From the Editor of
from the Editor of jetZILLA - the Online Magazine of Amateur Jet Propulsion from the Editor of jetZILLA - the Online Magazine of Amateur Jet Propulsion from the Editor of jetZILLA - the Online Magazine of Amateur Jet Propulsion

The  Maggie MuggsTM  low-speed ramjet project -
TESTING!   April 2005 - TODAY!
(last content update: 16 Jun 2005)
( Page 3 )
Click here to return to Page 1
Click here to return to Page 2

Ben Koopman's 'Maggie Muggs Clone' experimental low-speed ramjet engine (c) 2005 R Autrey
Ben Koopman and friend. Ben is holding his 'Maggie Muggs Clone' low-speed ramjet engine, after successful test firing


    III.   M A G G I E   M U G G S   T E S T   F I R I N G S

Photo Diary: The "Maggie Muggs" Low-Speed
Ramjet Prototype - PART III - TEST FIRINGS
by Larry Cottrill, Editor, jetZILLA Online Magazine
          - All photos this page Copyright 2003 Larry Cottrill - 

Table of Contents [Construction Sections I-IV go back to Page 1]:
I.  The parts lineup [28 August 2003]
II.  The tubular truss engine mounts [28 August 2003]
III.  Building the diffuser section [04 September 2003]
IV.  Bonding the diffuser/flameholder subassembly to
       the combustion chamber/nozzle shell [12 September 2003]

Table of Contents [Construction Sections V-VIII go back to Page 2]:
V.  Final major assembly steps [22 September 2003]
VI.  Details, details [22 September 2003]
VII.  Fuel and ignition system work [29 September 2003]
VIII.  Finishing up [03 October 2003]

Table of Contents [Maggie Muggs Test Firing Page]:
I.  Ben Koopman's Maggie Muggs Clone [April 2005]
II.  Maggie Muggs Testing Plan, Hints and Tips

I.  Ben Koopman's Maggie Muggs Clone [April 2005]:
Previous section   Next section   Back to Contents   Top of page   Page 1   Page 2
Subscribe to jetZILLA Online Magazine (it's FREE!) 

The first successful test firing of a Maggie Muggs type ramjet engine
was by Ben Koopman and teacher Randy Autrey at Gould Academy in 
Maine, USA during the last week in April, 2005:

Ben looks on as his teacher Randy Autrey attempts to balance 
the air input and fuel flow. It's easy to get too much fuel for the 
airflow, as shown here. However, Randy claims that once you get 
used to it, his 'squeeze bottle' method of delivering liquid fuel is 
quite easy to use, since it gives you instant control over the fuel 
pressure. From the mugs to the air source, Ben mostly used what they 
found available at school, so his out-of-pocket cost for the project 
was very low. One thing I recommended to Randy is that they try to 
get a good leaf blower; that would provide a lot more air for cooling. 
However, their initial tests were with what they had available, a 
standard 'shop vac', and it seems to work well enough: 

Just starting to get adequate air into the intake (c) 2005 Randy Autrey

When more airflow and/or less fuel flow is applied, the flame starts 
to look somewhat better - we're moving towards "lean" combustion:

More air, or less fuel, leans out the flame for better combustion (c) 2005 Randy Autrey

Continuing to lean out the burn. It looks like there's enough flame 
and noise at this point that the test run is beginning to draw a 
crowd. The mug parts were from teachers that were willing to donate 
their used coffee mugs to the project, so these parts aren't exactly 
like the ones shown in the plans; note, however, how Ben chose a mug 
shell that has a well-developed combustion chamber zone and a good 
long, smooth cone for the tail section - exactly the right approach!

Leaner running - better combustion, more noise (c) 2005 Randy Autrey

Leaning out the combustion even more makes the flame much less 
visible, but significantly louder [note that the unlookers are starting 
to back off a little!]. The sink strainer flameholder is one of the few 
parts that had to be purchased new for the project; it keeps the 
flame back in the tail section where we need it [unfortunately, the 
flameholder can't be seen in any of these photos]:

Still leaner running - closing in on perfect combustion (c) 2005 Randy Autrey

Once you get a really good lean run, the noise is a pretty intense 
'jet noise' roar, and in daylight the visible flame almost disappears. 
This is exactly the way your jet ought to be running. However, this is 
also a very hot way to run, and the epoxy construction can't be 
expected to take this for too long:

Fully lean running with fairly loud 'jet roar' noise (c) 2005 Randy Autrey

Finally, fuel pressure is cut back enough that flameout occurs, 
before the glued construction suffers any damage. Ben keeps the 
air flowing in for a while to cool things down:

Engine finally flames out; Ben keeps air flowing through for cooling (c) 2005 Randy Autrey

I first heard of this project via email back in mid-April, 2005, and briefly
corresponded with Randy Autrey a few times to offer encouragement and 
minor suggestions. On May 1, I received the photos shown here, attached 
to the following email from Randy summarizing successful construction and 
testing of Ben's Maggie Muggs clone ramjet:


          You may use any or all of the following on jetZILLA or 
          wherever you would like. 

