Test Report: Initial Taxi Tests

Lee Erb
EAA Chap 1000 Det 5, Arlington TX

Originally published May 1998

(Lee Erb recently did some initial taxi tests on his new project, and was nice enough to forward us this report)


After delivery on March 12, the Carburetor Air inlet system was cleaned of a Dirt Dauber Hotel which had restricted airflow to approximately 40 percent of the normal area. The system consists of a vortex sand remover with a standard see-through one-pint glass container (Kerr Mason Jar) and an oil bath cleaner. Obviously the system had been designed like all good agricultural aircraft (fixed wing and rotary wing) to operate in high dust environments.

Planned eye surgery (it was highly successful) on the Test Engineer resulted in delaying initial taxi tests. This permitted complete cleaning, sand blasting, and painting of the air inlet system. Even new vibration reducing couplings and clamps were obtained.

New electrical cables were obtained and installed along with the restored air inlet system during the recuperation period. A new battery was obtained but was not permanently installed to prevent accidental discharge due to inclement weather.

Test Planning

On April 25 the last minute equipment required for the engine start and initial taxi tests were staged. Modern video equipment (shoulder mounted) was prepared and two still cameras with telescopic lens were included. The mental equipment checklist was reviewed with many "what ifs" for emergency wrenches of various sizes, gasoline additive, and pillows for the ground crew.

A mental test plan was conceived with alternate scenarios depending upon the weather (changing) forecast and the number of the ground crew personnel that would be participating.

No test plan was written for in the heyday of this Flight Test Engineer they were considered somewhat restrictive. The pilots would sometimes come to early morning takeoff and get strapped in before taking on extra oxygen and asking, "What are we going to do today?" Fortunately I did not have project pilots that "needed extra oxygen" (We did not have any oxygen on board.)

The Day Arrived

On April 26, a quick review of the handbook description of the engine and operational controls was made before traveling 55 miles to the test site.

The battery was installed after electrical system review and minor modifications were made to the wiring system (enlarged the hole in the ground cable so that it would go on the starter attachment bolt). The gas cock was fully opened and the test engineer, wearing a common Project Police (jungle) hat, blue denims, and blue chambray shirt, climbed up to the cockpit. The SFTE emblemed jacket was not worn because of relatively warm ambient temperature.

After giving proper warning to the ground crew (now photographers) and assuring all was clear, the ignition switch was pulled and the starter button was engaged. Unfortunately the power cables to the starter relay were reversed and nothing clicked when the starter button was engaged.

The Test Engineer dismounted from the seat and nearly fell due to the lack of properly located steps. The gas cock was closed. The Electrical system was reworked. This rework requirement was not unexpected since no electrical system diagram was available since the system was changed from a positive ground to a negative ground and the generator had been replace with an alternator of higher voltage.

The Test Engineer remounted, warned the ground crew (now photographers), the ignition switch pulled and the starter button engaged. Rewiring the power cables to the starter relay produced the proper clicking but no reaction from the starter motor.

The taxi lights were turned on and functioned properly. They were turned off as they were not needed although rain clouds had darkened the afternoon sky and a light mist sometimes appeared.

The Test Engineer dismounted taking the route directly to the starter motor. Inspection of the cabling to the starter confirmed that the power line had been secured finger tight during the previous wire installation session. At once the cabling was secured with the proper sized wrench. Now that success was imminent, the gas cock was fully open. (Partially open would probably have resulted in a gasoline leak onto the electrical system.)

Engine Start!

The Test Engineer remounted, warned the ground crew (now photographers), the ignition switch pulled and the starter button engaged. The starter operated properly. Adjusting the governor and with a little erratic excitation of the choke, the engine sprung to life with a couple of puffs of oil smoke belching from the exhaust stack. (It must have been that Liquid Wrench that did not separate the pieces of the exhaust system like it was supposed to do.)

