Can anyone tell me?Does a nitro motor have to have an off set just like an electric motor?To the best of my knowledge,an electric motor has to have a 2-3 down and a 2-3 right degree mounting.Is this the same for nitro?

Yes. You are supposed to do that. I don't really worry about it too much and I have never had a problem. Now if you are putting the engine in a high performance 3D areobatic plane. Then you might need to worry.

Hold on there not so fast....the off set might be build into the firewall already and it could be hard to see....and depending on the airplane...the off set could be different...
Read your instructions carefully...if it doesn't say anything about an off set then it's already built in...or not needed

What i have are used trainer planes that have already been built.The problem is i dont have the build instructions to determine if the off set is built in or not.I guess i will have to tinker around a bit to figure it out.Thanks for the responses.

Originally Posted by ramdriver4

What i have are used trainer planes that have already been built.The problem is i dont have the build instructions to determine if the off set is built in or not.I guess i will have to tinker around a bit to figure it out.Thanks for the responses.

Built in offsets are detectable just by looking with your eyes.

Zor

Then you should be able to see the offset you may have to turn the plane over to see it...
Remember the plane has probably flown already...so if it were me I'd mount the engine and fly

without purposely hijacking this thread, what does offset do? why have it?

Part of the trim process for airplanes that need it.. Generally trainers and shome low wings with semi-sym airfoils.. I beleive mid wing where everything is in line with symetrical airfloils.. it's not required but I couild be wrong.
Right thrust counters the torgue and corkscrew type airflow from the propeller as it moves back to the tail forcing the tail right and the nose left. when looking from behind. Down thrust is required when under power as some planes will climb otherwise.

Anyone who wants to chop apart what I said here please do...it's just my current understanding of it.

Thermalin and all readers,

Originally Posted by Thermalin

Anyone who wants to chop apart what I said here please do...it's just my current understanding of it.

Thermalin _ _ _ chopping apart what you said (wrote) is the last thing I wish to do.

I will simply express my own analysis of what is going on based on my own understanding.

Originally Posted by Thermalin

Part of the trim process for airplanes that need it.. Generally trainers and shome low wings with semi-sym airfoils..

I think we could say "all models do need thrust line orientation (up, down or side). In some cases of model physical overall shape the need may actually have a value of zero which is equivalent to say there is no need for up or down or side thrust.

I beleive mid wing where everything is in line with symetrical airfloils.. it's not required but I couild be wrong.

I wonder what is implied by "everything is in line" .
There is 4 aerodynamic forces existng in flight;
Weight acting at the CG (Center of Gravity).
Thrust from the propeller pulling the model and giving it airspeed.
Drag which opposes the forward motion.
Lift fom the main wings and horizontal tail surfaces.

The fuselage may also contribute to some forces in any directions due to its shape. It usually is symmetrical seen from top or bottom and if it is not like a banana any side directed forces would cancel each other. In a vertical plane the fuselage is rarely symmetrical and some resulting forces may create positive lift or negative lift and even some torque trying to rotate the model along its lateral axis (changing the pitch attitude).

Right thrust counters the torgue and corkscrew type airflow from the propeller as it moves back to the tail forcing the tail right and the nose left.

As we look at the model from behind the tail _ _ _ or as the pilot is looking forward _ _ _

The propeller is turning clockwise and the blades have drag it tends to rotate the fuselage (the whole model) counter clockwise (CCW).
The corkscrew of the propeller blast hitting the vertical tail surfaces partly counteract the left rolling tendency due to the propeller drag because the vertical tail sufaces are above the longitudinal axis (rolling axis). It does however create a yaw torque because the vertical surfaces are way behind the vertical axis (yaw axis).

Some amount of right thrust trying to pull the model to the right can compensate for the above mentioned left yaw. As the airspeed is changed due to power setting this compensation may vary. Note that the airspeed is not always due to a power setting like in a dive.

So the right thrust angle setting is a compromise. It does not at all times exactly counteract the left yaw due to the propeller corckscrew wash.

when looking from behind. Down thrust is required when under power as some planes will climb otherwise.

The normal flying technique is to control speed with the nose attitude (pitch control) with the elevators and the rate of climb or descent with the power setting.

Many fliers wish to control speed with the power setting without creating a rate of climb. Of course reducing power beyond a certain amount will inevitably result in a rate of descent as the angle of attak self-adjust and may result in stalled wings if the nose attitude is not conntolled with pitch.

Setting a nose down line of thrust help to create a lower nose attitude with an increase of power thus allowing a higher airspeed without automatically creating a rate of climb. Again it is a compromise.

