up-dec7a.htm Small-Pogo Project


Small-Pogo Project


Status Updates


December 3-4, 1997

December 3,1997

I believe I have the control problem solved. Model aircraft gyros, mounted horizontal at 90 degrees from each other will be able to maintain a vertical orientation. Two photocells, mounted on the sides of the fuselage, 180 degrees apart, can be used to maintain rotational orientation with the sun (except at high noon in the summer) so that the operator knows which direction is left and right. With this arrangement the operator can control all six degrees of freedom.

I picked up two magazines today. The first is "Radio Control Jet International," Traplet Publications, Worcestershire, England. Their web site is (http://www.traplet.co.uk/traplet/). This magazine has articles and color photos of model jet and ducted fan aircraft. It also contains many advertisements for micro jet engines. Most are without price but one with 17 lbf thrust, weighs 3.3 lb with accessories, and costs $2,795.00 US. Another has 38 lbf thrust while yet another appears to have an afterburner. There are many more engines available than I had realized. The second magazine is "Radio Control Modeler," R/C Modeler Publications, Sierra Madre, CA. It's standard fare with many advertisements and prices.

I received a reply from Carr Precision of Portland listing their services and prices for each type of weedeater engine. He lists what propeller goes with each engine. For example, my Ryobi 31cc matches with a 16X8 @ 8000 rpm prop. The total kit is priced at $49. If he does the work on my engine (including machining the back plate and flywheel) his total charge is $165 US. The ready to fly weight of 51oz bothers me, I had hoped it would be considerably less. By comparison the OS 91 (15cc) weighs 25 oz and puts out 4.8 hp at 22,000 rpm. I don't know the horsepower of the Ryobi. Of the engines Carr has listed my Ryobi has the lowest finished weight per cubic centimeter, swings the most agressive prop, and at the highest rpm.

A friend at work is going to donate his "whatever" size and brand of weedeater because he says it has too much torque for him. It will be a good one to learn from.

Another friend gave me copies of the specs on the Futaba gyro he owns. He is willing to donate a radio control system to the effort. Yet another friend has ordered a 4 lbf thrust pulse jet which should be delivered in January. He wants to use this for a Small-Pogo entry.

In the original Pogo report I suggested the use of engines such as the GE-90 for helicopter-like lift. I ran across a picture in a 1962 "Janes' All the World's Aircraft" of the Bensen B-12 Sky-Mat. This uses a rectangular frame with 10 10 hp engines and propellers to carry him across the ground or water. It can hit 56 knots and jump 50 ft obstacles. It obviously never caught on but is still fascinating.

Tomorrow I will talk with an avid aircraft modeler about beginning the design and manufacture. I still hope to begin flight testing no later than early January 1998 with a full launch demonstration by the end of the month. Once proven, I'll invite a contact in ABC Science News to do an article on it.

Flash. As I'm preparing to close for the night I found another Ryobi conversion place about an hour drive from here. It is JAG Ltd, 7805 SVL Box, Victorville, CA 92392, (760) 243-6930. They also advertise a 31cc Jaguar engine with C.H. ignition which weighs 44 oz and swings a 16X8 prop at 8600 rpm for $248 complete. "I'm gonna to have to have a talk with that boy."

December 4,1997

I talked to one of the guys at JAG Ltd and got some interesting information. He said that the regular version, now on sale for $148 US has about 12-13 lbf thrust (weighs 4 lbm, 3 oz). If I put it in a duct it should put out even more thrust. This version requires a battery pack for the ignition which weighs only a few ounces. The more expensive version is not only lighter but requires no battery pack. But it's a hundred dollars more and probably overkill considering the 8 lbf+ I have to work with on the regular version.

I'll be picking up a "donated" weedeater from a friend this weekend. It will probably be used to try different ideas on.

I spoke with the "avid aircraft modeler" who doesn't have the time to work on this himself. He thought the Small-Pogo should be able to get to 8,000-10,000 ft before running out of air. He will get me the name of retired NASA Dryden guy who has done a lot with models. This weekend I'll post notices at the local hobby shop and model aircraft airport asking for collaborators. I'm ready to start buying parts.

A couple of us at work (on our breaks and lunch-hours) have been thinking of alternate propulsion power plants. I looked at leaf blowers because they have the same engines as the weedeaters and are designed to move air. Some have exit velocities of 180 mph and flow rates at the pipe of 388 cfm. Unfortunately they are also heavy (39.7 cc and 24.3 lbm). Another model with a 21.2 cc engine weighing in at 9.3 lbm has an exit velocity of 150 mph and a 310 cfm discharge. This is just one brand and there may be better ones. They all use centrifugal fans as opposed to axial fans.

Then we started thinking. The model jet engines use the axial compressors (fans) from turbochargers. Maybe we can use the axial fans from the leafblowers to make jet engines? These fans are functionally the same as those in turbochargers and, unless they use gear reducers, the tip speeds are nearly the same. The mass flow is much higher. This might make a kick-ass jet engine for real cheap. This will be pursued as time permits.

Another alternate propulsion idea is a pulsejet/ramjet device. During low-speed operation the inlet to a ramjet will be closed off by a cone-shaped plug with several reed valves that allow air to enter but not escape through the inlet. Then, at high speed, the reed valve assembly drops a short ways into the ramjet creating an inlet diffuser allowing normal ramjet operation. This and other pulsejet and ramjet ideas will be pursued as time permits.



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