Transonic Deceleration Problem

Transonic Deceleration Problem

Post by Larr » Wed, 31 Jul 1996 04:00:00



Just analyzed Cambridge accelerometer data from Kevin Turner's flight of
his Moneypit rocket at Black Rock. The motor involved was an M1939. The
rocket reached a peak velocity of mach 1.66. Gues what? The Cd/velocity
curve shows a *DROP*, rather than a peak. The derived impulse is also
conspicuously low. Tom Beach, who analyzed the data independently, got the
same result. Tom has hypothesized that since the Cd curves are derived
from coast phase data, the bow shock wave detaches when the rocket falls
below mach 1.0. It then runs interference for a short time. Sounds
plausible enough. (If it's true, a number of simulation programs have
to be corrected)

Analyze, the program I used to do the analysis, can simulate mach spikes
in the Cd curve - a feature intended for use in subsonic flights to
derive Cd curves for supersonic performance prediction. When I simulate
the spike this way, and use the resulting Cd curve to infer the thrust
curve, my derived impulse is very close. Tentative conclusion: the impulse
shortfall is from failure to recognize the rise in Cd in the transonic
region.

I've actually observed reverse spike effect in barometric altimeter data sets,
but barometric data are so noisey that I had dismissed the observation.

Wondering if anyone knows what's going on. Jerry?

TIA,
-Larry Curcio

 
 
 

Transonic Deceleration Problem

Post by Doug L Iver » Thu, 01 Aug 1996 04:00:00



Quote:

>Just analyzed Cambridge accelerometer data from Kevin Turner's flight of
>his Moneypit rocket at Black Rock. The motor involved was an M1939. The
>rocket reached a peak velocity of mach 1.66. Gues what? The Cd/velocity
>curve shows a *DROP*, rather than a peak. The derived impulse is also
>conspicuously low.

Strange things happen around the speed of sound.  I dont have any access to
data from rockets but my copy of Sierra's reloading manual for rifles has a
section on wierd things that happen near the speed of sound complete
with graphs of ballistic coeffiecient vs velocity.  The graphs show the
ballistic coefficient remains fairly constant until the velocity falls
to just above the speed of sound where it increases dramatically.  It
falls very sharply after the bullet slows below the speed of sound and
then increases till it reaches a second peak around 1050 ft/s.  Most of
the effect occurs within 40 ft/s of the speed of sound.  The BC changes
from .26 at 1150 ft/s to a low of .06 at 1110 ft/s.  The manual did not
offer any explanations or conclusions except that much more testing is
needed.

I dont know how much of this data from blunt nosed, lead core bullets
applies to rockets but if you know someone that has a Sierra manual it
is interesting to look at.

Doug

 
 
 

Transonic Deceleration Problem

Post by Dave Lyl » Thu, 01 Aug 1996 04:00:00


Quote:

>Drag Coefficient calculation
>program copyright 1983 Jerry Irvine
>Used as input for alt programs

>50 PRINT "TO ENTER NOSECONE TYPE SEE LIST BELOW,"
>60 PRINT "   ELLIPTICAL=1"
>65 REM ELLIPTICAL NOSECONE EQUATION IS APPROXIMATE ((L/D)>=1.5)
>70 PRINT "   OGIVE=2"
>80 PRINT "   CONIC=3"

Where does 'parabolic' fit in here?

Quote:
>110 INPUT "ENTER EXPOSED AREA OF EACH FIN (IN^2)",EA
>120 INPUT "ENTER TOTAL EQUIVALENT AREA OF EACH FIN (IN^2)",FA

Can you define these two?  What's the difference?

Quote:
>130 PRINT "ENTER FIN SPAN OF EACH FIN"
>140 INPUT "FROM FIN ROOT TO FIN TIP (INCHES)",BF

How measured?

Thanks,
Dave

 
 
 

Transonic Deceleration Problem

Post by Jerry Irvi » Thu, 01 Aug 1996 04:00:00


Quote:


> >50 PRINT "TO ENTER NOSECONE TYPE SEE LIST BELOW,"
> >60 PRINT "   ELLIPTICAL=1"
> >65 REM ELLIPTICAL NOSECONE EQUATION IS APPROXIMATE ((L/D)>=1.5)
> >70 PRINT "   OGIVE=2"
> >80 PRINT "   CONIC=3"

> Where does 'parabolic' fit in here?

