Maggie Muggs??

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milisavljevic
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Post by milisavljevic » Sun Mar 28, 2004 1:54 am

DELETED.
Last edited by milisavljevic on Wed Aug 18, 2004 8:16 pm, edited 1 time in total.

larry cottrill
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Post by larry cottrill » Sun Mar 28, 2004 2:55 am

milisavljevic wrote:Hello Larry,
. . .
If we apply a little mathematical reasoning to the problem we can make a somewhat more objective comparison:

(a) Black & Decker "Leaf Hog" = 1,440 Watts
(b) DynaJet "Red Head" = 82,300 Watts*

Note that the DynaJet consumes over 57 times the input power of the B&D leaf blower. Even with allowances for conversion efficiencies, the pulsejet is able to develop approximately 10 times the (mechanical) output power of the leaf blower. Black & Decker never had a chance. People tend to under estimate the chemical energy stored in relatively small quantities of liquid hydrocarbon fuels. As an aside, that DynaJet's 82.3 kW of input power is equivalent to 110 HP (one thirsty little pulsejet ;-).

I wish you the best of luck with Maggie Muggs!

Best regards,
M.
Mil -

What a wonderful post!

This is the kind of stuff I love from the forums! Of course, you're right -- the chemical energy available is downright profound. Too bad that the losses in really small pipes are so great. When you think of the temp at which a little pulsejet runs [when it's running right], that wattage seems like it must be about right. Look at the amount of red-hot surface inside a modern toaster [a few feet of thin resistance ribbon, probably not more than a square inch or two] -- that's about the same power consumption as the Leaf Hog.

Thanks for setting up the proper perspective for me!

L Cottrill

Mark
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Post by Mark » Sun Mar 28, 2004 5:06 am

It would be interesting to measure the thrust of the leaf blower, how much less it weighs turned on and exhaust pointed downward, just to know the thrust. Or if an augmenter or air amplifier would do anything or how varying the nozzle diameter affects thrust.
Mark

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Post by Bruno Ogorelec » Sun Mar 28, 2004 3:14 pm

milisavljevic wrote:People tend to under estimate the chemical energy stored in relatively small quantities of liquid hydrocarbon fuels.
A very acute observation, M. An eye-opener. Thanks for the reality check.

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Post by Mike Everman » Sun Mar 28, 2004 4:08 pm

I just measured the thrust of my Toro electric leaf-blower, 12A @120VAC, actually 117.9 VAC coming outta the wall. Blower with nozzle weighs 6lb.

Thrust on the bathroom scale, not very reliable but close:

1. with the slightly convergent blow-off nozzle: 1.5 lb low setting, 2 on high
2. with the nozzle removed, just the impeller exit: 2 low, 3 high.

Sunday morning experiments! Whee!
Mike
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larry cottrill
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Post by larry cottrill » Mon Mar 29, 2004 2:25 am

Mike Everman wrote:Thrust on the bathroom scale, not very reliable but close:

1. with the slightly convergent blow-off nozzle: 1.5 lb low setting, 2 on high
2. with the nozzle removed, just the impeller exit: 2 low, 3 high.
Mike -

Extremely interesting. The nozzle [presumably] gives you higher output velocity - yet, the total gas momentum is reduced. With a manometer, what you would find, I'm sure, is significant static 'back pressure' back in the volute exit that isn't there with the nozzle removed.

It would be interesting to do sensitive pressure gauge [i.e. manometer] measurements of the stream velocity in both cases, to see how that corresponds to your thrust measurements.

That is a lot more than I would have expected for thrust. This makes me think that maggie may not do so badly with the kind of static pressures I measured. Of course, who knows how good my 'pressure tap' design really is -- it will only measure static pressure accurately if the airflow near the shell wall is really laminar, i.e. smooth and parallel to the diffuser shell wall.

L Cottrill
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Maggie Muggs Page Re-design Complete [for now]

Post by larry cottrill » Tue Mar 30, 2004 12:32 am

If anyone cares to comment on it, I have re-built the Maggie Muggs site as two pages [will add a third later for testing], added a little WIP log to Page 1, and included my newly-designed jetZILLA logo at the top:

http://www.cottrillcyclodyne.com/Maggie ... aggie.html

Or, use one of the short links & kill the little pop-up:
http://bz9.com/maggie
http://bz9.com/maggiem

And, don't forget to pass the joke site onto your friends who don't have any idea who I am or what we do around here:
http://bz9.com/guess

By all means, do let me know what you honestly think of that logo! [Hint: try it with different window/screen widths.]

L Cottrill

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Post by Mike Everman » Tue Mar 30, 2004 1:04 am

Great build-up photos, Larry!
Mike
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Raymond G
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Post by Raymond G » Tue Mar 30, 2004 1:51 am

Larry,
Thanks for sharing all of your info. Maggie...she is a beautiful machine!

