I'm finishing up my Tiger .60 kit.
Before I drill into my engine mount....

Plans call for a 2 degree engine thrust.
I've bolted a 42" piece of angle aluminum in place of the prop.
I have one bolt holding the engine on and the mounts are jast far enough apart to allow me to rotate the engine slightly.
With the engine rotated to achieve the measurements in the photo, I'll tighten the one screw and mark and drill the other 3 holes.
This should give the engine the 2 degrees right thrust relative to the lead edge of the wing.

Does this look correct?

Thanks

Steve

How did you determine that 3/4" difference in measurement over 21" would equal 2 degrees of offset?

Popriv, that looks like a lot of thrust. I use a piece of string from end of prop to horz. stab and get 1/8 inch difference. Get good results. Works for me.

This has aroused my curiosity...[sm=72_72.gif]

I got the old math book out. double check my work though. I'm calculating about 3/8 '' movement on that 42'' stick. close to 2 deg. ?

I think it sounds right.

42sin(2)=1.46

I would mount the engine square in the mount. Then, I would use a craft stick behind the mount, sandwiched between it and the firewall. I think that 1 stick would get you in the ball park. Then, fly it and test it to see which way it falls off in vertical stall, and compensate that way.

Basic trimming 101

Starting with a model that has been built and balanced as per the kit instructions then it should fly quite well. Some simple trimming will help remove any minor building errors and generally take the model to a relaxing hands off type of flyer.

The following is a basic trimming process and as long as it is done in the order below it does not need to be an iterative and long drawn out procedure. Generally a couple of evenings will take you through the process.

All checking will be started with the model trimmed to fly straight and level (hands off)at a low to medium power setting. All checking will be done flying into the wind.

A couple of control facts need to be understood.
Control surfaces are more effective at higher speeds and less so at low or take off/landing speeds.
Engine thrust lines (sometimes known as the effect from prop wash) are very predominant at low speeds( landing/take-off) and are negligible at flying speeds.

Step one: Set Balance Point.

The starting balance point should be marked on the model.

Trim out to fly hands off straight and level into the wind at a low to middle throttle setting.

For a low wing aerobatic model:

Roll inverted, release the sticks and observe.
Severe dive ..... nose heavy.
Slight dive..looks good.
Straight and level..perfect.
Climb..bit tail heavy.

For a high wing or non aerobatic model.

Go rapidly to full power and observe the flight reaction.

Climb..nose heavy.
Very slight climb to no change..ok.
Dive..tail heavy

Add or remove weight as required and then repeat the test until you get the right balance point is found.
The plan balance point is usually quite conservative as a nose heavy model is sluggishly stable. As the true balance point is approached the model will become more lively and sensitive to elevator input and may require less elevator throw for normal flight. (low rate on the transmitter).

When the balance point is found mark it on the fuse as a future reference point.

Step two: Correct Thrust line.

This step is quite sensitive to the wind direction and extra effort should be made to always fly straight into the wind.
The objective of this test is to fly a shortish vertical line and observe what direction the nose of the plane falls to as the speed falls off and the plane comes to a halt.

Before taking off set the rudder at the neutral position and do not touch the rudder trim.
Trim out to fly hands off straight and level into the wind at a middle throttle setting.
Pull to the vertical and fly a half throttle vertical line with no corrections and observe.
Two things can happen:
if the model immediately starts to pull to one side then it is likely that the rudder is not straight. Go back to the straight and level flight and add a couple of clicks of opposite rudder trim (ie model pulled left...add right rudder trim) then repeat the test.
The model climbs reasonably straight and then pulls left/right etc as the speed falls to zero. This pull to the left or right is caused by the thrust line of the engine being incorrect.

To confirm this the test should be repeated a couple of times just to make sure its not the wind causing the problem. Typically the model will pull to the left as it comes to a stop. The model may also try to “fall on its back� or fall to its landing gear in combination with going left or right. The first step in correcting the thrust line is to shim the engine in the opposite direction to the way it falls. For example; pulls left then add some right thrust. It is usually best to correct the side thrust first before correcting vertical thrust lines.

