Okay, this is probably a very stupid question, but is there a way to measure how much thrust/power a glow plane has? Like for electric planes, you can just measure them with a watt meter, but how would I do that with a glow plane? The only reason why I am asking this is that I don't want my first glow plane to be underpowered.

Thanks in advance for any replies. LR

Just follow the manufacturers engine recommendations and it likely won't be underpowered, especially if you stay in the upper end of the recommended range.

Agree with ChuckW. If you already owned some glow engines, you can put the same prop on them and measure the rpm with a tachometer. This is a little bit useful for comparing the power of one engine to another engine. But if you just buy the largest displacement recommended by the airplane designer, you should be OK. For example, if the plane says ".40 - .60 two-cycle glow recommended", buy a glow engine about .60 cubic inches and you will be fine. You can even go higher than the recommended if you want but you will also be adding weight.

One way to measure thrust is to secure the plane with a digital fish scale linked to the plane. Run the engine, see how much it pulls. Compare props, or fuel, or mufflers, or settings.

Good luck,
Dave Olson

thats my preffered method....just remember what the fish scale limit is.... trust me, a 50cc methanol twin on a 20 lb spadmaking 24lbs of thrust on a 15lb scale is terrifing when it chases you around your yard

Speaking from experience, are you there?[sm=omg_smile.gif]

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thats my preffered method....just remember what the fish scale limit is.... trust me, a 50cc methanol twin on a 20 lb spadmaking 24lbs of thrust on a 15lb scale is terrifing when it chases you around your yard
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Dittos to everything that has been pointed out and I would just lke to add don,t bother falling into the trap of trying to decifer useful info from from manufacturers advertised power figures which are virtually useles in a real world.


One point on the stactic scale method it certainly can be usefull however this is only static thrust information so is not a totally accurate method either. It makes no account of how well the engine and prop combo unloads in flight and this a very important parameter.


Just as everyone has said the very best option is to use at or near the upper indicated engine limit That is suggested on virtually all model aircraft these days.

If you are trying to design your own airplane for your first glow aircraft then I would suggest you not attempt this untill you get some experiance under your belt.

John

Problem of measuring thrust with a scale is you have already paid for the engine whether it's too big, too small or just right (3 bears ). Not a very cost effective method and also doesn't tell you if it will fly the plane or not. Buy an engine in the upper recommended range size (you might go bigger if you had the experience you don't have yet).

deciferuseful = decipher useful ?

Power to weight is the answer. I have seen many computerized methods to measure the thrust but they all are not perfect, the best way as Scar mentioned is using a digital fish scale. Invest around 20.00 dlls. And you will have a very useful tool. Truth is that if you already have the plane and the engine you will have to work it out in some way but the idea is to have a next better powered model.
When building a kit or just about to buy an ARF model look at the weight, think also that there are in the market a lot of engines of the same displacement but with very different characteristics, just by example two engines that are of the same displacement like the YS 120 four stroke and the old Saito 120 four stroke, they almost weight the same but you will obtain a better thrust from the YS and it can handle a bigger prop. which is usually better for many applications.
As per the RPM you can find that different displacements of engines as gassers can give lower RPM readings than glow powered engines, but you will find a better thrust in those big and heavy gassers.

Thank you for all of the replies. Well, I decided not to go cheap and took your advice about buying the highest dispacement engine that the manufacturer recommended. If you're wondering, the plane I bought is a Hobbico Avistar. I was going to go with a .40 sized engine, but I decided to buy an O.S. 46LA engine today.

Perfect choice!

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deciferuseful = decipher useful ?
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Yes, a spelling and a typo error thank you for correcting it.


Agreed with Jester, yes a perfect choice[8D]

John

If you want to actually estimate the power a glow engine makes, use a tach to measure rpm at full throttle. Now take whatever prop was on that glow engine and put it on an electric plane and measure how many watts of power it takes to spin it at the same rpm with a wattmeter. If the electric motor won't spin it that fast, measure the watts at whatever speed the motor can turn it and then take the ratio of glow engine speed/motor speed and cube it.

For example, let's say your glow engine spins a 10x6 at 12000 rpm, take that exact same 10x6 and put it on an electric plane and throttle it up, let's imagine that your electric spins it 6000 rpm and draws 150 watts of power while doing that. Take the ratio of glow/electric rpm, in this case 12000/6000 = 2. Two cubed is 2x2x2=8 150 watts x 8=1200 watts.

In this case, your glow engine could be called a 1200 watt equivilent motor. To know the actual output watts, you need to know the efficiency of the motor you measured the prop with, most likely about 80% so 1200 watts x .8 =960 shaft watts. Convert to horsepower by dividing by 746.

Do not try to argue but to get info:
What happen when I have several electric motors, different ESC and different LiPos.
Would the readings be always the same?