<div><div>have built RC planes from age 14 to 20. once i went into professional school, and residency, etc..., i have not messed with it until 3 to 5 months ago.</div><div></div><div>i recently have built a super decathlon with 89" wingspan and a saito fg 36 4 cycle engine.</div><div></div><div>i checked the incidence of wing relative to the stabilizer and it is 3 degrees (positive).</div><div></div><div>i also checked the fin position relative to the motor, and the motor is 3 degrees to right of the fin</div><div></div><div>is this ok</div><div></div><div>i know the build required the engine to have down and right thrust.</div></div>

Seems right enough to fly it for the first flight. If transitions from idle to full power result in some directional change then fine tune the side thrust so suit. Certainly nothing you measured for angles will result in any major issues with the first flight.

That sounds like a lot of wing incidence, but I've never had a Decathlon. Is 3 degrees positive what the plans call for?

Like BMathews said, it sound about right.

Not to me !
that sounds like waaaay too much incidence for a model with usable wing loading
I have done scale downs using full scale dwngs etc., and on similar planes in full scale -incidence is always excessive

looks like 2 against 2

i appreciate the input

yesterday i got the engine running.
it is a saito fg 36 gas
i got 7800 rpm with a zinger wood prop 18 x 8.

the engine ran for 50 minutes on one tank of gas
with evolution oil 20 to 1 ratio mix.

the incidence is here:

http://www.dynaflite.com/techsupport/technotes.html


however, it is confusing to me

that is why i want your help.


what i did:


i used a Hangar 9 wing incidence electronic meter.

i placed the meter on the stab and zeroed it,
then, i placed it on the wing, near to root

it read 3 degrees +

the dynaflte website reads:
stab is -3.5
wing is -2

it seems to me, these measurements are done without a electronic meter where you can zero one out

so it appears to me, based on this, that the incidence would be 1.5 relative to the other??

i had read somewhere that wing incidence should be at least 0.5 degrees, and never negative.


the other issue is that when i built the wing, i used a balsa stick, placed on plans, to give the wing a "twist", that they refer to as "washout"

however, once wing is covered and mounted, the incidence is the same at the root as it is in the tip.

i wonder if this will have an ill effect??


thanks again gentlemen for all your help, and let me know if there is are any other suggestions.

i will call dynaflite as well and ask them for their advice as well, once i hear from them, i will post it

and of course, if i post on the maiden flight, that means it flew

if you do not hear from me, that means the plane is a goner.

spoke to dynaflite
they said the 3 degrees incidence should not be a problem.

seems to me that could give me a tad bit more lift and increase drag, probably can be corrected with trim once in the air.

also

the three degrees right thrust compared to required 2 degrees, he again said, it should not be a problem.

i will trust him and see what happens.

Too much incidence will just cause the pitch trim to be speed sensitive. You might get the plane in the air and find that you don't have enough down trim to get it level, but that's not the end of the world.
There is a reason why the manufacturer might recommend negative incidence angles. The fuselage has some lift characteristics too along with the prop placement causing some up or down pitch with thrust. So that particular model may fly best with the wing and tail both negative to the datum line but positive to each other. The thrust line is also a factor obviously.

If Dick is right and the wing incidence of three degrees is too much then it'll be taken care of by you adding in some down trim during the first flight. At that point the effective angle and camber of the tail section to wing angle will no longer be three degrees. It'll be whatever the CG location demands that it be to fly level at any given power setting.

All of this stuff is not cut and dry. It's all done on a "bell shaped" curve where when you're around the right spot the minor changes have only a little effort. It's not until you stray away from ideal by a larger amount or distance that you "fall off" the top of the bell curve and are working on the steep side slopes where a little difference makes a bigger change on how a model flies and handles.

