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Inlet trumpet dyno testing


kpr

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Unfortunately I'm too stacked with work at the moment to get any good test trumpets out in the next few weeks. Super keen to get in on some testing in the future though. 

Some tests that I would be interesting to try out, all using the same basic sizing for proper back to backs:

  • Aluminium vs. plastic - have heard reports of people losing power from trumpets flexing with intake pulses. Even in composites.
  • Printed with layer lines vs. smoothed.
  • Radiused entry vs. sharp entry.
  • Wide vs. tall elliptical profile.
  • Taper angle.

The issue with this stuff is likely to be very engine dependent in a lot of cases, so I am not sure how well results will extend to other engine setups. For example, the geometry that create the highest flow and the least wave reflection losses are generally opposing. So a motor that is airflow limited is going to make more power on a stack design that favours airflow over wave reflection. An engine with plenty of excess airflow potential is going to favour a stack with a better wave reflection. Still, will be interesting to do the testing for sure. 

Have you worked out your rough lengths for 2nd and 3rd harmonics? Doing a 2nd vs 3rd test would be cool too. Issue is to do it properly you have to change the whole intake really to keep the area taper the same. 

 

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Just now, BobbyBreeze said:

Aluminium vs. plastic - have heard reports of people losing power from trumpets flexing with intake pulses. Even in composites

This is what I was wondering about the long PVC intakes. It'd be pretty neat to see what they're doing with a slo-mo camera.

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Haven't got anything to directly compare plastic to ali.       as the ali  is 53mm id   the plastic  is 51mm id.   metal and plastic people need to standardize  their sizes hah.   keen to test if can find something though.   think one of my cams does 200fps,  probably not fast enough but will give it a jam

@BobbyBreeze  Happy to test your stuff at a later date.  

The first lot of tests I was trying to keep basic as possible.  Slowly  cutting a straight pipe down to show the reflected wave tuning
Then the same straight pipe at a fixed length with a range of bellmouths.   catching the 2nd harmonic.   these can be compared to my normal intake with taper

Would be nice to test all of the above with tapered runners.  But I think  combining the above findings, then adding taper and fine tuning maybe the way to go.  without spending days making  bin bound tapered test runners. 

From all the runner calculators,   the harmonic my normal intake is catching 8200ish rpm  should be the 2nd harmonic.   cutting roughly  100mm out should get the 3rd harmonic to the same 8200ish rpm.    so yep should see both these line up with i do the cutting down the straight pipe test.  

@Roman said the same thing re intake size,  which i agree with.   Both suspect the big bellmouths may not do a lot for my engine,  due to the runners being pretty large already.     

im really interested just to see what a boring old straight pipe    does vs an intake i've spent $$$ on and days making  with taper and good bellmouths

 

 

 

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Yeah I think once you have a bellmouth shape thats "good enough" its incredibly limited diminishing gains beyond that.

So im not expecting to see a design that has much if any gain over his existing inlet.

Like FSAE cars having to wheeze through a 30mm restrictor or whatever. Its absolutely crucial to maximize flow through the choke point.

But at 54mm even if you get vena contracta reducing your effective inlet entrance to say... 50 or 48mm... Thats still bigger than blacktop throttles haha.

However Im still keen to see what an obnoxiously large bellmouth results in.

It would actually be good news if it doesnt do anything, makes packaging easier for future projects haha.

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Do a three level Taguchi analysis for your factors. You'll be able to cut the number of experiments down significantly and get to the desired result faster.

(Warning: Taguchi analysis takes a fair bit to learn..)

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/If you want I can help develop an appropriate orthogonal array.

Would be good to produce a chapter for a book on intake factors one day

 

The basic Taguchi L9 (3 4 ) orthogonal array

Ie: Factor A: Runner length (1: 100 mm, 2: 200 mm, 3: 300 mm)
Factor B: Runner diameter (1: 45 mm, 2: 50 mm, 3: 55 mm)
Factor C: Bellmouth radius (1: straight, 2: 10 mm, 3: 20 mm)
Factor D: Something else

 

Taguchi is what the car manufacturers and industry use for rapid development. Allows for super quick improvements in processes and designs.

 

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Just now, ajg193 said:

Taguchi is what the car manufacturers and industry use for rapid development. Allows for super quick improvements in processes and designs.

Interesting, my students build model hill climb vehicles as a project where the ramp approaches vertical. It is basically an optimisation project with gearing, weight, centre of gravity (amongst other things). They really only have time to develop 3 or 4 iterations in a term that includes learning Inventor (they are only 15 too!). I've done some brief reading, I wonder if we could combine the data from across the class to develop a hypothetical best combo. Is there a Taguchi for dummys beyond reading Wikipedia? 

/sorry for thread hijack! 

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I have a 400 page book on Taguchi sitting on my desk. I'll look around at some point and see if I can find something a bit more basic.

 

The concept of it all sounds simple enough, but digging in and learning the intricacies of it is where it gets quite hard to make sure you're doing everything right.

Basically, as long as the variables you are looking at don't interact with each other (you will be able to tell if they do by looking at the results) you can just select one of the orthogonal arrays, populate it and run your experiment. Then with some fancyish yet still simple maths (I can't remember exactly what to do off the top of my head) you can determine the effects of each variable and predict an optimal combination. You then create an extra run with that determined combination to confirm your prediction.

Ie: The model predicts 50 mm diameter, 100 mm long, 10 mm radius and made from wood (original table may not have even covered this configuration) to give 40% more power at 7000 rpm compared to 45 mm diameter, 100 mm long, straight and made from plastic.

One of the most important things with Taguchi analysis is specifying a good quality metric in the first place.

Ie.

Let's say you want to do your RC car thing and each student will send the car up 10 times.

having your quality metric as "the number of times it made it to the top of the hill"  is really not a good metric as you don't get much information from it, just a pass-fail
but if you instead have "the distance/height obtained in each run" then you suddenly get a lot more data to use, you will get the max distance out of 10 runs, the mean distance, the standard deviation etc.

With a good quality metric you need less repetitions for each configuration. You also then have the ability to look at the data in different ways - such as optimising for lower is better, higher is better, closest to nominal is better, consistent is better etc.

 

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Printing the fourth pipe has nearly finished. (Will tidy up the grotty looking bits first)

Then just gotta do the tops then I'll send them up. 
95821460_235573267714263_8175957361651875840_n.jpg.8429879ec81e84a99183b9948908828c.jpg

I was going to glue the ends on, but maybe they could clamp together. That way could try with and without the tops. 
Or maybe have some different shaped tops for it.

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18 hours ago, ajg193 said:

Taguchi

I'm more of a build it, test it, then throw it in the bin kinda guy.    But if yourself or anyone else wants to use the data from the results, be my guest. 

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This ^    If someone wants to send me some i can  adapt  them to test.     I have some silvertop ones but are getting to be a bit of a straw,  due to the smaller diameter.  so lost motivation to make adaptors

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Now i'm going to have nightmares

https://vignette.wikia.nocookie.net/aaahhrealmonsters/images/b/bc/Oblina_Shrugging.png/revision/latest/top-crop/width/360/height/450?cb=20171017163339

 

Will likely do the testing next week after roman's  fine creation shows up.    Unless someone else has anything to offer, can wait a little longer.     But no panic will probably do a part 2 as already a lot to get through with my horrible creations alone  

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