Design a Jet With The Unknown Basics!

Throughout my time roaming the vastness of instructables, I've seen a lot of homemade jet engine designs. They vary from the very primitive hairdryer pointed at a beer can to the turbocharger hacked jet engines that power motorcycles. All of them have knowledge that can be taken from them, but nearly all neglect some very very basic principles you will find in all jet engines on real aircraft.

Unfortunately, I don't have the money or time to devote to making a jet at home, but I can give you all some important knowledge that you can apply to any engine you design! This instructable will hopefully  teach you how to design your own jet engine! Lets begin with the very basics. I know, I know... I'll try to be quick :)

Oh and WARNING: building and operating a jet engine comes with many hazards. You risk it exploding, loss of hearing, etc. Be careful please! The guidance I give you here isn't everything either. It is advanced basics, but basic never-the-less. I don't take responsibility for anyone's actions based on this instructable.

Phew... enough of that... come on, lets peel this onion!

Step 1 Compress Your Air!

A jet is dependant on air for combustion and needs a constant, compressed flow. This is done to cram as much oxygen as possible into the combustion chamber. That way you get a clean, powerful burn from you fuel. You will not get this with a hairdryer in the end of a beer can engine. This is because the faster a stream of air flows, the less pressure it possess. Sure the beer can engine looks like a jet, but it technically isn't. It lacks compressed air, among other things.

The MOST FUNDAMENTAL way to increase pressure is to form a DIVERGENT duct for air to pass through. A divergent duct starts out with a small opening at the front aka inlet and a larger opening at the outlet aka exhaust. This shape of duct will slow the air velocity down and increase the air's pressure as shown below.

There are three methods of compression that I will discuss. Each uses the divergent duct principle to compress air for combustion. These three are:

* Pulse jet
* Centrifugal compressor
* Axial flow compressor

Comments

[MistaMista]

Sorry, but in the second illustration, would there be a seal around the flame tube at the end of it so as to keep air from exiting unburned? Like would it be blocked off so that the only path for compressed air is to go through the holes in the flame tube and then get burned and exit through the end of the flame tube? Or should there be some opening for cooling reasons or something of that sort?

[--= Excogitate =--]

In the engines I've seen some of the air is used for cooling the turbine and engine housing. This excess air is 'unburned' and goes around the combustion chamber. Though I have not seen a design with a seal, I have seen ones that get closer to turbine inlet. I can't see why it wouldn't be possible to design one with a seal.

[MistaMista]

i assume the vanes are stationary yes?

[--= Excogitate =--]

Yes the stator vanes are stationary.

[pekka__]

What kind of steel can be used in the burner and exaust tube without getting ruby-red?

And does it happen with "industrial" jet turbines?

Thanks from Brazil.

[malleolus]

Let me rephrase, there is no metal that will not get red hot under these circumstances.

[malleolus]

You can use most types of steel, but there is no material (if left without any cooling apparatus) that won't get red-hot under these circumstances. For ease of building, heavier steels can be used for the flame holder if weight is a negligible issue(if the turbine is going to be used for a jet-cart or something similar, the wheels will make the weight somewhat negligible). If not then you need to build with the intention of either including a well designed cooling system or intending on replicating and replacing the part as needed, and honestly for a DIY engine you will be doing this anyways to improve on the part. Until you are absolutely satisfied with the part do you need to worry with greater work loads and times associated with the parts in question. When that happens, get a professional casting made and you'll probably want to get nickle alloys of a grade within your price range, higher quality (though more expensive at first) will last much longer, saving you money. Again, unless you are wanting to commercialize the engine you probably will be better off getting cheaper steels and just making several of them.

Industrial jet turbines are made extensively out of titanium alloys, which are both stronger than steel(3times I believe for equal weight) and only weigh 60% that of steel. Yes, they would get red hot, but the engines are designed with extensive and redundant cooling systems to keep that from happening since titanium has a nasty habit of gathering impurities at high temperatures.

[macgyverfan]

If you could get a hold of enough inconel steel, I suppose you could use that. however, I know nothing about the weight, so please do more research before taking my word for it.

