# Thread: Jet engine Shaft Balancing

1. Where to get expert help/advice on shaft balancing:

Where to find out how to build a tachometer circuit:

www.ee.sc.edu/classes/Fall06/elct401/lab02_files/AN-162.pdf

In light of the problem you have with the unavoidable math problems associated with certain aspects associated with the above topics:

joshua.smcvt.edu/linearalgebra/

In the mean time, enjoy your excursion into the technical field of jets via the use of SWAG analysis methods - based upon the commments and attitudes expressed in post #18, it should be an iteresting experience, not lacking for dull moments and/or excitement.

Please watch out, however, for shrapnel and/or hot molten metal. Things like that can unexpectedly occur when you improperly mix electrical sparks, explosive fuel and/or improperly SWAG'd shafts with sharp vanes spinning at ungodly high rpm's.

2. Smurf
Just to help you before you dig into making a model that will sit on a bookshelf and do nothing but throw dirty orange flames out the back overheating the turbine and grinding to an instant stop.

There are a few things you should know.
Don't get angry I'm just pointing you in the right direction

Building a model axial turbine is a serious undertaking.

In post #3 you mentioned 6 rows of blades at 45° what about the stator vanes?
Axial compressors typically contain between 8 and 16 stages.

Each stage is made up of rotor and stator blades and is called a cascade which is a complex array of aerofoils.
At each cascade the blades will vary in amount per cascade, height and width and also in pitch.
Each cascade must complement the other, any disruption of flow will affect each other stage giving poor or worse, no compression.

Sorry I cannot give you a size or angle nor will anyone else on this forum.
Not because they don't want too but there are so many factors to calculate and any one change to them will affect the final design.
Serious complex math.
My advice is purchase a book called Model Jet Engines By Thomas Kamps and this will give you some very much needed info on turbines.
Also join one of the many Yahoo groups that are involved with the design and building of model turbines. There is so much you can learn there.

Your Critical Rotational Speed to a shaft that is roughly 12" and Ø 0.5" at the root with bearings roughly 7" between each other is probably less than 50krpm

To work it out correctly you need some one with a technical background and professional experience in mechanical engineering and possibly a ball bearing engineer to tell you how many and what size bearings you require for this hostile enviroment.

Hang on I think there is a guy called NC cams who could point you in the right direction.
But it may be too late.

Please don't post replies that will offend others. Like NC cams said "you never know when you just might need their help some time down the road"

Also the best money you could spend on your turbine is this.

Measures Rpm to 250krpm, temperature to 1000degc. Controls fuel pump, valves for gas and fuel, starting motor or air solenoid.

Good luck with it

3. Also if you want to build your own tacho.

There are very inexpensive components that are called hall effect Ic's mainly the ugn 3503, coupled with a ring magnet and a few components makes a accurate and simple tacho + many other useful sensing applications.
Page 42 of melexis

Here is all the info you will need and don't say no one could help.
There were many great ideas thrown your way by many members.
Here is another.
You just have to put a little work into it

http://www.allegromicro.com/techpub2/an/an27701.pdf

http://www.melexis.com/prodfiles/0003715_hallapps.pdf

Beaker

4. I've already spoke to a ball bearing engineer at alpine bearings, we've pretty much worked the shaft sizes and bearing sizes, i already have my bearings from them, ya sorry for the info i'm saying like half the info for you guys to get the whole picture, but ya i will have stages in the compressor, right now i'm thinking 45, so that the air is getting changed directions constantly, the more the movment and resistance the more the airs being compressed. I don't see much of a right way to do things, theres lots of more research and design to jet engines to make them more effiecient but as long as its a pretty good design your going to get a decent engine, yes theres a right way but the right way is extremly hard to acheive, you need special software you need to prototype test, redesign etc. i'm not trying to build the worlds best jet engine i'm just having fun and building something cool, what ever goes wrong the first time i'll just know for the next time. I'm sorry that i don't sit at my desk and spend hours upon hours being a loner doing the engine on paper/computer, my case its paper. I'm what you call a hands on learner.... i like building and discorvering the problems so i can better fix it. Today i started the flame tube, its a weird shape, its not just a tube with holes. Its like a cone with another cone half the size going the other way....Very hard to describe

5. Just browsing the various sections in CNCZone here. Seems to me that designing your own turbine the first time out is like trying to build a computer with only an automotive electrical background. I bought a set of plans for a 25hp turbine back in college from the back of Popular Mechanics and found it to be daunting(and I think a little incomplete). Maybe Smurf should look for something like this the first time out? I'll start with an IC engine I think. The machining is so complicated that one should baby step to see success. Just my \$.02.

6. Guessing a compressor diameter of 6" gives 3,140 ft/sec at the blade tip at 120,000 RPM. That's Mach 2.85; I thought compressor efficiency heads due south when tip speed exceeds Mach 0.8 - 0.9.

Mariss

7. Smurf,

Your posts are fascinating, watching a car-wreck happen kind of fascinating. I'm not sure if they meant to be on the level or they are the work of someone with a very wry sense of humor.

