# Anybody want to build one of these?

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#### Turd Ferguson

##### Well-Known Member
It was the "no welding" bit that got me. What are you supposed to use: self tapping screws, pop rivets, glue?
Now that you have spent $25.00 to collected all your parts to build your engine, you must purchase a$1000.00 metal lathe in order to thread the parts. ( this is how things go in my life)
In "Diary of a Wimpy Kid: The Last Straw" Greg is reading the ads in the back of magazines where he finds ads for "X-ray Glasses, How to Throw Your Voice, Print Your Own Money Machine" then comes across an ad that says "Build a Personal Hovercraft [with ordinary hand tools] ! !" So he sends for and receives the instructions which say:

Step 1: Obtain an industrial twin-turbine gas engine

#### Topaz

##### Super Moderator
Staff member
Log Member
Pulsejets (of any variety) and airframes generally don't mix well. Yes, there's the heat problem, but that's generally resolved by mounting it outside the airframe and taking the drag hit while keeping the engine (and airframe) from melting. So that's not really the problem.

The problem is the sound and vibration. Light aircraft-style structures and huge and sustained vibration don't really play well. The latter tends to fatigue the former in pretty short order. The Messerschmitt Me-328 was probably the most serious attempt to build a manned, pulsejset-powered aircraft, and the problem they had was that the airframes didn't stay intact long enough for even the extremely short service life expected at the very end of the war. The only application found for pulsejets in aircraft was for the V-1 cruise missile, where the "operational life" was one flight.

Ground vehicles can just throw weight at the problem, and generally do.

#### Dana

##### Super Moderator
Staff member
The crash safety of that red hot glowing engine is what scares me... even if you survive the impact the brush fire will make it difficult for the rescue personnel to reach you...

#### BJC

##### Well-Known Member
HBA Supporter

This is a slightly crazy use for a pulse jet.
That is a good application; when they wreck, they melt through the ice and self-extinguish.

BJC

#### wsimpso1

##### Super Moderator
Staff member
Log Member
Just doing a back of the envelope calc on the go-cart. 60 mph on that cart means about 48 pounds of thrust and 8 horsepower made good at that speed.

No thanks.

#### TFF

##### Well-Known Member
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.

#### Jerry Lytle

##### Well-Known Member
Been used in model planes for 70 years or so:

#### ARP

##### Well-Known Member
It would seem possible to use a small pulsejet like this as the "hot section" of a sligtly more efficient engine. Simplest: put a casing around it to form an ejector (the exhaust gases "pulling" a large volume of entrained ambient air backward to make more thrust). This would also shield other airframe parts from the radiant heat and maybe decrease noise (a little). Or even some sort of turbine/fan on a single disk just to move more air with fuel that has already been burned.
Of course, the pulsing nature of the flow and its extreme heat are an issue. And did we mention the noise?
Vigilant1:- I have drawn up such a system with a bypass fan driven by a turbine in the pulse jet exhaust. The bypass flow should reduce the pulse jet noise as in a normal turbofan. Erosion of the turbine by the pulse stream might be an issue?

I built a pulse jet in the 60's with a valve but it would not maintain for more than a few seconds. I can confirm it was extremely noisy and got very hot!

#### 12notes

##### Well-Known Member
Log Member
Just doing a back of the envelope calc on the go-cart. 60 mph on that cart means about 48 pounds of thrust and 8 horsepower made good at that speed.

No thanks.
In fairness, the speed was limited by the length of the road, it was still accelerating when he had to hit the brakes.
Also, the guy who built it, Colin Furze, specializes in ridiculous contraptions, practicality or rationality usually has little to do with it, with exhibit A being his cake eating device - a motorcycle engine connected to a wheel made of a dozen spoons throwing cake into his face.

#### galapoola

##### Well-Known Member
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

#### quick582

##### Member
I've got a couple of ex-korean war drone pulse jets for sale. They powered the drones up to 350 mph! I believe they are around 175 lbs of thrust, they are very light in weight and very powerful, much more thrust than the homemade ones shown here! Surplus new in the box. \$1900.00 each.

I had a lot of good ideas for using them, but got old...

Marquardt PJ46-MA-2 pulsejet, 175 lbf (0.78 kN) thrust

Globe KD5G - Wikipedia

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#### Tiger Tim

##### Well-Known Member
I have drawn up such a system with a bypass fan driven by a turbine in the pulse jet exhaust. The bypass flow should reduce the pulse jet noise as in a normal turbofan. Erosion of the turbine by the pulse stream might be an issue?
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.

#### jedi

##### Well-Known Member
Back in 1956 a man put on a demonstration inside the high school auditorium with a Dynajet (pulse jet) . He had a small fan several feet behind it turning a set of wheels. Loudest sound that I have ever heard. Don't know how the windows of the building held up.

Dan
I think it was Dow Chemical that had a crew visiting middle schools with a science fair exhibit that ran a pulse jet in the school gym. Very interesting and noisy. Other products of interest where the basis of today's chemlight (Glow sticks) and Corell kitchen dining service.

I knew Joe (itallian last neme not spellable) who built and flew a twin pulse jet single seat aircraft. He only flew it three or four times and every flight ended with the aircraft either on fire or smoking badly. Longest flight was about 5 minutes. Engines were rear fuselage mounted as in the A-10 Warthog (Fairchild Republic A-10 Thunderbolt II - Wikipedia).

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#### GeeZee

##### Well-Known Member
HBA Supporter
Saw an article once where a pulse jet was used for metal deposition. Feed a wire of some metal into the combustion chamber and point the exhaust at something you wanted the metal deposited on.
When I was a kid I wanted nothing more than a strap on tip jet powered helo. Now, not so much.

#### Jerry Lytle

##### Well-Known Member
Someone sold plans to mount a pulsejet on a bicycle. from the dream ads June 1954 Popular Mechanics. In my generation kids were made out of tougher stuff (if they survived)

#### rv7charlie

##### Well-Known Member
It would seem possible to use a small pulsejet like this as the "hot section" of a sligtly more efficient engine. Simplest: put a casing around it to form an ejector (the exhaust gases "pulling" a large volume of entrained ambient air backward to make more thrust). This would also shield other airframe parts from the radiant heat and maybe decrease noise (a little). Or even some sort of turbine/fan on a single disk just to move more air with fuel that has already been burned.
Of course, the pulsing nature of the flow and its extreme heat are an issue. And did we mention the noise?
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

#### proppastie

##### Well-Known Member
Log Member
I think I know where the *idea* might have originated, but no takers so far on substantiating the claim of *increased thrust*.

Charlie
Probably thinking about a high bypass jet engine. ..which is really a turbine powered ducted fan?

#### lr27

##### Well-Known Member
Long ago, you could get such an augmenter to use with a Jetex rocket motor in your small model airplane. Not a pulse jet, but a similar idea. The principles aren't obvious to me, but I'm not ready to say it doesn't work.

At first, I couldn't get the cart video to load. Somehow, while trying again, before I saw anything, the name Colin Furze popped into my head. I wonder why? ;-) That boy is going to get himself killed someday. I'd be interested in doing some of the same things, but from much further away. I'd even be more careful than the guy on the Beyond the Press channel on YouTube.

#### poormansairforce

##### Well-Known Member
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
It may have come from the idea of adding a radius lip to the front of a ducted fan/prop. The extra air being pulled past the lip creates lift.....