Page 2 of 2

re: M15E--Doubled-Up!

Posted: Mon Jan 23, 2006 4:36 pm
by Zippiot
you said that the bend was added right? how much of a thrust difference did it make over its previous form?

Re: re: M15E--Doubled-Up!

Posted: Mon Jan 23, 2006 8:57 pm
by hinote
Zippiot wrote:you said that the bend was added right? how much of a thrust difference did it make over its previous form?
I'm hoping for NO difference. Testing is upcoming, so I don't have any hard evidence yet

Based on past efforts I don't expect any reduction--and possibly (hope!) a nominal increase in power.


Bill H.
Acoustic Propulsion Concepts

".......some day soon we'll be flying airplanes powered by pulsejets."

re: M15E--Doubled-Up!

Posted: Mon Jan 23, 2006 10:28 pm
by Zippiot
i got it, you build another one, but in linear form (or wutever it was before) and strap them both to a skateboard, each facing in an opposite direction. whichever way it goes is the more powerful one!!

Re: M15E--Doubled-Up!

Posted: Tue Jan 24, 2006 5:13 am
by hinote
Larry Cottrill wrote: Are you saying that this one actually expands & contracts 1/2 inch in its present, bent form (I would be astounded!), or is that the figure for its former, straight length?
Larry:

I didn't answer this question directly.

The 1/2-inch estimate is for growth in the entire length of the engine.

Another advantage of the u-bent engine is reduced overall growth--but you've got to watch out, for where it does and where it doesn't!

Bill H.
Acoustic Propulsion Concepts

".......some day soon we'll be flying airplanes powered by pulsejets."

Re: re: M15E--Doubled-Up!

Posted: Thu Jan 26, 2006 1:33 am
by hinote
hinote wrote:
Zippiot wrote:you said that the bend was added right? how much of a thrust difference did it make over its previous form?
I'm hoping for NO difference. Testing is upcoming, so I don't have any hard evidence yet
A brief test of the new, u-bent config today (in my driveway); I started her and warmed things up fully--and then applied the throttle to bring her up to full power.

The result is an operating frequency of 170 Hz (recorded with a video cam, and then crunched in the computer); this creates a new high acoustic temp value for me. (go ahead somebody--ask me about acoustic temp!)

It appears the u-bend isn't creating any compromise; I'll confirm the performance next week, with a field test of thrust and TSFC.

Bill H.
Acoustic Propulsion Concepts

".......some day soon we'll be flying airplanes powered by pulsejets."

re: M15E--Doubled-Up!

Posted: Thu Jan 26, 2006 1:44 am
by Dave
OK Bill
I'll bite: What is "acoustic temp"
Dave

Re: re: M15E--Doubled-Up!

Posted: Thu Jan 26, 2006 2:21 am
by hinote
Dave wrote:OK Bill
I'll bite: What is "acoustic temp"
First:--I suspect I'm treading on dangerous territory here; I really don't know enough to be an "expert"--so please bear with me!!

Look at this website:

http://hyperphysics.phy-astr.gsu.edu/hb ... ol.html#c1

The empty boxes represent 3 variables; if you enter any two, the third will be resolved, using a known equation for the dynamics involved (resonant frequency in a tube, using values for a particular temp). BTW I use the "open cylinder" column on the left; it corresponds to the valveless PJ type.

The obvious thing here is that the length of the pulsejet is known, and the operating frequency can be observed from careful observation during the operation of the engine. That leaves the resolution of the third variable--the temperature. The resolution of this number represents a complex set of operating temps inside the engine, over a wide range.

My understanding is that higher numbers represent better utilization of the heat extracted from the burning fuel.

For comparative purposes (particularly comparing engines of different sizes) it's important to enter the so-called "acoustic Length" which includes an end correction factor.

I've compared the results of several different engines noted on this Forum recently; the results vary from a low of almost ambient temp, to values that are pretty impressive.

For purposes of discussion, the current engine I'm referring to has displayed a max freq. of as low as 159 Hz, and (as noted above) a high of 170 Hz. These results have been largely created by changes in the intake configuration alone.

I would be interested in hearing from others who would like to enter their engines in the above-mentioned website--and are willing to post the results (for comparative purposes).

We can start another thread on this, if there's a consensus.

Bill H.
Acoustic Propulsion Concepts

".......some day soon we'll be flying airplanes powered by pulsejets."

P.S. notes:

1. M. is probably laughing in his beer; My simplistic view of this phenomenon isn't very scientific--but I think it represents something significant.

2. Use an end-correction of .3D for each end, added to the actual length dimension; this way, we can make direct comparisons with different engines submitted by different individuals.

re: M15E--Doubled-Up!

Posted: Thu Jan 26, 2006 3:11 am
by Eric
So what is the average temperature, and how does the frequency compare to the pipe frequency calculator, and what can you conclude from the results? :)

Eric

re: M15E--Doubled-Up!

Posted: Thu Jan 26, 2006 5:46 am
by Mike Everman
For grins, here's Bill's new engine frequency in comparison to other forum motors.