Calculating top speed on ice...

[ace_fedde]

Man, I'm getting inspired by these "alternative" applications of the Thunderchine and because of that some turbulence of ideas and questions is taking place in my head.

Let me first introduce myself. My name is Fedde and I'm from The Netherlands. I've been reading and studying this forum for over a year, registered and unregistered, and I did only a couple posts.

Back to my turbulence: Constructing a hovercraft out of a Citroen 2CV, using separate pulsejets for propulsion and maintaining the aircushion...
For this car of 550 kg with a surface of app. 6 sq.m. the raise of pressure in the cushion would be less than 0.1 bar. For a highly tuned pulse jet this might be a problem? (this is more a question than a statement)

For the cushion there is not so much max. thrust needed but max. displacement of air.
I know that for turbines a restriction in the exhaust can cause an increasement of thrust (higher pressure), but probably a slight reduction in displacement.
The same (reverse) effect i noticed when I unscrewed the endnozzle of my high-pressure watercleaner: an decrease of thrust but a increase of waterflow. Unfortunatly I don't know (yet) the physics in this matter.

Would it be possible to design a pulsejet (or a modification) with more displacement but lower thrust than, for example, the thunderchine? Would it help to add multiple augmentors? etc. etc.

I love to post these questions in this thread because all the experts seem to be gathered in this one. But if these are interesting questions to you guys too, it might be better to open a new thread?

Fedde

[milisavljevic]

Welcome Fedde!

Man, I'm getting inspired by these "alternative" applications of the Thunderchine and
because of that some turbulence of ideas and questions is taking place in my head.

I hope it feels better than a hangover?!

But if these are interesting questions to you guys too, it might be better to open a new thread?

Please do open a new thread specific to your topic.
I am happy to discuss a hovercraft application with you.
I know that others will, too. Let's keep this thread on topic.

Cheers,
M.

PS: The lift cushion is best supplied via a ducted fan; I can help you size one,
but open a separate thread if you want to discuss or build the hovercraft project.

[milisavljevic]

Looking good, mate!

Everything is spot welded except for the combustor and the intakes which will be done later this week.

Remember to roughen the interior of the combustor and transition cone (eg., bead blast); this includes
the starting fences, which are more susceptible to corrosion. Please WD-40 treat all the inside surfaces.

Intake note: the finished centerline length of the intakes, after flaring, is 189 mm. Measure this twice!

What do you think M of the starting fences we've made,
are they positioned the way they are supposed to?

They look okay, but can you post a photo taken from the front, on centerline, and maybe slightly below?
That is, similar to my "front view" sketch, on the centerline, but looking up into the cone at the fences.

From your photo, it looks like I should have specified taller fences (eg., 21-28 mm). I will think on this.

What is the distance between the center of the intake flare and the exhaust cone next to it?

I will have to look it up; however, the ejectors are located on, and by, the super cone. If you build and
locate these parts correctly (ie., transtion cone, intakes and couples, tail couple, entry and super cones,
splitter and ejectors), then the ejectors and intakes will be correctly set up. Trust me, and Rossco, too!

Note: provision for stacking and alignment errors were included in the design.

Keep up the good work!

Cheers,
M.

PS: Love that "pig mask" of yours! Who is that masked man?

[Johansson]

I´ve got access to a bead blasting machine at work so I´ll do that before I weld the combustor/transition cone to the tail. I´ll double check the intake lengths today but I think they are within tolerances.

More pics of the starting fences, check!

The masked mystery man is me by the way.

[milisavljevic]

Hello Anders,

I will be changing the spec on the starting fences; you can use the new design when you build
Thunderchines #2 & #3. It is too much trouble (IMO) to cut out the ones you have. No worries.

It was a big help for me to see how they look inside the real part and not just paper sketches.

Thanks!
M.

Update...The dimensioned drawings of the revised starting fences are now available. Enjoy!

[Johansson]

More work done on the engine, the intakes are fitted to the transition cone and I welded as much as I could before I ran out of Argon. I had a couple of pics for you M on the starting fences but I forgot the camera in the workshop so I´ll post them tomorrow instead...

Is there anyone that has tried to make a starting blower with two outlets so you blow air down both intakes at the same time? I am thinking of making a 12v blower so the engine can be started on the field without the need of compressed air.

Guys, what do you think of this design on the fuel injection? The injectors are Danfoss solid cone oil burner nozzles, max fuel pressure 5-6 bar and the flow rate will be calculated from the theoretical fuel consumption for E85.

[milisavljevic]

Hejsan Anders!

I had a couple of pics for you M on the starting fences ... I'll post them tomorrow instead.

Thanks!

Is there anyone that has tried to make a starting blower with two outlets?

