InigoMontoya

I couldn't care less about the AMA. I'm not under their jurisdiction.

rjbob

My Feedback: (8)

If you're self-insured, you had better own a few buildings and ten or twelve golf courses (to cover the law suits) if you're going to fly jets.

InigoMontoya

My insurance company is the US Government.

Randy M.

My Feedback: (38)

Yeah, alot of people have forgotten that the US Government is We The People!
This thread will be gone soon

InigoMontoya

Not sure of your intent there....

Are you saying that non-hobby apps are not welcome for discussion on this board (which I think I've been pretty clear I'm not coming from the hobby world from very early in the thread) or is that a political statement?

rjbob

My Feedback: (8)

Actually, non-hobby threads are NOT really welcome here as this is a hobby based forum.

You're apparently very happy just letting us know how intelligent you are and that you are going to do whatever you're going to do no matter what advice we give you.

Go blow up a few turbines...have a ball

Bye, now!

InigoMontoya

Fair enough. Do you have another forum to suggest that closer matches my inquiry?

Robrow

Come on gents, what happened to tollerance, I would have thought a rapid and safe start cycle would be of interest?

I will try to give some humble advice, though I don't regard myself as any kind of expert.....the biggest problem I think will be the differential expansion rates between the turbine wheel and the nozzle guide vanes. A very rapid rise in egt causes the lower mass wheel to expand quicker than the larger mass ngv's which can lead to blade tip contact and seizure (tip clearance is typically 0.10-0.15mm and reduces during a normal start sequence). The combustion chamber and other components also require time to heat up to achieve correct combustion, etc.

Airstart turbines do have the capability to shorten the start cycle because of the greater power available and also their localised cooling effect. Maybe a combination of multiple turbine impinging airstart nozzles and Silane could give a quicker start but I have no idea if you could achieve what you are looking for.

How do the engines you are used to dealing with get round these problems?

Rob.

BaldEagel

InigoMontoya

In the first instance I feel I must appologise for some of the intolerance that has been shown to you on this thread, a lot of contributors on here do not read the whole thread, but just scan read, so they may not have realised that when you say AIR START, you do not mean running up a turbine to speed with an air gun, but starting a turbine in mid air, hence your requirement for a fast start.

Personnaly I have found the disscusion interesting, even if not hobby related it will give us a different perspective into our turbines and their use outside our normal applications.

Mike

marc s

I second the last two posts, and again although I have almost no knowledge of turbines my suggestion would be to discuss the matter with a company who might just know the options and answers to your questions.
My suggestion would be AMT turbines, and the man in the know there is Bennie, the problem might be getting hold of him as he is a very busy man, good luck.

marcs

Harley Condra

My Feedback: (4)

I guess you didn't get my point. That was just an illustration about what some in the general public that don't know anything about what we are doing (and don't know anything about our equipment) will sometimes ask.
I didn't imply or assert anything about silane. I never mentioned the word silane.

You are the only one that didn't get it. Most of us that actually fly turbines, will get asked that question or another equally stupid question now and then.

My question to you is: Why would WE want to change from propane or Powermax to something that is probably more difficult and expensive to obtain, when our current starting gas works just fine.
The gasses we currently use are proven, inexpensive, readily available, and their hazards are well known, and they are probably less dangerous.
Now, do you get it?

Harley Condra

My Feedback: (4)

deleted

rcjetsaok

My Feedback: (7)

I find it intresting that you don't care how many engines you destroy, but by-god it's gonna start in 5 seconds !!!!! [sm=confused.gif] As far as your self insurance.. ( The U.S. Goverment ) who in the hell do you think IS the U.S. Goverment ????? US.. The people of this great Nation. Sounds like to me you and your people got a hold of some OUR stimulus money and have to spend it on some hairbrained idea like this. This sounds alot like the Midwest college that got a $450,000.00 grant to do a study on how a Housefly lands on the ceiling... Does it roll and stick, or does it loop and stick ????? WHO CARES !!!!! Get the damn fly swatter and kill the S.O.B. !!!!! Your wearing me smooth out !!!!

Dan M.

P.S. as far as you inflight restarts of Model Turbines... I have witnessed it done many times with a Jetcat in a BVM Bobcat by Mr. Tom Dodgen.

Vettdriver

After reading the WHOLE thread.

1) This guy isn't trying to build something for Florida Jets or Top Gun.
So, I doubt you have to worry about this showing up at your field and going through your RV window.

