Cirrus ST50 First Flight

Norman Howell

Originally published December 1994

Cirrus ST50

On December 7th, 1994, I was privileged to make the very first flight in the Cirrus Design/Israviation ST50 turboprop aircraft. For those of you who don't know what this airplane looks like, check stage left! Perhaps a little background is in order as well.

Cirrus Design Corporation was founded by Alan and Dale Klapmeier. They marketed a kitplane called the VK-30 for quite some time. It was a 4 place composite pusher with conventional wings and tail. Recently, Cirrus has decided to shift market focus towards certificated airplanes. The first is the ST50, which was built under contract for Israviation, a new general aviation manufacturing firm which will be based in Israel. The aircraft here is the proof of concept prototype, from which the refinements to the aiframe's handling qualities and propulsion will be made prior to releasing the mold shapes for production in Israel. The production aircraft will look similar to this, but will have markedly different structure and interior. This plane is basically going to fill the market gap between the Malibu and the TBM 700. The next airplane from Cirrus will be the SR20, which was the "Hangar X" airplane that has been the subject of a recent series of cryptic magazine ads. While walking around at Oshkosh this surnmer, I went into the Cirrus tent and met a classmate of mine from the Academy named Dean Vogel. We were good friends at the Academy, and Dean actually helped me on my Quickie project while it was under construction there. Later, Dean was an F- 15 driver and now he is a Vice President for Cirrus. We looked at the ST50 and he told me what it was all about. I asked when the first flight would be and he said "Late this fall". I wondered aloud who the lucky individual was who would get to do that, and Dean got this big smile on his face and said, "Let's talk. Got any turboprop time?" As it turned out, they did not have anybody with the company who was trained to do flight test, and I had gotten some PT6 time under my belt thanks to the Flight Test Center. Now it was time to get a little PT6 flying in something that did not look like a shipping crate for a Twin Otter.

I went up to Duluth for a planning meeting in late September, and the airplane was just a shell. I couldn't see how it would be flyable before summer 1995, but just after the EAFB Open House, Dean called and said that they were just about ready. I m a d e arrangements for a short leave of absence from the F-16 CTF, and traveled to balmy Duluth a couple of weeks ago. The airplane was finished all right, and signed off by the FAA. However, we had a large series of bugs to work out prior to actually being ready for the first flight. Rigging a PT6 to run through a drive shaft to a constant speed prop that had feather and beta capabilities was not a trivial task. In addition, the control system had a lot of friction in it since it was rather hurriedly put together the night before the inspector showed up (been there, done that). We patiently worked everything out and made ready to go on December 7th.

The weather in the morning went down so we aborted after some high speed runs down the runway. Everyone was kind of disappointed since I had actually lifted off the day before for a short runway flight. After lunch the clouds all went away and the sun came out...but it only provided light (no heat) as the OAT was about 17°F that day. We made a last minute adjustment to the engine rigging and went out with Dean in the chase plane along with two engineers. They launched and I got ready for an airborne pickup just like at work.

The liftoffwas exhilarating and the plane flew quite well, although the lack of wing root fairings made a huge amount of drag and some moderate buffet...sort of like a T-38 in the final turn. The ailerons were almost perfect right from the start...very smooth with hardly any adverse yaw, a very small friction/breakout band and a dead linear force gradient...perhaps some of the best lateral handling qualities I've seen in a production plane. Yaw was deadbeat and pitch was decent with a pretty fast response for an aircraft this large....but there was quite a bit of buffet on the horizontal so it may not have all been working. The propulsion was flawless and I tried to compare the engine related workload to what I imagined one would deal with in a big old Cessna piston twin with GTSIO engines...the ST50 is almost as simple as a jet with electronic engine controls.

Basically I flew a first flight profile similar to what was in a TPS Test Management Program paper called "Have Plan", one of whose authors was our own Russ Erb. It works great and a version has been incorporated as a script for first flight into the EAA Flight Advisor Program. I will probably write about that and publish a sample set of cards in an upcoming newsletter for us or for EAA Chapter 49. I came back to land after about a 40 minute flight...not too bad a touchdown but the main gear geometry does cause a bit of an abrupt derotation. Beta was very good and Our Lady of Blessed Deceleration was smiling upon us as I slowed down without having to use the brakes. There was a big crowd back at the ramp (natch!) and I got the customary bucket of water dumped on me...brrr! The sun had done little to warm up the day, and it was still 17° out there! It was a great feeling to have had such a text book flight and I look forward to going up there for some more flying of the ST50.

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Revised -- 22 February 1997