Deleted
Joined: January 1970
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Post by Deleted on May 13, 2015 3:31:06 GMT -5
IMO sounds normal compressor blades moving by the roots, will soon disappear once you get some rpms going. I'm sure Jetric will give a more concise answer ;-)
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Post by Johansson on May 13, 2015 3:56:53 GMT -5
I thought so too, but after hearing "viper"´s very quiet compressor spooling up on 12V I thought I should at least raise the question.
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Post by Richard OConnell on May 13, 2015 8:04:49 GMT -5
I agree with Nick. Working with Ernie on his Vipers and his J34-34, the small metallic 'plinking' sound at extremely low RPM is all too familiar. I've always attributed it to the compressor blades wiggling inside their key holes. I'm not sure if the gearbox is contributing to the sound in any way, but I've only heard it for a sub-second into start and for the last few seconds when the engine is shut down.
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jetric
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Joined: December 2014
Posts: 132
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Post by jetric on May 13, 2015 10:27:55 GMT -5
Hi Anders, Yep the rattling noise at very low rpms is perfectly normal its just the first stage compressor blades slopping from side to side in the small clearance that is allowed in the blades fir-tree root fixings this noise will go once the rotor speeds up and the centrifugal force centres the blades. That other guy with the viper that starts his up straight up on 24volts may be getting away with it if he is using the correct starter motor for the viper301 because the original starter motor has got a friction clutch tourque limiting device on the motors output shaft. If your starter motor is not powerfull enough I think Harry at jet engine trader has still got some original starter motors left for the viper301 also i think that Andy Pleszco with the jet mini's may still have one left for sale i dont know you'll have to phone him and ask, Rich. I wouldn´t want to risk breaking the drive shaft, so I´ll make it a 12/24V start. Thanks for the suggestion, I am very thankful for the hints you guys with experience in this engine give me. I am discussing the latest 12V rotating video with Viper, compared to his engine my one is rattling quite much. Do you have any thoughts about this jetric? Is it normal and will quiet down once I get a bit more power to the starter?
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Post by Johansson on May 18, 2015 5:12:29 GMT -5
Hi Rich,
No cause of worry then, great!
I just need to wire up a third relay and borrow a pair of batteries then before I can do the first wet cranking cycle. Should be interesting. :-)
/Anders
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Post by Johansson on Jul 29, 2015 16:22:01 GMT -5
I did some thinking and figured out that a manual switch for the 12V-24V change will be easiest, at least to begin with. I ordered a high amp marine battery selector that arrived today, I´ll couple the batteries so that pos.1 gives 12V from one of the batteries and pos.2 pulls 24V out of the two batteries in series. I´ve also made a 20 liter fuel cell from a stainless hot water tank, I´ll make sure to mount it a bit better later... A friend of mine is trying to get me a discount on a pair of batteries through the company he works for, I´ll know in a week or two if he can get it. Not much left to do now before a first real dry cycle of the Viper, finish the wiring, fill oil, prime the rear bearings, read the manual a couple of times more and give her a go! Cheers! /Anders
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gidge348
Senior Member
Joined: September 2010
Posts: 426
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Post by gidge348 on Jul 29, 2015 21:25:43 GMT -5
Hi Anders, I think what you are doing with the starter switch is the best/simplest way to go, but just an alternative this is the setup for the J34. It has a simple 12v control box Hooked to 3 batteries: Through 2 aircraft starter relays There are 2 leads, 1 x high amp for the starter and a second low amp for the igniter. The crew, connects up, spins up on 12V then onto 36V with the igniters going. The driver just puts on the fuel until a good start and then the crew disconnects. We tried a start on the weekend and the magic smoke escaped from the 36v relay . Still need to have a look, but may end up with the switch idea you have. Cheers Ian...
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gidge348
Senior Member
Joined: September 2010
Posts: 426
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Post by gidge348 on Aug 7, 2015 0:50:27 GMT -5
Oh well, decided to pull my 36v relay apart to see what happened. Outside looked fine Inside.... not so much. Not sure of the reason, but I have a feeling that when I hooked the pull down circuit to the relay to 12v that was not enough to hold a good connection and the contactor spring was pushing it apart, got an arc and the rest is history. OR The contactors were dirty started to arc and once again KAPUT... Any other suggestions? Cheers Ian...
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Post by Johansson on Aug 9, 2015 12:44:54 GMT -5
Sorry to hear about the relay trouble, you´ll know soon enough if the battery switch idea is something worth trying out.
As soon as the girls are asleep I will try to get a couple of hours of work done on the Viper, hopefully I can borrow a heavy duty crimping tool at work tomorrow so I can make the last of the battery cables.
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Post by Johansson on Aug 9, 2015 16:27:19 GMT -5
I made a tank bracket tonight so the fuel tank wouldn´t risk tipping over during a run. Bear in mind that this is only a test setup, that is why I didn´t bother to use anything more fancy than a wooden board to mount the tank to. I also made a bracket for the battery selector switch, I just need to fit some kind of mechanical stop so I can´t turn the knob all the way to 1+2 because that would short circuit the batteries... Cheers! /Anders
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gidge348
Senior Member
Joined: September 2010
Posts: 426
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Post by gidge348 on Aug 11, 2015 5:23:35 GMT -5
Hi Anders, wondering if you have disconnected the 1+2 circuit on the switch? Just thinking if you rushing around and accidently switch "1+2" rather than "off" things could get nasty Cheers Ian...
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Post by Johansson on Aug 11, 2015 13:27:34 GMT -5
I think you missed the last lines of text in my post Ian.
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Post by Johansson on Aug 11, 2015 23:42:12 GMT -5
I don´t think my idea with the proximity sensor RPM reading will work, the ignition seems to upset the panel gauge so the numbers makes no sense.
The tacho generator is still there so I think I´ll use that one instead, after a quick googling I found some information about it and realized that a simple frequency counter might work.
"%RPM indicator instruments usually conform to a common standard. The instrument indicates 100% when fed with an AC signal measuring 70 Hz in frequency. A two pole tacho-generator turning at 4,200 rpm will produce this signal. It is normally arranged inside the engine gearbox so that the tacho-generator is driven at 4,200 rpm when the engine is operating at maximum speed i.e. 100%.
Certain older engines may use other gear ratios and instrument calibrations, it is important to always be clear about the actual and indicated speeds of any running gas turbine. It is useful if possible to check a tachometer-generator and indicator instrument combination when removed from the engine. An electric motor can be used to rotate the tacho-generator at a particular know speed and the indicator reading noted. The drive to the tacho-generator on the engine can be examined and the speed ratio determined, this is achieved by rotating the main engine shaft slowly and watching for movement of the tacho-generator drive.
There are many other electrical tachometer systems, one simple system consists of a single phase tacho-generator and an AC volt meter. The EMF (electro motive force) produced by the tacho-generator is directly proportional to the rotational speed of the generator, as the speed doubles the voltage doubles. The generator output voltage can be measured with a simple low current moving coil meter and rectifier, the meter is calibrated in RPM."
If I understand this correctly I could simply use a frequency meter coupled to the tacho generator to measure RPM, right? To make sure I´ll remove the generator from the gearbox and measure the gearing ratio to see that it´ll reach 4200rpm at 100% engine speed.
Cheers! /Anders
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Post by enginewhisperer on Aug 12, 2015 2:40:27 GMT -5
yep, you may even be able to connect it to a normal automotive tachometer - but you'd have to calibrate it
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gidge348
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Joined: September 2010
Posts: 426
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Post by gidge348 on Aug 12, 2015 6:43:56 GMT -5
I think you missed the last lines of text in my post Ian. DOH...
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