I know someone else who was just thinking the same thing. A starting blower that you can mount
directly onto your kick is not a bad idea. Pushing air down both intakes will reduce the cross flow,
and thus start time (especially in the cold). Perhaps a motor from a powerful blow dryer (hårtork)?

I will write a separate post about your proposed fuel + fuel injection system.

Cheers,
M.

[weldion]

Is there anyone that has tried to make a starting blower with two outlets so you blow air down both intakes at the same time? I am thinking of making a 12v blower so the engine can be started on the field without the need of compressed air.

I have an old vacuum cleaner for car use down in my basement. Maybe we can reverse the fan and add some pipes in a way that fits the intake for the engine? I don't know how powerful it is yet, but I can have a look at it at least.

[milisavljevic]

To continue from above,

The flow rate will be calculated from the theoretical fuel consumption for E85.

The choice of E85 as fuel for your Thunderchine raises three (3) points that we can discuss here:

[1] Ethanol blends have lower energy contents than (typical) gasoline
[2] Ethanol blends burn at lower air-fuel ratios than (typical) gasoline
[3] Ethanol blends have lower vapour pressures and are thus harder to ignite in cold weather

Pulsejets are relatively insensitive to the energy content of fuels (ie., all other factors equal,
a 250 N pulsejet will develop the essentially the same thrust when operated with a variety of
fuels). The "variable" will be the mass flow rate of each individual fuel type.

From this, point [1] is a non-issue, providing your fuel injection system is correctly sized for
the density of the selected fuel; when I mentioned previously that Thunderchine burns some
1200 ml/min of gasoline, that volume flow assumed a gasoline density of 0.7277 g/ml.

Thunderchine was optimised for non-alcohol fuels in the sense that alcohol is already partly
oxidised. In practical terms, ethanol blends may reduce the throttle range away from the low
end, which by turns would make your pulsejet harder to start up (more on cold starts, below).

Thus point [2] spills over into point [3]: cold weather starting. My understanding is Sweden
reblends E85 in winter to E75 (the label does not change). Anders, is this correct? Unless you
have experience starting pulsejets on E85 fuel at -30C, I suggest you think about how to get
things warmed up inside the combustor when you attempt to start Thunderchine. Note that
I'm not suggesting you use another fuel, but ethanol blends are hard to start in cold weather.

Is there an option to reduce the ethanol content on your own (mixing in unblended gasoline)?

When you confirm the ethanol content of the fuel, I will send you an updated maximum flow
rate for sizing injection hardware. The 1200 ml/min rate (quoted elsewhere) does not apply.

Cheers,
M.

[milisavljevic]

.

I have an old vacuum cleaner for car use down in my basement. Maybe we can reverse the fan
and add some pipes in a way that fits the intake for the engine?

Cool idea! I assume it has a 12 V DC motor?

M.

[GRIM]

HI All

Just this weekend I tested my dual outlet adapter , see vid ,
I was not attempting to start the engine , just getting a feel for the blower, the smoke is the oil burning off of the outside of the duct ,

The blower was made from mild steel sheet , the design was loosely based upon some 100 hp blowers we have at work , the motor is a starter motor from a small japanese car and the impeller is the cooling fan from an industrial 3 phase motor , works great , I measured 280 cfm @ 110 mph from a single 60 mm outlet with a pitot tube , and I just use the truck battery to run it ,

The dual outlet was made from some scrap pulsejet parts , I did not manage to get equal flow from the two outlets , but I think it will work better than only one outlet,

I Have some drawings of the blower, Let me know if you want me to send them to you ,

G

[milisavljevic]

Hola, Joe!

Just this weekend I tested my dual outlet adapter.

I measured 280 cfm @ 110 mph from a single 60 mm outlet with a pitot tube.

Oh, mama...Now we're talkin'! That is serious airflow. Thanks for the video.

Just getting a feel for the blower...

And where, exactly, was your wife while this "getting a feel" was goin' down?

Seriously, your video makes it clear why the starting fences were necessary.

Keep up the great work, mate.

M.

[milisavljevic]

Hello Anders,

Guys, what do you think of this design on the fuel injection?

I am out of time for tonight (It's morning here, already! ), but two critical points for you
to consider are (1) where the mass center of the injection plume strikes the duct centerline
and (2) will you be able to avoid wetting the opposite surface of the duct? (not a good idea)

We know that the best answer to (1) is approximately 25% in measured from the inlet plane.

With 63 mm intakes and good atomisation, the plume may not wet the duct (noticeably). It
would be smart to knock up a third intake duct to experiment on, using water injection and
the actual hardware you plan to use in Thunderchine. This will answer both questions, quick.

Hint: simulate the starting procedure while fueling the experimental intake duct with water.

Not being able to adjust the injection point (1) would seem to a point *against* this method.

Cheers,
M.

