After digging into some background information i ran into an article in a "Code One Magazine" which may be of interest. Although a totally different type of aircraft, the article deals with a ground test to simulate a certain failure in the fuel system of a F-16. The similarity with the subject T7 is that its engine is also electronically controlled and the result of a simulation, engine rollback, comes remarkably close to what was experienced on G-YMMM. I know, totally different aircraft types but engine response seems not so different. Please read on . . . .
In this simulation the writer of the article, a senior experimental test pilot, describes the following:
Quote:
"Recently, I saw how the engine would quit in other than the normal airstart-test type of atmosphere. Although these tests were accomplished on the ground, I saw several things that I hadn't seen before, things I'd like to pass along. You can never know too much about the airplane.
I am sure that you are aware that there have been some as yet unexplained flameouts with the F110 engine. What we attempted to do was to try to induce as many potential malfunctions in the airplane as possible in order to shed some light on some of the past accidents/incidents. The airplane was tied down in the normal manner and then fully instrumented to record all the parameters of interest.
One large impression that I had was how tenaciously the engine will cling to life if it has fuel.
On one test, we had artificially closed the master fuel shutoff valve to only five percent of capacity, that is, ninety-five percent closed. (There is no way that you can do this in your airplane without some really weird failure, or a plumbing change like we had for the purposes of this test.) The boost pumps were off and the refueling door was open so the system was depressurized. The engine was in idle and running just fine. The test point called for me to snap-accel the engine to ninety-five percent. The engine only briefly touched ninety-five percent, immediately rolled back to ninety-two percent, and hesitated there for a few seconds. It then rolled back to about eighty-seven percent for a few seconds. Subsequently it flamed out, but had an automatic restart accomplished in time to catch the rpm at eighty percent. It stayed there for another few seconds, and then flamed out again. The engine then auto-transferred to secondary engine control, or SEC, and got another auto restart at seventy-two to seventy-three percent. It maintained this condition for a little while and then flamed out again, with an auto restart in SEC at about sixty-five percent where it stayed for a while and then slowly continued to decay toward zero rpm. From this, and other similar runs, I feel that if the engine is operating properly, you have little fear of its quitting as long as the aircraft is providing fuel." Unquote
The article was written in 1990.
Here is the link to the complete article:
http://www.codeonemagazine.com/archi...out/index.html
In the simulation above it was elected to close the main shutoff valve for 95 percent, only 5 percent capacity, and the engine managed to retain RPM above idle several times for "a little while", even with boost pumps off and the fuel system depressurized (air refuel door open).
Focussing on the T7 dual engine roll back again, just suppose both spar valves had temporarily closed for, say, 80 percent (only 20 percent capacity remaining) with boost pumps on. Could that have resulted in engine roll backs to a stabilized thrust level above flight idle and cause cavitation at the engine pumps as the engines initially responded and then rolled back because reduced fuel flow did not meet engine demand?
I assume similar simulations such as mentioned above would have to be performed to find answers or are there other means (computer simulations?) to observe engine behaviour under such conditions?
Regards,
Green-dot