[malleolus]

Foremost, to all the naysayers, let me say that I am studying to be an aerospace engineer and have taken multiple aerospace manufacturing courses for giggles, and the precision required is not nearly as bad as you are making it out to be. In commercial engines, the components are designed for consistency and safety at multiple loads and altitudes, not manufacturing cost. You only need .00x precision, but in commercial production, there is the 100x rule that means that the piece has to be true to .0000x to pass inspection. This is a safety margin, but the engine is not expected to be called into services that require it to need that great a precision. I can match the former precision with basic equipment and measuring equipment so long as I take it slow, using the "measure twice cut once" rule. It takes skill and steady hands, but it most certainly can be done, the better the equipment the easier it is mind you.

To OP, your post is a good general overview of the basic components, but I would not title it, in the future, the way you did unless you are going to go into detail as to basic manufacturing processes used for each component. Furthermore, you need to list an example of how each component is made, you seemed to only touch on certain components, leaving others out(like the turbine cooling apparatus) with only a "you can do that" statement. I'm not saying give a full build manual, but if you title it "Design a..." you need to give details on how to design each component, rather than an overview of each component. Be that as it may, you actually went into greater detail than most anything readily available on the internet that the regular person can understand, and I applaud your endeavor and urge you to expand your knowledge when you can by actually building one, it would be great fun and enlightening how something so simple in concept can get so complicated in manufacture. I'm currently designing a home built axial flow turbine myself and will post it asap.

Disclaimer: Unless you know what you are doing, do not attempt to build such a device. It does take a level of precision that you are not naturally born with and improper manufacture can lead to catastrophic failure, which can be deadly. Anything aforementioned was learned professionally and has been done repetitiously, building skill. Do not think under any circumstances that you can just pick any tool up and use it, you must practice practice practice with each tool will use before you even attempt such a project, and even then you must take well thought out precaution. Even if things go well, severe burns, hearing damage/loss, etc. are things you must take every precaution available to protect against during both the build and any testing. I nor anyone here will take any responsibility for your endeavors and any injuries or otherwise incurred by such a project.

I would say don't try this at home, but I know better. Don't try this unless you are willing to suffer any and all consequences.

[blinde001]

Has everyone read "Gas Turbines for Model Aircraft" by Kurt Schreckling & Keith
Thomas, or his earlier treatise on the subject, "Home Built Model Turbines".
It basically shows just how simple a basic jet turbine can be and how it is within
the capabilities of almost anyone with some skill to build one, albeit not as
finished or powerful as the newer commercially available models. It puts a lot of
this discussion in a somewhat different perspective.

[The 4th Doctor]

Also could you tell me where that picture of the turbocharger jet is from on the first page, looks like a good one nice afterburner, id also like to know how the exhaust turbine isent a pile of molten metal

[The 4th Doctor]

i like your interpretation/representation you are original and thoughtful in your writing, add to it why not.

everything seems reasonably accurate, try to get even more information theres lots of other stuff you could throw in here.
heres one thing i can think of mentioning

even turbojets tend to use no more then 25% of the available oxygen for combustion they run very lean, they have to because even with advanced materials its hard to keep those exhaust turbines from melting so even turbojets (i say turbojet attempting to highlight that they have no bypassed air) can have an afterburner directly attached to the exhaust

[Romanader]

Hey, I'd like to thank you for your instructable because it is in fact very interesting. I see no need to nitpick your article or say rude or pretentious things because I see the intent here is not to tell a 10-year old how to make a working cruise missile, rather it's to share some interesting and inspiring details about the arcana of jet engines. I appreciate the piece on Augmenters because I haven't seen that before in other articles. The picture of the jet suit is really neat. You may be interested to know those little purple-tipped jets are JetCat mini-jets. They were intended to power RC model jet planes but Visa Parviainen (fellow in the picture) and the BirdMan Rocket Team had a better idea by far. Thanks again for the Instructable.

[Romanader]

I am so sorry, I double-checked and I'm totally wrong. The guy in the picture is NOT Visa Parviainen, that's Yves Rossy. But those are still JetCat turbine jets. Visa flew the year before Yves on Tuesday 25th October 2005 . Yves flew on November 2006. They used entirely different setups, but both had to jump from an aircraft to launch. Yves flew over the English Channel and his suid costs about $200,000 to develop (I believe it, each engine is roughly $5,000, and that's without the control system, carbon-fiber wing, suit, etc., etc.).

