Well i read it, and it was some of it that i have to chew on a bit more to be able to say that i understand it.
One thing i just couldn´t fit into my picture of the world was the results i got when calculating resonansefrequency of reed valves.
Many valves from "tried-and-tested" designs gave res. freq. of about half the actual working frequency when put into EQ 12.3.
12.3 n=31800*(d/L^2) cps
n=natural freq. of reed
d=reed thickness (in.)
L=free length of reed (in.)
My own reeds made to be used at a freq. of about 200Hz (0.15mm*35mm) Should according to the eq. resonate at 98.9Hz.
Am i missing something here or is it just bedtime for me?
I just read "The Propulsive Duct"
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Bruno Ogorelec
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I have not devoted myself to the problem in much detail – I am convinced that valveless is the way to go – but the way I understand it, one should aim to have the natural frequency of the valves themselves far removed from the operating frequency of the engine, so that the valve resonance does not interfere with engine operation.
"If the frequency of the valves is purposely made about 30% higher than that of the tube, they will respond more quickly to pressure variations. .....
Blue spring steel is the best material for valves, but since the modulus of elasticity of all steels is approximately the same, you can use substitute materials if you compensate for loss of strength. The tube shapes which will resonate seem almost infinite (although it is hard to believe at times)..... There are a few conditions, however, which will not support resonance."
(1965 Experimental Aircraft Assn. Air Education Museum Foundation, Inc.)
And here is an aside I was just reading, "U.S Development--It is interesting to reveal just how close the U.S. came to perfecting a pulsejet engine independently during the war. Dr. Fritz Zwicky Of Aerojet Engineering Corp., began experiments with an "aeropulse" device during 1943, his group was immediately supported by BuAer, and considerable research was instigated early in 1944. At the same time, Lt. W. Schubert, U.S. Naval Engineering Experiment Station, Annapolis, Md. designed and built an aeropulse engine and operated it successfully, the first to be built and run in this country. His engine, however, was valveless and operated on acoustical principles rather than the simple mechanical principles of the pulsejet engine."
The article was entitled "Project Squid Probes Pulsejet" subheading "Five Eastern Universities Hold Navy Research Contracts" Aviation Week, December 1, 1947.
The universities given contracts were Princeton, Cornell, New York University, Purdue, and Brooklyn Polytechnic Institute if any of you live near these and want to see if something is still there on pulsejets.
Mark
Blue spring steel is the best material for valves, but since the modulus of elasticity of all steels is approximately the same, you can use substitute materials if you compensate for loss of strength. The tube shapes which will resonate seem almost infinite (although it is hard to believe at times)..... There are a few conditions, however, which will not support resonance."
(1965 Experimental Aircraft Assn. Air Education Museum Foundation, Inc.)
And here is an aside I was just reading, "U.S Development--It is interesting to reveal just how close the U.S. came to perfecting a pulsejet engine independently during the war. Dr. Fritz Zwicky Of Aerojet Engineering Corp., began experiments with an "aeropulse" device during 1943, his group was immediately supported by BuAer, and considerable research was instigated early in 1944. At the same time, Lt. W. Schubert, U.S. Naval Engineering Experiment Station, Annapolis, Md. designed and built an aeropulse engine and operated it successfully, the first to be built and run in this country. His engine, however, was valveless and operated on acoustical principles rather than the simple mechanical principles of the pulsejet engine."
The article was entitled "Project Squid Probes Pulsejet" subheading "Five Eastern Universities Hold Navy Research Contracts" Aviation Week, December 1, 1947.
The universities given contracts were Princeton, Cornell, New York University, Purdue, and Brooklyn Polytechnic Institute if any of you live near these and want to see if something is still there on pulsejets.
Mark
Ha, i figured it out at last!
But it took a couple of days before i thought of what the valves does and when.
Since most reed-valves have their restingposition at the valveseat and not between the endpoints of their movement (like in the winspire book) They will only move during the negative halfperiod of the pressurecycle.
That means they actually have a total movement corresponding to half the combustionfreq.
Think halfwave rectified AC, looks like this -^-^-^- (eeeh, nevermind i think you understand) In this case we only have the positive halfperiod deviating from 0 volts.
Same thing with the reeds, only they go to work at the moment CC pressure goes below atmospheric (0volts) and are about as fast to rest when CC pressure increases to atmospheric pressure and all the way up to max combustionpressure.
This leads me to believe it is rather pointless talking about valveresonance freq. in other ways than as a messure of their ability to move fast enough to do their job (which they do with siesta half of the time ;-)).
But it took a couple of days before i thought of what the valves does and when.
Since most reed-valves have their restingposition at the valveseat and not between the endpoints of their movement (like in the winspire book) They will only move during the negative halfperiod of the pressurecycle.
That means they actually have a total movement corresponding to half the combustionfreq.
Think halfwave rectified AC, looks like this -^-^-^- (eeeh, nevermind i think you understand) In this case we only have the positive halfperiod deviating from 0 volts.
Same thing with the reeds, only they go to work at the moment CC pressure goes below atmospheric (0volts) and are about as fast to rest when CC pressure increases to atmospheric pressure and all the way up to max combustionpressure.
This leads me to believe it is rather pointless talking about valveresonance freq. in other ways than as a messure of their ability to move fast enough to do their job (which they do with siesta half of the time ;-)).