Increased Gross Weight - Wood Spar Decathlons

always worth sharing when the topic comes up

Rainbow Spar Load Testing Video

Ron posted this video a little over a year ago. Ron owns Rainbow Flying Services, he holds STC's for a series of wood spar products that are widely viewed as an improvement over the factory design. His website is here https://rainbowflying.com/
champcitabriadecathlonforums.com champcitabriadecathlonforums.com
 
Red Owl said:
Well thank you Aft. I was operating under that belief that there had been either two or three failures. Don't know where I got that, but drawing it from memory was one of the primary reasons for the above rant. My opinion still stands - spar failure - even potential spar failure - just makes me very uneasy. Uneasy is something I don't want in my aviation experience so perhaps I over react.

I should also mention in this scenario, that I may over react because I lost a friend ( and his 12 year old son) due to in flight spar failure about 20 years ago. It wasn't a Citabria or Champ but it sticks with you when it happens in your circle.
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Sorry for your loss. Obviously flying anything is no fun if you can't enjoy it and we all need to make our own choices.

Back when I started flying I had read the accident reports of Bonanzas shedding their tails. Love the plane but wouldn't love worrying about that. Turns out most are cases of loss of control in IMC where they didn't belong and overstressing the structure. Easy enough to prevent.
 
aftCG said:
Sorry for your loss. Obviously flying anything is no fun if you can't enjoy it and we all need to make our own choices.

Back when I started flying I had read the accident reports of Bonanzas shedding their tails. Love the plane but wouldn't love worrying about that. Turns out most are cases of loss of control in IMC where they didn't belong and overstressing the structure. Easy enough to prevent.
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I did some commercial maneuvers and some instrument work in a S35 model V tail Bonanza. The V tail Bonanzas have delightfully light controls, but they are not all that stable in roll. Worse, they demonstrate a dutch roll characteristic in even light turbulence. When the aircraft is displaced in either right or left roll in turbulence, it also produces adverse yaw. Unfortunately, that coupled roll and yaw motion doesn't dampen out in the V tail Bonanza and the result is that the nose and wing tips then each carve a figure 8 path across the horizon. The roll/yaw coupling in the V tail Bonanzas, can become dynamically divergent and if left unchecked can cause loss of control. It's easy enough to dampen as you just momentarily cross the controls long enough to stop the motion then release and recover to normal flight.

But...try doing that every 15-20 seconds at night in turbulence in IMC. Keeping the needles where they belong starts to become work. Add some vertigo from the dutch roll with no outside visual reference, and suddenly you have inexperienced, and or non-proficient, and or not sufficiently current pilots entering into a spiral dive where the speed builds up enough to cause the ruddervators to fail. The Bonanza is a very clean airframe and it'll build up speed in a hurry. That combination of traits is what earned it the "V tailed doctor killer" moniker.

Those flight characteristics were complicated by the increase by 7" in the ruddervators' chord, which placed the leading edge of the ruddervator 16" in front of the ruddervator spar, with no change in the structure itself. That gave a longer moment arm for the forces acting to bend the ruddervators, with their leading edges unsecured to the fuselage, up and down. Structural failures started to occur as the aircraft had basically very little margin over it's normal Vne.

Beech eventually developed a cuff that attaches to the ruddervator root at the leading edge to anchor the leading edge to the fuselage to prevent, or at least delay that, spar snapping bending motion. They were pretty common on V tail Bonanzas by the time I started flying them in 1990. They do keep the tail on a little longer and allows a pilot more time to recognize the spiral dive and recover, but it just increases the speed at which the ruddervators will fail. The pilot still has to on his her game, being both competent and attentive to their instrument scan.

There were also related ADs later in the 1990s into the 2000s due to skin cracks in the tail section of the fuselage. I suspect in some structural failure accidents that just became the new weakest link in the structure.

Yaw dampers were an option on the aircraft, but many don't have one and many that do have on that isn't operative. They are almost a necessity if you plan on flying IFR in turbulence.

Accident rates for the V tail Bonanzas are now on par with similar performance Piper and Cessna singles, in large part because the V tail models went out of production in 1982 and as a fleet they are getting pretty old, with many of them retired or at least used less intensively for serious IFR transportation.
 
BB57 said:
This comes from an IAC "Technical Tips" publication, page 105:

file:///home/chronos/u-e3fbbe814d5e28e1fa8c738be4443f8432e0dfc7/MyFiles/Downloads/technicaltipsmanualvol1_0.pdf

"Dear Fred,

I have been asked to reply to your request for comparison differences in the Citabria and Decathlon aircraft.
Unlike the Cessna Aerobat, which is basically a beefed up Cessna 150, the Citabria and Decathlon are two different aircraft designed and certified independent of each other. For this reason, it would require a detailed description of both the Citabria and Decathlon fuselage and wing structure to properly describe the differences.
The fuselage of the Decathlon shares much of the same truss design of the Citabria, but structurally it is quite different.
*The material thickness of steel tubing is increased in many areas.
*The tail section has additional truss members.
*The wing attach and carry-through members are stronger.
*The fuselage is designed for 180 HP. The wing of the Decathlon is completely different and shares very few parts with the Citabria.
*The airfoil is a NASA 1412. This, for one thing, distributes flight load differently.
*The main spar is larger (wider and deeper).
*The rib spacing is closer (more ribs per wing).
*The front and rear wing struts are larger and stronger — adding greatly to its compression strength or negative flight loads capability.
The windshield of the Decathlon is made of thicker, stronger material and is supported with a center brace.
Another big difference is in the certification and operating limitations.
The Citabria is approved for aerobatic maneuvers listed on the placard on the panel. Only those maneuvers are approved.
The Decathlon is approved for a list of maneuvers and variations or combinations of those maneuvers which does not exceed the operating limits. Only the tail slide and lomcevak are not approved.
I have enclosed a copy of the Decathlon flight manual and the Citabria owners manual as a reference for you to compare operating limits and approved maneuvers in more detail.

I hope this explanation is adequate. If not, please do not hesitate to contact me. Sincerely, BELLANCA AIRCRAFT CORPORATION Richard M. Johnson Product Manager"
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Curious, how does the wing construction on the Scout compare to the Decathlon? Is it similar or completely different?
 
Not an expert. I think the Scout wing is similar to the Citabria wing. Not sure of spar size, but would bet they are the same as Citabria. I stand ready to be completely wrong . . .
 
Ron was kind enough to reply -

"Scout airfoil the same as Citabria. Scout rear spar much beefier than Citabria. Scout spars longer."

He didn't mention anything about rib spacing. I forgot to ask.

Excellent Thread Discussion - Thank you!
 
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