CHEROKEE OWNERS…….

FASTEN YOUR SEATBELTS by Jim Cavanagh 

If you have been a Member of the Piper Owner’s Society for very long, then you already know about Art Mattson. The Cherokee 140 owner who has developed numerous performance mods for this often overlooked family of Pipers and started a company to make these mods available to other Cherokee owners. He had won a number of races, both speed and endurance in his prototype airplane, before losing it in a freak accident in July of 1997. Since then, he has installed a couple of the mods on a new airframe and continues to develop more changes that take an already good airplane and transform it into a real performer.

 

AMR&D INC. Formed

Art’s company is called AMR&D, Aircraft Modifications Research and Development (not Art Mattson Research and Development as some may think). His original intentions weren’t to start a major modifications company, rather enable his little Cherokee to fly out of a short field located behind his home. Like all of us, having your house and airplane on the same piece of property is a lifelong dream and to make it come true, he had to perform some sort of magic on his plane

We all know that this type of magic is possible and that it can be performed two ways. You can either say "abracadabra" and install a huge expensive engine or say " presto Change-o" and add a STOL kit. Unfortunately, in aviation the term magic is interchangeable with money. Art took a different tack: he asked friend Chris Heintz, Austrian-born aircraft designer and father of the Zenith kit aircraft, if vortex generators would be a possible answer.

 

Rechanneling Air Flow

Vortex generators are little fences that re-channel air as it flows over or around an object. It is a fluid dynamics process where flow, eddies and currents create positive and negative air pressures and either create or defeat lift. Quite popular on more sophisticated airplanes, VG’s are used to enhance flow optimally to provide lift, speed or enhance control effectiveness at lower airspeeds. NACA discovered the benefits of VG’s way back in the forties and fifties, when wind tunnel and tuft testing of airplanes was the new science. Learning that air could actually move forward on a wing at some speeds or angles of attack, scientists developed ways of rerouting the slipstream to optimize its effectiveness.

 Although the original configuration enhanced low end performance as expected, Art discovered that his VG’s could also provide an unexpected increase in top speed. It is this configuration which he has certified. After a couple of years, he received a multiple Supplemental Type Certificate and since then has sold 200 VG kits. 

I first met Art at Sun ‘N Fun in 1992. We were both racing in what was them called the Sun 60 Air Race for stock land modified production aircraft. Art surprised everyone by defeating higher horsepower airplanes in his category, including a Cherokee 180 and an Archer with a tailwheel conversion. Since then, he has gone on to win his division every year, achieving speeds of up to 173 mph. Art will be the first to tell you that the speeds for these races, although documented, are dependent upon the formula, course, and winds for that particular race. Even though, from a standing start the numbers are pretty impressive. 

Anyone who races becomes seduced by performance and Art was no exception. From the VG’s, he began to scour the airframe for hidden speed. He developed a set of speed wheel pants that were just too complicated, a prop mod that was eventually STC’d, and an engine horsepower upgrade, which is also certified. He went on to a redesigned elevator tip, rotating beacon fairing, a uniquely simple and effective aileron, flap and elevator gap seals. Cumulatively, these changes can add up to 20 or more mph to a Cherokee airframe and varying reports from his customers confirm this. 

This past September, I was able to take Art up on an invitation to visit and fly his and one of his customer’s airplanes. The last time I was in Woodstock, IL. at Landings airport, where AMR&D is located, it was 7 degrees F. This time it was a scorching 90-95 degrees F at 10 a.m., and the humidity was around 74%. There was a little breeze to make things easier on us, and in a nutshell, it was not a good day for performance. 

I flew two aircraft that day, Art’s 1965 Cherokee (N6995W) and a 1965 PA28-140 owned by AMR&D customer, Vince Gazarkiewicz. Vince’s airplane was your typical Cherokee, with a decent interior, good paint, capable radio stack and was flown regularly VFR. The engine had just been overhauled and the 160hp conversion was installed at the time. Along with the engine conversion, the propeller mods had been completed, modifying the tips and increasing the pitch from 58 to 60 degrees. The prop is a Sensenich 74DM series. Naturally, the hallmark of an AMR&D converted airplane, the VG’s were installed. The only other mod was the installation of the Hoerner-style Met-Co-Aire wingtips. 

Vince was gracious enough to turn the airplane over to me for the afternoon. Our preflight showed that everything was in good shape, the oil was still clean and the fuel tanks were about three-quarters full. N4626R had no wheel pants, which according to the book increase the speed by 2 mph across the board.

