CARBON FIBER RUDDERVATORS

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Our  team has spent the past year learning the art of working with carbon fiber. We have started the process of application for the FAA STC. The first set will go on our 1952 V tail, N8966C for testing. 

We will show her at Sun N Fun 2024 and hope to be licensed to sell them to those in need shortly after the show.

See the full article published in the American Bonanza Society Magazine below:

THE BEECH BOYS. No, not the rock and roll band from the 60’s, but Brian DeWolfe, one of the “boys” did play the base guitar for numerous bands while living in Aspen Colorado when he wasn’t working for United Express. He claims he has taken off in more planes than he has landed in when he was a captain in the U.S. Army, 101st Airborne jumping out of C-130’s and Huey’s in the Vietnam years. 

Aspen is where he met another one of the “boys”, David Stiles, who was busy mountain flying T-210’s, 421’s and Merlin’s. 

The 3rd “boy”, John Roberts, was an FBO operator in Homestead Florida for 35 years and gave the others the idea for making ruddervators while working with Stiles putting together a V tail Bonanza that he had trucked down from New Hampshire after 14 years of storage.

The fourth partner is Rhonda Sofaer, from Key West Florida who brought a funding package to the group that allowed for the pursuit of the project. Rhonda is an airplane affectionado with a financing background.

For the scientific side of the design, the boys hired two engineers, one an aerospace engineer and the second, a materials engineer, to consult and assist with the structure.

The boys are old men; Stiles is the youngster at 73.  Roberts is in his 80’s and beats the other two on hours as well as years, with logged hours at 35,000 and type ratings in 747’s, L-1011’s, 707’s and 727’s, while serving in the Navy and thereafter flying mystery freight for Evergreen and Kalitta.

So why would a couple of geezers want to get into the aviation parts business instead of building something like walkers or wheel-chairs? To keep these beautiful and iconic aircraft flying of course. They started looking around for used ruddervators to go on the barn find from New Hampshire, and noted the lack of inventory and crazy pricing on what they did find. 

“We’re not the sharpest tools in the shed and do not make any claims about having a perfect solution, we’re just dumb enough to embrace the possibilities of building something new to replace something old. The smart people are building e-vtol’s.”

“Walter Beech’s original purpose in using the V tail was the thinking that sitting up high on the fuselage it would be out of the wake caused by the airflow over the wing at critical speeds. Beech had conducted wind tunnel tests and discovered that a reduction in the tail area resulted in an overall reduction in drag. Chief designer Harmon found that the V tail also had superior spin recovery characteristics.” 

“We know all the issues with flutter – there’s nothing new about that subject, first noted in 1916, and we’ve done all the math, but the simple stupid solution is just to slow down. If you need to go faster than your envelope, you’re in the wrong aircraft.”

“Countless studies by the FAA, Beechcraft and a variety of Universities and Institutes advises us that problems may occur with flutter at high speeds being the result, so we don’t need to rehash that here, but it is interesting to note a couple of consideration when addressing what flutter is and how to mitigate it.”

“Any surface of an aircraft that is exposed to airflow can develop flutter, but it is usually found on the control surfaces. There is a certain type of engineer who studies these effects, a mass property engineer.

We need to have the center of gravity located exactly on the hinge line. The Moment of Inertia is also critical. It needs to be minimized so as to avoid mechanical resonance. When the ruddervator is bent upwards as in pulling out of a dive, the mass on the outer end of the wing will have greater acceleration than the mass near the fuselage. So even with a balanced ruddervator, if the mass near the trailing edge on the end and a high mass loading on the leading edge inboard create an unstable condition. The resultant twist distorts the shape of the wing and the accompanying resonance may create flutter.

“Our ruddervators are not just a pretty replacement for the originals, they are designed, engineered and built to mitigate flutter. Ribs and spars have been installed in specific positions to increase damping and stiffness. The carbon fiber layers are laid in to increase tensile strength.”

“Our skins only weigh 478 grams per side or under 2 pounds per ruddervator, whereas the Beechcraft product weighs 4 pounds (without the counter-weight) we have ample room to install ribs and spars that the original units could not accommodate.

“This doesn’t mean you can go faster, just potentially safer.”

“There are two methods to control the flutter of aircraft structures, namely the passive and active control. Passive flutter control mainly increases the structural stiffness by changing the configurations of the structures which we have done, thereby reducing the deformations of the structures, like we are doing. 

With the development of active control technology, aircraft design has been moved from passive to active. Active flutter control can generate control force by controlling the voltage applied on smart materials such as the piezoelectric materials, shape memory alloys, and magnetorheological fluids through different control algorithms, and actively adjust the aeroelastic stability of aircraft structures. This was 1st discovered and used by Chuck Yeager in the XS-1 when he broke the sound barrier. He could adjust the tail to counter-attack the buffeting he achieved approaching Mach 1. ”

The V-tail as we all know and love are not without their drawbacks. While it requires only two surfaces instead of three, these two surfaces must be bigger or the plane suffers stability problems, specifically spiral divergence and Dutch roll. Effective control of both yaw and pitch requires a challenging control system. 

The V-tail has structural disadvantages with respect to a conventional tail. Because of the dihedral angle between the tails, there is no continuous carry-through structure like there is on the horizontal stabilizer of a conventional tail. Consequently, the materials used and the weight and torsional stability of the ruddervator is critical.

