extra 260 engine incidence?
 

I have a miles reed extra 260 80 inch span. the print calls for zero incidence on everything but no right thrust . the firewall is built straight with no thrust built in I plan on putting a dle 55 on the girl what do you guys think? I thought I would put two degree's in it. give me your input I can always ignore it LOL thanks chris

RE: extra 260 engine incidence?
 

I always start with zero thrust and add what is needed after test/maiden flying. I want to see how the plane reacts before I start making trim changes.

RE: extra 260 engine incidence?
 

Old school standard was 2 degrees right thrust to counter P-factor. But as Gray Beard suggested if the print calls for zero degrees then go for what is called for then make adjustments as necessary. Easiest way to tell is to pull straight up vertical and see if the airplane drifts to the left. if it does then shim the left side of the engine to cause a small degree of right thrust.

Note using rightrudder trim will help your vertical drift but it will also impact other flight conditions which will need to be trimmed out. Correct the problem at the source... The plane will fly better...

Just my 2 cents and fully anticipate someone will disagree with me... But thats okay... I know what works for me...

RE: extra 260 engine incidence?
 

As already suggested start with manufacturer and design specifications and change things when you see any need for it.

Zor

RE: extra 260 engine incidence?
 

If adding side thrust after the airplane is complete then the prop is no longer on the model C/L and the spinner backplate is misaligned with the nose ring.

Ed S

RE: extra 260 engine incidence?
 

I would set it up at 3 degrees right and .5 degrees up. This will mean offsetting the engine 1/4" left and 1/16" down from center. However this is just a start to getting a good flying airplane. After setting the engine up at these angles, set the wing to .5 degrees positive. This is about 1/16" trailing edge low. the stab should be set at zero. Start with the CG at 40% from the leading edge at the root.
Activate a couple mixes. The first you want is about 1/16 to 3/32" of up elevator with full rudder deflection. The second is just a noticable amount of opposite aileron with rudder application. What these mixes are going to do is help eliminate the control cross coupling that all Extras seem to have. The other major thing is to get the ailerons set up correctly. Make sure you measure them and make sure you get exactly the same travel for both ailerons up and down. Don't assume the because the throws are the same in your TX that you are getting the same on the surface. Once that is set up the throw in about 8% differental.


Make absolutly sure the elevator is perfectly aligned with the stab. Take note on the maiden if you needed up or down trim. For down trim, move the CG forward opposite for up trim. This all should add up to a fairly nuetral flying airplane that will respond pure to control inputs and require little to no corrections on uplines.

RE: extra 260 engine incidence?
 

NoEd, It is still aligned properly.

As I wrote to add side thrust "we have to change things".

In your case it appears that you have to change the engine mount position on the firewall.

Suggest you make sure your model really need some side thust before doing such a change.

Zor

RE: extra 260 engine incidence?
 

You are correct sir. How can you not be? If you build a model with a particular thrust line and the spinner's back plate has a gap between it and the model's nose ring of 'X' all the way around, and you change the engine's offset (horizontal/vertical) how does that gap *not* change?

To argue othewrwise is testimony of inexperience....<br type="_moz" />

RE: extra 260 engine incidence?
 

Double post....

RE: extra 260 engine incidence?
 

Gee guys maybe some reserch should have been done here........................The Miles Reed Extra 260 dosen't have a nose ring!! Even so, I gave the OP dimentions to adjust the position of this engine so that his prop hub would be centered in the cowl and have the correct about of thrust offsets.

RE: extra 260 engine incidence?
 

Hi speedracerntrixie,

I wish to thank you for researching and getting the facts.

The gap change due to a two (2) degree thrust offset is negligeable.
The sine of 2 degrees being 0.03489950
The sine of 0 degrees being 0.00000000

The gap difference on6 (six) inches firewall to prop would be 0.00365504 inch
.Less than four thousands of an inch (undetectable by eye)

On a 6 (six) inch firewall to prop distance thesideways motion would be 0.20939698 inch
Less than 1/4 inch. Actually 1/5 of an inch .

You were just about dead onwith your figures.

Any difference from the 6 (six) inches used here is proportional ___ In example a 9" firewall to prop would be 1 1/2 (one and half) time the above values.

Regards from Zor

RE: extra 260 engine incidence?
 

Thanks Zor, I have built lots of IMAC type airplanes and have notes on how much offset it takes for most 50, 100 and 150cc engines to get 3 degrees. As for the adjustments and mixing, it's what I start out with on any scale aerobat. Usually gets me 90% there. Trimming an airplane correctly is a science that seems to be dying. Most of what I see is guys getting airborne at full throttle and then pushing the trims for strait and level. Some will fuss with the CG a little but thats where it stops. Most airplanes at the field are flying way below their potential. But you know my feelings on this matter from other threads http://www.rcuniverse.com/forum/js/f...wink_smile.gif

RE: extra 260 engine incidence?
 

speedracerntrixie

I knew you were not the one with a problem.
I was more concerned with something I read about the gap changing.
I can only think of the gap as the distance from the rear of the prop to the front of the engine cowling.

Less than 0.004 inch change or even up to 0.010 change is negligeable but not everyone apparently think so.

In fact a gap change of 1/16" (0.0625") or even 1/8" (0.125") while detectable by eye would not change anything about the performance of the model.

For newbees ___
Some design specify some side thrust and some up/down thrust and often these are built into the firewall structure. These orientations are aimed at obtaining some model behavior desired by the designer(s).

Many models do not use any side, up or down thrust and fly beautifully.
It is difficult to really justify their necessity.

One of their purpose is to aim the thrust line of action in relation to the CG and exert some influence with variations of power settings. They are a compromise and would be optimum for only one power setting.

I am NOT saying they are useless.
Some modelers recommend some flight pattern to determine the required amounts.
Their usefulness are mainly for contesters that have to fly precice maneuvers, precice flight patterns.

For the average Joe (like me) it does not make much difference.
I am quite happy with a well balanced model, one that will glide on its own in case of engine or control failure, and has the best chance of landing like the old free flight models.

Enjoy your flying.

Zor

RE: extra 260 engine incidence?
 

Thanks for all the replies, lots good of information to mull over. I plan on following the prints as zero zero the good news is the cowl is oval shaped on front so you will not be able to tell as much if I have to move it thanks again Chris