lechuza

Hello, how is the relation of torque and horse power on gasoline engines? For example, and here I will mention a glow engine: the o.s. 1.60 fx glow engine have a 3.7 horse power at 9000 rpm, but what about its torque?, and the CRRC 26cc gasoline engine produces a 2.6 horse power at 8500 rpm, but how much torque it produces?

Why evolution engines specifications does not mention the power rated for some specific engine model, how can you tell its power and/or torque capacity?

Also, according to your experience, with a 26cc gasoline engine how is the heaviest airplane that you have flown?

Thanks, Isaias

rangerfredbob

My Feedback: (13)

horsepower is a simple equation of torque and rpm:

HP=torque*rpm/5252

working that backwards:

torque=HP*5252/rpm

tkg

My Feedback: (1)

Ya but that only tells you the torque at the max HP, not the max torque.
If you could find a HP curve/graph then you could have lots of fun with the math.

jerdavis

My Feedback: (3)

Here is the reason given by Jett Engineering as to why they do not give horse power rating for their engines:



__________________________________________________ __________________________________________________ __________________________________________________ _
Question:

Why doesn't Jett publish the horsepower of its engines?
Answer:

Jett reveals the power of its engines by publishing and guaranteeing the RPM each engine turns a specific propeller. This may be easily compared to similar data from the competition. HP figures are not so easily compared because there is no industry standard with which to test. As a result, each manufacturer tests independently of the other, often on uncalibrated equipment. In cases where competitive advertisements claim power on the optimistic side, Jett is forced to remain silent, or publish equally optimistic claims. Comparing RPM on a fixed and available brand of propeller is the only way to accurately compare engines.

It is usually ok to compare HP numbers generated by the same person, i.e., a tech writer. Just don't compare his numbers to someone else's.
__________________________________________________ __________________________________________________ __________________________________________________ _


Maybe this is why Evolution and several other manufacturers don't rate the H.P. of their engines.

Jerry

rmh

Being used to turn a fixed pitch propeller , you can really forget about the torque curves and just do as Jett does
Use a known load.
That's how full scale rebuilds are checked
Th power needed to accelerate a prop is not really an issue
the max prpm the engine will turn a known load is all you need to know.
The prop load increases from being a small flywheel to full air load in a VERY steep curve.
Some people want dyno curves -just as land vehicles use
-really not relevant

lechuza

Hi, I have a question about power:

For example, how the o.s. max 1.60 fx glow engine have 3.7 hp at about 9000 rpm, and how the RCS SV26 gasoline have about 2.6 hp at about the same 9000 rpm, as so the CRRC 26 gasoline engine have about 2.45 hp at about 8500 rpm, and all these engine are 26cc?

Isaias

lechuza

Hello, what can be done to a specific carburetor (in this case for example the walbro WT-694), to increase the horse power which it is rated?

Isaias

tkg

My Feedback: (1)

YOU CAN NOT MEASURE HP, you can only calculate it IF you know the torque the engine produces.
So an engine that has more torque at the same RPM as another will have more HP. Torque is influenced by fuel type (gas vs nitro), intake porting, exhaust porting, exhaust system, the size of the carb, compression ratio and so on. So all 26cc engines are not equal just because they are 26cc.
You can design an engine that would have less HP at 9000 rpm than another, but would pull a bigger prop at 7000 rpm than the other. Or go the other way some of the .40 sized pylon racing engines develop over 5hp, buts it at 22,000 RPM and their useless for most aerobatic flying

rmh

Hold on a second thar buckaroo-
electric motors can have power read easily because you can read the energy consumed and then "figgered "by the losses in motor efficiency
for exmple : IF a motor -say a 80% efficiency motor will turn a 16x10 prop at say10,000 rpm whilst sucking up watts equal to 5 horsepower . Then-we can see that 80% of 5 hp (in watts) was turning the prop.
or 80% of that
4 hp at 10000 rpm
now we know that this particular prop no matter how we turn it -or with what type engine - requires 4 hp to turn 10,000
Is my math correct ?
So for aircraft engines -the best methodof accurately knowing what the power is , you need load props -calibrated for the particular size engine.
OR just comare how various engines turn a particular prop
after all the really important question is "how well will the engine turn a particular prop.

tkg

My Feedback: (1)

Gee I didn't know an OS 160 was electric
Even if you had a calibrated set of load props, altitude, temperature, air density would all skew your numbers. About all you can say is that one engine turns the same prop faster than another engine. AN I mean the SAME prop, not one just like it or the same size.
In any case your still calculating HP

rmh

Just noting that the calculated HP is very misleading-as you know.
A prop is a prop -irrespective of what twirles it
I left out all the "factors" trying to make my explanation as imple as possible
IF
That'sIF you want a fast usable cheap "dyno" just run a series of props on an electric motor at various speeds and record the watts consumed
With that info and the necessary altitude density/etc., crapolla-you can get some usable numbers not "advertised torque and hp extrapolations.
It's good enough for full scale -

Lnewqban

Isaias:

Glow engines can produce more power than gasoline engines of the same displacement because glow fuel has more calorific power generated in the same amount of time.
The power of a reciprocating engine is limited mainly by how well it breathes, or sucks in the proper mixture of fuel and oxygen.
The nitro in the glow is like liquid oxygen, so other atmospheric gases that do nothing for the combustion stay out of the engine; hence, the combustion is stronger.

