Determination of Landing Parameters of High Performance Aircraft Using a Photogrammetric Approach 
Gary Robertson 
Gary Robertson & Assoc; Inc. 
Scottsdale, AZ USA 
COMMISION V 
ABSTRACT 
Photogrammetry is used as a structural test program to determine 
landing parameters for F18 aircraft. Parameters such as horizontal 
speed, sink, pitch "and roll rates are determined with high accuracy. 
Procedures are developed to relate this information to stress for the 
under carriage support structure. Photogrammetric procedures are 
discussed along with the post processing of the photogrammetric 
data. 
1.0 INTRODUCTION 
Photogrammetry lends itself very well to Aerospace applications. 
Our first photogrammetric aerospace application involved 
monitoring flight parameters of Remote Piloted Vehicles during the 
1970's. Later in 1980 we started to apply photogrammetry for 
aircraft crash analysis and later to quality assurance of aircraft 
manufacturing, in particular the F18 Hornet Aircraft. 
1.1 Project Definition 
The study undertaken involved photography of F-18 aircraft within 
three seconds prior to WOW (weight on wheels) and -.5 seconds 
after WOW with medium format cameras. Utilizing close range 
terrestrial photogrammetry the following parameters such as sink 
and horizontal speed, pitch, roll angles and rates were to be 
accurately measured. 
1.2 Background 
The project task was in support of the International Follow On 
Structural Test Program (IFOSTP). Discrepancies between the 
available Maintenance Signal Data Recording System (MSDRS) 
and actual occurrence have been noticed when comparing landing 
parameters with an independent high sampling pulse code 
modulated (pcm) data source from the Canadian Air Force 
Aerospace Engineering Test Establishment (AETE) flight test 
program. It was found that the aircraft's vertical velocity at weight 
on wheels appears to be largely overestimated by the MSDRS. 
Actual values were found to be 40 to 70 percent less than the 
MSDRS estimate. The likely reason is that the MSDRS computer 
algorithm for Vv yields the largest value out of the two seconds 
preceding WOW. While United States Navy (USN) pilots literally 
drop at constant sink rates on carrier decks Canadian Forces pilots 
"check" their landings in the last few seconds to reduce ground 
impact. At present, structural life estimates of the F-18 
undercarriage and support structure is based ori McAir calculations 
and tests conducted for the USN and make use of CF MSDRS 
data. The life obtained is thus likely to be overly conservative. 
Photogrammetry proved to be the best test alternative considering 
the time frame for acquiring the test information. 
2.0 COMPUTER SIMULATION 
Due to the varying situations and applications that may be 
encountered in a close range photogrammetric survey, a computer 
simulation of the survey is an invaluable tool. In this case, the 
coordinates of designated locations on the aircraft were generated. 
By assuming the locations of the expected camera station 
coordinates and orientation parameters, the photo coordinates of a 
point are generated synthetically. In order to provide a realistic 
simulation, these synthetic photo coordinates are disturbed (usually 
by a random number generator). This has the effect of synthetically 
introducing random errors into the system that are expected to 
occur in practice. By processing this data through the bundle 
adjustment program, various configurations of targeted points, 
camera station locations and control point information can be 
examined with respect to the achievable and expected accuracy. 
The simulated data indicated that overall accuracies would be from 
17 to 24 mm. for the sequences from 3.5 seconds to WOW. 
3.0 INTIAL FIELD PREPARATION 
The cameras selected for the photogrammetric monitoring were 
Hulcher model 108 70 mm camera with a maximum frame rate of 
20 frames per second and shutter speeds up to 1/4000 of a second. 
All cameras were equipped with a 165mm lens. The cameras were 
calibrated and checks were made for film flattening at the higher 
speeds. 
During the preliminary discussions for this project we considered 
type of cameras to be used, frame rate, and problems of 
synchronizing the cameras. In addition, simulations were analyzed 
for possible camera locations and target and camera distances. 
Several tests were made with the Hulcher camera to test for non- 
mechanical or non-electrical synchronization. These tests include 
the use of a Flash or strobe, Argon pulse flash and lights. As a 
backup Canadian air force personnel developed a rotating 
mechanical target large enough to viewed by several cameras. The 
target was tested and proved quite effective (Figure 1). The overall 
accuracy would be dependent on the ability of the cameras 
synchronizing. 
In addition video was used to supplement some landing sequences. 
3.1 Initial Photogrammetric Work 
Convergent photography was taken of a CF18 aircraft on the 
ground at a distance of less than 10 meters as-shown in Figure 2. 
The images were processed through our Bundle adjustment 
program, this provided a very accurate control reference for the 
aircraft. The control values would be used to determine accuracy 
and check data for the ground to air photography of the CF18 
aircraft. 
An arbitrarily defined survey system was established and control 
targets were placed and surveyed within the field of view as 
described by the simulation. 
Since the purpose of the study was determining landing parameters 
we wanted the data to describe at best typical landings. It was for 
this reason that the pilots were not briefed on what we were doing to 
avoid the possibility of altered landing procedures. All film was 
processed on site.