[joebanana]

Uh, "ball bearings"? Uh, no. Babbit bearings are the only type for turbines, under a high pressure oil bath. With turbine oil, regular oil causes vortices, and harmonic vibrations Ball bearings will explode at even sustainable speed. Another thing, there are usually a minimum of four bearing planes on a turbine shaft, how you gonna get the center ball bearing over the blades?

[--= Excogitate =--]

I'm quite familiar with jet engines and their subsequent parts. That being said yet another time, the only thiabng the distinguishes babbit bearings from anything else is the material coating on the BALL. Its like and IQ question; all babbits are bearings but not all bearings are babbits. Babbit metal/alloy is actually quite soft and readily damaged, so this doesn't make any sense too me. I work on jets for a living, so please don't be condescending the next time you want to talk to an author about something of concern. Thanks.

[joebanana]

Have you ever seen ball bearings in a turbine engine? They don't go over the shaft, and you need more than two end point bearings. And what do you mean the material coating the BALL? plane babbit bearings don't have balls, And yeah, they're softer than the shaft material so they don't wear grooves in the shaft, they wear instead, and are easily rolled out as compared to ball bearings where you'd have to disassemble the whole shaft to replace them. I don't work on airplane turbines, I rebuild co-generation gas turbines built by GE and Westinghouse. Regards

[--= Excogitate =--]

Oh and I've pretty thoroughly taken apart jets, so yes I have seen bearings first hand. Yes, roller bearings are common, but so are ball bearings. I wanted to keep this simple, so I left it at ball bearing so as not to confuse people. In fact, ball bearings are the ones that bear the most stress. They can carry both axial and radial loads. Rollers only carry radial...

[joebanana]

I'm still curious about how they get the ball bearing journal on the shaft? Plane babbits, the split type, Maybe I didn't emphasize "Plane", or "plain"(?) bearing, but, not "sleeve" bearing. The type in the old days they would pour in place, right in the pillow block. Upper half, and lower, basically two chunks of silicon bronze, or some alloy. All you need to do to inspect, or change, is remove the bearing cap, (depending on the location on the shaft, some have the bearing mount cast into the upper shell) and the top half of the bearing usually comes with it, then take the weight off the shaft and just roll the bottom half out, no need to pull the shaft all the way, then get it back in, if you know what I mean. And there's really no moving parts to come apart on failure. Ball bearings make a mess when they fail Regards

[--= Excogitate =--]

Well, perhaps wikipedia is wrong and thus I am too. However, I mentioned in the drawing that, yes, there would need to be more bearings arranged in the center of the shaft for support. You missed that, granted it was in the picture caption. Also, I see the confusion about the bearings being 'over' the the shaft. My pic wasn't clear enough... Again the specifics of babbit bearings all fall under the umbrella of bearings whether or not I'm right about the material specs. You can read the wiki yourself and edit the article if you feel so inclined. Sorry for the confusion, but this was meant to be a very simple introductory level guide to what constitutes a jet engine and what beginners will need to consider.

[Trying_to_build]

First thank you for the whole thing its GREAT, ive been surfing the net on how can i make a turbin engine,  its the only one with much info in it.

i have few Question tho,, how to design it am taking about the size and measurments for the parts and how to calculat the thrust will prduces.

Thx again man and keep it up.

[--= Excogitate =--]

Thanks a bunch :)

Truth be told, the mathatics behind the construction and performance is where my knowledge drops short.

There are so many variables. I can only offer general advice like more stages of compression exponentially increases air pressure/oxygen per unit volume. However, the structure of the compressor blades, inertia, bearing quality, precision balancing, etc will impact each stage's performance.

I suggest looking at RC jet designs and using the dimensions for your motor. This won't give you identical output however unless you match the quality of parts... which will be harder to achieve. This is something I need to do homework on too. Best of luck :)

[Trying_to_build]

Thx for your quick reply man,

Im trying my best on looking at RC jet designs but still dunno about the parts sizes but i found in a one website the material for each part, i'll try my best tho.