[Irvine.J]

Without going into detail,

Pulsejets are relatively insensitive to the energy content of fuels (ie., all other factors equal,
a 250 N pulsejet will develop the essentially the same thrust when operated with a variety of
fuels). The "variable" will be the mass flow rate of each individual fuel type.

No offence here M, but thats all pretty much wrong bud, for a variety of reasons. I agree that the idea that you can do most of this has been around for a long time but it just ain't true. (My two dollar calculator told me so)
Let me explain...

Ethanol (in all its forms) is probably on the list of worst fuel choices for pulsejet operation, (Except maybe acetone) and no matter how much you throw at it, it will never develop the same amount of power as gasoline, kerosene (which can be deceptively under-performing) or naptha.

For 1: E85/95 IS HIGH OCTANE, The OPPOSITE OF WHAT YOU WANT. Octane is simply a measure of Resistance to detonation, or, more incorrectly, "The level of compression required for combustion".

2: Ethanol is devastating to performance even when mixed with gasoline or kerosene (Miscibility permitting, which is crap anyway) and easily finds its way through pump seals.

3: Its not simply a case of dumping more fuel to bring up the power, it will still run rich and flame out without providing as much power as the engine can provide, its not a variable in terms of mass flow rate. E85/95 whatever is no exception either.

4: Our trials involving nitromethane, nitromethopentanes, napthas, benzines, R-151, and other nasty's, you name it, and mixed 1 liter containers of every single mix (and percentages from 2/5/10 and 20% of two, three and four part mixes, were ran through one benchmark engine to gauge performance. Needless to say the same were burnt through a number of other engines later; surprisingly, ethanol always had major deficits. The causes of this are its calorific value, heat of combustion and its latent heat of vapourisation all working against you, but here I'm just letting you know I was pretty thorough

5: The most he can hope for running the intended fuel and system is roughly 40-50% of his total obtainable thrust even if he had 10 bar to play with. You want to use a LOW octane fuel, not High octane. Adding even 2% Methanol will drop your octane rating by 10% or more for things like naptha's or nitromethanes, and I would suggest a vapourising coil is in order due to your high flow rate requirements.

6:Ethanol ended up being somewhere just above trying to run pure two stroke oil and lizards, lizards performed better...

6b: I would strongly suggest a pre-ignition with propane and a vapourising coil as your fuel delivery system, all you will require to throttle then is a tap between the pump and the coil, very straight forward. Since the environment is cold and density wont be much of a concern, you should be running something in the order of a kerosene/gasoline mix, or a naptha/gasoline/kerosene mix. It is tried, tested, and works quite well and is easy to fit. There are plenty of examples for this on Melanic's drawings and others.

7: Since the engine was designed for generic hydrocarbon use and not for a specific fuel, you will need to increase your naptha /white spirit (Coleman camp stove fuel) % until such time as you balance the flash speed to the frequency of the engine. I would increase in 5% increments until you find the best mix for your engine.

8: Your current setup (Viv and I will snicker at that drawing) wont work. Since the environment is cold and density wont be much of a concern, you should be running something in the order of a kerosene/gasoline mix, or a naptha/gasoline/kerosene mix. It is tried, tested, and works quite well and is easy to fit. There are plenty of examples for this on Melanic's drawings and others.

Since the engine was designed for generic hydrocarbon use, you will need to increase your naptha /white spirit (Coleman camp stove fuel) % until such time as you balance the flash speed to the frequency of the engine. I would increase in 5% increments until you find the best mix for your engine, but if you exceed 20% naptha, decrease your kerosene concentration for an increase in gasoline, and go back to 5% naptha and try again. Start at 70-25-5 G-K-N

Trust me, I been here.

A vapourising coil will do exactly what you want in the shortest time frame and be extremely safe and reliable. The propane tank does not need to be on the ski and is only for starting the engine and warming it up with rossco jector or some such.

Anyway, that's it for me, loggin off the ol forum for a bit. Some time, back to a store near you...one day. Peace and good will to all.

[milisavljevic]

Hello James!

While you may not believe this, or even care, I am ever so happy to see you back here, little buddy!

You want to use a LOW octane fuel, not HIGH octane.

I agree with you, but ultimately, Anders will select the fuel.

I would suggest a vapourising coil...

I agree with you - 100%. A most excellent recommendation.

A vapourising coil will do exactly what you want in the shortest time frame and be extremely safe and reliable.
The propane tank does not need to be on the ski and is only for starting the engine and warming it up.

As James recommends, use propane to warm up and start Thunderchine, then switch over to liquid
fuel fed in through a vapourising coil. This is proven technology, and it works great in cold weather.

Trust me, I [have] been [t]here.

Not well said, but true nonetheless. James has experience.

Cheers!
M.