The author and his partner finish a great airplane project and prepare it for the airshow circuit.
(From Kitplanes, 11/1995, Page 6, C)
By Randy Harris
Although many in the aerobatic community are moving swiftly to trade in their biplanes for monoplanes, there are still those of us who relish the attributes of a mature biplane design. The Skybolt is just such an airplane. It possesses many of the basic features a biplane is chosen for, and with some further development, it can become a solid performer in both competition and airshows.
Our Skybolt 300 was created with all of the latest available technology and the results are outstanding. The advantages of the monoplane can clearly be seen in aircraft like the Sukhoi SU-29 and Extra 300. Many times I have compared our Skybolt to the Extra 300 as they are similar in size and powered by the same 300-hp Lycoming engine. (See Table 1.) As you can see, the Skybolt empty weight is 75 pounds lighter than the Extra 300 even with the additional weight of a metal propeller. The Extra 300 and Skybolt 300 have similar performance. But I will concede that the Extra’s seating and visibility are much better than in the Skybolt.
Starting with a Model
I got excited about the Skybolt some years ago when my uncle built and flew a one-fifth-scale R/C model of it. Flying qualities were exceptional. The control response was smooth and it was very easy to fly, and I wondered if the full-scale version flew similarly.
Later I flew Dean Hall’s fabulous Skybolt, and I was hooked. In 1989 I sold my EAA Biplane and went searching for a partially completed Skybolt. What makes the Skybolt even more appealing is its large size, which is perfect for airshow work. For the last few years I had considered the possibility of getting into this exciting area of flying, and with a Skybolt I could get serious.
While attending airshows in the past, I have overheard several airshow spectators comment on the difficulty of determining the attitude and orientation of the smaller biplanes. The Skybolt would solve that problem, but it would require aerodynamic and control modifications to improve its agility to the standard set by the monoplanes.
Getting Ours
This Skybolt was built as a partnership with a coworker, Scott Runyan. His part in the project was mostly financial, but he did contribute to the construction as often as he could. At the beginning of the project I was on temporary assignment in Yuma, Arizona. Scott remained in Long Beach, California, and his help included a lot of time driving to Yuma. George Solsten was the originator of our Skybolt, having started his Skybolt project in 1978 at Flaybob Airport. Scott and I met George in the spring of 1990. George, age 76 at the time, lost his medical, but it took some coaxing to convince him to let us have a shot at finishing his airplane. We worked out a financial settlement and left a down payment.
George was a machinist, and as part of the deal, he agreed to help make any parts we might need. But George was not to share in the completion of the Skybolt. On the day we arrived to make the final payment, Scott and I were told that while on his way to the airport, George was killed when his car was struck head on by a drunk driver. George was a meticulous craftsman and the work done on the Skybolt was exceptional. He had completed the basic fuselage structure, the wing assembly, and had started on the sheet metal work.
In effect, this left us with a kit version of the Skybolt. We were a little intimidated by George’s high standard of quality, and admiring his craftsmanship gave us a new goal. We vowed to do our best to finish the Skybolt to the same standards.
Maximizing the Term “Experimental”
All modifications were carefully considered to extract the maximum advantages with a minimum of additional weight. The most significant modification was to increase the aileron area by 50%.
This seemingly minor modification created a domino effect. First, it necessitated increasing the tensional rigidity of the wing. We did this by changing the wing’s leading edge to plywood and gluing it to the front spar, creating a rigid D-tube. In addition, the rib bays of both wings at the I-struts were boxed in to further increase tensional rigidity. Along the remainder of the wing, stringers and plywood sheeting were added from the front spar on the upper surface to the 55% chord point. This was done to eliminate airfoil deformities due to fabric loading under high G conditions, thus increasing the G-to-buffet margin by 22%.
We sheeted only the upper surface because the positive-G excursions are larger than the negative. The wing, as you can see from the photos, almost looks like a composite.
To combat the fabric/paint fatigue damage inherent with larger engines, we added false ribs to the upper wing bottom surface inside the propeller arc. The lower wing bottom surface is plywood sheeted in the same area.
The ailerons retain the Frise design but have been recontoured with balsa fillers. The section thickness of the aileron was increased 8% by changing the top surface only, thus making it thicker than the wing section immediately in front of the aileron hinge. Tuft testing has shown greatly improved airflow attachment with this modification.
Randy Harris and his wife, Linda, are delighted with their 300-hp Skybolt.
The aileron end ribs were filled to reduce the gap between the aileron and wing. A new inboard hinge was added to each aileron to distribute the loads.
When flying Dean Hall’s Skybolt, I noted that the plans-built aileron forces were pleasantly light but lacked a sufficient center feel for point rolls. To remedy this on our airplane, the ailerons’ trailing edge was changed to a blunt configuration that is 3/8-inch thick. Although we achieved excellent roll acceleration and rates, the resulting increased stick forces are enough that spades were required to bring the ailerons back the original light feel.
