I am looking for someone to provide me with guidance, on up to a possible completed design for a tail section for the Twin Engine Jet Luge. After repeated real life testing and some simulation I have pretty much proven I need a tail section that will maintain the Center of Pressure behind the COG and limit harmonic yaw (wobbles) at speeds for 90 to 130mph. I would also like to incorporate a split rudder to act as an airbrake similar to he Space Shuttle to smoothly but quickly slow me down from 130 to 80 mph. The Jet Luge works very well up to about 90 mph without aerodynamic devices, butt then tends to start weaving the front end like it wants to swap ends... this is more pronounced at higher speeds and I end up having to back out at 119mph. I can only perform this test on a long and wide runway where I can let it run out instead of fighting it. I need to make the thing stable in a narrow track. One of the aerospace guys at NRL here in DC (where I work) told me I was like an arrow flying backward when I reach the higher speeds. I need the airbrakes because the Flintstone style of braking I do, although very efficient, is not possible at speeds over 80 mph. Now that I am adding a second 50lb turbine, getting the design right is more critical.

If anyone is interested in taking this on you may discuss it here or contact me offline.

For more info on the Jet Luge you can go here [link=http://www.jetluge.net]JetLuge Site[/link] check out the promo video

here is a pict.


Thank you
Bob

Well, you can certainly add a fin and even mount the jets to it. To figure out how large it should be you'd have to start by figuring out where your center of gravity is located and do a side view area calculation in something like CAD and then add the fin to the side view to move the center of area to a point behind the CG. Split airbrakes will be an option but if they don't open smoothly and together then it'll get ugly really fast.

On a non aerodynamics point don't forget to study the geometry of your wheels and how they steer. You may find that this is a larger portion of your troubles than the fin issue. Any sort of cyclical flexing in the board and wheel boggies may well start things going awry that are not airflow related.

Forgive the crudeness of MSpaint I am at work so that is what I have to work with. Here is my idea for how to get a speed brake design to work for the tail of an aircraft. I have yet to try it but I think I might with my next project. A similar design should work for your application.

I'm not sure I feel comfortable giving advice that could kill someone, especially with all the lawsuits flying around.

Hi Bob,

What you have described sounds like an ideal PhD project for some youg tiger. I suggest you make enquiries of a (local if possible) university that offers aerodynamics as a subject. It sounds great fun, playing with a wind tunnel and not an expensive supersonic one. Maybe one of the auto manufacturers is already experimenting in a similar area.

One of our local academies serving students up to 18yrs made quite a feature of their "economy run" cars as a means of engaging youngsters with their school work.Try to interest educational establishment in your project. Use the local newspapers to reach out and promote interest.

Best of luck with your project.





old git - - - - - - - aka John L.

NASA added a drag chute to the Space Shuttle (I believe during the design review following the Challenger accident). If you look at some of the landing video before the drag chute was added, there are some scary "directional excursions". If directional stability is your goal, I'm not sure that the Space Shuttle is a good starting point. Keep in mind that if your stabilizer is effective and the split rudder doesn't deploy symmetrically, you can expect a pretty good swerve.

You would have to gyro stabalize the split fins. I would go with a stationary or trimable verticle and a chute for breaking.