Nose high testing is what it sounds like. The nose of the aircraft is pitched high off the ground to simulate landing and take off. It is another component of ground testing, which is the group of tests that aircraft must undergo before first flight. Ground testing is mandatory for any new aircraft design or for an aircraft that has undergone significant structural modification.
So what role does nose high testing play?
Manufacturing Engineer Ruslan Pshichenko, explains two different use cases for nose high testing — and why it’s yet another milestone for XB-1 before first flight.
What is nose high testing?
RP: Nose high testing plays a critical role in ground testing during XB-1’s development. We ran the tests over the course of two days and we lifted the nose 12 degrees (or 14.5 feet off the ground) to simulate landing and takeoff.
We attached the aircraft to the massive gantry system that was fixed on the floor. We did not use the flight hardware nose wheel axle for the lifting operation. Instead we used a custom made axle with lifting hooks that attached to the gantry.
Also, our team attached a load cell (directly above the spreader bar) so that we were able to monitor and ensure the aircraft did not want to tip backwards. (0 lbs reading on the load cell would mean the airplane is already starting to tip!)
There were two components to nose high testing when it comes to XB-1 — the fuel system and the forward looking vision system.
Okay, let’s start with the fuel system test. How was that test completed?
RP: In short, this test is completed to ensure that XB-1 will transfer fuel correctly across its five fuel tanks during take off and landing when the aircraft is pitched at 12 degrees. Why? Because we want to ensure that the aircraft is always balanced.
To begin the test, XB-1 was first filled with 386 gallons of fuel across its five fuel tanks. Then, we had our Chief Test Pilot Bill “Doc” Shoemaker sit in the cockpit. While the nose was lifted 12 degrees, Doc would use the fuel control panel to initiate and watch as the fuel transferred among tanks on the multi-function display.
In addition, one of the engineers was monitoring the fuel parameters at a workstation nearby to see what the fuel tank levels were in real time.
During flight, the airplane’s center of gravity needs to be balanced in order for the pilot to control the aircraft. If all the fuel is incorrectly transferred between the five tanks, it could move the center of gravity either too far forward or or aft, which would make controlling the plane very difficult for the pilot — so we always want to make sure we are maintaining that balance.
Why do aircraft have multiple fuel tanks?
RP: Aircraft are not like cars, where you have plenty of space in the back for one large fuel tank. An airplane is a more contained area, so when designing a plane, you try to squeeze tanks wherever you can find the space that would also ensure a correct aircraft center of gravity location. The fuel tanks can be broken up strategically to better manage center of gravity and fuel slosh, reduce fuel tank pressures against adjacent structure, and eliminate shared failure modes in the system.
On larger aircraft, this tends to be in the wing, but for XB-1, the wing is really thin for aerodynamic purposes. XB-1’s five fuel tanks all live in the fuselage instead.
Let’s move onto the forward looking vision system. Can you explain this test?
RP: Due to the long nose & shape of the aircraft, a 12 degree angle of attack is quite steep when it comes to take off and landing — so much so that XB-1’s pilot would not be able to see out of the windscreen. The solution? A forward looking vision system, aka two cameras attached to the nose landing gear trunnion, projecting the horizon on a screen for the pilot to see the runway during take off and landing.
In order for this to be effective, we need to set the angle of the cameras to be pointed at the horizon when the airplane is at 12 degrees. The mounts for XB-1’s two cameras were designed with this in mind, so we can adjust the pitch of the camera.
Originally, when the cameras were installed, we didn’t know what angle they needed to be at, hence this nose high test was required so the team can position & lock both cameras in at the right angle.
Before starting the test, we chose a target building approximately 2 miles out on the horizon that we could see line-of-sight from our hangar at Centennial Airport. We then picked a corner of the building and had the aircraft pointing at it. To ensure the aircraft was truly facing the building, we used two plumb bobs (one hanging from the boom, another from the AFT fuselage, see image below):
From there, we ensured that the camera was looking at the same point as denoted by the two plumb bobs.
Was there a test pilot involved in this test?
RP: We had Doc get in the cockpit before the aircraft was raised 12 degrees. Doc was then able to tell us what adjustments were needed to point the camera at the correct spot, both longitudinal and directional adjustments were required. We had a technician adjusting the cameras per Doc’s direction until they were perfectly aligned with the corner of the building.
Once we were happy with the camera positions, we lowered the aircraft. Next, we made these adjustments final by drilling holes through the mounts to hammer in pins in order to prevent the mounts from ever moving.
We then lifted the aircraft nose up one final time to ensure nothing moved & to ensure Doc will have the optimal visibility through the forward looking vision system for take off and landing in Mojave once we begin flight test.
This is just one of the many components of ground testing for XB-1 to prepare for flight test. Learn more about XB-1’s ground testing here.