Back with the BIG LADY

[wakmat]

hello

I'm on the edge of my seat M,I will try to get some thrust figures today if I get time.

Thanks
Tim

[milisavljevic]

Hello All --

The shape of things to come is, well... Shaping up rather nicely at this moment.

The specification is complete and my talented CAD-expert is working up the 3D model.
Once proper plans and glamour shots are finalised, I will post it all up to a new thread.

May be a few days: the plans will include a lot more than a simple dimensioned image.

Not to mention Tim still owes me "Astor M special" thrust readings. (hint, hint)

Cheers!
M.

Btw., Tim: found Monto on Google! Just one question: where's the bloody pub?!

[wakmat]

Hello

M I had a rethink of my thrust stand,and am building a totally new one,my last one was as strong as a folded out clothes hanger,so I should finish up today with fab.The pubs in Monto are in Newton st(main st)one is at the top of the street and the other is at the bottom and you guessed it they are called the top and bottom pub.I prefer the top for my brain lubricating.
Heres a pic of my stand so far.

Thanks
Tim

[wakmat]

Hello


here's my thrust stand finished just got to add a set of fish scales,and strap the Astor to it and I should have some thrust measurements for you M.

Thanks
Tim

[milisavljevic]

Hello Tim --

Here's my thrust stand finished just got to add a set of fish scales...

Sweet! I like that angled carriage.

Hope you have or can get a 30+ kg fish scale for the shape of things to come.

Cheers!
M.

[wakmat]

Hello

I went on the hunt for some scales yesterday with no luck,might have to drive to the next town to find some.If I can't find a 30kg set I will just make a lever system to to double or triple the force on my sled.

Thanks
Tim

[Irvine.J]

Rarely does something beat the simplicity and cost effectiveness of a spring scale. I have one with a little slider that holds the position of the last recorded weight, just watch you don't melt them. EBAY!

[Irvine.J]

http://cgi.ebay.com.au/50KG-112POUNDS-S ... 240%3A1318

OHH PREETTTYYY

[wakmat]

Hello

Just got my fish scales, all they had was a 12kg max set so I'm rigging up some pulleys to reduce the pull ratio

M should definitly have some thrust figures today,I was going to do a minium thrust and a Max thrust,do 3 runs of each and get an average,does that sound ok.

Thanks
Tim

[wakmat]

hello

M here is your thrust figures.Full gas cylinder.
Temperature 34.9c
Barometric pressure 1009.9hpa
192m above sea level
First run (cold start) minimum 4kg,Maxium 12kg
second run (hot start) minimum 2kg,maximum 14kg
third run (hot start) minimum 2kg,maximum 14kg

Giving you an average 13.3333kg max thrust.
I almost got it lock in at 1kg,so the throttle range is pretty good,it will run all day at 2kg without making the chamber glow.
Hope this is alright M
Thanks
Tim

[milisavljevic]

Hello Tim --

Woohoo! Thrust readings! Thank you very much, Tim!

All they had was a 12kg max set so I'm rigging up some pulleys to reduce the pull ratio.

I would be sceptical of the readings taken from such a system, until and unless you calibrated it
carefully in the thrust range that you are measuring, and in particular, the thrust at the top end.

The fish scales (without the pulleys) need to be calibrated against a set of known weights, even
a gaggle of 2 liter soda pop bottles full of water will work in a pinch. What concerns me more is
the pulley system: it will have some play in it that may adversely affect thrust reading accuracy.

If you did calibrate it at the top end, then good on you! In any event, I am grateful, and you are
no doubt reading close to true as the top end readings fall very close to the predicted maximum.

If can confirm that you are measuring 14 kg (hot start) with a calibrated system, then I want to
know! Thrust is 17-27% better than the model, well above the error band, so this is interesting.

Btw., the wide throttle range is proof that the shorter intakes are the match to this combustor.

Thanks again, mate!

Cheers!
M.

[milisavljevic]

Hello Tim --

It will run all day at 2kg without making the chamber glow.

Your Astor M special is clearly moving a lot of air, even at such a low throttle setting.
Think of it like a turbofan (jet) engine's bypass ratio. Thank you for providing me all
the weather details and the altitude of your test site. I can enter all of the data right
into the model and watch the changes waterfall through the simulation, "Matrix"-like.

Btw., the effects of your altitude, the heat and low pressure combine to increase the
sea-level equivalent static thrust; the model defaults to sea-level, 15 C, 101.325 kPa.

Cheers!
Keith

[wakmat]

Hello

M,I did calibrate the fish scales,and they were maybe 300-350g over what the weight was,as for the pulleys before I started the engine I remove all the slack from the pulleys,the readings are to the closest 500g,towards the top end of the throttle range it was hard to get a reading as the scales where bouncing slightly.So with a 2 to 1 reduction to the scales the error could be alot more than the 300-350g error.I know these scales are fairly inacurate and my pulley system probably made it worse,so I have a set of electronic shop scales I'm going to strip down and use.


Thanks M

Tim

[Irvine.J]

Hey wakmat, electronic scales are bad, almost all electronic load cells are, with the exception of a few very expensive ones.

Problem is their sample rate is very low, maybe 3 or 4 samples per second, giving you a completely fudged reading. For instance on two seperate load cells i've used I rarely (even on the big 12/15lbs get more then 2 or 3 lbs) where as the fish scales read true and oscillate back and forth maybe +/- 0.5 lbs true thrust on the bigger engines and don't really oscillate at all on the little ones. A straight in-line spring scales is definitely the way to go man. Once your load cell gives your reading, you test against that weight the engine pulled on your spring scale with your electronic scales for double checking your results. Easy, cheap, and very accurate.

[milisavljevic]

Hello Tim --

M, I did calibrate the fish scales.

Thanks for confirming this, mate! While James' post was rather hard to follow (I think he was hungover
when he posted...) he was basically correct: if the load cell has a low sample rate, it's use as a scale for
thrust measurements is limited. You really are much better off scoring a larger fish scale from eBay.au.

The scale James posted the link for is ideal, as it's full scale reading is roughly double what you'll need.
If eBay isn't your style, why not drive over to the coast to get a larger scale there? Must be lots of them.

That sweet thrust trolley you have built deserves nothing less.

Thanks again for your efforts! Your reward is coming soon!

Cheers!
M.