Since in 1983 Chuck and I did not bother to put in parabolic yet, you have
to use eliptical as an approximation, not that that introduces much error
as compared to some other "features" of the program.  Note:

Quote:
> >110 INPUT "ENTER EXPOSED AREA OF EACH FIN (IN^2)",EA
> >120 INPUT "ENTER TOTAL EQUIVALENT AREA OF EACH FIN (IN^2)",FA

> Can you define these two?  What's the difference?

Exposed area is the side area of one fin on one side

Equiv area is that area plus the root length times the body radius to
"kludge" an estimate for fin interference drag by projecting the fin all
the way to the centerline of the rocket.

Quote:
> >130 PRINT "ENTER FIN SPAN OF EACH FIN"
> >140 INPUT "FROM FIN ROOT TO FIN TIP (INCHES)",BF

> How measured?

Span is measured from the body to the tip as the longest perpendicular
line possible.  How much wood hangs in the wind.

Jerry

--

Box 1242, Claremont, CA 91711 USA
Opinion, the whole thing.

 
 
 

Transonic Deceleration Problem

Post by Jerry Irvi » Thu, 01 Aug 1996 04:00:00


Quote:

> Just analyzed Cambridge accelerometer data from Kevin Turner's flight of
> his Moneypit rocket at Black Rock. The motor involved was an M1939. The
> rocket reached a peak velocity of mach 1.66. Gues what? The Cd/velocity
> curve shows a *DROP*, rather than a peak. The derived impulse is also
> conspicuously low. Tom Beach, who analyzed the data independently, got the
> same result. Tom has hypothesized that since the Cd curves are derived
> from coast phase data, the bow shock wave detaches when the rocket falls
> below mach 1.0. It then runs interference for a short time. Sounds
> plausible enough. (If it's true, a number of simulation programs have
> to be corrected)

> Analyze, the program I used to do the analysis, can simulate mach spikes
> in the Cd curve - a feature intended for use in subsonic flights to
> derive Cd curves for supersonic performance prediction. When I simulate
> the spike this way, and use the resulting Cd curve to infer the thrust
> curve, my derived impulse is very close. Tentative conclusion: the impulse
> shortfall is from failure to recognize the rise in Cd in the transonic
> region.

> I've actually observed reverse spike effect in barometric altimeter data sets,
> but barometric data are so noisey that I had dismissed the observation.

> Wondering if anyone knows what's going on. Jerry?

Here is a section of code from the cd vs velocity program (Let's not fight
over who's code it is today.  It has had two different copyrights over
time.)  I believe it has also been published in CRm.

I agree with Larry that the transonic spike must be accounted for
especially since it never goes fully back down:  Rare Irvine ascii art!

o                     o            oooooooooooo
                     o o   oooooooo
 o                  o   ooo
          oooooooooo      
  oooooooo

The program below gives the real picture.  Feel free to put it into a real
program style and upload the useful version to sunsite in the Irvine
programs or USR directory.

I also think there are effects at transonic where the bow shock passes
over the air ports giving a time where the static and dynamic ports are
not in similar regions.  This could possibly be solved by making both
ports along a concentric ring around the rocket instead of high and low.

I still think a pitot tube is a very underutilized device in HPR rocketry.

Quote:

> TIA,
> -Larry Curcio

Material:

CD program:

Drag Coefficient calculation
program copyright 1983 Jerry Irvine
Used as input for alt programs