Powering It
Our Skybolt is powered by a 300-hp Lycoming IO-540-K1G5D. With headers and some mild tuning, it now puts out about 330 hp. This is the dual magneto/dual oil cooler version. It has a unique accessory case that enabled us to use a very short (10-inch) mount. We have no recesses in our firewall and are able to remove and service all of the accessories without pulling the engine.
Our engine was removed from a Piper Lance. During the removal we took photos to be used for reinstalling the engine on the Skybolt exactly the way it came off. The nosebowl is the standard Firebolt version from Starfire Aviation. It’s a little pricey but well worth the cost. The inverted oil system on our airplane is also unique in that we still use standard oil pickup with the inverted system. I am surprised no one has tried this yet on the “cookie sheet” oil sumps. So far we have had great results in all flight phases. (Most installations use a welded boss on one side of the sump.) Engine temperatures are regulated by a cowl flap at the base of the firewall. The tight engine installation gave some concern during the building stage. However, it has proven to be very satisfactory.
Drag Reduction
The Firebolt mods by Mac’s design can add substantially to the speed of any Skybolt. The Marquart/Stinson gear is a little heavy, and so is the canopy arrangement, but both are worth the extra speed. The canopy has given us a great appreciation for the durability inherent in Mac’s. We have given hundreds of rides and have had no problems getting people into and out of the Skybolt with no harm to the airplane.
Attention to detail in the finished aircraft emulates the workmanship of George Solsten, the first builder of this Skybolt.
Most homebuilts tend to be on the fragile side and when exposed to the general public, they suffer. The airplane can be flown with the canopy open up to 4 inches. The wingwalk areas of our Skybolt are cleverly hidden under the fabric. Instead of the usual black nonskid paint on the wing surface, we installed a serrated plywood panel under the wingwalk area and doubled the fabric covering over it. This is small potatoes as far as drag reduction is concerned, but it works well and gets rid of a common eyesore. Only time will tell if the fabric will hold up against the abuse.
To further prove our insanity, we installed flush fasteners on the fuselage and fabricated fairings for every appendage. Normally one does not consider a biplane worthy of drag reduction, but we needed to improve the Skybolt’s acceleration and close the gap between normal level flight speeds and vertical maneuver entry speeds.
Getting an airplane to the airport is one of those awkward, necessary steps.
Runnin’ it up. The 300-hp Lycoming IO-540 deserves a good static test before final assembly.
An under-the-skin wingwalk looks good and reduces drag a bit.
Here’s final paint …some of it, anyway. Two years went into the paint design and application.
The cockpit is Spartan. Both front and rear have a minimum of instrumentation, flooring and amenities with the exception of cabin heat. Because we lack an interior, the noise level is high, and in the future we intend to address that. If I were to build another Skybolt, I would modify the seating to add more rake to the seat backs and more seat pan area for thigh support. Up to this point all the biplanes have similar seating, which at best is poor. We really need to start designing planes from the inside out.
More Important Stuff
The remaining important contributor to the Skybolt’s construction was my wife, Linda. We weren’t yet married as I began this project, and I became convinced that if any woman could love me through such a period of selfish reclusion, I had better take a closer look at the possibility of matrimony. So, during a long dusty drive across the hot Arizona desert, towing Skybolt parts to Yuma, I proposed.
Timing might have been a bit inopportune, but after a long pause, she looked over from the seat of the truck, wiped back the sweat and faintly mumbled those unforgettable words: “Well… OK.”
Ah, the beginning of true romance. A man in a pickup truck, towing an airplane, and a new promise for the future. We were married aboard a McDonnell Douglas MD-11.
Linda shared my joy each time I clawed at the gate of our condo when the UPS van parked out front. There is only the childhood anticipation of Christmas that can compare to the experience of finally receiving a new Aircraft Spruce order.
The ritual was repeated each week until the Skybolt was finished. I miss those days.
The Paint Controversy
Our Skybolt’s paint scheme has been a subject of controversy. I can at least give you some insight into the thinking behind the two years it took to finalize it. First, since we intended to do airshow work, we wanted a bright, colorful design. We also wanted to break from tradition and use some modern colors, yet retain some conservatism that has been generally found in aviation paint designs.
Our best sources for ideas were the sport truck and boating magazines. In addition, a trip to your local R/C model field will confirm that many model airplane paint schemes contrast colors to aid in the pilot’s ability to distinguish attitude and position. We wanted to afford the airshow spectator the same consideration.
For example, when our Skybolt is in a rolling maneuver, the contrasting light-colored bottom and dark top gives good attitude awareness, and the red wingtips add a fluid consistency. Our Skybolt has been likened to a clash between a Navaho Indian blanket and a Nike tennis shoe. But an astute observer will notice that the design on the wings is not feathers, but a red-on-blue fade transition that is pulled apart like a puzzle. Look closely!
The covering is the Poly-Fiber process up through the white Aerothane base coat. Fabric is the new 2×2 style. The colors are PPG DBU base coat with clear Durathane over the entire airplane. The DBU base coat is great due to its 20-minute drying time, which allowed the color coats to go on quickly.
