School Project-- GOT QUESTIONS on -- K-PT 07X --

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snakeye
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School Project-- GOT QUESTIONS on -- K-PT 07X --

Post by snakeye » Thu Sep 28, 2006 9:59 am

Hi all,

I'm pretty new to pulsjet's although I did a lot of research on them on this forum and other site's like aardvark.
Someone from pulse-jets.nl sent me a good but simple valveless pulsjet design. That was the K-PT 07X.
Now I've got some questions:
The diameters are pretty weird sizes (in mm are they), and I was thinking about buying standard DN sized pipes, cause welding sheet metal into pipes takes to much work and is pretty difficult. now for my quistion:
Do I have to make the pulse jet with the EXACT sizes given in the design? or can I take standard pipe sizes that are pretty close to the blueprint? And does it RUN with that slightly other sizes?

The second question:
there is a U-bend in the design... but there is also a little description written on the blueprint like : the u-bend is 90 degrees! but A u-bend is normally 180 degrees cause it isn't a u bent if it's 90 degrees.

I need some explanation.

THanks in advance.

Jimmy

this is the engine I was planning to build
==> http://www.pulse-jets.com/phpbb2/viewtopic.php?t=3185 <==[/b]

mk
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re: School Project-- GOT QUESTIONS on -- K-PT 07X --

Post by mk » Thu Sep 28, 2006 4:33 pm

"Snakeye",

Cool, that the design is evaluated by others as well. =)


I do not know which kind of pipes you are referring to. For me it was always way cheaper and easier to simply build the tubular and conical sections by hand.
Therefore, could you please state the pipe specifications, like material, wall thickness, ID or OD? And maybe where you got it from? That would be interesting for me, too.

If the pipes' IDs are only off by a few percent compared to the stated dimensions, you should at least get a running engine. The latter seems to be enough for a school project, does it not?
However, please let me advice you, that building as exactly to spec as possible is very important in successful pulse-jet building and running.
Every detail that is not treated with the necessary amount of prudence will come back during operation. If you change any dimension, the reported power levels and fuel consumptions may no longer be true for such an "interpreted replica".

Anyway, the major criterion for the diameters of the K-PT 07X being of the sizes they are, was the given ID of the two 90° bends, which now form the 180° U-bent.
mk

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DIN (for germany) or NEN (for the netherlands) or whatever

Post by snakeye » Thu Sep 28, 2006 8:24 pm

nen means (in english, cause it is a dutch ) national standards (or something like that). but anyway, if I go to "steel vendor" and I say: can I have 1700mm NEN50,2 (this is an example I don't know the actual standards) tube, he knows that I want a steel pipe with a length of 1700 mm with an internal diameter of 50mm and a 2mm thickness of the pipe metal.

so It's something like a size/thickness/diameter standard.

I hope this is clear now...?

and yeah I get it with the bend(s).

The reason why I wanted to know that, is because it saves me build time with standard tubes. altough I found out that the steel that can be used is 1mm thick mild steel, and I didn't read that before now on the drawing, and that mild steel is easy to bend and weld.

I hope someone has some more tips or any kind of information for me and I'll keep you up to date

thanks in advance

Jimmy

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re: School Project-- GOT QUESTIONS on -- K-PT 07X --

Post by mk » Thu Sep 28, 2006 9:05 pm

Allright, I got the NEN standard and can follow from now on. =)*

However you decide, I would strongly suggest to post the pipe standards (as you introduced them) before you start any building, this in order an estimation on the "how well will it still operate" question might be given. This procedure could in the worst case help you to avoid any headaches.

In any event, 1 mm wall thickness sounds perfect and should last long enough. Much depends on proper mountings. Mine were crude and improper, such as the smaller diameter tailpipe section deformed quite noticably over running time. After the cut-off things looked worse than I would have suspected them from an outside view.

A further note: If you want to employ the injector as shown, please use the upper distance range, the one not stated in brackets, that according to the blueprint.

BTW a U-bent is not necessary for operation, but for avoiding inlet-to-tailpipe thrust cancelation.


*) "=)" was first introduced by "fricke". I hope it is no problem if I borrow it once in a while?

---

Further tips? Hmmm...let's see:

- Building to spec.

- Smooth internal surfaces. E.g. reducing the number of small burn-throughs and bumps. Those are normaly caused once in a while during the welding procedure, at least when being unexperienced and/or not careful enough.

- Properly alligning segments and/or sections. This means the pipes have to be as (center-line) parallel as possible, and the joins or join planes have to fit to each other properly, too.