This isn't to say that you won't gain by fine tuning to perfection. Just that MOST small things won't cause a crash.

another question?
thank you all for your comments
i am considering them all.

i was balancing model, with recommended CG of 3 3/8 inches posterior to leading edge of wing.

the plane weighs 18 pounds,
and it has an FG 36 saito engine
the servos are in the rear bay

i thought this would help to balance the plane

turns out the plane is now tail heavy

i have placed both batteries as far forward as possible, '
i even built a wood upright frame for the two batteries that will rest just posterior to the gas tank.,  in this position, the two batteries are anterior to the CG point.

even then, plane is still tail heavy

i have added weights and it requires 10 ounces.  with this, the plane is level.


do you all believe that now, plane weighs near to 19 pounds
and
the dynaflite plans state weight would be within 16 to 18 pounds

can this extra weight have ill effect on plane?


thank you all very much

Extra weight will always have an effect, generally negative for an aerobat. That said, it's not like you're overloading the plane to the point that it won't fly. I'd try to move those batteries under the tank if possible to avoid stuffing lead into the plane, but 10 ounces on an 18 pound plane isn't going to kill you.

great
thank you
maiden flight will be sunday
i will keep you posted<br type="_moz"/>

For that size plane, you should add the necessary weight to bring the CG to the recommended point. On a large quarter scale plane, it is not uncommon to have to add a large amount of nose weight to get the CG in the proper place. I've seen some that required in excess of two pounds. If you try to fly it tail heavy, it will probably be it's one and only flight as it will be very hard to control. It is always better to rearrange the internal equipment to bring the CG into it's proper place but is sometimes hard to do. From your comments, I am assuming you are not a skilled flyer. If my assumption is correct, I'd highly recommend that you get an experienced pilot to give you a hand and to make the first flights.

absolutely

i have spent over 1500 dollars on this plane


my friend is experienced and we have flown before together

we both have Jr 9503 tx
and we use the trainer cord

he will take over if i am in trouble.

thanks for your advice though


<br type="_moz" />

Keep -the - speed -up
The prime cause of problems in scale stuff is letting speed drop below controllability speed.
I am assembling (as we speak), a 1/5 scale p51 which as designed , has a very limited speed envelope. Especially during landing approach
The flier is a good full scale and model pilot but STILL- this design has very non forgiving landing characteristics (especially using scale gear!!)
The Decathalon - in scale configurations, not nearly as unforgiving but still will not typically be a floater- as a model .

Update:<div>today was the maiden flight.</div><div>
</div><div>engine was going strong and did great throughout.</div><div>
</div><div>upon takeoff, plane climbed, </div><div>i then began to notice the plane kept trying to climb.</div><div>
</div><div>i adjusted the elevator trim to give it down elevator, i maxed out this trim, and plane still flew with tail down.</div><div>
</div><div>then i also noticed plane kept trying to roll to left, i adjusted the aileron trim to counter that, but even then,</div><div>
</div><div>it was a very strange flight.</div><div>
</div><div>believe it or not, i was able to land plane in one piece, only damage was one side of landing gear was bent some.</div><div>
</div><div>no other damage.</div><div>
</div><div>
</div><div>i have a lot of work to do,</div><div>
</div><div>i know there is a difference between incidence of stabilizer with the wing that is 3 degrees</div><div>and</div><div>the CG is right on.</div><div>plane was tail heavy, but with 10 ounces in the front of plane, it balances out</div><div>
</div><div>
</div><div>i do not know what is wrong, </div><div>
</div><div>any advice would help.</div><div>
</div><div>thank you</div>

hi
i flew plane today.
CG was on at manual recs,

however, during flight, it looked tail heavy

i tried to adjust with elevator trim,

this improved somewhat.

i was able to fly around a bit
but it did not fly right

kept trying to roll to left also

so i landed it

something is wrong.

one time, i saw my friend's home built coroplast plane fly, and it was doing similar thing.
he then adjusted both ailerons to be down some, i think, if i remember correctly.

