg is bent also.

Timberwolf wrote:Not an uncommon system on the landing gear. The spring gear on the murphy rebel with a setup like that does exert the load on that single bolt, in almost pure tension. Sure, there is some shear load associated, but it’s negligible in regards to what the bolt can handle. The most common failure mode is the bolt stretching from a hard landing. It’s pretty easy to spot by noting a loose bolt during the resulting inspection. I’m only familiar with 1 bolt failure event, it it was concluded that this was the result of repeated hard landings. Bottom line, don’t tighten a loose landing gear bolt on this kind of gear; replace it.

http://wrayt.ca/rebel%20site/test_results.html

That’s solid information and much appreciated!

Battson wrote:Yes, I am sure it's very well engineered for normal use and I don't want to question their design engineering. It's always amazing how small the bolts are.

My question was about surviving an impact with an unexpected obstacle, typical of backcountry flying. This is nothing to do with the design for normal use, more about crash survivability.

Yes ultimate tensile strength is 125kpsi, but they start to yield much lower, their shear strength is what matters in this case and that is only 76kpsi with a long arm attached to the other end.

Let's say the gear leg gives an advantage over the bolt of 4x. I calculate an impulsive force of about 620kg will shear the bolt off.

My rough working on the back on an envelope came to the conclusion, if the plane weighs 1,200lbs (540kg) when landing, and one gear leg it hits an obstacle big enough to slow the plane by 21 knots (in 1 second), then your gear leg is shearing that AN5 bolt.

(Edit to fix mathematical error)

The Bellanca/American champion line all have gear like that after '65ish. I've never seen a failure of the inner bolt, but the original outer U bolt that they had would crack. The fuselage tubing will usually give before the bolt will.

gbflyer wrote:

There is no issue with the bolts holding I assure you. The gear leg is bent also.

Not sure what I am looking at here, but it does not look like a good news story

Thanks for all the comments, very interesting discussion for inquiring minds

Also, Airtractor gear mounts the same way. They've been hauling 500 gallons loads off my grass strip all summer with no worries of wrecking the gear. They take a beating.

Battson wrote:

gbflyer wrote:

There is no issue with the bolts holding I assure you. The gear leg is bent also.

Not sure what I am looking at here, but it does not look like a good news story

Thanks for all the comments, very interesting discussion for inquiring minds

You’re looking at the gear leg and strut attach basically ripped off a S20. Same gear and forward structure as a S21. No bolt failure.

Gbflyer,
Anymore info on the S-20 you would care to share? Asking due to a recent conversation discussing the crash worthiness of the S-21. Since the cage assembly is essentially the same as the S-20, our talk revolved around how well it will protect the occupants.

Don’t want to derail the build thread and get in trouble.

Work and life continues to hamper progress on the Outbound, but last weekend I managed clean and rearrange the hangar. Got my 172 on lift and put away all the parts from our firewall forward kit that arrived last week. Today I got a couple hrs to work on fitting the boot cowl. The boot cowl is pretty straight forward but the top skins have a lot of pre-load when you wrap them down the side. Makes it challenging for locating holes. Happy with the results though!

Anyone worried about the single centre bolt one can use a much stronger NAS bolt.
In case of an over stress it will rip the fuselage apart instead of failing the Bolt.
On this design all the force is pulling away from the passenger compartment instead of having parts entering the passenger compartment.
The straight through gear as on some other home-build is not a bad -- idea it also for more flex instead of the energy ramping up dramatically with limited flex. A tubular steel gear would provide the best absorption short of a proper trailing link with a shock. It all comes down to weight.

A little more progress lately. Rudder pedals, brake cylinders, control sticks, seats, and a little fabric on the baggage floor. More to come!