REPRINTED FROM SPORT AVIATION, AUGUST 1997

ART MATTSON'S
AMAZING
CHEROKEE 140
BY JACK COX

173 mph... in a Cherokee 140?

Denver to Oshkosh (903 statute miles) nonstop at an average of 127.4 mph....in a Cherokee 140?
No, those weren't typographical errors in Sun 60 and Great Cross Country Flying Race reports in past issues of Sport Aviation. They were just a couple of the amazing statistics chalked up by Art Mattson of Woodstock, IL. in his 1967 Hershey bar winged Cherokee 140, N1690J. He has been racing the airplane in the Sun 60 closed course air race at Lakeland, FL. since 1992, with the following results:
1992 1st in class - 149 mph
1993 1st in class - 160.86 mph
1994 1st in class - 173 mph
1995 1st in class - 153.54 mph
1996 1st in class - 153.64 mph
1997 1st in class - 154 mph
The 1992, '95, '96 and '97 speeds were race averages from a standing start around a triangular course, and the 1993 and 1994 numbers were representative of top speeds on the straight-aways. The speeds from 1992 to 1995 were set using a stock 150 hp Lycoming 0-320, and the 1996 and 1997 speeds were set the same engine boosted to 160 hp by the substitution of higher compression pistons.
Note that all these speeds were ground speeds timed by persons other than Art Mattson and were in competitive events against other aircraft. Art makes no claims other than these for his Cherokee.
So how does he do it... in an airplane for which Piper claimed a max. level true airspeed of 144 mph?
It all started in the 1990's when Art bought N1690J and decided it needed better short field performance. He had been attending every EAA Convention at Oshlosh since 1972 and had picked up a lot of performance tips in the forums. He was especially impressed with what he heard about the benefits to be derived form vortex generators (VG) and decided to give them a try on the Cherokee. Sure enough, on his first takeoff with four VGs mounted on each wing near the root, he was off and climbing in about 3/4 the length the airplane had previously needed to lift off. That was certainly impressive, but the big surprise was yet to come. When he leveled off and pulled the power back to normal cruise rpm, Art was surprised to find that his indicated airspeed was higher than it had previously been.
That didn't make any sense, he thought. VGs weren't supposed to enhance an airplane's speed, just its low end performance and stall characteristics. Yet in all his subsequent flights the results were the same. Depending on how smooth the air was on a given day, the Cherokee was averaging between six and eight miles per hour faster than it did before the VGs were installed.
"I got tired of people calling me a liar when I told them I could cruise at 130 mph with the VGs, so after I heard about the Sun 60 at Lakeland , I decided to fly down and enter. I won my class, so from then on I let the Sun 'n Fun numbers speak for themselves. That sort of started my drive for speed and I've been at it ever since."
About the same time he was experimenting with the VGs, Art also modified his Sensenich fixed pitch metal propeller. This involved cutting the ends of the blades into a concave shape like a hoerner wing tip. He picked up about three miles per hour in cruise with this mod, but it also increased the engine's static rpm, so he an additional two inches of pitch bent into the blades, which increased the speed by another six to eight mph, depending on the smoothness of the air.
On a roll now, Art kept heeding the words of the forum speakers at Oshkosh and sealed the aileron gaps and the stabilator trim tab gap, both with 3-M urethane leading edge tape. By sealing them one at a time, he found he gained two mph for each of the three gap seals Another pleasant surprise was a significant increase aileron effectiveness throughout the airplane's speed range, but especially, on the low end. Still more speed, although in small increments, came from installing late model Piper wheel pants and Met-Co-Aire wingtips. Art designed and built his own Hoerner type stabilator tips and achieved both a small increase in speed and more responsiveness at low speed.
JIM KOEPNICK