          My name is Randy Autrey and I work at Gould Academy, 
          a college preparatory boarding and day school in the 
          western mountains of Maine. I am a private pilot and I 
          also fly model airplanes. One of our students at 
          Gould, Ben K., saw the Maggie Muggs project on the 
          internet and asked if I could use it to fly one of my 
          model airplanes. I told him it looked like a fun 
          project and that we should build and test it. That is 
          exactly what we did. 

          We grabbed some freebie mugs from faculty members and 
          bought a sink strainer at Wal Mart. Ben used a dremel 
          tool to cut the mugs and we drilled a hole for the 
          brass tube injection system. We used JB weld to 
          assemble the mugs with the understanding that it was 
          only rated for 600 degrees F. Our first test fire was 
          with the small drilled brass tube which was flattened 
          in the center for a spray bar. We used a model 
          airplane fuel bottle to pressurize the gas mixture for 
          injection. The mug did ignite and produce a flame. It 
          was immediately obvious that we did not have enough 
          fuel. We went back to the lab to change the injection. 
          This time we just flattened the end of the brass 
          tubing and JB welded the tube to the front of the mug. 

          As you can see from the pictures we had plenty of 
          fuel. I like the pressurized bottle injection system 
          because you can control the flow. We started out with 
          light pressure during ignition and increased fuel 
          delivery as we increased shop vac air flow. You can 
          see this transition in the series of pictures of the 
          big flame 'blow torch' look during ignition to the 
          chiseled flame near the end. Just when the sound 
          changes and the flame becomes a chiseled point it is 
          time to shut down. This produces a lot of heat very 
          quickly when it hits efficiency. 

          This is a great project with very low cost and 
          construction effort. This was great for the students. 
          We are very pleased with the results. This Maggie Muggs 
          really draws a crowd. 

          We are planning on firing it again but this time we 
          will run it at night to see the transition from 
          ignition to chiseled flame. We hope to have a video 
          clip available soon. Stay tuned for more. We started 
          working on a valveless pulsejet so we will let you 
          know how that works out. 

          I would like to thank Larry for a fun design and all 
          of the emails he sent. Great job Larry. 

          Randy Autrey
          Gould Academy

After test firing, Ben's Maggie Muggs clone is still in good 
condition - Ben can take pride in building a finely-crafted, 
nice-running engine!

Ben Koopman and friend show off his Maggie Muggs clone after test firing (c) 2005 Randy Autrey

II.  Maggie Muggs Testing Plan, Hints and Tips:
Previous section   Back to Contents   Top of page   Page 1   Page 2
Subscribe to jetZILLA Online Magazine (it's FREE!) 


1.  Secure engine to test bench, locking heat shield in place
2.  Secure blower loosely to test bench
3.  Align blower carefully on engine centerline, BOTH horizontally 
     and vertically while gradually tightening blower mounting
4.  Make final check of blower alignment and spacing and secure 
     tight to test bench - be sure airflow covers entire engine
5.  Start spark ignition and verify good spark by visual sighting
     from behind exhaust nozzle
6.  Start blower and again verify good spark by sighting through nozzle
7.  If possible, make preliminary thrust measurement - this is the 
     blower thrust minus total engine drag
8.  Open fuel valve until combustion is achieved
9.  Continue to open fuel valve until large, rich-burning flame 
     is observable - if this isn't obtainable, stop the test, your 
     fuel supply or valve is inadequate - otherwise, continue:
10. If possible, measure and record the rich-running thrust and 
     fuel flow
11. Reduce fuel flow to leaner running condition, pulling the flame 
     forward inside the nozzle - run for a few seconds and observe 
     the J-B Weld seam at the engine mid-point - if any signs of the 
     epoxy softening, shut off the fuel and allow time for the blower 
     to cool the engine - otherwise, continue:
12. Reduce fuel flow further, pulling the flame forward into the 
     aft region of the combustion chamber - if combustion is 
     observed inside the diffuser section, shut off the fuel and 
     allow time for the blower to cool the engine! - otherwise, 
13. Shut off the spark ignition system - if the engine quits, shut 
     off the fuel and allow time for cooling! - otherwise, continue:
14. Try to obtain a running condition where only the nozzle zone is 
     visibly red hot, with no red heating of the combustion chamber - 
     if this is not obtainable, shut down and allow the blower to 
     cool the engine - otherwise, continue:
15. Run for several seconds and again observe the engine mid-point 
     seam - if there are signs of the epoxy softening, shut off the 
     fuel and allow time for the blower to cool the engine - 
     otherwise, continue:
16. If possible, measure and record the lean-running thrust and 
     fuel flow and the diffuser static pressure
17. Finish testing by quickly shutting off the fuel flow completely
18. Allow the blower to run until the entire engine structure is 
     cool enough to touch safely, then shut down blower
19. Adjust measured thrust figures by subtracting the unpowered 
     thrust value obtained in Step 7, above