Sounds like the balance is too far aft, and the air speed too slow. The wing/tailplane incidence difference won't make a lot of aerodynamic difference to this airplane. Move the balance to 1/4 the chord back from the leading edge, add some downthrust to the engine, try a prop with a bit more pitch and a bit less diameter, and place a long straight stick on the bottom surface of each of the wing tips to make sure they are are both at the same angle, and the same as or slightly less than the angle at the fuselage side. Correct as required then try again.
Evan, WB #12.

hello
i want to show you my balance

please let me know if this is not acceptable.

thank you.

from what i see, in the coronal plane balance, the right wing is lower than left.

but on sagital view of plane, it looks ok to me, or maybe tail is slightly lower,

let me know if this would account for unusual flight.

thank you so much<br type="_moz" />

Looking at your photo of the model suspended from the wing tips shows it hanging slightly tail-down. If you are suspending the model from the intended CG, then I'd say you're still a bit tail heavy. Suspending the model from above as you are doing tends to mask the actual CG point. I'd suggest that you add more nose ballast until the model is absolutely level.

You may also be seeing the effects of the greater than intended wing incidence and lack of washout. Both of these will reduce your trim speed i.e. making it appear to want to climb.

If the model still wants to climb after you have definitely balanced it to the correct CG, then you can assume it's an incidence problem.

Regarding the tendency of the model to turn left: You may find that a bit of right rudder trim rather than aileron trim will be much more effective. High wing designs such as the Decathlon exhibit an interaction between yaw and roll which causes yaw offsets to appear in the roll axis. It's called "rolling moment due to sideslip", or "dihedral effect". Aileron trim is often quite ineffective in fixing the turning tendency that you are seeing.

Dick

thank you so much for your advice.

the airplane has a rear bay where the three servos are for the rudder and elevator.

the three servos weight a total of 11 ounces.

i have added 10 ounces of weight to nose of plane,
and this is the result, the pictures you see.

as of today,
i have removed the 3 servos from rear of airplane
and i am going to place them as far forward as possible, to hopefully shift weight forward, and therefore, hopefully prevent me from having to add more wights to front.

i will show you picture of balance once complete.

now, one more question.

i checked the inidence of wings from root to tip.

in both wings, the tip is +1 degree more relative to root of wing

i also noticed
that left wing is not even with right wing when measurements were done at root of right and left wing
the difference is 1 degree.

thanks again<br type="_moz" />

One degree?
that's 1/4" difference in one foot -
IF the Leading edges are slightly lower at the tips - that's fine How are you measuring degrees?
The wing profile appears quite non critical so I would suspect just trimming it and keeping speed up, will solve most issues
a decent CG is 25% of chord -from f ront - nose up or down a tiny bit when balance testing is no problem.
Biggest problem on models such as this?
weight

bad news,

i moved the 3 servos from rear bay to front compartment,
the three servos weigh 11 ounces.

i had 15 ounces of weight under gas tank,
and another 3 ounces in cowl area.

after moving everything

i see it is maybe not tail heavy now, maybe,,

but i still have to use the 15 + 3 ounces

i was hoping i could use less weights,

i also checked that the surfaces on bottom side of ailerons and elevator were flush.

good news is that now, when i do CG test, the nose is slightly lower than tail, and the top of wing is completely parallel with the floor.<br type="_moz" />

And from what you say you have 'wash-in' at the tips, this will not help, and you have different angles from one tip to the other, thats like having permanent aileron trim. It will want to roll away from the highest incidence, and yaw towards the highest incidence. Heat the covering and warp the tips to a degree or two negative compared to the root, and make them both the same. Use the 'Aileron/Rudder' mix in you transmitter, initially 50% rudder with aileron. You may be able to tweak the struts to help hold the wing straight. Move everything inside forward to achieve 25% chord balance. The set up you otherwise describe is for a 'Speed Stable' airplane, that is, at any selected power level there will be an elevator trim setting and airspeed that will correspond to 'Straight and Level' flight. Once found, any variation of power will affect altitude, and any variation of trim will affect airspeed, provided you do not change both at the same time. This is the easiest way to learn to fly, later you will be able to switch off the A-E mix and learn to co-ordinate rudder and aileron to turn without slip or skid.
Evan, WB #12.

Why build a plane with the highest strength to weight materials possible, then add a ton of lead to the finished product....?

Might as well build the plane out of heli-arced aluminum tubing.................