 

Technique by Mattson

The aircraft was not light with the fuel, Art and myself on board. We held the door open until the runup was completed and only buttoned up when we were ready to roll. I had asked Art to fly left seat and show me his technique for a maximum performance takeoff. I contented myself to sit there and watch his movements and the airspeed indicator as he advanced the throttle and dance the pedals to keep us lined up and it was quite a show.  

With the VG’s, airflow over the Cherokees wings is greatly enhanced. We had watched a video tape made by a physics teacher at Embry Riddle, showing the stalled condition of the wing at various stations at low airspeeds. I don’t know if Art has tuft tested the wing with his VG’s installed, but it felt like angle of attack had been taken out of the equation when he rotated and lifted off. His technique is to accelerate the airplane to 45mph, quickly pull in two notches of flap, count to two and pull the wheel back into your stomach. It is a very daunting procedure from where I was setting. 

But it worked! I couldn’t believe the deck angle as we sprang off the ground. It was more like a Maule than a Cherokee. The entire takeoff run had just been about 400-450 feet, and I would estimate that it was just a second or two to 50 feet AGL. The book says the roll alone would have taken 800 feet on a standard day, and another 900 feet to clear the 50 foot obstacle. We had to have been flying out of another book!

 I quickly calculated that the fuel, Art and I weighed in at 570 lbs., roughly 280 lbs. less than the normal useful load, but still it was about an 8,000 feet D.A. day!

 Art held the climb for a bit, then let the airplane accelerate to 70mph and he raised a notch of flaps, then at 80 mph indicated he cleaned up the airplane and we began to fly normally. The rest of the climbout was at 85 mph and about 500 fpm. 

Once at 3,000 feet MSL, we poured the coals to her and waited as the noise level and airspeed raced each other to the max. It takes a lot of time to overcome the inherent drag of an airframe, particularly one that is not cleaned up much. Eventually, though, we settled in on a steady 139 mph TAS and a veritable symphony of wind noise and engine roar. A passing thought was that designers who don’t expect their airplanes to go fast don’t do much to cancel out wind noise. Art needs one more STC!

 Coming back to the airport, Art demonstrated a short field landing and with an approach at 70 mph, cutting back the throttle over the fence, we quickly dropped in and touched down at about 47 mph, about 8 mph lower than the book. With judicious braking, not heavy, we were able to stop in about 400 feet.

 

The Novice’s Turn

We next taxied back for my turn and from the right side I tried to reproduce Art’s takeoff. It wasn’t bad, but I experienced what a lot of his customers do: it doesn’t feel natural to be so abrupt in a Cherokee. Art had told me of some of his customers complaining that their takeoff performance doesn’t match his. He has questioned them and flown with some and determined that most of the performance complaints is due to their lack of aggression with the controls. 

"They’ve got to trust the numbers," he told me, so I did. Still, it felt funny forcing the airplane off the ground when all you’ve ever heard and read about Cherokees tells you it can’t be done. I shot two takeoffs like this before Art had me stop and let him out. He wanted me to experience what the airplane would do when it was light. And it was dramatic! 

It may be difficult for some of you to get excited about a dowdy old Cherokee. Its reputation is that it is about as exciting as a wild night in Mayberry with Aunt Bea. True, it will never be a Cessna 185 or a Maule MX-7, but performance, as is thrill, is relative. I shot three takeoffs solo and each was a little shorter and a little steeper. Flying alone is simply fun. I have a tendency to be slightly distracted when someone is with me, whether in an airplane or on the golf course…anyplace where focus has an effect on your personal performance level.

 When we stopped for lunch, Art showed me the propeller that had been on the airplane when Vince brought it to him. It was so far out of tolerance that you didn’t even have to use a measuring device to see it. The blades had been dressed so many times that they were very thin and merely taking off and cruising had caused them to be bent forward. I put a tape measure on it and one blade was an eighth of an inch longer than the other, and the blade width was different on each end. Sensenich has definite parameters for their props and this one just needed a coat of paint to be a permanent wall decoration.

 

Gap Seal Installation

After lunch, Art , his son Scott and I cleaned the wings for the installation of the gap seals. Vince had asked for the seals and Art thought it would be a good time for me to fly the airplane before and after. We didn’t have time to do a complete installation, since the application time takes about an hour per control, so I had to fly it with just the aileron gaps sealed. Art said that this is the most important of the three.

 Flying an airplane on the same day is a great way to get before and after impressions. I was fortunate to be in the right place at the right time. By this time, the fuel was down to about one-third, but it was up to 96 degrees. Power up to 45…two notches…count to two and pull. By now I was getting fairly comfortable with the routine and noticed almost immediately how much smoother the roll force was. They just felt more solid with the gap seals. I flew wing wobbles up to 3000 feet and left the throttle in all the way to see what happened to the top end. Again I had to wait about 5 minutes. This seems like a long time in cruise mode, but the result was an increase over the earlier reading by 2 mph. Allowing for a few bumps, the needle on the True Airspeed Indicator vacillated around 141 mph for so long that I considered this new speed to be valid.