The sound of the engine start was recorded by a shoulder mounted video recorder. However, no specific engineering noise data were recorded or attempts made to determine if Cat II or Cat III noise requirements had been met. (We had left our Cat I (Tosha) with our Bulldog I (Little Mack). Someday we will tell you about our Little Mack ‘n‘ Tosha at home.) One ground crew member did remark that the engine "ran soft."

Technical Discussion

The engine was permitted to idle a bit. Governor response was checked and appeared to have immediate response to control inputs. (Nothing like those 10-second responses of the Westinghouse J-22’s in the Phantom (Phantom ONE that is) or the greatly improved 5-second response of the J-34’s in the Banshee.)

Due to low system rpm (450 idle), the alternator was excited by the alternator exciter button so that it would charge. The battery was initially charged at about 12 amps and gradually reduced to approximately 2 amps.

Engaging the engine to the motive-power units was not smooth due to the high gain built into the control unit. Also, even though the foot print was large, the pressure had been sufficient to settle the wheels into the sand an extra two inches between March 12 and April 26. This required a bit of rocking to get the wheels out of the sand.

At some point in the longitudinal dynamics of moving from the hangar ramp (parking area) the exhaust stack moved and hit the cowling. There was no dangerous condition apparent for initial taxi tests so the testing was continued. (The exhaust stack is a planned replacement LRU before major operations are conducted and when funding becomes available.)

Taxi tests were conducted for approximately 10 minutes. Nose wheel steering gain and response were evaluated. The gain was relatively low. The nose wheel response was immediate, however, the vehicle response was sluggish. The nose wheel tended to slide sidewise in the sand. At this time no effort has been expended to determine if it is due to a tire design defect, influenced by the vehicle c.g. location, or is inherent in the narrow tracking of the dual nose wheels.


After being parked next to neighbor’s industrial tractor, the engine was shut down by reducing governor rpm setting and closing the ignition switch. Following instructions in the Operator’s Handbook, the primary control lever was placed in neutral. No tie downs were installed because the Hangar Owner was going move it after he cleaned the hangar and stored his newly acquired lumber.

Two minutes later the force of gravity produced a horizontal lateral movement in the reverse direction. Fortunately the castering nose wheel castered 90-degrees in the sand and thereby produced a horizontal force that reacted against the horizontal gravitational force and the vehicle momentum. No damage was induced before it was reparked and chocked.


Several still JPEG photos have been reduced from the video and a 10-second .WAV file was produced from the same source. The development of the still photography film will be subcontracted in the near future to the local grocery store.

Considering that it has been 30 years since the Test Engineer had soloed a similar vehicle, and it has been 60 years since he had dual instruction on a narrow tracking dual nose wheel arrangement, and he did not get bucked off (no seat belt but a strong Control Wheel) due to the high gain of the motive control unit; the engine start and initial taxi test were deemed highly successful.

Future Testing

Next taxi tests are tentatively scheduled for May 3 depending upon weather. Tests will include attempts to reduce the gain in the clutch. Other tests will be determined by the availability of a "slow moving vehicle" plate and condition of the driveway at the Texas Buckeye Ranch.


And, alas, immediately after reaching home base it was realized that the gasoline additive had not been added to the old gasoline. The gasoline in the tank has been there only six months and had not congealed yet. There will be another week to add the additive.

Ya know, maybe a written test plan would have helped.

"And then it rained."

(Clutch? Slow Moving Vehicle plate? WHUT in the HAYLE is he talkin' about?! Click to see a documentation photo from the taxi tests. All will be made clear…)

EAA Chapter 1000 Home Page
E-Mail: Web Site Director Russ Erb at erbman@pobox.com

URL: http://www.eaa1000.av.org/fltrpts/taxi_test/taxi_test.htm
Contents of The Leading Edge and these web pages are the viewpoints of the authors. No claim is made and no liability is assumed, expressed or implied as to the technical accuracy or safety of the material presented. The viewpoints expressed are not necessarily those of Chapter 1000 or the Experimental Aircraft Association.
Revised -- 13 March 1999