I have another question. The steps you have here dose it apply on Turbofan?

[lemonie]

An Instructable is a step-by-step guide showing how you made or did something.
This isn't an Instructable.

While you've talked a lot about jet engines it's little use for actually building one. E.g. "you could probably use roller blade bearings" - "You could just house the bearings in a container with a bath of oil" "a simple method is to use flyweights system" no I don't think so. Much of this is vague, guessing, or not about manufacturing parts, which is why Instructables are things that you have actually done and made.
It's one of those things that there maybe should be a section for, but there isn't (yet). The site is for DIY that has been done.

You comment on Homemade engines you've seen on instructables, but the only one that actually qualifies is this:
www.instructables.com/id/How-to-build-your-own-Jet-Engine/
So I'll happily agree with your statement that nearly all neglect some basic principles you will find in all jet engines on real aircraft, they should have done some research like this perhaps.

L

[Rahdzhillaxxx]

While Excogitate may work on the engines and know how they operate etc. I machine the raw castings that go into the engines.  All those little blades are made up of a very,VERY, specific nickel based alloy that withstands great amounts of pressure and HEAT. some of the little blades cost as much as 2500 dollars to cast and rough into shape before they are ever ready to get put into an engine. Just remember that making a metal machine that compresses hot gasses and great pressure you will be likely to have a lot of trouble with hot flying rollerblade bearings. and anything from a source of parts other than dedicated aerospace parts.  I'm not saying it cant be done just a kinda dangerous project to improvise on.

[--= Excogitate =--]

Hence the reason I directed people to A: start with pulse jets and B: scrounge up a turbo charger and use it or take the impellers/turbines out. This removes the need for 'dedicated aerospace parts' :)

Anyone attempting to build an engine of any sort should consider the dangers without saying and I did throw in the obligatory 'it's dangerous' note. ANYthing combustible is DANGEROUS, which I hope I conveyed well to begin with.

As far as money (and to elaborate on specific jet parts a little more) there are PLENTY of hobby jet builders that improvise/design one and you can purchase an RC jet for 2500 dollars so it isn't improbable in the least. Anyone can do it if they want to. Yeah, roller blade bearings not ideal at all, but I shouldn't have to clarify that if you're going to go all out on a nice motor anyway. Using them for a scrap 'build in a day out of garbage to see if we can' engine; that would be the place for those. Again, I suggested a scrap turbo or pulse jet so you could omit bearings in the 1st place. I also noted the need for oil lube and cooling systems to keep your bearings in good shape and a means to detect overtemp.

With that being said, Rahdzhillaxxx is a good voice of reason and should consider the aforementioned factors. I made sure to stress that this covered the BASICS (in title) and 'fundamentals'. You should look at EVERY instructable including his with your own current abilities, skill, and proper equipment in mind! But, don't get discouraged and don't be afraid to try something if you feel you are competent. You can do anything if ya set your mind to it :)

(Funny question while we're on the topic of safety: Weren't you semi-opposing the proper and legal use of helmets in the 48volt electric bike instructable?)

Link: http://www.instructables.com/id/48V_Electric_Flat_Tracker/
  

[Rahdzhillaxxx]

On this thread I only wanted to share information on the subject of what actual turbine jet engine parts are made of. I dont wish to discourage anyone from trying to build something they want to. the more information that there is the better people can decide on what direction they wish to take.
On the subject of helmets, I dont oppose the use of them.  in fact I think I mentioned that  I sometimes use one some times not. What I do promote is the individuals choice. I stress individuals C H O I C E.   I have aced the course to be a riding instructor and have had the experience of nearly three decades of riding.  I've been blessed with the luck to have never been injured while riding. In my capacity when instructing I would never promote my personal views on the subject, only what the law requires of new riders.
I wont respond further on this particular subject as its off topic and one of those issues where most people are going to believe what they believe no matter the relevant facts or lack of.  I didnt post here to needle you I was actually reading this thread and tossed my 2 cents about my knowledge of what the actual rolls royce jet engines are made of, not picking an argument.

[lemonie]

Yes, high precision & high performance bits, you don't make them in your shed...