1 PRINT "Program name CD.BAS"
2 PRINT ""
3 PRINT ""
4 PRINT "     "
10 REM      PROGRAM TO DETERMINE THE COEFICIENT
11 REM      OF DRAG OF A MODEL ROCKET
12 REM  
14 PRINT "     "
16 PRINT "     ROCKET CD DETERMINATION"
19 PRINT "     "
20 PRINT "     "
21 INPUT "ENTER ROCKET DIAMETER (INCHES)",D
30 INPUT "ENTER TOTAL ROCKET LENGTH (INCHES)",LT
40 LET A=3.1415*((D/2)^2)
50 PRINT "TO ENTER NOSECONE TYPE SEE LIST BELOW,"
60 PRINT "   ELLIPTICAL=1"
65 REM ELLIPTICAL NOSECONE EQUATION IS APPROXIMATE ((L/D)>=1.5)
70 PRINT "   OGIVE=2"
80 PRINT "   CONIC=3"
90 INPUT "ENTER NOSECONE TYPE=",NC
100 INPUT "ENTER NOSECONE LENGTH (INCHES)",LC
110 INPUT "ENTER EXPOSED AREA OF EACH FIN (IN^2)",EA
120 INPUT "ENTER TOTAL EQUIVALENT AREA OF EACH FIN (IN^2)",FA
130 PRINT "ENTER FIN SPAN OF EACH FIN"
140 INPUT "FROM FIN ROOT TO FIN TIP (INCHES)",BF
150 INPUT "ENTER THICKNESS OF EACH FIN (INCHES)",TF
160 INPUT "ENTER NUMBER OF FINS",NF
170 LET EA=EA*NF
180 LET FA=FA*NF
190 INPUT "IS THERE A BOATTAIL? (YES=1,NO=2)",BT
200 LET BL=0
210 LET BD=D
220 LET SB=0
230 IF BT=2 THEN 280
240 INPUT "ENTER BOATTAIL BASE DIAMETER (INCHES)",BD
245 INPUT "ENTER BOATTAIL LENGTH (INCHES)",BL
250 LET SB=((1+((D-BD)/(2*BL))^2)^.5)*(((2*BL)*(D-BD))/(D*D))
280 INPUT "IS THERE A LAUNCH LUG? (YES=1,NO=2)",LL
290 IF LL=2 THEN 340
300 INPUT "ENTER LAUNCH LUG DIAMETER (INCHES)",LD
310 PRINT "IS LAUNCH LUG ON"
320 PRINT "   BODYTUBE=1"
330 INPUT "   FIN ROOT=2",LP
340 LET C=(EA/NF)/BF
345 LET F1=(1.328)/(((1000000!)*(C/LT))^.5)
350 LET CF=2*F1*(1+(2*(TF/C)))*(FA/A)
360 IF NC=1 THEN 400
370 IF NC=2 THEN 440
380 LET SN=((((LC/D)^2)+.25)^.5)*2
390 GOTO 460
400 LET SN=((3.1415*LC)/D)+1
430 GOTO 460
440 LET SN=2.67*(LC/D)
450 GOTO 460
460 LET ST=((LT-(LC+BL))/D)*4
470 LET S=SN+ST+SB
480 LET BF=.002926437#
490 LET CG=BF*S*(((.0025*LT)/D)+(60/((LT/D)^3))+1)
500 LET CB=CG+((.029*((BD/D)^3))/((CG)^.5))
510 LET CD=CF+CB
520 LET DC=0
530 IF LL=2 THEN 580
540 IF LP=2 THEN 570
550 LET DC=5.75*((LD/D)^2)
560 GOTO 580
570 LET DC=3.45*((LD/D)^2)
580 LET CD=CD+DC
590 LET V=(162.476)/(LT/12)
592 PRINT "     "
593 PRINT "     "
594 PRINT "     "
595 PRINT "     "
600 PRINT "AT A REYNOLDS NUMBER"
610 PRINT "OF 10^6 THE ROCKET"
620 PRINT "VELOCITY IS=";V;"(FT/SEC)"
630 PRINT "AND THE CD IS=",CD
632 PRINT "     "
634 PRINT "     "
636 LET R=(LT/12)/.000162535#
640 LET CD1=CD/((100000!/(R*V))+1)
645 LET CD3=(CD+CD1)/2
652 PRINT "THE OVERALL REPRESENTATIVE CD"
653 PRINT "(WHICH IS THE AVERAGE OF THE CD VALUES"
654 PRINT "AT REYNOLDS NUMBERS OF 10^6 AND 10^7)"
655 PRINT "IS=";CD3
660 PRINT "     "
662 PRINT "     "
664 PRINT "     "
670 PRINT "DO YOU WISH TO SEE HOW"
680 PRINT "CD VARIES WITH REYNOLDS"
690 PRINT "NUMBER AND MACH NUMBER?"
700 INPUT "(YES=1,NO=2)",C9
710 IF C9=2 THEN 1400
755 PRINT "     "
756 PRINT "     "
757 PRINT "     "
760 PRINT "   CD        REYNOLDS NO  V(FT/SEC)"
770 PRINT "-------------------------------------"
780 PRINT " INFINITE      0.0           0.0"
790 FOR I=1 TO 60
795 LET V=10*I
800 LET CD2=CD1*((100000!/(R*V))+1)
810 LET RE=R*V
820 PRINT CD2,RE,V
830 NEXT I
840 PRINT "     "
850 PRINT "     "
860 PRINT "     "
862 PRINT "ASSUMING THAT THE SPEED"
863 PRINT "OF SOUND IS 1100 (FT/SEC);"
864 PRINT "     "
865 PRINT "     "
870 PRINT "   CD          MACH NO     V(FT/SEC)"
880 PRINT "--------------------------------------"
900 FOR I=1 TO 65
910 LET V=900+(I*20)
920 LET M=V/1100
930 IF M<.9 THEN 980
940 IF M>=1.05 THEN 1100
950 LET CD2=CD1*(1+((.7/.15)*((V/1100)-.9)))
960 GOTO 1200
980 LET CD2=CD1*((100000!/(R*V))+1)
990 GOTO 1200
1100 LET CD2=CD1*(1.27+(.53*EXP(((-5.2*V)/1100)+5.46)))
1200 PRINT CD2,M,V
1300 NEXT I
1400 END

