Cox Engines Forum
You are not logged in! Please login or register! Guests are limited to posting in the "General Questions (Guest Posting Allowed)" section only. Becoming a member is fast, easy and FREE!


Log in

I forgot my password

Search
 
 

Display results as :
 


Rechercher Advanced Search

Latest topics
» Mattel HotWheels.. 1970..
by Davenz13 Yesterday at 11:39 pm

» looking for cox 049 teedee parts
by Jason_WI Yesterday at 11:27 pm

» Deal of the year :)
by Cox International Yesterday at 10:29 pm

» NANO's .01 /.02 /.05 Sizes & Vidz Speed Planes
by 1/2A Nut Yesterday at 9:31 pm

» Dan Gurney Eagle
by Bill steklenski Yesterday at 7:54 pm

» Babe Bee ID Question
by Tee Bee Yesterday at 5:24 pm

» Back when I was buying engines by the gross, and bye bye engine wall........
by batjac Yesterday at 4:48 pm

» Finally stopped my engine vibration problem
by Ken Cook Yesterday at 4:29 pm

» P-38 Lightning-Roddie style..
by roddie Yesterday at 4:09 pm

» Unknown glow heads
by Cox International Yesterday at 2:06 pm

Cox Engine of The Month
February-2018
coxaddict's

"Another Twin Born 2-2-2018 weight 4 oz."



PAST WINNERS
Speed Contest 2018
CEF Traveling Engine

Win This Engine!
The Traveling Prop
Gallery


World of Aviation

Turnigy thrust stand conversion

Go down

Turnigy thrust stand conversion

Post  Davenz13 on Sun Oct 22, 2017 8:15 pm

Originating from the “My Money is on the Table” thread I thought it might be better to have the stand conversion as a separate post.
The idea being to covert a Turnigy thrust measuring stand, designed for electric motors, to be able to test fuelled motors.  



The main problem to me seemed to be stopping fuel residue from gumming up everything.
I made a platform to mount it on and removing the control panel from the base, placed it behind a piece of wood away from the engine stand, extending and running the wiring underneath the platform.





The aluminium plate (cut by a mate of mine who’s runs a water jet cutter, very handy machines) is for covering the engine stand to hopefully keep most of the fuel residue off it. The three sides, left, top and right will be folded back to form two sides and a top over the engine stand. The flat top of the engine stand will protrude through the slot (the X shaped engine mount is removed for fitting) and the area below the slot is for fixing the cover to the plywood base.  



I bought a cheap science stand (ebay $7 out of China, free shipping) mainly for the clamps for mounting the tacho, and also allowing for adjustment fore and aft with different size engines.



Cover folded and seams welded and mounted to base





Of course the Bee’s engine mounting holes wouldn’t fit the supplied mounts   DAMMIT! so a suitable mount had to be made out of a piece of scrap alloy.



Next bend up some 6mm stainless rod for the tacho mount. Ran it through some steel cable clips to act as bushes and fabricated a backstop for the rod but leaving a gap so it can be removed if needed.







Bolted a couple of steel tabs to the base so the whole unit can be clamped in a vice.

Probably overkill but there may end up some bigger motors being tested  lol!





Drew a design for the tacho mount and sent it off to my mate for cutting out.



Bent it up at one end and made a hole for the tacho lens to fit through. Made some slots fore and aft (front slots hidden by clamps) for rubber bands holding the tacho unit.
All clamped up ready for welding tomorrow.





Once that’s done I think we’re good to go
avatar
Davenz13
Gold Member
Gold Member

Posts : 259
Join date : 2013-11-28
Age : 62
Location : Palmerston North, New Zealand

View user profile

Back to top Go down

Re: Turnigy thrust stand conversion

Post  1/2A Nut on Sun Oct 22, 2017 8:29 pm

Well done Daven a Greenie for your efforts and sharing with us!!
Look forward to your tests!!
avatar
1/2A Nut
Diamond Member
Diamond Member

Posts : 1506
Join date : 2013-10-20
Age : 54
Location : Texas

View user profile

Back to top Go down

Re: Turnigy thrust stand conversion

Post  Davenz13 on Sun Oct 22, 2017 11:13 pm

Cheers for that Brad.
Gathering fuel ingredients and hope to start testing in about a week. Will try to get videos of test to post.
avatar
Davenz13
Gold Member
Gold Member

Posts : 259
Join date : 2013-11-28
Age : 62
Location : Palmerston North, New Zealand

View user profile

Back to top Go down

Re: Turnigy thrust stand conversion

Post  Oldenginerod on Mon Oct 23, 2017 4:15 am

Dave. While I have little understanding of the technical "nuts & bolts" of a thrust meter, I am concerned that, in my humble opinion, the centre thrust line of any engine mounted to the stand would need to align with the centre of the original mount. I'm assuming that the stand works on leverage and any deviation to the length of the "lever" will skew your results.

Rod.
avatar
Oldenginerod
Diamond Member
Diamond Member

Posts : 1986
Join date : 2012-06-15
Age : 55
Location : Victoria, Australia

View user profile

Back to top Go down

Re: Turnigy thrust stand conversion

Post  Surfer_kris on Mon Oct 23, 2017 5:15 am

Yes, the measurement is most likely based on leverage around a rotation point.
One could easily recalibrate the scale though. With a non running engine would could use a dynometer to pull on the prop axis and read the "trust" meter in order get a conversion factor.

