thrust to weight how to measure it ?
 

am i right
on the ground i put a rope a round the tail with a set of scales on it between the holding stake
at full power take a measure of 2 kg at 12000 rev on my tacho
plane is a great plane extra weight 3.2 kg
am i right in thinking that this should be more pull on the scales
or cant it be measured in this way

RE: thrust to weight how to measure it ?
 

On what surface are you measuring.. grass or concrete and what is the motor size and prop diameter and pitch.

I beleive what you are measuring is the pull of the prop / engine combination which does depnd to some extent on the weight of what it's attached to butper wikipedia the thrust to weight the thrust to weight calcuation has propulsive efficiency component which is a whole other set of calculations.

So for your situation without knowing ending or prop Ibelieve your generation a more than half the thrust of the total weight. Ibeleive this would be plent ot fly in a scale manner but there will be no hovering with this setup. All conjecture on my part and would be interested to hear what others say.

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RE: thrust to weight how to measure it ?
 

hi yer sorry would help

most of the time i use to do this test on grass but now i have a table that i use and scale conected to my fence

motor is a mark one or two not sure Irvine 61 normal muffler and i tested 12 x6 11x7 and 11 x 4
with a smaller muffler from a 40 size i was only getting 9000 rev on a 12 x 6 and it would not take off
put on a 60 muffler had to shorten a little to fit and now on a 11 x 7 12600 rev and 2 kg pull on the scales i have not had a chance to fly it yet

RE: thrust to weight how to measure it ?
 

Well, one thing for sure.. you can certainly test how strong the tail is on that aircraft.

CGr.

RE: thrust to weight how to measure it ?
 

Unfortunately you are performing static tests which may not be indicative of actual "in air" performance.

Your .61 is rated at 1.7hp ( unrealistically! ) at the high end of the RPM scale.... 16000 RPM.

To spin a prop that fast you would have to use a small diameter prop, but you would loose almost all thrust.

The prop "unloads" in the air, letting it spin faster in flight.

You didn't say if the engine is new. If so you'll need to run it for a good while before it will develop full power... also what Nitro content are you using and at what altitude are you taking off from.

Both make a big difference.

RE: thrust to weight how to measure it ?
 

where i fly is 56m above sea level
i use 5% fuel
and engine is very used there is quite good compreson
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RE: thrust to weight how to measure it ?
 

Remember that ratings are given under optimal conditions and normally with 15% or higher Nitro content.

That said, your .61 is doing OK for an 11x7 prop, and it appears the 12x6 is bogging it down... however the latter may be due to mistuning.
With the different prop you need to modify the tuning.

If you saw a net RPM increase WITHOUT re-turning the engine, then you likely had it too rich to begin with.

RE: thrust to weight how to measure it ?
 

Thrust measurements on higher pitched props is pretty much meaningless. This is because most of the prop is stalled, thus creating lots of drag on the engine, but little thrust. The unload mentioned by Opjose occurs as the prop starts working, and becomes un-stalled. Normal for small 2C engine is about 1-2 thousand rpm increase over the static ground rpm.

RE: thrust to weight how to measure it ?
 

Hi,

Sorry to post it here but I've confiused on the calculation.. you guys know ASP 4st .70 can pull plane weight 4kg?

RE: thrust to weight how to measure it ?
 

That's a small engine for a 4kg plane.

If the wing loading is low, like in a trainer it may be possible to fly that plane, but it will not likely do loops from level flight and it will not fly straight up.

I have a .91 four stroker on a 9lb plane and I find that I really should have gone with a 1.20 four stroker instead.

RE: thrust to weight how to measure it ?
 

That way of measurement is accurate enough.

As others have explained, lower pitch - higher diameter propellers will provide more static pulling force and more capacity for hovering the plane, if 3-D is your thing.

This is a good article:

http://findarticles.com/p/articles/m...8/ai_n8918840/

RE: thrust to weight how to measure it ?
 

i need to set very light for my 5yr old NP seawind 60, no need loop, roll etc.. just can normal fly and aborad any error on landing will be good.. you think .70 will be enough? any props recommended?

RE: thrust to weight how to measure it ?
 

No I do not think it will be enough.

That plane needs far more thrust to be pulled through the water to take-off speed.

If you want to save weight try a 2 stroke .60-.75, the latter would be my choice.

In a four stroker you'll need at least a .91...

RE: thrust to weight how to measure it ?
 

ok thanks.