 I headed back to the airport and decided to shoot one more takeoff. It was too hot for any more of this foolishness, This time I got cocky. I was feeling good and when I pulled her off I really pulled her off. It was the only time I got the stall horn to honk and when I got back, Art was grinning ear to ear. I guess I had nailed one!

 Art and his assistant Will had been installing wheelpant on Art’s personal airplane and it was time to take it up. This airplane has always been slower than his first Cherokee. Whether rigging, tools left by the builders or something else, it just hasn’t been able to produce the good numbers. Art reasons it might be the design of the aileron skins, which have the stiffening beads fabricated outward, as opposed to the inward beads of his original plane. At least the performance increase from stock to modified is the same in both, which demonstrates the effectiveness of the mods, but Art has the speed bug now and he can’t help but be disappointed.

 The airplane has the prop mod, gap seals and VG’s and that is about it at this point. He has decided to keep the engine in the 150 hp configuration to aid in evaluating the different mods he has planned. He admits that he had been bitten by the speed bug and went all out for speed and not all his customers are interested in an engine mod. He needs to know what each mod will do with a standard engine.

 

Difference in Takeoff Performance

Naturally, the takeoff performance is different. It was still light years ahead of a standard Cherokee, because of the VG’s. With a stall speed lowered by 8mph, you’re going to see a difference. At top end, the airplane can achieve 135 mph, and normally cruises at 120mph and I could feel Art’s frustration, since his first airplane had broken 180 mph over a dozen times under Sea Level conditions. On a more pragmatic level, I realize that this is a test airplane and that each mod will generate a performance change. Each of these will then be documented against a known value. The speed will come later, as will the increased horsepower, I’m sure. I asked Art to shoot a couple of takeoffs for the camera, and the day was over.

 

Working with the FAA

Men like Art search for speed like treasure hunters look for gold. It is easy to become obsessed and in aviation this leads to a great deal of frustration. Ask anyone in the business; the act of developing a mod is a time consuming but rather enjoyable voyage. Gaining FAA approval, on the other hand, is the difficult work. Every time a new inspector is assigned to your area, you have to begin again. The inspector’s learning curve about you, your business, and your reputation is steep and interminable. What kind of person is he, or she? How does their personality affect their work? Are they decision makers or simply marking their time until retirement?

 Where this affects the consumer is in the pricing of the mods. Most of the cost of a mod, whether it is Art’s or anyone else’s, is in the development of the paperwork. The materials in a set of vortex generators cost about $60-70. But it took a couple of years, drawings and countless flight tests to get them certified. A few customers complain about the prices Art has on some of his STC’s, but that just reflects what you find throughout the rest of society.

 

Other Mods

AMR&D has a variety of mods in the works, including electronic ignition, aerodynamic cowling/nosebowl and a tuned exhaust. He was also studying a set of stall fences that will be mounted at the wing/wingtip line and has had fairly good results from a short test run.

 

A Popular Cherokee

During a debriefing with Vince, he had an opportunity to puff up his chest and lay on the anecdotes.

Before the mods, he had taken nearly the entire runway to get off with full fuel on a hot day. Now he regularly outperforms his friend in a C-172 with a STOL kit. Another friend, working on his commercial rating, has access to a number of aircraft and prefers the handling and performance of 46R. In cruise, the airplane could barely achieve 115 mph and 2,500 rpm with throttle wide open, and now Vince plans for 125 mph on a hot day, and 130 cruise on a cool day, these at 2,400-2,500 rpm.

 Landings are different, also. His approaches need to be flown at 70mph and 60-65 over the fence or he’ll float forever. He told me that after the mods, he had to learn to fly the airplane all over again. Does he like it? Well, he put seventy hours on it in August and September.

 Mattson has a good thing going. He has a small, basically one-man shop, very unpretentious and quite casual. He has been lucky enough to turn his hobby into a business and if he sells enough mods he may be able to turn it back into a hobby at some point.

 As with the rest of aviation, different businesses use different methods to achieve the same result and the true beneficiaries of their competition are the aircraft owners. Art has some high profile competitors who probably have good products, but I can’t write much about them because I haven’t flown their airplanes. I have flown Art’s airplanes and can vouch for the amazing differences his mods create. I’ll tell you, they’re like no other Cherokee 140’s I’ve ever flown.