Orange Crush does a full loop!

Greg Fannin launched his "Orange Crush" at XPRS 2005 on a long burning Cesaroni N1100 in an attempt to break the N-motor altitude record.        (Thrust curve available here.)

Shon Heiner captured this video showing the Orange Crush liftoff, loop and climb to altitude.  A slow motion "zoom-in" of the loop itself is included at the end.  In this video clip you can see the rocket rotate almost 360 degrees in a pitch plane while in mid motor burn.  It yawed out of plane toward the end of the maneuver but then yawed back again as it ended the pitching and wound up going in the same direction it was originally headed.  It was a jaw dropping experience watching it live!

Play High Resolution MPEG2  Video   (12.9 MB file)

Play Low Res Windows Media Player Video  (2.5 MB file)

Two very short videos of just the flight trajectory are also available.  They are small file sizes so they may work better for dial-up users.    (These were provided by Jamie Clay.)

View  Windows Media Player video clip    (200KB)

Recording Altimeter Data

Orange Crush carried a G-Wiz recording altimeter on this flight.  Greg has provided the altimeter data files so that anyone that wants to help analyze the flight can use them.

Click here to download the raw G-Wiz data file. 

Click here to download an ASCII text version of the raw data file.

Artie Lekstutis took the altimeter data from this flight and created a detailed spreadsheet of all the critical parameters. The rows in the spreadsheet are color coded according to what was visible in the video at that moment in time. Yellow= visible deviation.  Orange=significant deviation.  Red=severe deviation from flight path (>90 degrees).

Click here to view the spreadsheet as a pdf file.

Artie Lekstutis also took the first 1.5 seconds of the flight video, magnified it 6.5X, and overlaid it with the calculated altitude, thrust and velocity from the altimeter data.  Two versions for the windows media player are available.  One is normal speed and one is 10X slower.

Play normal speed video.

So far there is still no consensus as to what happened.  Most people have concluded that the rocket was simply unstable.  That may be, but if so, why?  Was it some sort of dynamic instability? The static stability margin for this rocket was 2.26 calibers.

Apparently, for some reason, the CP momentarily moved forward of the CG and the rocket did a loop.  Momentum carried it onward in the direction it was already going and eventually the proper CP/CG relationship was restored.  Perhaps because of the propellant consumed or perhaps because a disturbance subsided.  In any event, with the rocket back into a stable configuration, it pointed its nose into the air stream in the direction that momentum was already taking it and proceeded as normal.

The CG location was double checked by direct measurement to be 79.88 inches and agrees to within about 0.3 inches of what was predicted by RockSim.  The Barrowman CP calculated by RockSim is 9.124 inches aft of the predicted CG.  This is 2.26 calibers of static margin.

The published thrust curve for the Cesaroni N1100  motor has a high initial thrust which then regresses to a lower long burn tail.  The liftoff weight of the rocket was right at 37 pounds.

Wind Speed and AOA Discussion

There was a slight breeze at ground level when Orange Crush was launched.   At the time, it was estimated to be in the 5-7 mph range and can even be heard in the sound track of the video.  The wind was basically blowing from left to right in the video.  You can even see the first puff of smoke translate away from the pad just before liftoff.  It is possible to estimate the wind speed by measuring how far this puff of smoke travels and scaling the distance using the known length of the rocket in the image.  It is a rough estimate since the puff of smoke has very ill defined edges as it disperses and also because it might not be traveling exactly across the field of view.  For example, it might be traveling slightly away from the camera.  At any rate, by scaling the dimensions off two images that are 35 frames apart, it looks like the smoke puff translated 147 inches or 12.25 feet. The video is at 30 frames per second so 35 frames is 1.17 seconds.  Therefore, the smoke traveled 12.25/1.17 = 10.5 feet/sec.  This is equivalent to 7.2 mph. The wind speed above ground level remains unknown.  The bottom line is, Orange Crush DOES appear to "lean into the wind" slightly right after liftoff. 

This crosswind will offset the initial angle of attack (AOA) slightly.  RockSim calculates that Orange Crush departed the 8 foot launch rail going 59 mph.  A 7 mph crosswind creates a 6.8 degree AOA. However, as Orange Crush weather vanes more into the direction of the wind and as it rapidly picks up speed this AOA will decrease.   It seems unlikely that this small AOA caused the stability margin to degrade enough to produce the loop maneuver.  On the other hand, our wind data is all at ground level.  Could there have been a gust of wind up a little higher?   It would have to be a very strong gust of wind and it would have to be fairly low since Orange Crush started to lean to the left almost right from liftoff.  The lean just kept getting worse until suddenly it swapped ends.   No such gust was felt at ground level.

Motor Discussions

One question that keeps coming up is whether there was any off center thrust from the motor. However, the motor nozzle was carefully inspected before and after the flight.  No problems were seen.  The assembly of the motor was very straight forward and the nozzle should have been properly aligned with the axis of the motor.  There is really no evidence in the video of any angled thrust from the motor.

The N1100 motor has an offset core in the motor grain known as a moon burner.  Some people have questioned whether it is possible to have a slight thrust asymmetry in this configuration that could cause some vectored thrusting.  If so, it has not been well documented.  If it did exist, perhaps Greg was unlucky and a small vectored thrust component happened to push Orange Crush in the same direction that the wind was also pushing it.  In other words, two small factors combining to create a more significant effect.   Maybe, but this also seems very unlikely.

Could the motor have lost pressure?

Frame 41:  The extended exhaust flame has re-established itself.   Once again it is about half as long as the rocket is itself.  These last two frames are consecutive frames in the video.  They are only about 30ms apart in time.