Flying the Fastest Sweet Potato in the Bunch
Text and photos by Budd Davisson, Air Progress, Oct '90,


Geronimo Down
The Hoerner tips greatly improve the Geronimo's slow speed handling

Factory specs, verified by a long string of pilot reports, show the single-engine ceiling has risen from 5200 ft to 12,000 ft and the single-engine rate of climb is now 500 fpm where the original only had 180 fpm at sea level (if lucky). One of the factory's favorite demonstrations has been to take the airplane off with one engine caged. Obviously not a recommended procedure, this action certainly shows a Geronimo is not an Apache.
The 60 percent cruise at 10,000 feet is reported by Seguin to be over 190 mph on only 17 gph, which isn't bad. The increased cruise speed is nice. but the other performance increases are equally important. For instance. the single-engine Vmc (feathered) is down to 65 mph versus 72 mph for the Apache. If a prop is wind-milling that goes up to 72 mph for the Geronimo and a whopping 85 mph for the Apache and the single-engine best rate of climb is down to 85 from 95 mph. This lets the Geronimo fly approaches at 85-90 mph without being in a questionable operating environment. Slower approaches mean shorter landing rolls, which are made even shorter by the dual caliper brakes that can really drag the Geronimo down from speed in a hurry.
A small number of Geronimos were made with the 170 hp 0-340 Lycomings and one of them belongs to Henry Tienken of Lafayette, New Jersey. Where we usually wind up cruising all over the countryside to find airplanes to fly for pilot reports, in this case it meant walking out my hangar door and across the runway to where Henry ties his Geronimo down at Aeroflex-Andover Field in New Jersey.
Henry has owned his airplane for nearly six years and the purchase was the result of looking long and hard for one. He was looking for a twin that would give him the room and robust performance of his old Navion when he stumbled across the Geronimo. The plane had been donated to JAARS, the missionary jungle fliers, who found the airplane really didn't fit their mission. But, the Navion did. So, a little negotiating later, the airplane was on its way to New Jersey.
Tienken's airplane is a full Geronimo conversion, meaning it has all of the airframe and interior mods. It's not unusual to find an airplane that has only as partial mod, maybe the engines and the nose but not the interior or wings. Only the 170 hp engines keep his from being absolutely full-boat. As such it can't take advantage of the gross weight increase that comes with full conversion — his is still 3500 lbs while a 180 Geronimo is 4000 pounds.
As would be expected, walk-around is typical Apache/light twin. The airplane has no unusual features, other than peaking at the rudder hinges, which is actually a holdover from the old Apache days when the rudder took quite a beating during single engine training. The Seguin people replace most of those parts during the conversion. They, however, cannot get away from the periodic inspection and AD on the propeller clamps.
It had been many years, 15 or more, since I sat at the controls of an Apache of any variety and I had forgotten that the cabin is really large and comfortable. If Henry was looking to replace his Navion with anything of like size, he didn't have much choice — it had to be a Geronimo (or maybe an Aztec). The perceived size of the cabin has been noticeably increased by the simple addition of the third window, which lets a lot of light into the back area where the fifth seat hides.
The panel is so large that it's fortunate all the pilot-accessed controls are well arranged because the pilot would really have to stretch to get something on the other side of the panel. The Geronimo panel is laid out along modern thinking, with the standard "T" pattern and a sizable space (completely filled in Tienken's airplane) for the central radio stack. Seguin couldn't do much with the placement of the various air controls that hide down under the throttle quadrant. Getting to those requires you already know where they are and can grab them blind, or you lean down and squint.
The fuel system. hasn't been modified from the Apache and the control panel still sits down between the seats, with the cross feeds locked out by a little gate gizmo.
The trim is the old overhead crank system Piper was so in love with in the 1950s, but there's a variation on a theme with two cranks mounted on the same shaft — a short one for the rudder and a long one for the elevator. The rudder trim is very logical, since cranking it one way or the other is the direction you'd want the nose to move. The elevator crank has potential for being initially confusing, although it is clearly marked and, for reasons I can't explain, I didn't once start the wrong way and then have to backtrack.
The Lycomings popped into life on the second blade, as the single starter switch was toggled first left, then right. Pressures up, we headed out toward the end of Aeroflex's 2000 ft runway.
I hadn't read the Geronimo literature prior to the flight, which turned out to be a mistake. I didn't realize the airplane was being touted as a semi-STOL airplane by virtue of its ability to get on and off so quickly. Its stall speed is so much lower and the plane accelerates so quickly, that Seguin usually advises getting the airplane off the runway about 65 mph and hugging the ground until best single engine climb speed is reached, a matter of only a couple of seconds. Original Apache technique was usually to keep on the ground until at least Vmc was reached because the airplane accelerated so slowly and was so marginal if one should quit. Many pilots would hold the Apache on until they had best single-engine climb speed. As it turns out Henry still uses Apache technique, mostly because he doesn't have the 180 engines. From what I saw, I'd say the airplane could still be lifted off and accelerate since it moves out much faster than an Apache and accelerates in the air much faster than on the ground. Also, it takes a fairly heavy hand to keep the Geronimo on the ground that long. As soon as the yoke is lightened up, it literally leaps off the ground.