Normally, the maximum torque is reached at lower rpm than the maximum rpm, where the maximum HP is determined.
It is a phenomenon of internal friction and best regime for breathing.

rmh

There is enough horse do do about power -hp and torque in the model engine business to fertilize the entire state of Kansas.

remember this
1 the engine which burns th most fuel per cyle -has th most torque
2 If you change fuel types you can't compare volume of fuel burned.
3 maximum torque occurs when maximum breathing takes place
4 the maximum breathing of any engine may quickly play off or stay very high -depending on engine design but mostly on the exhaust system design in the case of our engines
even some four cycle types have very good breathing over exteme rpm changes
these engines have what is called a flat torque curve
look here at the Honda F1 curves.

lechuza

lnewqban and all : thanks for the responses , but in a way to know engine behaviors, can I supose that for example a 15 lbs. model with a glow engine of 3.7 hp and a 16x7 2-blade propeller will behave in the air(speed and maneuvering) as if this same 15 lbs model would have a 2.8 hp gasoline engine with the same 16x7 2-blade propeller? it is curious because once I had a CMP Cessna 182 ARF with calls for a 1.20 to 1.60 glow engine, but I put a Super tigre .90 glow engine and this modelflew excellent, with half throttle in level flight.I believe that 1.20 to 1.60 would have make this model overpowered, so how the designers of a specific model are based for determining the engine size range for that model?

Isaias

the Wasp

My Feedback: (1)

<div>""so how the designers of a specific model are based for determining the engine size range for that model?"'</div><div></div><div>well that is like asking why a given 16ft boat can handle a 500 HP V8 while the other 16ft boat can only handlea 100HP 4cylinder ,,</div><div></div><div>it's because the Designer went to Design School so he knows all the Math Formulas,Stress Factors andLift vs Drag,,</div><div></div><div>look at today's Seagull Models, with a span of only 70 inches it calls for a 180 4st (30cc), it has a Wing Area of 967 sq in,,</div><div></div><div>http://www.horizonhobby.com/Products...ProdID=SEA5500</div>

rmh

The prop and the speed it runs is all that matters -
gas/electric/glow -whatever .
The actual differences in gas n glow is weight of the powerplants and weight of the fuel load .
It is more practical to use a "performance" fuel and a small light engine on small models
just as it is more practical to use performance batteries and an electric motor on very small models
The trade off of power to weight is really an opinion in many cases
Iuse electric power up to a 5 pound model - glow up to 9-10 pounds then gasoline engines upwards of that
BUT
Glow engines can fly much larger models than10 pounds
it's all a compromise -just like airfoils and wing loadings
you just decide what the "soup" should taste like then stirin the ingredients
It helps to know what those ingredients are but time n experience (not a lot of math)will help you sort things out...
Trust me on this

mrbigg

My Feedback: (21)

Let me throw this out there. You have the two airframes, same brand prop, same ready to fly weight, two different engines. Both engines spin the prop the same RPM on the ground. In the air though, one out pulls the other on an upline. Could this engine be making more torque than the other (under max ground RPM) and is using that torque when the engine is "dragged down" on the upline?

Kweasel

My Feedback: (29)

How does a propeller thats moving foreward place more load on an engine than when sitting still? (I know its possible but we're talking about models here) If a particular engine is loosing power in verticals then its most likely going lean.

the Wasp

My Feedback: (1)

<div>""(not a lot of math)""</div><div></div><div>surely you don't believe that !! designers don't just set downand draw without using math</div><div></div><div>with math you know,</div><div></div><div>angle of attack,</div><div>wing load,</div><div>wing area,</div><div>thrust angle,</div><div>airfoil,</div><div>drag,</div><div>lift,</div><div>axis,</div><div>length,</div><div>width,</div><div>cord,</div><div>dihedral</div><div>CG,</div><div>vertical taper,</div><div>horizontal taper</div><div>weight,</div><div>strength,</div><div>distances,</div><div>aspect ratio,</div><div>and how large your control surfacesmust be..</div><div></div><div>basically the entire aircraft, and I'm sureI missed a few more !!</div>

mrbigg

My Feedback: (21)

If that the case then,a perfectly tuned engine on a plane the "seems" to have really good vertical will eventually quit pulling the higher it gets in the air. Of course the air is thinner the higher the atitude. I've witnessed engines that spin siilar RPM on the ground but one outpulls the other in the air. Similar plane weights. Engines were tuned properly also.

gkamysz

My Feedback: (19)

If the same prop is turning at the same RPM on the ground, then both engines are making the same amount of torque at that RPM. If one engine is at it's peak HP on the ground( increasing RPM results in less HP) and the other is at a point in the power curve where increasing RPM results in an increase in power, that would explain much of the difference. This assumes the engine RPM increases some amount in the air. If it was possible to measure RPM in the air, you would find that the airplane the performed better has greater RPM that the other airplane in the same manuever.

rmh

Mostly the designer takes a known quantity then modifies it based on some new idea or info
rarely if ever ,is the clean sheet design with all new numvbers a smashing success

just look at full scale

nonstoprc

My Feedback: (90)

Can a dynamometer accurately measure a RC engine's torque on the ground? 

gkamysz

My Feedback: (19)

That's is what dynos are for. However there aren't many for model size engines.

rmh

There are dynos and then there are dynos</p>

 for aircraft engines - th e most practical ,are calibrated  load  props</p>

 just bolt it on and run it up.</p>

 The  acceleration  abilities of  engines which are  for  "geared "to the  earth  are not of any real use here.</p>