Please put your "I am new and need help" question here.

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Re: Please put your "I am new and need help" question here.

Post by Mike Everman » Mon Mar 28, 2016 7:53 pm

Yeah, start one in the valveless section. Suggested title: "variable frequency valveless" or somesuch. Sounds interesting. A range can be accomplished by length change, not much can be accomplished by throttle, and unfortunately the limiter is the fact that combustion chamber length and intake length need to change in conjunction with exhaust length to get the most range.
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Re: Please put your "I am new and need help" question here.

Post by cb68 » Mon May 16, 2016 8:30 pm

Does anybody know of a company that builds a high quality engine for R&D purposes?

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Re: Please put your "I am new and need help" question here.

Post by pulsethug » Thu Jun 22, 2017 5:29 am

Hi guys! I'm REALLY happy the valveless forum is as large as it is.

Yeah I'm prolly going to need help at some point. I purchased a 10 lb thrust stainless thermojet (5" dia chamber) and I am in the process of duplicating the design in 1mm thick titanium. I'm finally starting to get some traction on it.

Here is the original stainless jet I am trying to copy.
org-pulse-jet.png
Here is the titanium jet so far:
TiJet.png
So the reason I am building one or more titanium valveless jets is to see if it is possible to mount one (or two) on an R/C aircraft and be able to taxi into position and take off from a standstill with no assist. That's it. I've never seen it done on youtube. I've seen Bruce Simpson sort of do it with a valved jet, but then Bruce walks on water so he doesn't count. :wink:

The airframe I'm planning on using will be like the very large foam-board delta or bat wing designs. Something with a lot of lift. I don't care about speed. In fact the slower the better for what I am trying to achieve.

The reason for titanium is the obvious one; weight. But it's also tougher than stainless for applications like this. I don't have the number right at hand, but I calculated a 1mm thick jet would weight ~2.5lbs. Slightly less than half that of the stainless model. If the TiJet works well, lasts, and gives adequate thrust, I should be able to get something airborne. That's the plan anyway. Talk at you later.

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Re: Please put your "I am new and need help" question here.

Post by Mark » Thu Jun 22, 2017 11:18 am

Is your titanium a grade 2 type or what? I'm not sure but it seems like titanium might react with the air or have lower working temperature than what you may need. It has a higher melting point than iron by a few hundred degrees F but working temperature I'm not sure. Maybe it would hold up, I don't know. There's 321 stainless steel with a little titanium in it that's used for high temps I know.

Maximum service temperature of Titanium alloys is mostly limited by the creep and oxidation resistance. Today's Titanium alloys are specified for a maximum service temperature of 600°C. However they are used typically for temperatures around 540°C because the parts have a service time of several thousand hours.
https://www.amt-advanced-materials-tech ... mperature/

"Properties of commercially pure titanium"
https://books.google.com/books?id=GEHA8 ... re&f=false

"Grade 2/commercially pure titanium only suitable for exhaust parts that are not exposed to temperatures higher than about 600 C."
http://c.ymcdn.com/sites/www.titanium.o ... z_2008.pdf
Last edited by Mark on Thu Jun 22, 2017 6:25 pm, edited 2 times in total.
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Re: Please put your "I am new and need help" question here.

Post by Mike Everman » Thu Jun 22, 2017 1:43 pm

Welcome! Start a build log thread for this titanium jet. Should be good. Can't wait to see the color of it running. I have a similar Thermojet, but a bit smaller. Looks like you areabout ready to weld.
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Re: Please put your "I am new and need help" question here.

Post by pulsethug » Tue Jun 27, 2017 3:55 am

The grade is CP-2 Mark. Some quick google-fu didn't reveal much as far as the operating temp of a typical thermojet. Your concern re: temperature may be a valid one. I know for a fact that titanium brought up to weld temps must be flooded with shielding gas while it cools. Titanium is an active metal I believe; so like aluminum and magnesium it will burn. They use it in fireworks for bright white stars.