Not everything Art tried proved to be dramatically effective. Another idea he had was to place VGs on the top of the fuselage , just behind the windshield. His theory was since the top of the fuselage was an airfoil shape, it might benefit from the VGs in much the same way as the wing. The results were inconclusive, however. Art did not notice an increase in speed, but, on the other hand, there was no decrease or any sort of resulting handling problem.
"They didn't hurt me, so I've never bothered to remove them," Art says.
Completely caught up in his quest for speed, Art decided at the beginning to go the full nine yards with his modifications. He had the FAA put the Cherokee in experimental - R&D category and proceeded to obtain Supplemental Type Certificate (STC) for the wing mounted VGs, the aileron and the stabilator trim tab gap seals, stabilator and prop modifications - all of which he now sells to other Cherokee owners. Art has maintained his airplane the Experimental - R&D category because he is still trying to come up with more speed, but when his customers install his STC'd mods, their aircraft remain in Standard category. Each time Art has raced his Cherokee, he has had to have it re-licensed in the Experimental - Exhibition and Air Racing category, then return to R&D when he gets home. The paper work has been a real pain, but the FAA has been cooperative over the years.
Most recently Art has turned his attention to the engine compartment... where low drag guru Roy LoPresti says the most speed is to be gained in the typical production airplane. Art started out by replacing both mags with ElectroAir electric ignitions.
"I didn't have any second thoughts about replacing both mags. We've been using electric ignition in our cars for years, and even in the harsh winters we have in the upper Midwest, we almost never have a failure. They've worked perfectly in the airplane right from the beginning, and I've noticed a half gallon per hour fuel savings with the electric ignition. I ran a set of big wires to the plugs (Taylor "409" Spio Race Wire), one set that is shielded and one that is unshielded. This is to prove to the FAA that we don't need to shield the electric ignition. One of the benefits of using unshielded wires is that if one of them begins to go bad, you'll start to get static in your radio. It's a early warning that tells you to check your wires.'
As mentioned, Art also installed new pistons and pins, upping the compression to 8.5 to 1 and the horsepower from 150 to 160. He has STC'd this mod also, which carries no operating limitation. The engine still has a 2700 rpm redline and a 2000 hour TBO, but it does require the use of 100LL avgas.
"This does not appeal to those who want to use auto fuel, but my STC is a simple and relatively inexpensive way to gain an additional 10 horsepower by doing what amounts to a top overhaul."
At Sun 'n Fun in April showed up for the Sun 60 air race with a new cowling for his Cherokee. Still a work in progress, he is addressing cooling by reshaping and sizing the air inlets, experimenting with the air flow thought the cylinders and out the cowl, etc. Of great importance to Art is getting the head temperatures as close possible for all four cylinders. He aggressively leans his engine virtually from start up to shut down, and must have as small a differential between CHTs as possible to avoid cooking a cylinder.
Art also emphasized the importance of proper rigging.
"There are tremendous gains to be had in properly rigging a Cherokee. I've had people gain between five and eight mph just by rigging theirs properly. Getting ailerons and flaps set properly is really important. I try to get everybody to go back to ground zero, to what Piper calls 'neutral rigging' and start from there."
Art Mattson is typical EAAer in many respects. A native Chicago (Lake Forest), he grew up in the north side communities of Half Day and Prairie View. Attended the University of Illinois for two and a half years and dreamed of becoming an Air Force fighter pilot, but it just never worked out for him. He worked for U.S. Gypsum in their research department for seven years, worked for an aluminum foundry in Chicago and, finally, some 23 years ago he started his own water well drilling business, which he still operates today. Twenty years ago he moved his family to Woodstock, IL, just northwest of Chicago.
ARNOLD GREENWELL

Interested in aviation"...since I could see something fly," Art soloed in an Aeronca Champ in 1958, but had to put his flying on the back burner when marriage and the responsibilities of raising four children came along. Two of his sons grew up sharing his interest in aviation and became pilots, and finally in 1990 Art got his Private license.
"I was determined I was going to finally get to enjoy flying. I really enjoy piddling around and tinkering with things, developing stuff like the modifications on my airplane. My wife also flies, so I'm having a lot of fun and maybe helping others got a lot more performance and economy out of their Cherokees."
Art's goal is to get his 160 hp Cherokee up even with his sons' 200hp Mooney. He typically cruises between 150 and 160 mph and can top out right at the air plane's 171 mph redline. He'd like to make whatever structural changes are necessary to be able to safely boost his top speed into the 180 mph range and get perhaps another five mph in cruise. He recognizes this will be quite a challenge, however. The Cherokee was optimized originally for the ease and economy of manufacture, and, as a result, the early models were fairly dirty, aerodynamically. It was relatively easy for him to increase his airplane's speed by the first 10 mph or so, but it became increasingly difficult after that.

JIM KOEPNICK
"That's the fun part, though. The greater the challenge, the greater the fun."
If you want to talk to Art about his work and his Cherokee STC's his address is:
A.M.R.&D. Inc,11412 Charles Road, Woodstock, IL. 60098-8764, phone: 815/338-7347.