2) This is either private sector or a govt. contract/grant money to move forward with some research.

3) If item #2 is correct, what makes it so hard to beleive that a $4000 turbine wouldn't/couldn't be viewed as disposable.
Cruise missle/ target drone powerpalants are much more expensive and are every bit as disposable.

4) Their are some narrow-minded, intollerant *****$ in this world.
Just because we fly RC jets doesn't put us at higher station in this hobby . . . . much less in life.
It doesn't mean we're smarter. It means we can afford it . . . that's all.
Heck, it doesn't even mean we have better flight skills.
I've been to several jet meets where people were told not to fly over XYZ spot. But, I saw it repeatedly because people couldn't fly a right-hand or left-hand pattern.
Which two waiver holders signed off on those guys ?


His question was simple. . . .
Does anyone have any knowledge of or have experience with Silane in small hobby sized turbines.

I guess his answer is No.

A10FLYR

My Feedback: (1)

WOW!! What a hard group.

siclick33

What are you guys on? I can see very little in the way of constructive help from most of the replies. If you don't have something helpful to say then maybe it's best to keep quiet?

As for the original question, I have absolutely no idea what Saline is but would question the figures you have on start times. A kero start engine might be that slow but, at a guess, I would say a propane start is much quicker than 1 minute. You won't get the 3-5 secs you mention but what is the maximum time that would be acceptable?

InigoMontoya

Honestly, I don't know. While I know a bit about what's possible from my experience as a user, I am not a turbine design guy (my expertise lie elsewhere). I suppose if I was I wouldn't be here asking questions.

That said, the turbines I'm familiar with employ pyrotechnics. The pyro charges all go more or less simultaneously. One blows open the fuel supply. One is a gas generator that spins up the turbine pronto-like. And one is an igniter. They start FAST. If I had to guess, I'd say that they just build to lower tolerances and just take the efficiency hit.


Thanks for the POC.


In the hobby as a whole? You wouldn't. However, I've seen many hobbies wherein people do much more dangerous stuff than anything being discussed here and when asked why they were doing it "that way" rather than the "normal way" their answer tends to be, "Because I wanted to see if it would work." To them, the hobby was more about the science behind the hobby than anything else and they want to push the science and expand their mind. In other words, I don't expect many of you to have the experience I'm asking about. I was *hoping* that one or two of you might, however, have the experience or at least some insight (like the differential heating rate problem mentioned in the first post I quoted in this post).

ww2birds

My Feedback: (14)

After catching up on what I thought was a troll trying to wind us all up and laugh at us (which still may be what is going on here, and if it was, he has succeeded very well), let me try something constructive just for the heck of it.

If the problem at hand is how to quickly re-start a turbine in the air (vs. what I originally assumed, using compressed air vs. electric motor to start on the ground .. that's what we all call "air start"), then I'd suggest the following:

1) In my observations, start time has little if nothing to do with the time to ignite the starting gas (propane or powermax butane/propane mix). It has to do with the feedback loops and control system in the ECU being careful about sequencing the start to avoid damage from overtemp, or flooding the motor with kero if the propane is not burning, etc. So changing to a gas that ignites faster is not addressing the actual issue creating the time to start... if the definition of "start" is the user gets control of a stably running turbine.

2) Kerostart is much slower than gas start .. so probably not a candidate here. Reason is that it takes time to preheat the ceramic igniter (which has to be big enough to have a sufficient thermal mass so it does not cool off immediately when kero mist is sprayed on it). On the JetCat and Behotec turbines I have run, this takes 10-18 seconds, and the whole start cycle is slower than gas start.

3) A practical first step would be to make some actual measurements on a COTS turbine, and begin to understand what makes up the "start time budget". You'd do this at first by simply observing the start process with the monitor box plugged in. Then you'd have some actual knowledge about where the time is spent and what it would take to reduce it. You could easily accomplish this with a trip to the local jet flying field, without having to purchase a motor.

4) I'd then contact a few of the folks who build the ECUs and see if one of them (JetCat, Gaspar Espiell, ProJet) would be interested to work with someone on a specially programmed ECU that had a fast start mode that reduced a lot of the safety/protection features to do a much faster start in an application that could tolerate much more risk to the hardware.

I believe this would be a more constructive path to follow than dumping a "sound byte" post and then getting aggressive with people who are seeming not to be helping enough.