With the side thrust corrected you should see a noticeable improvement during take-offs and landing overshoots. The quick application of power should now have the model tracking straight dwom the runway with no tendency to pull/roll left.

The test can then be repeated to check for down thrust correctness. If the model “falls on its back� then you need some down thrust. If it falls to the landing gear side then you need less down thrust. Unless you are planning to do hovering type maneuvers or some advanced aerobatics it is probably not worth worrying about getting the down thrust angle correct.


Step three: Aileron Roll correction.

This is a very easy test to do and corrections can be made at the field.

Climb high and throttle to idle speed.
Push down to a vertical dive give full right aileron and observe.
If it rolls axially then no corrections are needed.
If it rolls as if in a barrel then you need less 'up' aileron throw on the right side.

Repeat the exercise for the left roll.

If you have a computer radio and one servo per aileron per channel, ie left servo on ch2 and right on ch6 with 2 and 6 mixed then you can adjust the aileron travel individually on the radio. If the servo's are joined with a Y harness or a single servo is used then you will have to adjust the throws mechanically.

I have found that mid wing type planes usually do not need any aileron differential. High wing and low wing models typically need some differential so that the down aileron travel is about half of the up aileron travel.

Step four: Remove rudder bad habits.

This is not worth doing if you are flying a trainer model as the rudder on a trainer is not very effective.
Also if you do not have a radio with mixing capabilities then this step can not be done.

Fly straight and level and give full right(or left) rudder and watch.

If the plane dives then mix some up elevator trim into the rudder.
If the plane rolls rapidly then correct correct with some aileron mixing.

Remember to check and correct for both left and right rudder.


Step five: Loop trim.

Straight and level, medium power.
Pull up and do three reasonable tight loops in succession. Do not add any corrections.
If the plane tracks well but drops a wing then it is heavy on that side and you need to add a balance weight to the other wing tip.
If the plane tries to corkscrew ie each loop is progressively further left (or right) than the other one then you have a aileron that is not in alignment to the wing. If the plane tracks left then the leading edge of the left aileron is either high or low in relation to the trailing edge of the wing and is causing the plane to skew to that side. You need to correct the aileron alignment.


END

I didn't write the article, but found it and keep it handy as a reference. Hope you find it helpful.

Good luck.

Wow, Bingo.. we ought to keep that one as a sticky!!!

Instead of doing the math, I just use a cheap protractor and draw the angle on a piece of paper using the actual prop size. Then measure the distance from prop tips to the wing leading edge on the drawing and transfer the measurements to the airplane. Works well for me, but downthrust is a different story. I use a bubble levels and angle scales for that.

Popriv,

The easiest way is to use an incidence meter to set stab, wing, and thrust settings. An incidence meter is a good investment having been a great tool for me for years once I realized its true values. You can setup thrust lines using a level and a protractor albeit more difficult. Building them straight from the ground up certainly results in more enjoyable flying.

Your on the right track in getting your airplane setup correctly. Personally I try very hard to get everything setup mechanically correct first before ever going to the computer mixing. Centering the trims via linkage adjustment as much as possible to ensure the greatest mechanical advantage for the servos. Take your time use the trimming information above taking everything one step at a time. Test fly between changes being sure to take notes as to what you have changed and how much so a change can be easily be lessened or reversed. Your end result will be a good flying machine.

This is how I arrived at those measurements.

Using Illustrator I drew two horizontal lines 11.25" apart. (this is the distance from prop to LE of wing) The top represents the prop and the bottom line represents the LE of the wing.
The prop line is 42" long only because thats the length of the aluminum I'm using.


Then I select the top line (the prop) and apply a 2 degree rotation to it.

The left side of the line moves away from the LE and the right side moves towards the LE. The drawing in Illustrator is full size and I can take the measurements from it.

Looking at the engine it seems extreme to me and I dont want to drill until I'm sure.

