Dhumla Ground Trial 3

after hauling around 4t of fuel and performing the same exercises aircraft is taxiing back to the HAB. Crew report no obvious issues as long as the plane is handled properly. C7/Genesis will have a final ground test Mon before clearing the aircraft for flight trials

flight crew is already aboard the Dhumla, readying the aircraft for its third and final round of ground testing - time to see how she really handles when up to speed on the runway! We will barely avoid actually taking off, if all goes well

aircraft is ready and flight crew have permission to taxi out to Rwy27. All run-up tests will be done from this end of the runway as after Rwy09 runs out and you drop off the threshold it is a steeper slope downwards that ends up in the water

aircraft is lined up for its first run, which will accelerate at full throttle to 40m/s and then use the wheel brakes to come to a stop. Aircraft has been loaded with just over 1/4 of its fuel capacity, an average flight between any two airfields around Kerbin

aircraft is taxiing back after traveling 1.2km down the runway - Tedman kept the throttle on a little too long they actually hit 53m/s but still had no trouble coming to a stop & held a straight line. That's a little over half the length of the runway they used up

set for the second run, this time after accelerating to over 40m/s the engines will be put into reverse thrust mode to bring the plane to a halt without using the wheel brakes until speed drops below ~10m/s

that time it only took just over 300m of runway, which is as expected. Wheel brakes on this aircraft are not meant to stop it after landing, but are mainly used when taxiing. Now that we have confirmation of good performance from both, time to move on to the first real test!

already near the end of the runway, after a quick turnaround the crew are set to perform a takeoff roll, which will bring them up to 80m/s, after which they will apply reverse thrust and wheel brakes to come to a halt as soon as possible - hopefully before running out of runway

after nearly 700m to reach takeoff speed the aircraft was brought to a stop with over half a kilometer of runway left. So far, so good - the aircraft was designed to be able to abort a takeoff attempt. Crew is taxiing back for the next test, which will have flaps set for takeoff

design data for the aircraft shows that in this configuration we need to be able to exceed a 9° angle of attack to remain flying, and the aircraft can handle a 10° angle of attack before stalling, hence our takeoff speed of 80m/s

yikes! That was a stressful test as the aircraft swerved back & forth across the runway after Aldeny applied the brakes and kicked in the reverse thrusters. Thankfully neither wing dipped low enough for the propellers to gouge out the surface & they stopped well short of rwy end

taking their time on the taxi back to calm down nerves. It got a little tense there obviously. Crew transcript as the aircraft careened down the runway:

Ted: you got it?
Aldy: I've got it
Ted: got it?
Aldy: got it. I got it
Ted: okay just let me know-
Aldy: I GOT IT!!

not quite, because the aircraft won't be maintaining that speed, but will still be accelerating, and quite quickly at that. More specifically this is the rotation speed to begin the takeoff where the nose can begin to be lifted off the runway twitter.com/baserunner0723…

we just repeated the test with similar results, although the crew was ready for it this time and were able to work together to keep the aircraft under control better. They will reset for one more run but raise the flaps back up again

test complete, no troubles at all coming to a stop. Lowered flaps causing instability is not something that was anticipated - hurray for testing! The Genesis team will have to figure it out but for now aircraft is taxiing back in to receive a full load of fuel for one final test

weighed down with 4t of fuel, the aircraft is taxiing back out to Rwy27. Flight crew will actually back it up after turning around to ensure they have the most room possible. Even though takeoff speed is now only 5m/s faster, the mass that is moving is much greater!

so ends this week of operations. Catch up on anything you may have missed via our Ops Summary and have a great weekend! kerbalspace.agency/?p=8523