- Secure and suitable mountings. They have to keep the engine on its place, but will also have to allow for thermal expansion of the duct. Another issue is deflection of stress from critical, i.e. thin-walled and hot, parts of the structure.

Further help can be provided on request by further progress. This includes starting and operating the engine, which we could deal with later if necessary.

Are you going to collect any figures? An independant thrust and/or (T)SFC measurement from your side would be much appreciated, but is not demanded from my side.

EDIT: Improvement of comprehensibility.
Last edited by mk on Fri Sep 29, 2006 10:50 am, edited 2 times in total.
mk

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re: School Project-- GOT QUESTIONS on -- K-PT 07X --

Post by snakeye » Fri Sep 29, 2006 6:56 am

what you mean with collecting any figures ? you mean pictures ?
and what is (T)SFC measurement ?

I would like to do all the measuring cause it fills my school paperwork and it isn't useless so tell me about it please!

allright. about the pipe's I'm going to get them today, and I'll just buy some pipes with diameters (internal) that are as closest with the blueprint.

I don't get you with the borrowing thing ? :s

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Re: re: School Project-- GOT QUESTIONS on -- K-PT 07X --

Post by mk » Fri Sep 29, 2006 10:24 am

snakeye wrote:what you mean with collecting any figures ? you mean pictures ? and what is (T)SFC measurement ?
Okay, maybe I was a little too fast.

Pictures would be cool, but what I wanted to express is whether your goals were similar to the following:

(1) Measuring (sea-level) static thrust, abbreviated "SLS", which demands a kind of thrust stand somehow.

(2) Recording the overall charackteristic frequency, abbreviated "OCF", which might be done by filming the engine during operation. Later on the movie file can be treated further to reduce it to the sound recording, which might then be analyzed with a suitable software.

(3) Measuring (time-)specific fuel consumption, abbreviated "TSFC" or "SFC". This would demnad the measurement of continous SLS together with fuel consumption over a given ammount of time.
For the time being, I would not recommend that you try to attempt it right now.

Well, you do not need to do so, of course. It was only a question, because I do not know how far you are in pulse-jets already.
BTW is it going to become your first pulse-jet built?

So with respect to the above paragraphs, now ponder whether it might be possible for you to attempt one or the other measurement. For the time being I would not necessarily encourage you to attempt (1) and (3). You will be busy enough with building and running the engine.

However, if you have or can get a digital camera with video function, the easiest measurement you could do would be (2), the OCF one. In this regard you would only have to film the engine from a certain, fixed perspective for about ten seconds. The rest, as e.g. sound extraction and anylysis, can be done by others and/or me.

snakeye wrote:about the pipe's I'm going to get them today, and I'll just buy some pipes with diameters (internal) that are as closest with the blueprint.
Maybe you just ask, which of NEN standard pipes your raw-material seller can provide you with, just before you are spending your money?
You could give him a call if it is too far away from your place, which, eventually, would not make it worth to take the expenses of driving to the seller twice.
snakeye wrote:I don't get you with the borrowing thing ?
Please do not take this one too seriously. It was merely addressed to "fricke".
mk

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re: School Project-- GOT QUESTIONS on -- K-PT 07X --

Post by snakeye » Fri Sep 29, 2006 3:54 pm

Hey I bought me some pipes for about 40 euro (that like 45 dollar I think),
I got the normal sizes ( 2x 36, a piece of 76, and the bends and sheet metal for the cone at almost the end), except for the last piece of exhaust pipe (the normally 90.5 mm ) I bought a 98 mm pipe. I don't think that is going to be a big problem do you ?

and I have another question: how do I make the cone out of sheet metal ? do you have any calculations for me or some explanation on how to make a sheet metal layout for a cone that is 36mm on one side, and 98mm on the other?

I think I'm going to do all the measurements but I'll ask you to explain me how to when I have a running pulse-jet.

greetz Jimmy

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re: School Project-- GOT QUESTIONS on -- K-PT 07X --

Post by Eric » Fri Sep 29, 2006 8:18 pm

For making cones you can use my excel based pulsejet calculator, you enter the dimensions of the cone and it will give you what you need to make the flat pattern, and also you can calculate how much it will weigh by entering in the material thickness and metal density.

Eric
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re: School Project-- GOT QUESTIONS on -- K-PT 07X --

Post by leo » Fri Sep 29, 2006 8:36 pm

Jimmy the easiest is to use Eric his calculator, alternatives are on this web sites.
http://www.i-logic.com/conecalc.htm
and
http://www.pulserate.com/
Alternative you can find it out yourself, it will look good in your School Project.

