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Vigilant1

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I keep waiting for someone to explain the physics behind the idea that an eductor (correct term) can *increase thrust* by dragging extra air along with it. I think I know where the *idea* might have originated, but no takers so far on substantiating the claim of *increased thrust*.

Charlie
Okay, I'll bite.

Nomenclature varies ("eductor," "ejector," "augmentor") and is not standardized.

P.M Bevilaqua from Rockwell explains how it works in this paper.

FWIW, he calls it an "ejector."

From that document (thumbnails, click to enlarge):

1586915555763.png1586915758308.png

Some text and a diagram from another document. Note that the ejector "can almost double the thrust . . ."

1586916544407.png
1586916661544.png
 
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ARP

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Could a pulse jet handle the back pressure that a turbine in the exhaust stream would create? I’ve thought it would be fun to make a pulse jet turboshaft to power a mini bike or something but that’s always been a head-scratcher.
I see no reason why it would cause a problem. The pulsed exhaust and some of the by-pass fan air would go thorough the turbine reducing temperatures to prevent the whole thing melting. The rest of the fan air would keep the housing cool and expand providing additional energy and surrounding the high energy/noisy jet exhaust at the outlet. The valveless pulsejet/s have the intakes pointing in the same direction as the exhaust so any backfiring goes in the same direction.
 

Pilot-34

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yes but the same wacky guy made a bicycle, much more dangerouser
build the bike frame out of thin walled aluminum, add some fireproof wings and go buzz some city

That seems like one of the most practical useful things I’ve ever seen!
I have a few miles of fence row I need to light off and burn each year.
We also have a 15 mile bike trail near here that really needs to burn its right of way each year that could find it handy.
 

Urquiola

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Has anyone run a model plane pulse jet? Horribly noisy. One a couple of hundred times bigger, no way. Supposed the V-1 sound can make you nauseous. Would have hated flying a R-1, manned V-1, for multiple reasons.
What if you make the pulse jet blow inside a duct, this reduces noise, air from suction generated by pulse jet exhaust flowing around, this cools outer pulse jet parts, and something like the hard rubber pieces used for attaching engines to car frames to blunt vibrations from jet reaching fuselage in a wild way? Blessings +
 

Urquiola

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Okay, I'll bite.

Nomenclature varies ("eductor," "ejector," "augmentor") and is not standardized.

P.M Bevilaqua from Rockwell explains how it works in this paper.

FWIW, he calls it an "ejector."

From that document (thumbnails, click to enlarge):

View attachment 95525View attachment 95526

Some text and a diagram from another document. Note that the ejector "can almost double the thrust . . ."

View attachment 95529
View attachment 95530
This concept has a common use in the turbine engines tested having the outflow going inside a duct, as in fig 1 above, sometimes turbojet gas outflow nozzle is a bit before or after the ejection tube entry ring, but wonder if calculations are available about overall thrust results. Yes, a common name is 'Thrust augmentation ejector nozzle', or so. Blessings +
 

henryk

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he calls it an "ejector."

=for "cold jet"...


=DAYSON...


=Ejectors,Coanda...


=Ejector,thrust augmentation
 
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Sockmonkey

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Flint, Mi, USA
What if you make the pulse jet blow inside a duct, this reduces noise, air from suction generated by pulse jet exhaust flowing around, this cools outer pulse jet parts, and something like the hard rubber pieces used for attaching engines to car frames to blunt vibrations from jet reaching fuselage in a wild way? Blessings +
Lockwood pulsejets are helped a lot by an augmentor duct, though it's generally placed just after the nozzle.

Ducts like that actually work better with a pulsing flow than a steady one.
Sticking little augmentors on the end of rear-facing exhaust pipes of a piston engine would actually give you useful amounts of thrust.
I see no reason why it would cause a problem. The pulsed exhaust and some of the by-pass fan air would go thorough the turbine reducing temperatures to prevent the whole thing melting. The rest of the fan air would keep the housing cool and expand providing additional energy and surrounding the high energy/noisy jet exhaust at the outlet. The valveless pulsejet/s have the intakes pointing in the same direction as the exhaust so any backfiring goes in the same direction.
I've seen vids on youtube of a guy doing that.

If you wanna know about pulse jets, this site has links to a lot of good stuff.
Also.
 

Urquiola

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I keep waiting for someone to explain the physics behind the idea that an eductor (correct term) can *increase thrust* by dragging extra air along with it. I think I know where the *idea* might have originated, but no takers so far on substantiating the claim of *increased thrust*.

Charlie
Perhaps an 'eductor' won't increase thrust, but for sure will reduce noise, and speed of propulsion gas jet exhaust, you can even consider having an 'Stipa' type of ducted fuselage, with a pulsejet instead of an ICE, same applies to cars, having cooling fan behind radiator makes it work in the hot air from radiator, both power loses and cooling efficiency are worse, the good place for a cooling fan is in front of radiator, sending incoming air from speed towards radiator, the current approach for most cars is a thermostat controlled electric fan in front of radiator.
W Keller from Sachs published a SAE technical paper about their 'Small Wankel Engines', it all had air cooled housing, charge cooled rotor; experimental data showed a blowing fan is much better than an aspiration fan.

If the heat in outer side of pulse jet is added to the outgoing air column, this would increase thrust, and efficiency, as the heat, the energy, previously lost in flight air will be added to propulsion air, just the duct must be drawn and calculated, sized, but perhaps the approach could be as simple as designing a ramjet tube, then put the pulse jet inside, intake to pulse jet in the highest pressure area of ramjet, enlarging the dimensions, the area, of ramjet duct, as to have a total area as if the pulse jet cylinder, or other ICE, were not there. This may require some 'area ruling', as size of pulse jet duct is not same all along its length.
With the small pulse jets offered in eBay, it won't be difficult testing the concept of 'augmentor' o 'ejector', but I lack a dyno or other way to obtain figures, also, it's not same the combined: 'pulse jet inside a ramjet duct' on a bench than in flight.
A team of German Model makers built a Me-328 scale model with pulse jets; other flew an unmanned VariEze or other Canard with two pulse jets, there are many designs that can be adapted to this combined propulsion system. Blessings +
 

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