I guess I'll just have to see how a TiJet performs. I'm thinking CP-2 will be flexible enough to withstand the vibration. As always it's the welds that suffer first. I specifically choose preformed titanium tubing and cones to eliminate seem welds. We'll see how that works out.

Do you have any idea how hot a thermojet should get?


Mike: You are in luck sir. I did a run on Thursday of the stainless thermojet with red-flame colorant. Check it out in the attached video.

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Re: Please put your "I am new and need help" question here.

Post by pulsethug » Tue Jun 27, 2017 4:05 am

I'm having trouble uploading the video file. It's 17MB, so maybe that's the problem. I'll see if I can get my son to put it on youtube so I can post the link.

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Re: Please put your "I am new and need help" question here.

Post by pulsethug » Tue Jun 27, 2017 4:27 am

Here's a youtube link to the video":

https://www.youtube.com/watch?v=ZpDM9gwQskU

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Re: Please put your "I am new and need help" question here.

Post by Mark » Tue Jun 27, 2017 3:09 pm

I've some powdered titanium which is more like sand that's used for fireworks. A trick you probably know to identify titanium is to put a piece on a grinding wheel and note the white sparks. If your titanium jet should take fire it would be kind of neat to see and a first perhaps, going from a glowing red to a blinding UV radiating white hot but that's not something I would expect. The lithium chloride colorant you probably use as a flux. Maybe some boric acid would be something to try for a green color. You can buy a large bottle at the dollar stores for really cheap as roach powder. Copper works too, the older stuff with patina makes a pretty flame. In methanol vapor it really reacts.

https://www.youtube.com/watch?v=GIstWmvSkbA
https://www.youtube.com/watch?v=jEdK4BQCr_8#t=1m53s

There was this fellow that melted steel by putting some tubing up the tail of a Dynajet if someone wanted to make sparks.
I had sent him some titanium alloy tubing and it only warped and changed colors in the same test.
https://www.youtube.com/watch?v=uqXiOnWkhAY
https://www.youtube.com/watch?v=F8vqfphZ73A
An article on the video if you scroll down
http://jetzilla.com/Vol01Num06/jetZilla.html#Article_1
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Re: Please put your "I am new and need help" question here.

Post by pulsethug » Tue Jun 27, 2017 6:12 pm

Mark,

I bought the lithium chloride specifically for it's methanol flame coloring capability. Strontium nitrate produces red as well. My two faves are lithium for cherry red and boric acid for the ghostly green. I'll have to give copper a try. Is there some specific copper salt you would recommend e.g. copper chloride? Would the copper salt vibrate blue or green? A bright blue would be awesome.

For those who are unfamiliar with what we are talking about, methanol is the only liquid hydrocarbon that acts like water in that it can dissolve ionic metal salts. Methanol is also very simple and tends to burn completely and does not release any excess carbon atoms. The type of salt dissolved in the methanol will vibrate in it's intrinsic spectrographic color within the methanol flame. Carbon vibrates bright yellow, so it is very important that no carbon based substances are allowed to contaminate the methanol/salt mix. Any carbon contamination will make the flame burn bright yellow and swamp out any other desired color.

The powered titanium you speak of is probably titanium sponge. Titanium sponge is the raw titanium metal produced during the electrolysis process to refine the metal. And yeah, it burns very hot! Now I have heard of solid magnesium catching fire, but not titanium, or aluminum for that matter. Aluminum flakes and powder are used extensively in fireworks as well. Titanium was the metal used for the SR-71 spy plane. So I'm hoping it will not burst into flames. At least not right away. Once the airframe is 100 feet in the air, then it's ok :mrgreen:. Thanks for the links by the way. I hope to have the TiJet tig welded up in the next week or two. I'll keep all of you posted.

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Re: Please put your "I am new and need help" question here.

Post by pulsethug » Tue Jun 27, 2017 6:16 pm

Mike,

Could you please relo this titanium jet sub thread to a new top level thread. Or give me a couple hints on how to do it. Thanks.

