vmsguy

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

opjose

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.

Flying freak

Somthing like this?

Steven

opjose

[link=http://www.youtube.com/watch?v=kQdW44BNBWM]Click me![/link]

Click on the above for a much simpler setup.

Gray Beard

My Feedback: (-1)

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.

scratchonly

You can google Aero design propeller selector, safe dounload. I have checked it against measurements with a scale, it seems very accurate.

brett65

My Feedback: (18)

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.

Gray Beard

My Feedback: (-1)

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!!

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?

combatpigg

My Feedback: (3)

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.

HighPlains

My Feedback: (1)

Total waste of time

except

for those guys hanging on the prop.

brett65

My Feedback: (18)

You're kidding right?[sm=50_50.gif]

Gray Beard

My Feedback: (-1)

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!!

brett65

My Feedback: (18)

Yeah, I just want to do it for the heck of it. For s&g's!

combatpigg

My Feedback: (3)

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.

kid chuckles

Yes to Brett65

Allfat

My Feedback: (1)

How did you change the pitch of a prop? I am curious because I am looking into this for a future project.

combatpigg

My Feedback: (3)

One way is to twist the blades. How much can be done safely? I don't know......but the idea is to heat the plastic just enough to allow a tweak.
I have seen large diameter, high pitch APC props cut down in diameter and recontoured to net an increase in pitch........[might as well carve your own from scratch].
I've carved my own pusher props out of maple with great results. I use layout lines drawn with a fine line marker, a jig saw and a sanding drum for the main tools. The thrust-o-meter saves R&D trips down to the proving grounds. If my planes have good vertical, the rest takes care of itself.