Should they be on the level, may I offer you some kindly-meant observations:

1) "engineers tend to over do things so that only engineers can do the job". There is no engineer cabal or conspiracy. Engineers don't "over do things". Engineers specialize in solutions that are just adequate to the task (plus a safety margin) and nothing beyond that. Can you imagine an "over-engineered" 747? It would weigh 10 times as much and would never get off of the ground. Only hacks "over-engineer" because they have no clue what the limits are and and the choices that must be made to satisfy conflicting requirements. It's like composing a symphony when you are tone-deaf.

2) "i want to build a engine by myself using "wild a\$\$ guess'es." There is no holistic engineering. There may be holistic "wild a\$\$ guess'es" for product style and appearance, the artistic stuff, but the guts of the product is engineered by engineers by the numbers, using equations and computers to help them.

Most good engineers I kinow are humble people. If a design is wrong, no amount of explaining why it should have worked changes things; it does't work. They can complain to their freinds how their "wild a\$\$ guess'es" were so good that an exemption must be made; it still does't work though. Mother Nature must be satisfied and she must check-off on the idea before it works. This makes engineers humble, they understand there is an objective and real "right and wrong".

The best engineers are also pessimists. They really believe if a buttered toast bread falls from the table it will land buttered-side down. They plan for it. I really want to fly on an airliner designed by that person. I really want "specially trained personals in different feilds applying excessive amounts of calculations" for the airplane I'm on.

3) You are a "stream of consciousness" kind of a guy. It shows in your writing. That's good if you are in sales or other people-oriented areas. It's not good if you have to have analytical problem solving skills. It is too disorganized in thinking for that. If you are young, work on that and change it. Organize your thoughts. Write one sentence per thought. Use paragraphs to seperate thoughts on a single subject.

4) "i asked for a simply circuit and u went over board with all your 29017 ic's". You asked for help. A person kindly provided it. You kick them in the face because it wasn't what you wanted or it was too complicated for you to understand. Ask = please, answer = thank you. What part of that is hard to understand really? Have good manners, having them goes a long way. Practice your people skills (you know, the honey vs. vinegar thing).

5) "I'm sorry that i don't sit at my desk and spend hours upon hours being a loner doing the engine on paper/computer" and "I simply don't FEEL like doing it, cause i'm lazy and i don't care." This one really bothers me. It shows a contempt for the hard work and effort it takes to become good at anything. Maybe you are too lazy and you think it should come to you anyway. It won't.

Goood ideas require "wild a\$\$ guess'es" AND the skills and tools to see them through. The second part takes hard work. I'm guessing "prolly be at a 45 degree angle" and your ineptitude with (4) means you are 19-something. That is a good thing. It means you are young enough to able to still remake yourself. If you are much older, forget it. The other give-away is the "i'm better then smurf and this is why" remark. It shows a lot of insecuirty.

If you are young, lose the attitude, it gains you nothing. If you are much older, forget it, it's hopeless and nothing will help.

Mariss

8. I say don't listen to a word of what Mariss says. Just go ahead and build it! Jesus had a crown of thorns and you could go one better with a crown of (turbine) blades! Might make for good reading in the "Scary Stuff" thread.

9. Guys, dont stop. Im THIS close to canceling my cable in favor of following this thread. I understand smurfs stand on things, its easy to imagine things are easy enough, spinning wheel, metal shaft, some wires, little fuel "prolly" nail the whole thing down to a 2 x 6 or something to stabilize it. Ahh the details can be oppressive RPM, FPS, PSI, forces, masses, gasses. I say for safety sake just make the whole thing out of playdoh, thats what I do.

10. Aluminum is playdough at that speed. Seat-of-the-pants quality time with my calculator shows 1,226,615 G of acceleration for a 6" diameter disc at 120,000RPM at the tip. A 0.1 ounce blade would see over 7,500 lbs of tension.

A little unfair because all the mass (0.1 ounce) is assumed to be concentrated at the circumference. My excuse is I'm not an ME and I didn't feel like pulling out my college physics books to calculate a radius distributed force.

Engineering is a good thing. So is the education behind it. It allows you to figure things out beforehand to see where disasters may lie.:-)

Not to worry. The "prolly 45 degrees blade angle" insures it won't see 100RPM let alone 120,000RPM.

Why am I being so mean? Why am I sticking my nose into this? It is because of the original poster's contempt for knowledge, the effort it takes to obtain it and especially his contemtp for those like NCcams and others that offered it gratis. It takes effort to provide references, circuit diagrams and to tap-out a thoughtful reply. I know; I have spent up to an hour to generate a helpful reply so I know what effort is involved. It is a kick in the face to be called an idiot and a loser in reply. I really dislike ungrateful behavior and the original poster certainly meets all that critereia.

Mariss

11. Well if it isnt going to even run, I may as well keep my cable tv hooked up for the time being, perhaps even read a book or something. I wish the young man well, and hope he can learn to accept help as help, and realize that people that know more than him about certain matters arent trying to act better than, or to confuse him with unnecessary details. If that were true, doctors for one would, seem like major A-holes wouldnt they?

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