Solution to problem?
Goodyear Crosswind Landing Gear
Rumoured control issues in Richard Branson's WhiteKnightTwo rocketplane-piggyback "mothership" craft appear to be persisting. Reports have it that the innovative aircraft smacked one or both of its tails against the runway during a recent test flight. The WhiteKnightTwo prototype on the runway in Virgin video The tale of the …
Obviously for a new machine it's necessary to not only practice maneuvers but also expose handling flaws. However I wonder if anybody has done a rigorous analysis of the cost/benefit of landing practice in the form of "touch and go"? Brief scrutiny of the AAIB and NTSB databases reveals that for every actual off-field accident or genuine landing incident there seem to be perhaps 10 cases of aircraft being bent/broken while the pilot was performing landing practice maneuvers. Maybe there's a curve to this, with a sweetspot beyond which the probability of an accident increases with further practice?
Accidents don't happen up in the air, except in the extraordinarily rare case of a mid-air collision. Damage happens when airplanes encounter dirt, so it's no surprise that pilots tend to crack up airplanes during takeoff and landing practice. These skills are critical to practice on a regular basis. To fly an airplane is really pretty simple. Cruising from A to B is a no-brainer, and there's very little learning that takes place while in level flight or while making course corrections.
The place where flying skill comes into play is during the takeoff and (especially) landing phase of flight. That's when judgment of angles and speeds, maneuvering ability and multi-tasking all come to the fore. But for every hour of "normal flying", a pilot may only spend a minute or two on the transition from air to ground. That's why good pilots sharpen their skills by going out to the field and doing a dozen laps around the pattern, focusing on those critical moments when the airplane transitions from a ground-based to sky-based vehicle. To further heighten the training effectiveness, we don't just do this practice in perfect conditions. We intentionally land crosswind at times, because sometimes you *have* to land that way and it's good to know how before you need it. We may practice in gusty or turbulent conditions, because again, sometimes you don't have a choice, and there's no pulling over to the curb when you're flying. If you aren't ready for the worst, it's sure to come and bite you when there's no alternative.
Test flights on a new aircraft are designed to find out how the airplane flies, and to uncover any flaws that might not show up in simulations. A simulation is only as good as the numerical model, and we know the models aren't perfect. Flight test refines the model and improves the simulation accuracy. I'd be surprised if there *weren't* problems during the testing phase; it would suggest that the tests aren't rigorous enough.
A tail scrape isn't a major accident, by any means. Based on the past history of these aircraft designers, I'm sure that by the time the program is complete they'll have figured out what tweaks to make and they'll have an aircraft and spacecraft that work properly.
I once had the privilege of being shown round Edwards Airforce Base by a retired USAF pilot. Amongst all the awesomeness, I got to watch a B1-B doing repeated touch and gos. Apparently it was a regularly administered punishment for pilots who had flunked a landing.
Beautiful plane and it made one hell of a noise when taking off again.
As for this story. It's a non-story in many ways, these sort of issues are regularly found when prototypes are flown for the first time. It's hardly a problem to worry about. After all to take just one example the very first 747 had problems with its flaps and with wing flutter during the test flights; despite that, Boeing produced one of the most awesome pieces of machinery ever designed.
tail scrapes were common on passenger flights in earlier times.
When exiting B727 via rear ramp one could look up and see scrapes.
I have been on DC9s with a horrible scraping sound aft on a steep take off.
As for other aviation, a mild tail scrape is not good practice, but happens.
A lack of rudder authority does bother me though.
A mere 15 knot cross wind is no threat or most well flown aircraft.
Not unheard off either.
Early Super Sabres needed extra vertical surface for starters.
Black Helo because they can scrape bellies too. Paris might do to
Given the wingspan on this thing it's not surprising they're having lateral stability issues with those tiddly rudders. These people were clever enough to get the X-prize, so I can't imagine something as trivial as this is going to slow them down much.
Still, bags not be the test pilot that has to spin this beast (or more correctly, the test pilot who has to get it out of the spin).
Many aircraft have had a lack of horizontal stability and have had rudder / fin area added as a result.
Maybe the reason why they didn't want to increase this too much was turbulence in the tail region when carrying its payload. The jumbos used to carry the Space Shuttles around had a similar problem. Note how there isn't any tailplane between the booms either like on other twin boom aircraft? In this case it could be a trade off between stability in flight and landing.
It's a bit rich of the Flight International dude to make that comment. I'm sure the design team of Scaled have forgotten more about aerodynamics than he knows...
"The jumbos used to carry the Space Shuttles around had a similar problem."
A small point. The Shuttle is carried about the fuselage on the NASA Jumbo. Flow interference between it and the rudder are virtually certain. White Knight 2 carries its payload below the wing between its 2 fuselage booms. That seems a long way for distorted airflow to move upward.
Having said that the rudders do look quite small. However any non-wing surface adds drag which needs more engine power to overcome and actuators to power it. Scaled certainly have access to CFD but I don't think they quite trust it. They seem to prefer the fly a bit, break a bit, fix a bit approach. Either they hit a size that works or they run out of funds. Time will tell.
Keep in mind SpaceX had to destroy 3 vehicles to get a successful launch. These guys haven't totalled any of theirs.
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