L

[--= Excogitate =--]

#1 nay sayers annoy the bawjeezus out of me. #2 I've seen Lathes bought for 2000 dollars that can get to 10000th of an inch precision. That's enough for even commercial grade engines as far as I know.

That said, I stated very clearly to you in particular before, this article isn't supposed to help people replicate a commercial jet engine. I strongly encouraged people to salvage parts. I'm surprised this concept is foreign to you seeing as how we are discussing this via insructables accounts.

Please stop whining, you are bugging me. Congrats if that's what you where aiming for. If so, you can stop leaving useless remarks in the chat knowing you've succeeded in pestering me. If not, realize your comments as they stand aren't very welcome and act accordingly. I've been courteous enough, I think. Come on... it says be 'positive and constructive' right below the friggin comment box. I played my part, now you can either play yours or not and move on, ok? Thanks.

[lemonie]

You may have missed this, but I was replying to the comment Rahdzhillaxxx posted, not yourself (although I know you get a notification because it's on your piece of work).

L

[--= Excogitate =--]

I didn't miss it. I came to reply to Rahdzhillaxxx and happened upon your comment (assuming...). Just getting tired of not much positive. I think more people need to read what I write and digest it so I don't have to repeat myself. That and practice the doctrine of not saying anything at all if they have nothing 'nice' to say. Thank you again.

[lemonie]

I wasn't saying anything to annoy you and the statement "you don't make them (special-alloy precision-engineered blades) in your shed" is neither a dig at you nor untrue.

L

[--= Excogitate =--]

Negativity, despite it's debatable truth (which is subjective and limited to a finite experience) still gets at most people. I understand that I was stern, but it just looks like hole-poking from my vantage.

Never took it as a personal 'dig' but merely a half truth. The half-glass-empty truth that seems to prevail in your comments. That is what bothers me. I haven't met many folks that aren't bothered by such remarks.

I'm just an advocate of the glass-half-full perspective when it isn't getting it's due attention. Balance is key to the success of anything including statements.

[lemonie]

I admire your view on life, but my comment to Rahdzhillaxxx was "matter of fact", balance I welcome it is valuable.

L

[--= Excogitate =--]

I think it's plain to anyone that passive-aggressive politics riddles your comments. The world needs people that are up front, not cowards. You have proverbial skill, but sadly lack valuable character. I've seen it in this thread and others you've posted on. Balance is something that you don't understand because the root of the matter stems from your view of what constitutes an instructable. I find it hard to believe you've changed so quickly... You'll say whatever you can to justify to yourself that your vantage is the only right way. True sign of a sociopath. I think it may surprise you, or perhaps you may find a new sense of pride now knowing your identity among the rest of society.

[Lithium Rain]

You're coming off as very belligerent and nasty. Ad hominems are Not Nice and weaken confidence in your primary arguments anyway. Also, while we're on the subject, in addition to no fewer than six ad hominems, I count at least two grammatical errors, at least one non sequitur, a redundant statement, and a sentence fragment in your comment. Not a sterling example of powerful prose.

[--= Excogitate =--]

Well, I'm glad everyone that initializes such conversations in a provocative manner can call me belligerent. Is that not the same if not worse for simply starting it? Most people call it 'trolling'. And about grammar; if you can understand what I say its good enough for me. The whole purpose of language is to convey something and I did. Is there anything regarding jet engines? Thanks. "The argumentum ad hominem is not always fallacious, for in some instances questions of personal conduct, character, motives, etc., are legitimate and relevant to the issue." -Wikipedia

[lemonie]

Hmm yes, I'm not bothered by being labeled as a sociopath.
Please consider that you've never met me and plain-text communications are wide-open to interpretation.
(Why did you pick that up after >5 months rather than ignore it?)

L

[--= Excogitate =--]

Words suffice. And I've seen others respond in a similar means to you, albeit to a lesser degree. So, perhaps you should weigh the past and present experiences you've had with others and reevaluate your methods. As for not ignoring this, it's new to me. I was gone for sometime. Time is relative.

[lemonie]

Yes it is so.
I can't see the need to re-evaluate the content not-fitting the format, call it a difference of opinion if you wish but it doesn't.

L