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In the 1980's, out at Lucerne Dry Lake in California and other launch site across the country, some of the model rockets being launched, and many of the high power rockets being launched, were going supersonic. At least we were pretty sure that they were going supersonic.
But the question was, how could we measure the actual maximum velocity the rockets were reaching? Remember, integrating accelerometer instrumentation packages were 5-10 years in the future.
Optical tracking was very common, with trackers like myself, Jerry Irvine, Fred Brennion, Bill Wood, and many others. Into the 1990's we optically tracked rockets up to 38K ft using baselines between the trackers of up to 3.4 miles. (Once onboard instrumentation packages were available, optical tracking declined very rapidly, see Chapter 20 "Theodolites' Demise" in "Large and Dangerous Rocket Ships".) With the optical tracking, we could determine the apogee altitude that the rockets had reached. By running early DOS Flight Simulation Software (the Rogers Aeroscience ALT4 and CD2 programs), we could determine that the Flight Simulation was accurately predicting the apogee altitude. If the Flight Simulation software was accurately predicting the apogee altitude, then we knew that the maximum velocity and the maximum Mach number predicted by the Flight Simulation software were probably pretty accurate.
The technique developed to directly measure maximum velocity, and thus maximum Mach number, was using a 35mm camera taking a long exposure photograph of the rocket in flight at night with a slotted disk rotating in front of the camera. A reference light (a flashlight) was located a known distance from the launch pad. With the long exposure photograph, the light marking the known reference distance would be to one side, and then there would be a series of dots as the rocket gained altitude as the flame of the rocket motor would be seen by the camera as the slot in the disk went by the front of the camera. The speed of how fast the slot went by was measured by using (as I remember) a light emitting diode and a photoreceptor on the other side of the disk, and (as I remember) an oscilloscope.
The long exposure 35mm film was developed as a slide, and then the slide could be projected on a wall, and butcher paper could be taped on the wall and used to make marks for the rocket flame dots and the reference distance flashlight dot. There was one 35mm slide per flight. The reference distance dot could be used to turn the rocket flame dots into distances above the ground. There would be a few flame dots grouped together at the launch pad as the rocket began to accelerate, using the lowest flame dot, we could pretty accurately know where the launch pad ground level was, and also by comparing to the reference flashlight dot (assuming the camera was level). For the example which will be presented here, the time between the slot passing in front of the camera, and thus the time between rocket flame dots, was 0.008 sec.
To my knowledge, and others correct me if they know of an earlier successful attempt using whatever method, the first supersonic model rocket flight, where the rocket was actually directly measured going supersonic, was a tower launched F67 flight by Chuck Mund in 1984/1985. The tower launched F67 rocket reached Mach 1.21
I remember Jerry Irvine had the 35mm slide, we projected the slide onto butcher paper on a wall, and I marked off the points. I still have the butcher paper in my archives.
As I noted, unless someone has an earlier flight using whatever technique to directly measure velocity, this was the first measured (not estimated, but measured) supersonic model rocket. It also beat whatever high power rocket that first directly measured that it had gone supersonic, which occurred later.
Attached is a presentation I presented on reducing the data from the Chuck Mund F67 supersonic flight which I presented at the 1985 Rocketcon Conference held in California. It presents the time and altitude data from the long exposure 35mm film picture, and how the data was reduced to get the velocity. On Pages 4-5 of the presentation the flight data is the first two columns on the left, the time (every 0.008 sec) and altitude above the ground data at that time point. The third column from the left is the velocity data, using the analysis technique presented on Page 1. The first time point has a different time because as the rocket took off the early flame dots were bunched together, and an estimate was made on what the time was where the first time/altitude point could be determined. This was important because an "absolute time" had to be determined because as part of the analysis I wanted to compare time points from the flight data with time points from the ALT4/CD2 Flight Simulation. Part of this estimate was assuming a nominal burn time, and backing up from that burn time. After that point each of the time points has a delta of 0.008 sec. On Page 5 is the assumed brunout of the rocket and thus the burnout altitude.
The rocket had a plastic nose cone with a blunt nose tip. A lot of the presentation is on how I was adjusting the ALT4/CD2 drag coefficient (CD) drag models around Mach 1 to account for the blunt nose tip (ALT4/CD2 assumed a sharp nose tip) to have the ALT4/CD2 Drag Predictions and Flight Simulation match the flight data. (The modern RASAero II software has a very good blunt nose tip wave drag model.)
The model rocket nose cone used on the rocket had the typical commercial model rocket blunt nose tip. The blunt nose tip is so a young model rocketeer won't injure himself if he or she pokes himself/herself in the eye with the rocket, and there may also be mold design limitations for the mold which made the nose cone where a blunt nose tip needed to be added.
The velocity shown in the reduced flight data in column 3 is the average velocity over a 0.032 sec interval. (See the analysis method on Page 1 on how the 0.008 sec per slot turns into 0.032 sec for the reduced data). The maximum velocity (averaged over a 0.032 sec interval) was 1324.85 ft/sec, the speed of sound from the temperature measured at the time of the flight was 1095.81 ft/sec, the maximum Mach number was Mach 1.21.
On Pages 4-5 the further columns moving to the right are ALT4/CD2 Flight Simulations where I am varying the Drag Coefficient (CD) models to see how they match the flight data, especially the CD around Mach 1 as it is affected by the nose bluntness.
As Initiator001 has noted, there were later "Mach Busting" sessions using the camera and slotted disk setup, with multiple flights per session. Initiator001 and others can provide more details. I don't seem to have the data for those flights in my archives.
My 1985 Rocketcon presentation on the first directly measured supersonic model rocket is attached.
