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Device for measuring thrust - 6/24/2008 7:56:33 PM   
vmsguy


 

Posts: 477
Joined: 4/4/2007
From: Woodville, WI, USA
Status: offline 		this is probably the wrong forum to ask this, but no forum looked like the obvious place.

Moderators please feel free to move as you see fit.


Here's my question...

Has anybody built a motor test stand appuratus that can actually measure thrust / performance ????

If a testor mechanism was built, it'd allow for a more scientific comparison of prop/motor comparison.

If there is a link, or a thread.. Please point me to it....



Thanks,

Lyndon



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RE: Device for measuring thrust - 6/24/2008 8:18:07 PM   
opjose



Posts: 5832
Joined: 11/26/2005
From: Poolesville, MD, USA
Status: offline 		These devices are very simple.

Many of the popular RC magazines show them in use.

One easy way to do this is a simple fish scale anchored at one end, and the other tied to a plane.

A bit more elaborate is a normal weight scale, with an "arm" ( like an upside down "T" ) on the scale, and a hinge at the other end of the "T".

The motor is attached via a line, etc. to the long part of the "T".

As the prop "pulls" it places a downward force on the scale, indicating thrust.



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RE: Device for measuring thrust - 6/24/2008 9:56:53 PM   
Flying freak


 

Posts: 1359
Joined: 6/29/2006
From: granby, QC, CANADA
Status: offline 		Somthing like this?

Steven

Attachments
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RE: Device for measuring thrust - 6/24/2008 10:10:27 PM   
opjose



Posts: 5832
Joined: 11/26/2005
From: Poolesville, MD, USA
Status: offline 		Click me!

Click on the above for a much simpler setup.



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RE: Device for measuring thrust - 6/25/2008 5:07:52 PM   
Gray Beard


 

Posts: 2023
Joined: 4/21/2003
From: Hemderson, NV, USA
Status: online 		If you go to www.evflyers.com this club site has one they built and take to the field with them to test thrust and props on/with different planes and engines. They even have A chart showing the readings of different engines they have tested. It was worth the look and I even signed up with them. Very simple and clean unit.

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RE: Device for measuring thrust - 6/25/2008 6:56:45 PM   
scratchonly


 

Posts: 946
Joined: 6/3/2006
From: winnipeg, MB, CANADA
Status: offline 		You can google Aero design propeller selector, safe dounload. I have checked it against measurements with a scale, it seems very accurate.

< Message edited by scratchonly -- 6/25/2008 7:01:00 PM >

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RE: Device for measuring thrust - 6/25/2008 9:14:50 PM   
brett65



Posts: 1075
Joined: 12/21/2007
From: Oklahoma City, OK, USA
Status: offline 		I'm gonna make me one, I like making the homemade stuff. I put together one of the string and plumb bob cg machines last weekend, and it works great! The homemade lowtech stuff is fun, all I need really is a fish scale to make the thrust machine.

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RE: Device for measuring thrust - 6/25/2008 9:36:53 PM   
Gray Beard


 

Posts: 2023
Joined: 4/21/2003
From: Hemderson, NV, USA
Status: online 		Cool, I used to have the string and plumb bob CG thing set up in my old shop, as long as you knew the datum line you could get the CGs dead on as I recall, been A while.
One little thing, the better the scale the better the results. I use my fish scale for weighing planes but I have to keep in mind this is A fishermans scale and it's MY fishermans scale, it tends to make things just A bit heavy if you know what I mean. I would build A plane for someone and they would pick it up, I have all the stats ready for them too. Then they get it home and put it on A real scale and they are even more thrilled, it came out way lighter then what I told them.
Anyway, it works well on trout!!

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RE: Device for measuring thrust - 6/25/2008 10:07:31 PM   
kid chuckles


 

Posts: 774
Joined: 5/2/2007
From: Granbury, TX, USA
Status: offline 		I guess you would have to actually go fishing to get the fish scale. I don't think in the stores the fish still have them. Or the ones we eat don't. Maybe a different store might but don't think so. I guess you could buy a live one and take a scale from it. But seems extreme just to measure something. What would a fish scale do anyway? How would that help you?

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RE: Device for measuring thrust - 6/26/2008 1:52:01 AM   
combatpigg



Posts: 9826
Joined: 11/22/2003
From: arlington, WA, USA
Status: online 		Thrust calculators assume that all propellors are created equal. The truth is some are more equal than others.
I'm interested in knowing how much my prop/engine combo can bench press without feeding the force through some Rube Goldberg setup. I set a stand up where the engine has to lift itself plus a known quantity of weight against gravity. I know what the ball park amount should be based on what a thrust calc says, then fine tune the test load with .5 oz weights until equalibrium is reached.

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RE: Device for measuring thrust - 6/26/2008 2:04:53 AM   
HighPlains


 

Posts: 2669
Joined: 3/2/2003
From: Over da rainbow, KS, USA
Status: online 		Total waste of time

except

for those guys hanging on the prop.

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RE: Device for measuring thrust - 6/26/2008 4:51:36 PM   
brett65



Posts: 1075
Joined: 12/21/2007
From: Oklahoma City, OK, USA
Status: offline
quote:

ORIGINAL: kid chuckles

I guess you would have to actually go fishing to get the fish scale. I don't think in the stores the fish still have them. Or the ones we eat don't. Maybe a different store might but don't think so. I guess you could buy a live one and take a scale from it. But seems extreme just to measure something. What would a fish scale do anyway? How would that help you?


You're kidding right?

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RE: Device for measuring thrust - 6/26/2008 5:09:37 PM   
Gray Beard


 

Posts: 2023
Joined: 4/21/2003
From: Hemderson, NV, USA
Status: online 		Read his handle.
Like High says, no real reason for one. We had one at one club that was used to find the better props for our racing classes, that was good.
Thing is they are just Plane Fun!!

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RE: Device for measuring thrust - 6/26/2008 6:13:48 PM   
brett65



Posts: 1075
Joined: 12/21/2007
From: Oklahoma City, OK, USA
Status: offline 		Yeah, I just want to do it for the heck of it. For s&g's!

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RE: Device for measuring thrust - 6/27/2008 2:33:08 AM   
combatpigg



Posts: 9826
Joined: 11/22/2003
From: arlington, WA, USA
Status: online 		I've used mine to help develope props that nobody makes. For example, 7x2 & 8x2 sizes for small 3D glow projects. There are other examples where no "off the shelf" prop for your application is readily available. I'll bet the Wright Bros. did thrust testing before committing to a final prop design.

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