1:20 scale model wind tunnel build - help!

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   OK well some progress has been made.
The fan has been replaced with a 350mm, all metal, commercial extract fan, which is producing around 31mph in the test section. Some way off the required 400mph but it'll have to do!

Photos here:

The test section of the wind tunnel seems to work really well - if you insert a piece of string or cotton through the flow straightener and into the test section it holds almost level and without turbulence until almost the end.

I've also 3D modelled 6 existing fully-faired HPVs to give some kind of benchmark:
- Slash's Beano
- Jack and Derrick's Donkey
- Davis? frame with blue sock
- LeeW correx Challenge Fujin (above)
- Correx boxed misc frame?
- Geoff's HPV Heaven streamliner

So far I've only 3D printed one as a test - LeeW's correx machine - printed at 1:18 scale.

I ran it as a test tonight for the first time - unfortunately it's highlighting a measurement issue - the lego dolly is producing too much stiction so the results are too innacurate - three separate runs resulted in 2.xxg, 3.xxg and 4.xxg of horizontal force (or Newton equivalent to keep Mr Perry happy  ) ie far too much error to produce consistent results.

Youtube video here hopefully:

So I'll have to investigate very low capacity load cells to solve the measurement issue (no idea where to start here quite frankly - any ideas anyone?) , and maybe up the print scale to 1:15 - I think the test section will take it OK.

Edited by russellbridge - 29 June 2015 at 10:37pm

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russellbridge Members Profile Send Private Message Find Members Posts Add to Buddy List BHPC Member Joined: 21 October 2013 Location: Manchester Status: Offline Points: 843	Post Options Post Reply Quote russellbridge Report Post Thanks(0) Quote Reply Posted: 29 June 2015 at 10:20pm
	OK well some progress has been made. The fan has been replaced with a 350mm, all metal, commercial extract fan, which is producing around 31mph in the test section. Some way off the required 400mph but it'll have to do! Photos here: The test section of the wind tunnel seems to work really well - if you insert a piece of string or cotton through the flow straightener and into the test section it holds almost level and without turbulence until almost the end. I've also 3D modelled 6 existing fully-faired HPVs to give some kind of benchmark: - Slash's Beano - Jack and Derrick's Donkey - Davis? frame with blue sock - LeeW correx Challenge Fujin (above) - Correx boxed misc frame? - Geoff's HPV Heaven streamliner So far I've only 3D printed one as a test - LeeW's correx machine - printed at 1:18 scale. I ran it as a test tonight for the first time - unfortunately it's highlighting a measurement issue - the lego dolly is producing too much stiction so the results are too innacurate - three separate runs resulted in 2.xxg, 3.xxg and 4.xxg of horizontal force (or Newton equivalent to keep Mr Perry happy ) ie far too much error to produce consistent results. Youtube video here hopefully: So I'll have to investigate very low capacity load cells to solve the measurement issue (no idea where to start here quite frankly - any ideas anyone?) , and maybe up the print scale to 1:15 - I think the test section will take it OK. Edited by russellbridge - 29 June 2015 at 10:37pm

GeoffBird Members Profile Send Private Message Find Members Posts Add to Buddy List BHPC Member Joined: 20 September 2005 Status: Offline Points: 2396	Post Options Post Reply Quote GeoffBird Report Post Thanks(0) Quote Reply Posted: 29 June 2015 at 10:47pm
	Wow, that's brilliant Rus! Proper Job. Could the lack of repeatability (technical term ) be down to something else? The old MIRA model tunnel (an open loop design like yours) used to give different results if someone opened the door to the room it was in! Is the anemometer (if you can say that word then you are still sober!) showing a constant airspeed? Load cells in wind tunnel balances are usually a flexible metal support with a piezoelectric wire glued to it. That's as far as my electrical knowledge goes I'm afraid. Should be fairly easy to make one and link it up to a meter. You could then calibrate it by mounting it vertically and applying weights. Someone with some knowledge of electrickery will tell you if I'm talking b#ll#@ks
	Right Time - Right Place - Wrong Speed

russellbridge Members Profile Send Private Message Find Members Posts Add to Buddy List BHPC Member Joined: 21 October 2013 Location: Manchester Status: Offline Points: 843	Post Options Post Reply Quote russellbridge Report Post Thanks(0) Quote Reply Posted: 30 June 2015 at 9:17am
	Thanks Geoff - praise from Caesar! It is in a shed with a big door, but all the tests were done with the door closed so I don't think it's this. The wind speed is stable at between 30-31mph. I'll have to do some research on load cells or equivalent... These are the bikes I've used: from left to right: - LeeW correx Challenge Fujin (above) Length: 2660mm Effective frontal area: 0.358m² - Geoff's HPV Heaven streamliner Length: 2540mm Effective frontal area: 0.443m² - Davis? frame with blue sock Length: 2360mm Effective frontal area: 0.395m² - Jack and Derrick's Donkey Length: 2300mm Effective frontal area: 0.340m² - Slash's Beano Length: 2230mm Effective frontal area: 0.309m² - Correx boxed misc frame? Length: 2590mm Effective frontal area: 0.419m² Please could anyone with access (esp. to Beano and Donkey) check the length measurements for me - I've scaled them from photos / wheel diameters - so there may be some errors above - looking at this fresh this morning, both Donkey and Beano look a bit too small in comparison to the others. I'll correct them if there are... Edited by russellbridge - 30 June 2015 at 9:22am

SamR Members Profile Send Private Message Find Members Posts Add to Buddy List BHPC Member Joined: 30 June 2015 Status: Offline Points: 1	Post Options Post Reply Quote SamR Report Post Thanks(0) Quote Reply Posted: 30 June 2015 at 5:42pm
	This looks like it's coming on really well. The "Correx boxed misc frame" is one of the earlier Crusaders on a Davis D6 frame. That body no longer exists (split in half on the way to an event) but it had a length of 2340m and a frontal area of 0.383sq m not including the wheel.

GeoffBird Members Profile Send Private Message Find Members Posts Add to Buddy List BHPC Member Joined: 20 September 2005 Status: Offline Points: 2396	Post Options Post Reply Quote GeoffBird Report Post Thanks(0) Quote Reply Posted: 30 June 2015 at 6:33pm
	This any help: I think the blue bike is the Kingcycle Wasp now owned by Andy TS - don't forget to model the gaffa tape
	Right Time - Right Place - Wrong Speed

GeoffBird Members Profile Send Private Message Find Members Posts Add to Buddy List BHPC Member Joined: 20 September 2005 Status: Offline Points: 2396	Post Options Post Reply Quote GeoffBird Report Post Thanks(0) Quote Reply Posted: 30 June 2015 at 6:35pm
	I made the HPV-Heaven frontal area 0.4 m2 BTW.
	Right Time - Right Place - Wrong Speed

atlas_shrugged Members Profile Send Private Message Find Members Posts Add to Buddy List BHPC Member Joined: 03 November 2014 Location: Cambs Status: Offline Points: 1025	Post Options Post Reply Quote atlas_shrugged Report Post Thanks(0) Quote Reply Posted: 30 June 2015 at 9:15pm
	Could you use an air bed rather than a trolley dolly to reduce stiction? It would be good to also model Ristretto Brian