One thing I don't get is how the JB Weld will hold up to combustion temps. I readilly admit that I know little about this wonder welder, but I would imagine if the engine works well, that it will be glowing hot. Will JB hold up to that? Am I being too optimistica about the engine temp

Thanks,
Raymond

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Post by larry cottrill » Tue Mar 30, 2004 4:27 am

Raymond -

The theory is [hold onto your hat, now!] that the combination of the large volume of cooling air, inside and out, and the low conductivity of stainless will save the bonded seams from destruction. Some of that will depend on how hard you push Maggie with fuel, of course.

The air's effectiveness as a coolant is easy to underestimate. The ship that I designed and built for my Dynajet had the engine fully exposed to air -- and visibility. Since this was a U-control plane, I [the pilot] was always in an excellent position to observe the engine in full-power flight. Would you believe, only the tiniest zone right at the nozzle throat was observably red! [This was at a clocked speed of 90 MPH.]

Compare that to the static run picture below [no forced air cooling] to judge the difference.

Note the scorch pattern on the wood base - a perfect graph of the radiant heat distribution of the Dynajet. This is the result of innumerable 15-to-20-second static runs.

L Cottrill
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Post by Raymond G » Tue Mar 30, 2004 6:22 am

Larry,
Thanks for the PJ pic. So perhaps the real question is what kind of temps can JB stand up to. I've just begun experimenting with 'furnace cement' myself, though I cannot give any recommendations yet positive or negative. It is supposed to be good to 3000 odd degrees though, and I was suprised at its useful consistancy. It might serve your projet well, if the JB proves not up to the task.

Regards,
Raymond

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Post by Mike Everman » Tue Mar 30, 2004 7:37 am

I've been wanting to get some of that cement ever since Mark posted an E-bay item for a 5 gallon bucket of it. I've priced it since, ouch! Should have bid on it back then.
I don't think either will work in the environment, frankly. Especially the motor mounts. While Maggie is beautiful, Larry, fillet bonds without any lugs will almost certianly fail with the first couple of back-fires. It's the least favorable condition for fracture toughness. The joint on her mugs might do OK for a while and it may be cooled substantially by ram air, but again, it's not the best situation for keeping a seal for any duration due to thermal cycling. It may mechanically hold together, and maybe you could wick something in to seal it again, but the first thermal cycle should delaminate it.
I'll shut up now! I don't mean to be negative at all, Larry. I would be happiest to be wrong in this. I have a good deal of experience with this type of bonding.
Mike
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Post by Raymond G » Tue Mar 30, 2004 7:42 am

I've been wanting to get some of that cement ever since Mark posted an E-bay item for a 5 gallon bucket of it. I've priced it since, ouch! Should have bid on it back then.
Mike, I picked up an 8oz (?) can or "Rutland Furnace Cement" at the local hardware store for about $1.50. I've seen it at Lowe's too. It is quite tenacious, though I haven't tested it yet.

Regards,
Raymond

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Post by Mike Everman » Tue Mar 30, 2004 7:52 am

Ooh, I'll check for that. Exhaust sealer is good, too, but not that cheap, I think. I was looking more in the aluminum oxide-based ceramic putty. $90/gal., and high-performance mica-based adhesives, $90/half gal. Spendy. Maybe not, it's probably more than I'll ever use.
Mike
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Post by larry cottrill » Tue Mar 30, 2004 1:35 pm

Mike Everman wrote:I don't think either will work in the environment, frankly. Especially the motor mounts. While Maggie is beautiful, Larry, fillet bonds without any lugs will almost certianly fail with the first couple of back-fires. It's the least favorable condition for fracture toughness. The joint on her mugs might do OK for a while and it may be cooled substantially by ram air, but again, it's not the best situation for keeping a seal for any duration due to thermal cycling. It may mechanically hold together, and maybe you could wick something in to seal it again, but the first thermal cycle should delaminate it.
Mike -

Yes, I've been aware from the beginning of this project that the probability of failure is fairly high. I think of Maggie as a sort of prototype, the basic idea being to see if self-sustaining operation is achievable, not whether you end up with a practical flight engine. If the basic geometry is sound, I can always make a second, more sophisticated, one by welding it up. Of course, even that would have the possibility of metal fatigue failure after thermal cycling, especially at the joint between the diffuser and the hot chamber.

I do like the idea of the high-temp furnace cement, though. But, most materials like that have limited tensile strength and fairly high brittleness. It's hard to design an ideal configuration that will really take the stresses of repeated cycling when built from non-exotic materials.

I'd be fairly happy, though, if Maggie could sustain good runs of 15 or 20 seconds with measurable thrust and without falling apart. A good 'science fair' demo machine. The plan for a run would be: start the spark, start the air, open the fuel tap to start combustion, kill the spark, note the thrust during warmup, kill the fuel, but let the air run until cooldown is achieved. Then, examine for obvious damage. Realistically, a few cycles of that is probably the best we can hope for, but, who knows?

L Cottrill

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