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re: School Project-- GOT QUESTIONS on -- K-PT 07X --

Post by mk » Sat Sep 30, 2006 3:45 pm

Wow! 40 EUR for pipes!

Well, to keep it short: 98 mm ID pipe seems way too large. Sorry!
The 98 mm ID pipe would be some 8 % off relatively to spec. That would already cause tailpipe expansion problems, together with timing alterations.

While you were able to get all the other pipes in the right sizes, and because forming those large ID pipes in decent quality is really not too complicated, I would strongly suggest you simply form that large diameter tailpipe piece by hand. Maybe before forming a cone, so you can get a feeling for the material.

What you are going to safe by using the 98 mm ID ready-made pipe segment would, IMO, not be worth the expense of eventually f*cking up the layout. Also IMO, much more could be gained by analyzing an independent, exact replica of -07X.

Herein, please do not consider the 98 mm ID pipe as wasted money. Rather it gives you the possibility to build a simple augmenter for the intake (later on). If not, it may be used in further projects.

---

Eric and "Leo" already stated possibilities for creating flat sheet patterns for cones and tubular sections.
Personally I do highly recommend the usage of the cone and augmentor construction sheet of Eric's "Pulsejet Calculator 1.4", which comes as MS Excel spread-sheet. For me that always worked easiest.
You may only want to decide whether you are going to use length-wise join overlap, or not. Doing an overlap could improve internal weld quality if you are not to experienced, or if you are using thin (stainless) steel.

Furthermore, I would suggest you choose a slightly longer-than-spec layout for the cone's sheet calculation -- maybe some 2 mm or so; and of course, the diameters have to be adjusted then as well. The above just in order to grind or file the ends to proper (join) planes, and the length down to its calculated theoretical counterpart. Both of the latter would have to be done after length-wise welding, of course.

How you get the sheet pattern on metal might remain to your imagination.
But on the one hand you could do paper models of the section roll-offs, while on the other hand you could directly mark the roll-off dimension on the metal sheet.
For accuracy, the first suggestion of the above might be recommended.

EDIT: Spelling and grammar improvements.
Last edited by mk on Sun Oct 01, 2006 12:41 pm, edited 1 time in total.
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re: School Project-- GOT QUESTIONS on -- K-PT 07X --

Post by Eric » Sat Sep 30, 2006 7:20 pm

Yea making your own tube section is not nearly as hard as making a cone, just cut out a rectangle of the right dimensions and roll and weld it.

With almost all of my engines the only prefabricated part I use is the J bend.

I take it the engine is going to be stainless and thats why it was so much for pipes?

Eric
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re: School Project-- GOT QUESTIONS on -- K-PT 07X --

Post by leo » Sat Sep 30, 2006 9:14 pm

Jimmy you can grind a small piece out of the 98 mm ID pipe to get it down to the right size, then weld it together again.
Would be not to much work.

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re: School Project-- GOT QUESTIONS on -- K-PT 07X --

Post by Eric » Sun Oct 01, 2006 1:25 am

25 mm might be a bit to grind off over the whole length, but you could cut the section out with a bandsaw, or even a hacksaw. Its just a matter of if the pipe is thin enough that you can nicely reform it without it becoming tear drop shaped.

If you dont think the pipe will reform well then dont even use it for the tail. Like Marten said it could make a nice augmenter for the intake, and the staggered engine layout works perfect for single augmentation. Something like this:

Eric
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re: School Project-- GOT QUESTIONS on -- K-PT 07X --

Post by snakeye » Sun Oct 01, 2006 4:50 pm

yeah I'll cut a bit off the original pipe to make it a bit smaller, and that cone calc. is nice indeed!...

but do you guys think the engine won't run with that 6mm bigger pipe? would be pretty strange if 8 percent makes such a difference, I only need a running engine not a 100 percent good engine...

thanks for all the replies guys ... thank you very much!

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re: School Project-- GOT QUESTIONS on -- K-PT 07X --

Post by Eric » Sun Oct 01, 2006 6:02 pm

Well the problem is that the 8% increase in diameter has 18% more area. It should run fine but its not going to run exactly like the original.

It could be a useful thing to try, if you use an advanced fuel injection method the base power output should be greater, so the engine should be able to handle the 18% increase in area in the expansion section and might get a decent increase in thrust.

I find the cone calculator a lot easier than those other programs that output the cone pattern into a autocad file, mainly because if its too big to print then you have to reverse engineer the dimensions from the autocad drawing anyway. Glad you find it useful :)

Eric
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