Any major flaws with this valve design?

[mk]

Jerry,

Just to add some things to Bill's post:

Pulse-jets can be throttleable. Offering quite a large range as well.
The latest smaller valveless ducts I've operated on propane could be throttled from e.g. 0.5 kgf (or even slightly less) up to at least 5 kgf, rather 6 to 7 kgf. I cannot tell the upper end exactly due to stand construction failures. While there is no reason for me to doubt that similar ranges would not be obtainable with larger pulse jets.

It merely appears just to be a matter of time, money and effort to get the liquid fueling "problem" solved.

[dynajetjerry]

Mike and all,

I should add that Aeromarine's 205 lb. thrust pulsejet had no augmenting components that were outside the basic engine and it was tested on automotive gasoline of 1950, only. Tenney and his crew ran out of contract money and time before all conceivable improvements could be developed. Also, my comments about the severe limitations in throttling of pulsejets referred to valved types. I suspect that valveless designs, when thrust is greatly reduced, lose their resonances and become more like pressure jets than pulsejets. I'm only guessing because John Melenric's 3 in. valveless is the only one of that kind I've actually seen.

A liquid-fueled valveless appears to be where most research should be devoted, especially if one can be devised that does not require a complex and heavy fuel pumping system or pressurization.

I will be most anxious to see specifics on a valveless design that has a specific fuel consumption of less than about 2.0 lbs., especially if it is suitable for model airplane use. Generally, making such engines smaller also reduces their efficiency (something to do with the laws of physics.)

Jerry Wiles

[hinote]

A liquid-fueled valveless appears to be where most research should be devoted, especially if one can be devised that does not require a complex and heavy fuel pumping system or pressurization.

That's where I'm headed, sooner or later. It's interesting to noteh that SNECMA used low-pressure liquid fueling, quite early-on. They also started their engines on liquid fuel only

I will be most anxious to see specifics on a valveless design that has a specific fuel consumption of less than about 2.0 lbs., especially if it is suitable for model airplane use. Generally, making such engines smaller also reduces their efficiency (something to do with the laws of physics.)

I'm pushing on some designs for that, right now. 2.0 is pretty do-able at this point for a complete package. I think 1.5 for model-sized engines and 1.0 for larger are attainable goals.

[hinote]

I suspect that valveless designs, when thrust is greatly reduced, lose their resonances and become more like pressure jets than pulsejets.

I've noted a surprisingly strong wave action in the sims I've been running.

I've attempted to instrument my engines, to determine peak combustion pressures at various throttle settings, to verify numbers being used in the software; no luck (yet) though.

[Hank]

Hello- Bill, solve the atmospheric dependence problem of these engines and you place in posterity will be assured.
Regarding "throttle" of the pulsed combustion duct- Who is working on the variable geometry required for something thet would produce a smooth transition? Just metering the fuel isn't the answer.

[Viv]

Hello- Bill, solve the atmospheric dependence problem of these engines and you place in posterity will be assured.
Regarding "throttle" of the pulsed combustion duct- Who is working on the variable geometry required for something thet would produce a smooth transition? Just metering the fuel isn't the answer.

that would be me then:-) but thats another story;-)

Viv

[hinote]

Hello- Bill, solve the atmospheric dependence problem of these engines and you place in posterity will be assured.
Regarding "throttle" of the pulsed combustion duct- Who is working on the variable geometry required for something thet would produce a smooth transition? Just metering the fuel isn't the answer.

Since I've demonstrated not less than 10:1 turndown ratio on all of my engines, I don't feel it's an issue.

[Hank]

Hello- Bill, solve the atmospheric dependence problem of these engines and you place in posterity will be assured.
Regarding "throttle" of the pulsed combustion duct- Who is working on the variable geometry required for something thet would produce a smooth transition? Just metering the fuel isn't the answer.

Since I've demonstrated not less than 10:1 turndown ratio on all of my engines, I don't feel it's an issue.

Bill- I don't know what you mean by this. Please explain.

[hinote]

Since I've demonstrated not less than 10:1 turndown ratio on all of my engines, I don't feel it's an issue.

Bill- I don't know what you mean by this. Please explain.

"Turndown" is the ratio of the maximum power level, divided by the minimum. For example, an engine capable of 50 lbf max that would "idle" at a minimum of 5 lbf would have a turndown ratio of 10.

BTW I've also demonstrated a turndown ratio of nearly 20.

[Eric]

I have had turndown ratios approaching infinity :D Its even easier with linear engines that dont have any recouperation, which is sorta "cheating" but oh well.

The valved engines definately are less able to be throttled, only because the valves take some force to open, but you dont really need that much throttle range.

Eric

[Bruno Ogorelec]

but you dont really need that much throttle range.

Bill, you're a pilot. How important is the throttle range?

[hinote]

How important is the throttle range?

I think 5:1 is probably OK--but something like 8 or 10 is optimum; anything more is probably overkill.

[larry cottrill]

How important is the throttle range?

To me, what would be more important, at least for a light aircraft, is that the thrust at idle isn't a significant fraction of the drag at minimum operating speed. That is, I would want the glide at idle to have the same slope as an unpowered glide. You don't want to have to jump through any hoops to get the shortest glide possible with a small but safe margin above the stall speed of the aircraft.

This would be impossible to achieve with the combination of high maximum power and low throttleability.

L Cottrill

[dynajetjerry]

Hi, Guys,

While reading all the interesting comments in this thread, I began to wonder about throttling a PDE. I am not aware if this has been discussed or if the group at WPAFB has published anything. Assuming such an engine does not really resonate, I would expect one to be capable of an almost zilch minimum thrust regardless of its maximum.

I have a confession to make to all of you: Almost all my limited know-ledge and suspicions about pulsejets are the result of hands-on work rather than calculations or readings. I've also gleaned a little education from observing the work of others. In other words, "I ain't got much book learnin'." The very interesting discussions many of you have posted are, mostly, outside my field and I must accept what is said, being too ignorant to reach my own conclusions.

Jerry

[hinote]

I think 5:1 is probably OK

Actually, It's probably not appropriate for me to comment on this; being the pilot of a prop-driven aircraft doesn't really qualify me for jet power.

Specifically, the prop not only creates power, but also creates a lot of drag during power reduction; this makes it a great airbrake for glidepath control during landing.

Modern jets almost always include some sort of spoiler or airbrake, for glidepath control; the aircraft is just too drag-free to fly a "normal" landing pattern without them.

I was actually considering the power range suitable for taxiing.