Cooling air is just as important as combustion air!
1.  Use the biggest air mover you can obtain. My choice was the
     electrically powered Black & Decker Leaf Hog, capable of 
     120 MPH maximum air velocity, but any large-volume, high 
     velocity blower will work. A big shop vacuum is probably 
     just barely adequate for this application.
2. Position your air mover far enough from the engine intake so 
     that as much of the engine exterior as possible is constantly 
     bathed in high-speed airflow during and after a run. There 
     MUST be good airflow over the entire rear section of the 
3. Make sure you have a 'quick cutoff' fuel valve that will let 
     you shut off fuel immediately if there is a failure of your 
     air mover. In fact, if you can figure out how to do it, it 
     wouldn't be a bad idea to route your fuel through an electric 
     valve with an air-driven switch for automatic shutdown in 
     case of air supply failure!
4. After a normal test run, make sure you keep your blower running 
     until the entire engine cools, to protect the J-B Weld bonds. 
     Even thin stainless holds heat a surprisingly long time and 
     heat flow from the tail cone forward after the run could 
     still lead to softening or degradation of the epoxy bead at 
     the engine mid-point if cooling is stopped too soon!

Start out running rich and work toward lean!
1.  As soon as possible after you get ignition, try to get enough 
     fuel flowing to develop a rich-burning flame. This will keep 
     most of the combustion well to the rear, to minimize heat 
     buildup in the tail cone and, therefore, heat conduction to 
     the front end. 
2.  After you establish rich combustion, you can start leaning 
     the air/fuel mixture, gradually pulling the flame front 
     forward in the rear section of the engine, while regularly 
     testing the midsection J-B Weld bead for softness. 
3.  If the midsection epoxy bead starts to soften, you have  
     reached the limit of how lean you can set up the run with 
     the cooling you have available. At this point, it's time to 
     shut down the fuel [while letting the air cool down your 
     engine] until you can find a more effective air supply.

Start out with slow-burning fuel!
1.  Start your testing with a slow-burning vapor fuel such as 
     propane or butane. That will make it easy to control the 
     position of the flame front in the engine by adjusting the 
     fuel flow.
2.  If your air supply is so strong that you can't get the flame 
     front to move forward into the tail cone, reduce the entering 
     air velocity by putting more distance between the air nozzle 
     and the engine intake. Make sure you maintain good aiming of 
     the air nozzle so that you will have adequate cooling air 
3.  If you can achieve good engine operation, then you can try 
     more powerful, faster flame speed fuels such as MAPP gas. 
     You will probably want the highest possible entering air speed 
     for this to keep the flame front well in the rear of the 
     engine, and so throttling won't become over-sensitive.
4.  It is strongly recommended that you provide a fuel pressure 
     regulator at the supply point, so you won't be fighting 
     pressure changes due to changing fuel temperature:

Improved propane cylinder regulator and valve setup - Copyright 2004 Larry Cottrill
A good propane regulator and valve setup, built from an old-style Victor
high volume air regulator and needle valve. This has proved more than 
ample for the fuel demands of my small pulsejet engine prototypes, and 
should work fine for testing Maggie Muggs.
Photo Copyright 2004 Larry Cottrill

Test Firing 'Must Have' List:
1.  Type A-B-C fire extinguisher
2.  Hearing protection
3.  Safety goggles
4.  'Quick shutoff' valve in fuel line
5.  Largest volume blower you can find & reliable power
6.  Outdoor or VERY well-ventilated 'fire safe' test site
7.  Reliable fuel lines in good condition
8.  Reliable ignition spark source

Test Firing 'Optional' List:
1.  Thrust measurement stand for blower & engine
2.  Water manometer for diffuser pressure measurement
3.  Water manometer for velocity pressure measurement
4.  Pressure regulator for fuel gas

Previous section   Back to Contents   Top of page   Page 1   Page 2
Subscribe to jetZILLA Online Magazine (it's FREE!) 

"To God Alone be the Glory"
- Johann Sebastian Bach 1685 - 1750

The Maggie MuggsTM miniature aviation powerplant
         - now under development by

Corporate Main Office
11905 NE 110th Ave
Mingo,    IA 50168-9500


Page updated: 21 June 2005

Copyright 2005 Cottrill Cyclodyne Corporation
- All rights reserved -