Experimentals have come a long way
How far? Dave gives his history of almost 2 decades trying and flying aircaraft from all over the world... full article
The Thunder MustangThere is no feeling like raw power. When I worked for Air Ambulance, I loved doing new pilot training in the Lear 20 series. Thereís no other civilian plane that will give you that push back in the seat, 6,000 fpm, nose-to-the-sky feeling of a light Lear.
Well, now there is... and itís called the Thunder Mustang. Mere numbers donít describe the feeling you get when you push the power up on this plane. Truthfully, it kind of snuck up on me, too. During the first taxi tests and several early flights, the power was brought in slowly. On each subsequent flight, I brought it in a little faster until, finally, I was just letting off the brakes and firewalling it. But it wasnít until I saw a video of the first public flight that I realized my take-off rolls were about seven seconds and initial climbs at about 40 degree angles.
Where did this plane come from and how did I get to be the lucky one to play with it?
I met Dan Denney several years ago and worked with him on the testing and subsequent redesign of the Kitfox IV Speedster. During this program he showed me a picture of an engine and told me of this next project. I must admit to being a bit skeptical as many had tried to capture the aura of a Mustang, but no one had really succeeded. Years ago I joined a club in California that had a Mustang and a T-6. It was truly a great adventure but the cost and logistics were just too much and I sold my share. Now Iím really lucky as my friend Jerry Gabe lets me fly is rare A-model Mustang.
My doubts about Danís plane increased when I got to fly the Stewart Mustang at Oshkosh two years ago. The S-51 was a blast to fly. It felt like a Mustang and even though the performance was not quite as inspiring as the full size airplane, I figured it should fill the needs of those wanting a scale P-51. Fortunately for all of us, Dan pushed on and has created a plane that has a mystique all its own. Iím constantly amazed at the enthusiasm this plane garners wherever it goes. At Oshkosh and Reno the Thunder was displayed next to the Legend, and even though the Legend was flying and the Thunder was just a static display, there was a sense of something special about the Thunder Mustang. Personally, I donít think that anyone could look at that Falconer V-12 engine installation and not be awed. It just looks right Ė like an engine truly made to fly.
This is a theme that runs throughout the project: donít just make it right, make it the best possible. For example, this is the only composite kit I know of that has no wet layups. Because of the use of carbon molds, the parts are so exact you just Hysol them together. Even though the cores are an aluminum honeycomb, which is really state-of-the-art, Dan is now incorporating a process to anodize the core so it could pass the Navy corrosion tests. Now, how much salt the core is going to see sandwiched between carbon skins, I donít know.
As the date for the first flight approached, Dan and I decided to tow the airplane to Boise International Airport for the first flights. Because we were testing a new engine and a new airframe, we wanted all the advantages of Boise: a longer runway, no city at the end of the runway and advanced crash/fire rescue capabilities. We decided to do the first few flights in Boise with our engineering test personnel before our first pubic flight back at Nampa.
Before the first flight, I was treated to a new experience. Ryan Falconer, who designed the engine, came out to do the last minute tweaking on the installation. I sat in the cockpit while he sat at a table next to the plane with his laptop computer. He would ask me to run at such and such rpm, then heíd look at the timing, fuel flow, etc., and make small changes to the parameters and transmit the changes to the engine. The engine just kept getting smoother and smoother, yet not a wrench or screwdriver was anywhere near it. This engine even has the capability of telemetry where ground observers can see real time whatís happening as I fly by. Ryan says that the unit is also capable of receiving changes in the air from the ground, but because of the consequences of a bad keystroke, we have not tested this feature. We can, however, download the data and phone link it to Ryan and have him modem changes back to us to reload into the onboard computer.
So how does it really fly? Letís go for a flight and Iíll point out some of the unique things about the Thunder Mustang.
First off, just starting the engine is different. There is no mixture control, no primer, no carb heat or alternate air; just turn on the master and ignition and hit the red button. The computer will determine if itís a hot start or if youíre at a high altitude airport and akjust the timing and enrichment as required. This engine is really silky smooth. As you taxi out, a slight S-turn is required to clear the area directly in front of the nose. To maneuver in tight areas, just as in the full size Mustang you push the stick forward of neutral and the tail wheel unlocks for full swiveling. In the runup area, set coolant and oil doors, set trims to zero (there isnít that much torque) and youíre accelerating so fast that the rudder is best just left at ď0Ē), flaps up, bring the power up to 3,000 rpm, cycle the propeller a few times and then turn off the left engine. The Falconer V-12 is built and installed as if it were two six cylinder, inline engines, each with an independent computer for ignition and fuel injection, that just happen to share the same crankshaft. This is an area that makes no sense to me. How can you turn off six cylinders and have the engine still stay smooth as silk? Maybe Ryan can explain it. Anyway, the rpm will drop to 2,200; then return to ďBothĒ; and then turn off the right six and see it also drop to 2,200. Now a final check around the cockpit and weíre ready to go.