Charles E. (Chuck) Rogers
In the 1980's, out at Lucerne Dry Lake in California and other launch site across the country, some of the model rockets being launched, and many of the high power rockets being launched, were going supersonic. At least we were pretty sure that they were going supersonic.
But the question was, how could we measure the actual maximum velocity the rockets were reaching? Remember, integrating accelerometer instrumentation packages were 5-10 years in the future.
Optical tracking was very common, with trackers like myself, Jerry Irvine, Fred Brennion, Bill Wood, and many others. Into the 1990's we optically tracked rockets up to 38K ft using baselines between the trackers of up to 3.4 miles. (Once onboard instrumentation packages were available, optical tracking declined very rapidly, see Chapter 20 "Theodolites' Demise" in "Large and Dangerous Rocket Ships".) With the optical tracking, we could determine the apogee altitude that the rockets had reached. By running early DOS Flight Simulation Software (the Rogers Aeroscience ALT4 and CD2 programs), we could determine that the Flight Simulation was accurately predicting the apogee altitude. If the Flight Simulation software was accurately predicting the apogee altitude, then we knew that the maximum velocity and the maximum Mach number predicted by the Flight Simulation software were probably pretty accurate.
The technique developed to directly measure maximum velocity, and thus maximum Mach number, was using a 35mm camera taking a long exposure photograph of the rocket in flight at night with a slotted disk rotating in front of the camera. A reference light (a flashlight) was located a known distance from the launch pad. With the long exposure photograph, the light marking the known reference distance would be to one side, and then there would be a series of dots as the rocket gained altitude as the flame of the rocket motor would be seen by the camera as the slot in the disk went by the front of the camera. The speed of how fast the slot went by was measured by using (as I remember) a light emitting diode and a photoreceptor on the other side of the disk, and (as I remember) an oscilloscope.
The long exposure 35mm film was developed as a slide, and then the slide could be projected on a wall, and butcher paper could be taped on the wall and used to make marks for the rocket flame dots and the reference distance flashlight dot. There was one 35mm slide per flight. The reference distance dot could be used to turn the rocket flame dots into distances above the ground. There would be a few flame dots grouped together at the launch pad as the rocket began to accelerate, using the lowest flame dot, we could pretty accurately know where the launch pad ground level was, and also by comparing to the reference flashlight dot (assuming the camera was level). For the example which will be presented here, the time between the slot passing in front of the camera, and thus the time between rocket flame dots, was 0.008 sec.
To my knowledge, and others correct me if they know of an earlier successful attempt using whatever method, the first supersonic model rocket flight, where the rocket was actually directly measured going supersonic, was a tower launched F67 flight by Chuck Mund in 1984/1985. The tower launched F67 rocket reached Mach 1.21
I remember Jerry Irvine had the 35mm slide, we projected the slide onto butcher paper on a wall, and I marked off the points. I still have the butcher paper in my archives.
As I noted, unless someone has an earlier flight using whatever technique to directly measure velocity, this was the first measured (not estimated, but measured) supersonic model rocket. It also beat whatever high power rocket that first directly measured that it had gone supersonic, which occurred later.
Attached is a presentation I presented on reducing the data from the Chuck Mund F67 supersonic flight which I presented at the 1985 Rocketcon Conference held in California. It presents the time and altitude data from the long exposure 35mm film picture, and how the data was reduced to get the velocity. On Pages 4-5 of the presentation the flight data is the first two columns on the left, the time (every 0.008 sec) and altitude above the ground data at that time point. The third column from the left is the velocity data, using the analysis technique presented on Page 1. The first time point has a different time because as the rocket took off the early flame dots were bunched together, and an estimate was made on what the time was where the first time/altitude point could be determined. This was important because an "absolute time" had to be determined because as part of the analysis I wanted to compare time points from the flight data with time points from the ALT4/CD2 Flight Simulation. Part of this estimate was assuming a nominal burn time, and backing up from that burn time. After that point each of the time points has a delta of 0.008 sec. On Page 5 is the assumed brunout of the rocket and thus the burnout altitude.
The rocket had a plastic nose cone with a blunt nose tip. A lot of the presentation is on how I was adjusting the ALT4/CD2 drag coefficient (CD) drag models around Mach 1 to account for the blunt nose tip (ALT4/CD2 assumed a sharp nose tip) to have the ALT4/CD2 Drag Predictions and Flight Simulation match the flight data. (The modern RASAero II software has a very good blunt nose tip wave drag model.)
The model rocket nose cone used on the rocket had the typical commercial model rocket blunt nose tip. The blunt nose tip is so a young model rocketeer won't injure himself if he or she pokes himself/herself in the eye with the rocket, and there may also be mold design limitations for the mold which made the nose cone where a blunt nose tip needed to be added.
The velocity shown in the reduced flight data in column 3 is the average velocity over a 0.032 sec interval. (See the analysis method on Page 1 on how the 0.008 sec per slot turns into 0.032 sec for the reduced data). The maximum velocity (averaged over a 0.032 sec interval) was 1324.85 ft/sec, the speed of sound from the temperature measured at the time of the flight was 1095.81 ft/sec, the maximum Mach number was Mach 1.21.
On Pages 4-5 the further columns moving to the right are ALT4/CD2 Flight Simulations where I am varying the Drag Coefficient (CD) models to see how they match the flight data, especially the CD around Mach 1 as it is affected by the nose bluntness.
As Initiator001 has noted, there were later "Mach Busting" sessions using the camera and slotted disk setup, with multiple flights per session. Initiator001 and others can provide more details. I don't seem to have the data for those flights in my archives.
My 1985 Rocketcon presentation on the first directly measured supersonic model rocket is attached.
Charles E. (Chuck) Rogers
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