credit Flight / caption: WK2 fourth flight indicated further directional stability issues
So now during a straight forward touch and go manoeuvre Virgin Galactic's WhiteKnight Two (WK2) prototype Virgin Mothership Eve struck its tail as the pilot fought to control a roll left due to a 15kt cross wind, which normally should not be a problem
Its further evidence that Scaled Composites, for all its expertise, did not realise the degree that a two fuselage aircraft with a Boeing 757 scale wing would require larger vertical fins
With vortex generators added and a second horn and an increase in the size of those horns the aircraft still appears to be suffering from directional instabilty. The horns, for those of you who don't know, are the tab like squares that appear to extend from the rudder into the fin and are designed to jut out in the direction opposite to the movement of the rudder, inducing forces to stop any natural tendencies for the rudder to swing back to neutral - its normal position
The big question is, can this WK2 prototype carry SpaceShipTwo (SS2)? A provocative question but while landing in a 15kt crosswind presents such a challenge the carriage of SS2 is not going to occur any time soon
See more pictures and read more detail in this story
click through to access a larger version of the photo of the moment of the tail strike
click on this image of the moment of the tail strike to see a larger version of it in the same browser window. Note the dust kicked up by the port boom's tail fin's impact
This large picture, which Flight has paid for, is offered to readers for personal use such as computer screen backgrounds please do not use for commercial websites
on April 22, 2009 6:54 PM | Reply
Well, the kind of people with enough money for this ride tend to be suicidal anyway.
Not sure how bigger V stabs would stabilize roll, although they would degrade yaw in a crosswind. The problem seems to be a huge moment of roll inertia from those dumbbell fuselages & not enough aileron authority.
on April 23, 2009 12:55 AM | Reply
Take a page from Boeing and add winglets. They don't DO anything, but they LOOK really sweet.
on April 23, 2009 5:20 PM | Reply
Fortunately (for fans), Scaled has decided to offer a rare flight test update; to set the record straight... Go Burt Rutan!!!!
http://www.scaled.com/news/test_program_wk2_update_release.pdf
on April 23, 2009 6:47 PM | Reply
About time. And unsurprisingly the statement confirms everything Flight has written about the test programme.
on April 24, 2009 3:51 AM | Reply
"Not sure how bigger V stabs would stabilize roll, although they would degrade yaw in a crosswind. The problem seems to be a huge moment of roll inertia from those dumbbell fuselages & not enough aileron authority."
Might I recommend you read about dihedral effect and slip-roll coupling. The size of any flight vehicle's vertical stabilizer has a direct impact on lateral/roll stability.
"would degrade yaw in a crosswind" - I'm not sure what this means.
Larger verticals would not necessarily degrade the vehicle's yaw stability performance in crosswind conditions. A prime example of an airplane with significantly large verticals that has absolutely astounding crosswind performance would be another of Rutan's designs, the Long-EZ.
WK2's roll authority is more than sufficient and the yaw "issues" seen to date are not due to fuselage shape or placement. Two fuselage sections does induce greater yaw-stability challenges but those effects are dealt with in this case by the wing's dihedral planform and the high moments seen by the verticals being placed far aft on the booms.
on April 24, 2009 9:28 AM | Reply
Again, if you look at the photos we have published the roll is visible and if you were able to see the sequence of images we were offered you would see the roll almost in its entirety. In the third photo we published WK2 is clearly rolling left and very low to the ground, not a nice situation to be in. I'll be posting a blog entry son that will explain the control issues and why you can need to use rudder for a roll situation.