I'll double check with a protractor and go 2 degrees off of a centerline running straight up the fuse..

steve

Steve:

You approach checks with rudimentary trig. Sin2* = 0.0349. If you multiply that by 42", you get 1.466", just under 1-1/2". Half of that is the differential on each side, so the port side (looking down) is 11.25" + .75" = 12", just as you measured. The starboard side in 11.25" - 0.75" = 10.5". That's a little more than 2*, so you might want to go 11.75" and 10.75".

If you want the prop centered on the longitudinal centerline of the plane, you need to drill the mounting holes just slightly to the port side of the firewall. You can do the math as above, just use the distance from the firewall to the back of the prop. Which probably works out to somewhere between 1/8" and 5/16" to the left of the centerline. While the math is accurate, I'd still figure out a way to clamp the whole engine/mount assembly in place, then eyeball everything to make sure it looks right.

Fred

Hey falldowngoboom,

Thanks for the check. My mounts are already mounted to the firewall so I'm not going to offset there. (Your right but I hadnt thought of that)
I made the mounts wider than the engine by a little less than 1/16" then centered the engine and drilled one hole to hold the engine in place.
This leaves a little wiggle room to rotate the engine.
I'll make a 11.75" and a 10.75" brace between the LE and the ends of my aluminum " prop ". I'll clamp everything in place and then drill the holes.

I have to check at home but I believe your numbers will reduce the amount of rotation I'm showing in my photo?

Like I said it looked like alot visualy they way I have it now?

Steve

If by "... reduce the amount of rotation..." you mean "Will the engine sit straighter in the motor mount?" the answer is yes. Think of it this way: if you have the same distance (11.25") from the LE to the "prop" on each side, in theory you'd have 0* of right thrust. The further you twist the engine clockwise (when looking down), the more right thrust you'll get. With 1/16" on each side of the engine in the motor mount, you've got enough wiggle room to adjust the right thrust as Bingo Field suggested above.

This all assumes the the firewall is build with 0* of right thrust. On a lot of kits, the right fuselage side/doubler is shorter than the left side, so there's automatically some right thrust built into the airframe. You might want to check your firewall to make sure it's 90* to the fuselage sides. I looked at the directions for the Tiger 60, and it appears that's the way Goldberg designed the firewall, and all the side thrust comes from mounting the engine "crooked" in the mount. While there's nothing wrong with that, I'd be more prone to mount the engine square to the mount, and shim the back of the mount to develop side thrust. One or two #8 washers would probably be all you need.

By the way, this is one of those deals like love, grenades, or nuclear warfare: close counts. While you don't want any left thrust, even if you build the Tiger with 0* right thrust, about the worst that happens is the plane pulls a little to the left on takeoff and vertical uplines. If you get too much right thrust, then it'll pull to the right. But anything between 1* and 2* will work, especially on a Tiger 60. As you get more and more familiar with the plane, you can experiment to see what works best for you. As Bingo suggested, you can easily put shims or washers between the firewall and the back of the motor mount to adjust side/down thrust to suit your needs.

You should end up loving your Tiger. I had one of the 40 size ARF's, and thoroughly enjoyed flying it. Let us know if you need anything else.

Regarding taking your time: One of the most difficult things for me to do was to learn to work on only 1 thing at a time. You will maintain greater consistancy in your efforts, and you will know when you are done with each step. I used to try and do 3 or 4 things at once, and it resulted in misinterpreting the results, and making many changes incorrectly. Just one step at a time, and it comes together much faster.

Tiger 60 - one of my favorite flyers. See my gallery.

Washers used to shim the mount are ok, but only temporarily. They compress the wood and the angle then changes.

http://www.airfieldmodels.com/inform...ine_offset.htm

Actually, the above website is a whole lot of great information

Amen to that... Paul's got so much good info at his site it's scary.

I drilled and screwed the engine down using this setup...
one screw drilled to hold the engine in place. 42" aluminum angle bolted in place of the prop. a 10.75" and 11.75" spacers to align the engine and then I drilled out the other three holes to get my 2 degrees right thrust.

I'm happy with it..


Steve

popliv,as long as it works and flys right, go with it. It's not that complicated

Just trying to get it as " right " as I can.
I wont know if it works and flys right until I fly it...



Next one wont be as complicated.

Steve