These yaw and pitch can always be compensated more accurately by the trim settings from the transmitter.

Voila _ _ _ the way I see any reason to use side thrust or up and down thrust.
I can see some advantages in a training model for the beginner learning how to trim his model and how to fly straight and level, making level turns (approximately level) and learning with a model in which the design settings are unknown.

Like for what power setting and speed was the decalage set for that trainer ?
Was it designed and built for normal response to the power setting or else ?

If it is an RTF (BNF) where was the CG set ?
If it is an ARF where is the CG due to the installations made by the user ?

All factors that affect the behavior of the model in flight.

All part of what makes this hobby so fascinating and so addictive.

Enjoy your model while playing with thust line and CG location and even the decalage angle wings to stabilizer.

and have lots of fun and a few frustrations

Zor

Without typing an essay, if your model doesn't have offset built in, I wouldn't worry about it.

Get an experienced pilot to help you. He can make suggestions, if any are needed, after he sees the model fly.

Very few of my models have side, or down thrust. As stated earlier, it depends on the individual model.

What Tom said about the individual model, but I would add; individual model versus power plant. We tend to WAY overpower our models, with the result that more offset is needed.

Les

ok cuase its pooring outside and I'm bored, I will try and simplify an answer!

ta start with most planes will fly without "engine off-set"

an old school,simple set of numbers was 3 deg's rt and 3 deg's dwn!

off-set refers to the angle of the propshaft, to the angle of the thrustline!

becuase a prop does not give linier thrust, most precision arobatic airplanes, use an off-set to aid the airplane to track strait, without compinsating for yaw cuased by the tourqe of the engine!" or motor for you electric guys, "

as noted earlier, the engine should be mounted square to the firewall!(most the time, I did have an old ARF that came with washers on the left side of the motormount, giving it right thrust, plane never realy flew that great!)

most manufacturers will have built in thrust at the firewall if the airplane needs it!

Originally Posted by whiskykid

>
>
off-set refers to the angle of the propshaft, to the angle of the thrustline!
>
>

Think again _ _ _

The propeller shaft IS the line of thrust.

Zor

Originally Posted by Zor

Think again _ _ _

The propeller shaft IS the line of thrust.

Zor

if that was the case! you would't need ta off-set the motor!

if that was the case! you would't need ta off-set the motor

Without wanting to start a mud flinging contest......The above statement is incorrect.....

The propeller shaft IS the line of thrust

This statement however, is correct. Explanation in simple terms:

The propeller is mounted on to the propshaft exactly perpendicular (90°) to the shaft. As the prop spins, it creates thrust straight backwards from the propeller, which is parallel to the propshaft. Fact...It does not matter which way the engine is pointing, the thrust is always parallel to the propshaft. EG: you could mount you engine pointed straight down, the thrust from that prop will go straight up.....extreme downthrust.

When you offset the engine, the degrees of right thrust or down thrust indicates the angle between the propshaft and the longitudinal axis of the fuselage. That is the important factor.

Now, on to the reason for needing downwash/or even upwash sometimes. It all depends on where the "center of drag" is located. For most aircraft, the wing is draggy part of the airplane, drag is byproduct of lift (basic aerodynamics) For example, lets take a Kadet Senior trainer. It has a big, thick, draggy wing, and it is located on the top. So, in flight, picture a small "parachute" attached to the top of the airplane, this tends to pull back on the top of the airplane, making it want to pitch up. Since the engine thrust line (propshaft) is below wing be a fair bit, the more throttle you give it, the more it wants to pull the bottom half of the plane, and therefore the nose pitches up. Therefore, the Kadet Senior's and Seniorita's have a substantial amount of downthrust built right in to the firewall.

Now, we can apply the same principle to a low wing plane. The wing on the bottom will want to make it pitch down. Therefore less downthrust, or even upthrust is needed. The reality is though, most low wing airplanes are higher performance, and have less draggy airfoils, so on many of them, zero degrees of up/down thrust is good enough.

Another factor in how much down/up thrust is needed has to do with the engine placement. on the nose, on the tail, a pylon above the wing, all factor in to the design. Like Zor mentioned earlier, there are a bunch of other factors too, like CG, incidences and so on.

As far as right thrust, well, that has been talked about, torque, P-Factor, spiral slipstream....etc.

SIDE NOTE:

I wonder what is implied by "everything is in line"

Simple Zor, the engine thrustline, wing center line, and horiz. stab are all centered on the fuselage longitudinal axis......eg: Yak 54, many control line stunt designs.