(Bloodhound update)
By Dr Ben Evans
Will BLOODHOUND Fly!?
The question of how we keep Andy Green safely pinned to the deck whilst travelling at almost 1.5 times the speed of sound is one that has been hanging over me for what seems like an eternity
http://www.bloodhoundssc.com/news.cfm?widCall1=customWidgets.contentItem_show_1&cit_id=4397
I am REALLY hoping that they will do some upset analysis. According to the web site, their analysis shows that the body generates lift. It's round on top and flat on the bottom, it should not have taken CFD to tell them that it would lift. It also doesn't take CFD to redesign it so that it doesn't. They are canceling this lift and lift in other components by running slight negative alpha on their struts and canards. The downforce created by these changes is highly sensitive to alpha and the playa is NOT FLAT. Especially at those speeds.
I was contacted multiple times recently by a London reporter who had interviewed Dr. Evans. The reporter wanted me to respond to several criticisms that Dr. Evans had about the struts on the Breedlove/Fossett car creating the "shock waves that lifted the back end up". I asked the reporter to have Dr. Evans contact me with his concerns, which he has not. The struts were set at a negative alpha just like Bloodhound. While the problem is more complex than this, it bothers me that:
1. The Bloodhound solution is to have negative alpha on the struts of a lifting fuselage, while the Breedlove/Fossett car had a zero-lift fuselage and struts running at 1 degree negative alpha. Yet the Fossett project is criticised to the press as if this was not addressed at all.
2. There is this assumption out there among both bystanders and people who should know better that "SHOCK WAVES!!!!" lifted one strut and not the other of a vehicle traveling at M 0.89. Considering the struts had a leading edge sweep of 75 degrees and would not create compression waves until M 3.8, this is simply not credible. While the root and strut-to-wheel fairing interface do create compression waves, these pale in comparison to the hard shocks shown on Bloodhound's wheel fairings. I won't debate the design here, other than to say that I would design wheel fairings without these hard shocks.
3. I would be much more impressed with some data and discussion on the forces and moments at varying lateral slip angles and varying pitch angles that were encountered (and unplanned for) on Thrust 2 and SSC. This should rationally lead to some explanation of the control forces and control displacements needed to recover from various transients. Add inertia effects and this is stability and control analysis. I have always said it would be a good exercise to go back and put SSC's actual dynamic behavior into a full motion simulator and see how many pilots could hold onto the instability with the lateral force from the car telling the pilot it's going the wrong way. Andy was a lot better than most people realize.