I think this is the first time this system has been used on a fabric airplane. The shine is incredible and conjures up questions on whether the paint is dry. It has the appearance of being laid on heavy, but is only two coats of very thin base coat and two coats of clear. If anyone has experience with the DBU/DU process, I would like to know about long term results. It sure is an easy way to paint.
The red-white-and-blue paint scheme is the key to the Skybolt 300’s excellent airshow visibility.
| Table 1 | ||
| Extra 300* | Skybolt 300 | |
| Type | monoplane | biplane |
| Seats | 2 | 2 |
| Wingspan | 23.4 ft. | 24.0 ft. |
| Length | 26.3 ft. | 21.0 ft. |
| Weights: | ||
| Empty | 1470 lb. | 1395 lb. |
| Gross | 2095 lb. | 1950 lb. |
| VNE | 220 knots | 208 knots |
| Cruise | 178 knots | 176 knots |
| Roll Rate | 340°/sec. | 290°/sec. |
| Climb | 3200 fpm | 3200 fpm |
| Range | 415 nm | 390 nm |
| *Data provided by Aero Sport Inc. | ||
Interested in Performance?
The Skybolt weighed 1395 pounds empty with a minimum of instrumentation. To save more weight, we have no gyro instruments and no extensive avionics. Only a King KX 155 navcom and KT 76A transponder are mounted below the panel. Surprisingly, the Skybolt will top out at 214 mph in level flight. Cruise speed at 75% power at 6500 feet is 202 mph (176 knots) at fuel consumption of 18 gph, but we usually chose a more reasonable 186 mph at 60% power for 13 gph. To save fuel, we do most of our acrobatic practicing from 5000 to 8000 feet and 60% power. At the lower altitudes and high power settings, the Skybolt will reward the uninhibited with a vertical four-point roll, plus one aileron roll and still cap off at the top. The roll rate is timed at 320°/second. We have set the VNE at 240 mph (208 knots) and routinely zoom past the 200-mph mark during practice.
All control surfaces are mass balanced for flutter protection, but the elevator balance has caused an unusual stick force anomaly: During spins the stick will go hard over (full aft if upright or full forward if inverted), and a small force is required to center the stick for recovery. We have discovered the cause of this and will eventually incorporate a fix.
Scott and I are both very happy to be finished with the Skybolt (so are our wives), and we are both practicing as often as money permits. We would be happy to share any information we learned about the Skybolt with anyone else building one. It would seem a tragedy to waste everything we learned to long term memory loss.
SKYBOLT PLANS are available from Steen Aero Lab for $165. Contact the company at 1451 Clearmont St. NE, Palm Bay FL 32905; call 321/725-4160. An info pack costs $10. [Address updated from original article ed]
Skybolt Update
It’s been almost a year since this article was written. Since then, quite a saga has unfolded around us with the Skybolt as the centerpiece.
The biggest thrill was to receive one of the coveted Plans Built Champion trophies at Oshkosh ’94. This was completely unexpected since by then, our Skybolt had been subjected to an abusive 150 hours of hard acrobatic practice and was definitely not typical of the pampered showplane examples around us. I commend the Judges for their ability to appreciate details beyond the surface.
The Skybolt also won first place awards at Merced and Copperstate.
Getting to and from Oshkosh from Long Beach was an adventure in itself. We flew formation off the wing of a friend’s Turbo Comanche. The disappointed owner had to run his turbos to keep up with us. Since then we have passed Mooneys, Bonanzas, a few twins and a Staggerwing Beech. The Staggerwing was a little tough, though; we were indicating 210 mph as we slowly overtook a beautiful candy apple red example. I had no idea they were that fast.
The Skybolt provided an even greater adventure during a coast-to-coast trip from Long Beach, California, to Virginia Beach, Virginia, with photographer John Getsy. Along the way we gave rides to other Skybolt builders. Many got pumped up with enthusiasm and went on uncontrolled building sprees.
In Virginia — my home state — I offered rides to any relatives willing to go. One never knows how many relatives he truly has until showing up with an offer like that. Aviation awareness in my family has reached an all-time high. The return flight took us through Texas during the October floods of 1994. We spent four days in Houston dealing with low IFR, floods, floating fire-ants, snakes, a tornado and a hotel fire — enough fun, fear and education to fill a separate article.
Once in the Skybolt we were warm and dry, which is more than I can say for all the Stearman pilots departing their annual fly-in at the same time — at 100 mph and in an open cockpit. You can only take so much character building.
Our Skybolt is now part of the family. It is a tremendous source of fun and adventure for Scott and me. We share it with others by giving rides to those who may never get a similar opportunity. We display it at West Coast fly-ins, and we’ve recently provided airshow performances for groups raising money for charity such as the Young Eagles. The Skybolt is a crowd-pleaser wherever it appears. Airshow fans rave over the paint scheme and visibility during the aerobatic displays. It is a big airplane and many are surprised by its agility.
The bottom line: We’re delighted with our Skybolt and plan to keep it a long, long time.