Flight test 1 through 3 were conducted to investigate power required, power available and neutral point determination for the purpose of compiling a comprehensive performance summary table for the Kopp BD-4. The summary table contains both operational and design performance specifications useful to both the engineer and pilot alike. In this report results from flight test 4, phugoid mode determination, will be discussed and the summary table expanded to include those results.

The longitudinal phugoid mode is physically described as a damped vertical oscillation of the aircraft’s c.g. trajectory about the horizontal flight path with the velocity decreasing (or increasing) during an altitude increase (or decrease).[1] Mechanically this mode results in an exchange of potential energy with kinetic energy including subsequent loss of energy due to aerodynamic drag, which provides damping to the system. Generally, an aircrafts phugoid mode even when unstable does not greatly affect a pilots ability to safely handle the aircraft as the frequency is typically much lower than the frequency of pilot corrections. However, during IMC flight where pilot workload is increased, due to navigational procedures (chart reading, added communications, etc), an unstable phugoid will require the pilot to diligently monitor the aircrafts altitude and airspeed providing less hands free time for chart and communications work. This is especially true in single place aircraft where a single pilot must handle all the duties of flight. A total of six data collection runs were conducted in the Kopp BD-4. Three runs each were conducted at airspeeds of 100 and 140 mph (V_ias). Both stick free and stick fixed response were recorded during this test. Additionally, the prototype data acquisition system G.A.I.M.S. (general aviation inertial measurement system) was utilized to capture the phugoid mode by recording variations in normal acceleration during a single stick free maneuver. The data collected by hand will be used to help validate the general accuracy of the G.A.I.M.S. unit.

Part I – Flight Test

General Information

This test was conducted in the Kopp BD-4 on 8 Sept, 2000 departing from Monterey Peninsula Airport (MRY) at 10:00 am. Conditions at take-off were:

Wind: 310/8

Alt: 29.96

Sky Clear

Rwy: 28R

Crew and altitude assignments were as follows:

Table 1 Crew and altitude assignments

Crew	Altitude	Gross Weight (approx)
LT Ken Kopp / LT Jeff D’Latri	5500 ft	2025 lbs

The test area was restricted to Salinas Valley from Salinas to 15 miles South East of King City. Crew coordination and a thorough test procedures briefing preceded each flight. Data collection sheets were developed, printed and discussed in detail prior to flight as well. Specific responsibilities were delegated as follows:

Table 2 Flight Responsibilities

Responsibility	Pilot at the Controls	Pilot Not at the Controls
Flight Safety	Primary	Secondary
Airwork	Primary
Test Procedure		Primary
Data Recording		Primary
Communications	Primary	Secondary
Navigation	Secondary	Primary
Visual Lookout	Secondary	Primary
Emergencies	Primary	Secondary

ATC flight following was utilized to the maximum extent possible to aid in collision

avoidance. King City and Salinas Muni were designated primary diverts in the event an emergency due to mechanical failure or weather occurred.

Flight Test Technique

The aircraft was trimmed in level flight at 5,500 ft (indicated) at an initial airspeed of 100 mph (V_ias). The aircraft was slowly decelerated by smooth application of back stick (yoke) against trim until an airspeed change of –20 mph was attained. The yoke was released and the aircraft allowed to fly hands free until all oscillations had ceased. Upon yoke release a stop watch was started. Altitude, airspeed and time were recorded at the highest and lowest altitude of each cycle. This process is identical for the stick fixed case except that the yoke was held in place by the pilot throughout the maneuver. The entire procedure was repeated at an airspeed of 140 mph. An extra run was conducted for each airspeed where the initial input was an acceleration vice a deceleration. Additionally, during the 100 mph stick free (decel) run the GAIMS unit was started at exactly the moment the yoke was released and data recorded automatically throughout the maneuver. This data was serially transmitted to a host laptop computer connected to the unit and stored in a file for future analysis.

Part II – Data Reduction

All recorded data was entered into an excel spreadsheet for data analysis. As was done in previous flight test all airspeeds and altitude measurements are corrected for static position errors according to the following relationships.

Data for the first 100 mph stick free run was collected and reduced in the excel spreadsheet table shown below.

Table 3 100 mph Stick Free (initial decel)

100 mph Stick Free with initial decel of 20 mph							Oat	63 F
Trim Conditions		Vcas	Vcas
Hi	Hc	mph	mph			sigma			Alt	A/S
5500	5507	100	102.03	Cas	Hi	std	Hpc	Hc	Amp	Amp
	Time	A/S	delt Vpc	mph	ft		ft	ft	ft	mph	e time
	0	80	6.36	86.36	5600	0.8528	27.35	5627	120	-16	0
	12.18	110	0.58	110.58	5450	0.8481	3.49	5453	-54	9	12.18
	28.42	85	4.99	89.99	5560	0.8523	22.85	5583	76	-12	16.24
	45.85	105	1.27	106.27	5480	0.8492	7.21	5487	-20	4	17.43
	54.68	90	3.85	93.85	5500	0.8517