There is/was a nice thread on RCU on how to measure trust (some time ago now); http://www.rcuniverse.com/forum/1-2-1-8-airplanes-70/1562254-1-2a-thrust-o-meter.html


avatar
Surfer_kris
Diamond Member
Diamond Member

Posts : 1417
Join date : 2010-11-20
Location : Sweden

View user profile

Back to top Go down

Re: Turnigy thrust stand conversion

Post  roddie on Mon Oct 23, 2017 6:50 am

Really nice work there Dave! Does the Turnigy unit measure thrust through a conversion of torque? In other words; does the motor/engine-mount move/turn "radially"? A few years ago, I built two prototype "dyno's".. for measuring thrust on a linear-plane (pulling-force) through the use of digital hanging-style luggage-scales. I'd thought about "torque".. and how to build a mount that would turn like a dial.. but there are so many variables.. that I didn't pursue it. There's a thread here on the work I did.. and the Turnigy-unit came up in the discussion at that time. I like what you've done with it.

My first attempt was a "beam-design" that pivoted on a central-pin.. but there were variables involved that directly affected accuracy with varying-weight engines/set-ups (fuel-weight.. etc.) and balancing the beam. The design; as well as the need for it, was met with some controversy.. Huh... and I ended up abandoning the design for a "direct-pull" through the use of a floating-fixture placed in a small tub of water. The scale was attached rigidly to the tub via a horizontal tray to hold it stationary. The floating fixture has 1-2" of travel and uses a hook to engage and tension the scale-hook. A simple square block of buoyant-foam was used to float the fixture in 1-2" of water (approx. one gallon)

The prototype needs refinement.. Laughing ... but it does seem to work.




avatar
roddie
Top Poster
Top Poster

Posts : 5678
Join date : 2013-07-17
Age : 58
Location : N. Smithfield, Rhode Island

View user profile http://www.stilburnin.com

Back to top Go down

Re: Turnigy thrust stand conversion

Post  Davenz13 on Mon Oct 23, 2017 3:55 pm

Very valid points being raised here.
The test stand comes with two mounts, one larger than the other and the center line of the larger mount is higher than the smaller one when mounted on the bed table. The bed table runs through bearings on two horizontal rods running fore and aft. Through a hole in the rear of the table is an upright post wired to the digital meter. When the engine pulls the table forward the table pushes on the post. Since the table slides forward and doesn’t pivot I’m not sure if it would have any gain in readings from the increased height above the table, it might even have the reverse effect by causing the bushes to bind a bit on the rods and reduce the readings.
The main reason I built it is to have a constant and hopefully reliable test bed so that any variations in prop, fuel or exhaust can be accurately measured and seen as whether they’re improvements or not in the engine being tested. With a throttled engine one should be able to plot a revs/thrust graph.
The bed is set up for Baby Bee engines (or any with the same back plate) at present and is at the same height (or very close to) the supplied small mount so there should be no problems in seeing accurate comparisons between them, apples with apples so to speak. If the actual thrust reading is slightly out it won’t really matter, it will still show variations.
If your bathrooms scales are set high or low they might not show your actual weight but they still show if you gain or lose some.
All good in theory but then, so was the Titanic
avatar
Davenz13
Gold Member
Gold Member

Posts : 259
Join date : 2013-11-28
Age : 62
Location : Palmerston North, New Zealand

View user profile

Back to top Go down

Re: Turnigy thrust stand conversion

Post  fredvon4 on Mon Oct 23, 2017 4:04 pm

When I first notice the Turnigy test stand I though long and hard on getting one...hey they are actually pretty cheap

The the how do I keep castor OUT of the works set in....

I like this idea and exercise in the shield but I would want to see how the sensor is actuated to set in my mind if or if not fuel oil is really a problem....

Looking forward to how this turns out... I wish I had this relative device back when I was trying to see how various venturi opening sizes effected the TeeDees I was fussing with

I actually could see a tach race where top RPM and Thrust...given a set fuel and prop were in the mix for the contest...

Top RPM is not the best gage of the POWER of a particular engine
avatar
fredvon4
Diamond Member
Diamond Member

Trusted Seller
Posts : 2292
Join date : 2011-08-26
Age : 62
Location : Lampasas Texas

View user profile

Back to top Go down

Re: Turnigy thrust stand conversion

Post  roddie on Mon Oct 23, 2017 11:39 pm

I believe that a static-thrust meter is a valuable tool for model aero-engine performance-measurement.
avatar
roddie
Top Poster
Top Poster

Posts : 5678
Join date : 2013-07-17
Age : 58
Location : N. Smithfield, Rhode Island

View user profile http://www.stilburnin.com

Back to top Go down

Re: Turnigy thrust stand conversion

Post  Surfer_kris on Tue Oct 24, 2017 5:12 am

I would actually be more interested in a torque reading myself.

The static thrust at a given rpm tells you something about the prop itself, but not so much about the engine really. The in-fligth thrust values are also very easy, and more fun, to test in the air. Smile

The torque and rpm reading would instead give you the power curve of the engine, which says much more about the engine and which prop-loads that one can/should use.

Below is a power plot for a few .15 engines based on my own data. The values are very inaccurate though as they assume a prop-load based on the propsize alone, and there are no reliable source for the individual props that takes blade area and shape, true pitch and true diameter into account. With a torque reading one could bolt any wooden stick in the front, and still get an accurate power reading. bounce

can't upload the picture.... x)
avatar
Surfer_kris
Diamond Member
Diamond Member

Posts : 1417
Join date : 2010-11-20
Location : Sweden

View user profile

Back to top Go down

Re: Turnigy thrust stand conversion

Post  Sponsored content


Sponsored content


Back to top Go down

Back to top

- Similar topics

 
Permissions in this forum:
You cannot reply to topics in this forum