Acceleration isnít really the term to describe the launch of the Thunder Mustang. You fly off at about 90 mph, select gear up and keep pulling back to stay below 150 mph until the inner gear doors close, then stop pulling back and youíre at 175 mph, which is your best rate of climb speed. Several times Iíve pegged the VSI and it goes to 6,000 fpm. Thatís 60 miles per hour vertical speed. One oddity of the climb is that you canít get a steady manifold pressure reading because the Vision Micro Systems, a neat box with all the engine gages in an LCD display, reads to the tenth of an inch and youíre losing five inches every minute in climb and the tenths just keep scrolling by.
As you level off for cruise, usually within three minutes of take-off, the speed builds rapidly and at 65% power at 10,000 feet, the true airspeed is 308 mph burning just 25 gallons per hour. The plane is very stable solo and at full aft CG it is still positively stable but the stick force per G is very slight, so aerobatics with passengers will require a light touch. The other oddity of aft CG is on landing roll. A little more attention is required on the rudders as the directional stability is slightly degraded. Nothing like a Pitts or such, more like a Cessna 180.
The wing on the Thunder has a modified airfoil that allows the speed to build and not have the ailerons get really heavy. Rolls are easy with just one hand, unlike the full size Mustang which gets very heavy on roll above 250 mph. On the other end of the spectrum, slow flight is easy. With liquid cooling you can reduce power without fear of shock cooling and that big prop is a great air brake. Flap speed is 170 mph and the gear speed is 150. The Thunder is a rock and flies the pattern at 120 with great visibility and allows for a wheel landing at about 90. The stalls, both clean and dirty, are non-events and, again, as in the takeoff, you can add power and not worry about torque rolls and such. The one bad facet of this plane is related to that big prop. My first three attempts at a power-off 180 degree approach were unsuccessful and I had to add power to make the runway. Finally, by pretending Iím a helicopter and autorotating at 120, I found I could make a 180 approach from 1,200 feet abeam the numbers. Pulling the prop back to low rpm really helped, but in the event of loss of oil pressure that wouldnít be an option. I think a couterweighted prop would be an asset as the loss of oil pressure makes the blades move toward high pitch, low rpm.
What do I think it takes to fly this plane and what would you fly to get ready for it? Anyone with some Glassair III or Lancair IV time would be fine. Some tailwheel time also is a must, but except for the T-6 there isnít a tail wheel airplane that would simulate the handling very well. Itís a system plane and the pilot must monitor temps and adjust coolant and oil doors, etc., but the flying tasks are easy. Dan, who owns a Glasair III, is going to ride with me in a T-6 at Hollister when we bring the plane down for the ground vibration test prior to the high speed flutter tests. After an hour or so of landings, heíll be the second Thunder Mustang pilot. (Editorís note: Thatís Dan in the rear seat in this monthsí cover shot and in the photos accompanying this article. Shortly after this article was written the Thunder Mustang was flown to Camarillo, CA where ground vibration testing was administered by Sandy Friezner, a specialist in this highly esoteric field who is often called upon for his services by the major aerospace firms. Martin Hollmann did the flutter analysis and reported that is was the first instance in which he found no flutter speeds within the range of analysis, which in this case was 0 to 600 knots true airspeed.)
Weíre so pleased with the way this plane gets up and goes that we have entered the Aeroshell 3D Speed Dash at Sun Ďn Fun í97, and we also plan on racing at Reno in the Unlimited Category. I guarantee youíll be able to pick out the sound of the Thunder from the other planes on the course.
Postscript: Itís been two years since Thunder Mustang closed its doors but there is light at the end of the tunnel. A new group bought the rights to the tooling and the plan is to start producing the kits again. Contact www.thundermustang.com for more information. Dan Denny started Precision Aircraft to assemble Thunder Mustangs for customers all over the world. Contact Dan at www.Precision-Aircraft.net
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