A more polite and productive approach would have been to state the problem trying to be solved up front, then review what work and thinking had already been done. That would have generated a qualitatively different response from the group. I'll bet they would have been standing in line to help if treated with a modicum of respect vs. a smart-alecy post.

It would also be the sort of behavior that a properly-trained scientist or engineer would display.

FWIW,

Dave

InigoMontoya

The vehicle will fly exactly once. After that, it will sit in the back corner of some field and rot. Whether the engine is in flyable condition at that point or not doesn't make much difference. As the entire vehicle is intended for a one-off experiment, yeah, I consider the engine disposible..... Which is also why I'm trying to keep things cheap and go with a consumer level turbine.

1) Safe to say.
2) Right now it's neither. A few of us engineers are observing a particular methodology and we think it's obsolete. We believe we have a better way (read: cheaper). So we're looking into an experiment that either will or won't prove our point. There is currently no money at all. On our own damned time (the "OMG, my tax dollars" crowd can kiss my ass) we're trying to put together a proposal for some discretionary funding (at which time that crowd can complain but since the goal is to spend say $100k to save many millions over time, my sympathy for them is minimal).

InigoMontoya

Not trying to restart. Trying to start. As I said previously, it'll be boosted. Admittedly, there may be zero effective difference between those two scenarios but I mention it in the event that there is.

I realize that there's a feedback loop, but I was hoping that perhaps the early parts of the cycle are temperature rather than time driven. Perhaps code that says "do this until temp = 500 deg" rather than code that says "do this for 10 seconds." That's actually where my thoughts for silane came from. I was thinking in terms of ways to cut corners in event-driven logic (but if it's time driven I'm screwed, of course).

I'm not aware of any local jet flying field. We're a bit remote (zip code of 93555). There is a local RC airstrip, but again, I don't believe they fly jets there (or at least, I've never seen one and I actually have to drive by it every day on my way to work...lots of stuff flying, but never a jet).

That's on the todo list.

Tried that in the UAV forum. Got exactly zero response.


Oh, and somebody asked where I got the "1 minute start" number. Of course I can't find it now, but I was watching some youtube video of a JetCat start sequence on the recommendation of a user from another forum. They were all indicating start times of about a minute and the video corroborated that. Yes, it was a bench test, not an inflight start (there, I'm even using your terms!), but it was the best data I had to go on.



And no, I'm not a troll.

crustychief

I think the intent of the OP was to reduce the amount of government funding for initial research by asking those intimately familiar with day to day hobby turbine use. I can not believe some of the smug, pretentious people posting on here, please read the whole post before commenting.

FILE IFR

After 2 pages on this topic. you're obviously not getting the answer your looking for. Use the next bussiness day and be at your office with your "desk and such" after 10:30 AM and call Bob W. to pick his brain.... You'll get a straight answer.

InigoMontoya

Missed this post on the first couple passes....

That's actually a damned good question. I use the 3-5 seconds (actually faster, I suspect but it's been a while so I'm willing to allow for fuzzy memory) as a benchmark of what's possible since I've seen that in the past but that doesn't mean it's a hard requirement. What is? Not sure... But figure I've got a heavy weight low-lift vehicle at reasonably low altitude that's gonna crash if I don't get that engine going. 1 minute is right out. 15 seconds? I dunno... I'm not comfortable with that number but if it turns out that this is the best that can be done with off the shelf perhaps I could just boost to Mach 0.5 with a planned Mach 0.3 takeover? IE, just overspeed the boost (reasonably easy to do) and just plan to slow way down before the turbine is up to full throttle.



BTW, I want to thank those who've responded this morning. I came back just to see if anybody had another forum suggestion. To see that there was additional discussion was a pleasant surprise.

blubberpoke

My Feedback: (39)

No matter what fuel you use to warm up the chamber its going to more costly then propane.
More exotic means much more danger and more cost, 15 secs is not alot of time. When all else fails KISS it .
Keep it simple stupid. [&:]

digitech

My Feedback: (10)

its all done in the software you can heat what you want it wont go faster.
it will use some timings in how long from igniton fase to fuel ramp
Fadec ecu,s this trick might work since it ramps as soon the temp gets to a pre set temperature.
but then this can also be done with propane.
in the past on some older versions of the jc ecu i could control lots of settings and could influence some timings like starter cut off rpms,.
but the good thing is with jc ecu,s that they come preset for any kind of turbine they have.
so my tip dont go there.
jc makes drone turbines p-200SX , they are started a bit different i think .
so stick to but/prop mix wich cost almost nothing at any supermarket