JEND motor data file for ALT2,3,4

Data file format for a rocket motor
Compatible with other rocket programs
copyright 1983, 88 Jerry Irvine

00  MRev 01......:
01  Designation..: E25USR
02  Data date....: 07-27-90
03  Manufacturer.: U.S.ROCKETS
04  Cost.........: 6.95
05  Grain type...: B
06  Propellant ID: 571
07  O.D..........: 0.938
08  Case Len     : 2.75
09  Wgt Units....: G
10  Specs........: T
11  Wt Prop. gms.: 20
12  Load Wt. gms.: 41.5
13  Burn time....: 1.60  
14  Favg Lbs.....: 5.59999
15  Favg Newtons.: 24.9088
16  TotImp Lbsecs: 8.95999
17  TotImp Ntsecs: 39.8540
18  REM1.........:
19  REM2.........:
20  Time /Thrust.: 0.00    6.00    
20  Time /Thrust.: 1.59    5.20    
20  Time /Thrust.: 1.60    0.00    
61  Mass Fraction: .482
62  Isp lb/s/lb  : 203.2
63  Rating.......:   40-E-25
64  Pct Full.....:  99% E

Maybe I will post more after comments come in on this post.

Jerry

--

Box 1242, Claremont, CA 91711 USA
Opinion, the whole thing.

 
 
 

Transonic Deceleration Problem

Post by MMcReynl » Thu, 01 Aug 1996 04:00:00


Quote:
>>The rocket reached a peak velocity of mach 1.66.  The Cd/velocity curve

shows a *DROP*, rather than a peak.

General comment:  As best I remember from my Fluid Dynamics class, Cd
rises in the transonic region and then drops substantially above the speed
of sound.

                                             Marc McReynolds

 
 
 

Transonic Deceleration Problem

Post by Larr » Fri, 02 Aug 1996 04:00:00



Quote:
> Strange things happen around the speed of sound.  I dont have any access to
> data from rockets but my copy of Sierra's reloading manual for rifles has a
> section on wierd things that happen near the speed of sound complete
> with graphs of ballistic coeffiecient vs velocity.  The graphs show the
> ballistic coefficient remains fairly constant until the velocity falls
> to just above the speed of sound where it increases dramatically.  It
> falls very sharply after the bullet slows below the speed of sound and
> then increases till it reaches a second peak around 1050 ft/s.  Most of
> the effect occurs within 40 ft/s of the speed of sound.  The BC changes
> from .26 at 1150 ft/s to a low of .06 at 1110 ft/s.  The manual did not
> offer any explanations or conclusions except that much more testing is
> needed.

Well, I ran out and got the book, but mine has no such graphs. Maybe mine
is old. There's no date on it...

I'll check out other copies.

Regards,
-Larry

 
 
 

Transonic Deceleration Problem

Post by Doug L Iver » Fri, 02 Aug 1996 04:00:00



Quote:


>> Strange things happen around the speed of sound.  I dont have any
access to
>> data from rockets but my copy of Sierra's reloading manual for
rifles has a
>> section on wierd things that happen near the speed of sound complete
>> with graphs of ballistic coeffiecient vs velocity.  

>Well, I ran out and got the book, but mine has no such graphs. Maybe
mine
>is old. There's no date on it...

>I'll check out other copies.

Mine is about the 3rd edition and is about 6 years old.  I guess old is
relative when talking about reloading manuals though.  I have a friend
who only uses manuals printed before 1980.  He claims lawyers have made
the new ones too wimpy.

Doug