“Why do we need counterweights anyway?” asks Stiles. “The ruddervator surface moves and applies a load to the stabulator. The stab bends under the load and stores that energy like a spring. The spring uncoils and the ruddervator wants to move back to its original position. Spring and release, spring and release = flutter. Putting the counterweight ahead of the hinge position gives us mass balance. Additionally the cuff was added to the stab to give it more stiffness so it could not start the bending.”

Next for the “boys”, came seeing what the industry was doing about the obvious problem, which seemed to be a lot of discussion but not much action, and even more myth associated with the challenges that may or may not exist with building a replacement part, which Stiles calls “Voodoo Science”.

Stiles, with an industrial design and engineering background building packaging machinery for industry for 35 years, started the process by purchasing a good set of 1952 ruddervators, then two more sets to cover all the 3 primary designs that Beech incorporated in the V tail production. First, he had them laser scanned by EMS in Tampa, Florida, then he ripped them apart to study the manufacturing techniques and the magnesium’s properties.

From EMS, the drawings went to Fri Dimension of St. Petersburg, where Stiles had specific pieces made with 3D printers, then molds made in fiberglass and gelcoat. In these molds he casted parts in various weaves of carbon fiber and resins from Fiberglass Coatings of St. Petersburg.

He also purchased and tested materials from Europe and Asia for comparisons although the company wanted to keep their product American made. “Most US manufacturers of carbon focus on a particular weave, 2X2 twill, which is great for general purposes and excellent for draping but retains more epoxy and has limited strength characteristics compared to some of the offshore weaves. We use several different weaves and epoxies in different areas of the part. We have also eliminated the metal hinge components and replaced it with a carbon fiber/Kevlar hinge with incredible strength and wear characteristics. The hinge on a V tail is one of the potential areas where flutter may grow due to the loose fitting of the hinge components and the way the airflow is disturbed even though flutter is a leading-edge occurrence. Our carbon fiber hinge has no flow-thru and is tight to the body of the ruddervator.”

The ribs and spars are made of a “lattice sandwich”, where layers of carbon fiber are top and bottom to a honeycomb material which increases the strength of the carbon without adding weight.

Rather than digging back into the archive of metal technology, they began researching what replacement materials were out there and which one is best suited for production. Carbon Fiber was the obvious 1stchoice but not the only material out there.

Numerous other fibers and resins were tested over the ensuing months, but they kept coming back to carbon and epoxy.

Not all carbon fibers are the same nor are the resins. Stiles suggests that he may have done hundreds of tests involving all the variables associated with their Reno Ruddervators.

“Despite all the excellent properties of carbon fiber, it can become electrically conductive when connected to the aluminum and magnesium of the surrounding surfaces, and this needs to be mitigated. We disconnect the electrical connection of two parts by placing an electrically insulating fiberglass gasket between those parts.

“We use epoxy resins without any hydrolysable linkage, such as ester bonds, to mitigate water penetration into the composite and then to decrease the real cathodic surface area.

The Reno Ruddervators are also primed with an anti-static paint and then painted to the customers’ choice, then balanced before being released for installation.

“If we let our units go without priming and paint, we might face an additional liability area, so its best that we do it in-house.”

Tests results were logged and included testing for torque, tensile strength, galvanic corrosion, torsion, and all the other considerations in manufacturing a replacement part.

“Why would we throw away these magnificent airplanes because we don’t have replacement parts for them?” Stiles questions. “I don’t have a million dollars to buy a nice new 4-place aircraft, and a two seater is just too small for my mission, and even those can easily run over ½ a million dollars.” He goes on.

“We understand that there is not enough profit in building replacement ruddervators for the big guys and the mom and pops can’t take the financial risk or locate the liability insurance, so that leaves a few risk takers and the geezer squad like us to come up with a reasonably priced alternative”.

When we first went shopping for financing, Stiles approached his aviation insurer. “They immediately cancelled my insurance. Not that I had done anything – we were still in the ‘considering’ phase. So just thinking about building ruddervators was bad enough to rattle the insurance issue, which we consider to be one of the biggest hurdles.”

Renovation Aviation LLC started in Stiles’s garage in St. Petersburg Florida and they are now building a facility in Live Oak, Florida. “We wanted to be around a strong aviation community but rural. This county in Florida, Suwannee has more private airstrip subdivisions than anywhere else in the world. The homeowners are typically retired military pilots or FBO operators who want to be around like-minded retirees, and we hope to tap into that community for our future employee base-more geezers.” Says Stiles.

FAA applications have been submitted and the boys are working with the Atlanta ACO to get their ticket. “The first set will go on our D-35 for field testing, and we have already had requests for more info on when they will be available to those in need.”

“Pricing is undetermined as yet but will be reasonable” Stiles goes on, “we have no interest in gouging – we’re all retired and in pretty good financial shape, but it is a business, we have investors and we need to show a profit and pay back our investment group as well as paying our team a good wage for the quality workmanship that will be required of them.”

“We are grateful to Walter and Olive Beech and the original Bonanza design team lead by Ralph Harmon to allow us to participate in the continuation of the V tail legacy. We hope that our little contribution will help keep the fleet flying safely for decades to come.”

Stiles can be contacted by email at sparkskeywest@gmail.com.