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Re: Please put your "I am new and need help" question here.

Post by Mark » Tue Jun 27, 2017 8:29 pm

My titanium powder is pretty lackluster if you just light it with a torch it just sort of glows/burns white hot and sometimes goes out on its own before the entire pile burns up. Sort of like the accounts here with swarf when machining the stuff. Just now I tried heating some 1/4 inch tubing of titanium with a propane torch red/yellow hot, I'm not sure if it was 6/4 alloy or what but it had an unusual characteristic of flaking and the flakes sort of build up until the tubing has a "glittery" collection of particles stuck to it, as if fibers from a Coleman lantern mantle had been glued to it, they glow in the flame from the torch. The flakes seem to form as the tubing cools and turns black. Repeated heat cycling brings out more and more flaking. On the plus side the tubing didn't give any hint of catching fire.
http://www.practicalmachinist.com/vb/ge ... re-163372/

Here's an energetic titanium event though.
https://www.youtube.com/watch?v=NDhnwLheoU4#t=3m21s

Grade 2 forms cracks in automotive exhaust systems and the oxidation resistance is insufficient this Porsche article says at around 700 C or 1292 F. The SR-71 airframe heated 600 - 900 degrees F according to 3 sources I recently looked up.
http://c.ymcdn.com/sites/www.titanium.o ... z_2008.pdf
Painting it black made it 75 degrees cooler.
http://www.wvi.com/~sr71webmaster/srqt~1.htm

Looks like copper sulfate for green, copper (I) chloride for blue. I'd try some copper carbonate, the stuff that forms on copper naturally, like the patina on old copper tubing or the Statue of Liberty. It makes a very pretty color whatever it is. If you've ever put methanol in a closed end tube and lit the other end like a barking dog chemistry experiment, the color is very vivid using old copper tubing, making a green flash.
https://en.wikipedia.org/wiki/Colored_fire
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Re: Please put your "I am new and need help" question here.

Post by Mark » Wed Jun 28, 2017 2:07 pm

Tidbits
I polished some titanium with very fine sandpaper spinning the pieces on my lathe instead of hand sanding. A smooth surface helps produce pretty colors when the tubing is heated. If you don't the colors don't come out as varied or vivid.
So these were heated with a propane torch, waving it about until some colors appeared. It's not nearly as nice as electrically anodizing but kind of fun just tinkering.
The dull colors if you don't sand them first ...
download/file.php?id=13562&mode=view

download/file.php?id=13565&mode=view
download/file.php?id=13569&mode=view
download/file.php?id=13572&mode=view
download/file.php?id=13571&mode=view
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Re: Please put your "I am new and need help" question here.

Post by pulsethug » Thu Jun 29, 2017 8:29 am

Cool. Do you think the color would stay that way if reheated?

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Re: Please put your "I am new and need help" question here.

Post by Mark » Thu Jun 29, 2017 2:45 pm

The colors are pretty fragile. Even handling them over time makes them fade. And if you linger too long when heating in one spot the colors become dull. But I don't know if that's because my tubing is an alloy and pure titanium might do better. Maybe a coating of lacquer would preserve the colors. I have a long piece of 2.5 inch diameter pipe that I thought would be neat to make all sorts of varied patterns on it. There's some videos on YouTube where they heat-treat/colorize exhaust pipes and such. The main point is to have the metal very clean when you start - no fingerprints that will show up after the effect takes place. Or maybe you'd want to have fingerprint patterns of some sort or design for an artistic slant. Speckles would be kind of an interesting effect, maybe using pinpoints of heat. One particular color comes up, and then the next so generally it's the amount of time that determines the color. I blasted a section of my 2.5 inch diameter pipe with heat and it's still somewhat colorful and mostly blue but if you want all the delicate rainbows you have to limit/control the thickness of the titanium dioxide that forms the interference colors.
Some spork and other videos showing heat treatments.
https://www.youtube.com/watch?v=6KxmxwO5w4c
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