AEROMASTER RCU

WHILE BUILDING THE TOPFLIGHT STINSON RELIANT SR-9 THE OLD INCIDENCE PROBLEM CAME UP AND ON THE PLANS IT SAID TO SET IT UP WITH +1 DEGREE INCIDENCE.SHOULD IT BE THAT CLOSE? I MEAN AFTER ALL IT IS JUST A MODEL AND I DON'T THINK THAT IF YOU MISS IT +OR- A DEGREE IT WILL CHANGE ANYTHING.
I WILL SAY THAT I ORDERED THE HORIZON HOBBY DIGITAL INCIDENCE METER AND BRACKETS TO MOUNT ON THE WING AND WITH MY LUCK THE METER DID NOT WORK SO I HAD TO SEND IT BACK.
AT THIS POINT I NEEDED TO GET ON WITH THE SET UP OF THE WING SO I USED A TRANSIT TO SET IT UP AND NOW I AM WITHIN .008 OF BEING ON 0 DEGREES.
BOY,WHAT A OVER KILL !


IF YOU USE ENOUGH GLUE!!!!
AEROMASTER RCU

Mike Connor

My Feedback: (5)

If it calls for incidence there is probably a reason. I would set it close and trim can take care of the rest. It may be a difference of flying good and flying very good.

AUTiger

Wing incidence is typically determined through wind tunnel testing and is designed to minimize drag at a certain operating condition (i.e. cruise flight). It's typically determined through wind tunnel testing. and for GA or Homebuilts is usually around 2 deg. and 1 deg. for transport aircraft.

Because your model is based on the real model, I'm assuming that the wing incidence is only specified because that's what the full scale aircraft uses. Like Mike Connor said, just try to get it as close to 1 deg. as possible (if you're gonna build it, might as well build it right). Within reason, you shouldn't notice any difference in flight characteristics if you're only a degree or so off.

Bax

My Feedback: (11)

With models, a good designer will build and fly it and try different setups to see which works the best. Exact scale positioning is secondary, especially in "Sport Scale" models. Flying characteristics are paramount. The 1 degree angle of incidence of the wing on the Top Flite Stinson Reliant was determined by flight testing. A fiddle here, an adjustment there, and the model was flying as the designer wanted it to fly. Get the different flight surfaces as close to the specifications as possible, and your model will fly as intended by the designer.

One degree DOES make a difference between flying "OK" and flying "Great".

AEROMASTER RCU

THANKS FOR ALL OF YOUR INPUT (ALL OF YOU).THE ONLY THING WITH A WING TUBE AND BOLTED TO THE FUSE,YOU CAN'T CHANGE THE INCIDENCE AFTER YOU HAVE BOLTED THE WINGS TO THE FUSE,SO I AM HOPING THAT THE + .018 WILL FIGURE OUT TO BE ABOUT 1 DEGREE.
LIKE I SAID I HAD TO USE A MACHINIST TRANSIT BECAUSE MY OTHER TOOL WAS DEFECTIVE.


AEROMASTER RCU

da Rock

Actually, you can. Move the bolt hole. It's actually pretty easy.

With a round wood rasp, file the hole toward the way you want it moved. Check the incidence as you go until you've got that perfect. Then fill the useless part of the hole with anything. Epoxying in some scrap wood works. You don't have to be neat because after the epoxy cures, you clean the hole up to be nice and pretty. The wood rasp does a good job of this too.

AEROMASTER RCU

THANKS FOR YOUR INPUT

AEROMASTER RCU

Mike Connor

My Feedback: (5)

Is the + .018 inches or degrees? Not sure I understand what you are saying but raising the front or back of a 14" cord wing 1/4" would change the incidence about 1 degree according to my CAD program

Edit - Change 1/8" to 1/4"

fredsedno

Gentlemen,
If my trigonometry is still correct :the sine of 1* for 1" length is .0174 thousandths or for a 14" chord[14x.0174] which would be .2436, just about 1/4" [.250]

still not the sharpest tack in the box,Fredsedno

Mike Connor

My Feedback: (5)

Did you just repeat what I just said or am I not the sharpest tack in the box?

da Rock

Yup.
So it's probably right, right.

beepee

One degree of variance in the wing incidence will not affect flight enough to notice for a sport flyer. One degree of variance in the relative incidences of the horizontal stabilizer and the wing will make a difference. If you can vary the tail incidence, just keep its relationship with the wing consistent with the plans and you should be fine.

Bedford

AEROMASTER RCU

MIKE;
THE MEASUREMENT IS 18 THOUSANDS BECAUSE I HAVE A BRUNSON 75 H MACHINIST TRANSIT THAT WAS USED IN THE AIRCRAFT INDUSTRIES AND HAS A ADJUSTABLE DIAL IN THOUSANDS. I GUESS THAT IS A OVER KILL BUT I HAD THIS AND I DID NOT HAVE A INCIDENCE METER.

THE HORIZ.STAB WAS ZERO WHEN I DID THE MEASURMENT AND THE HORIZON INCIDENCE MOUNTING BRACKETS WERE USED TO SET A SCALE ON TO GET THE MEASURMENT.
BETTER THAN GUESSING!
AEROMASTER RCU

Mike Connor

My Feedback: (5)

It sounds to me like you have an excellent incidence meter. With fredsedno's #.s and your transit you should be able to set it perfect.

beepee,
Wouldn't changing the incidence in relationship to the fuse also change the incidence in relationship to the H-Stab? Maybe I am not understanding you.

Flypaper 2

I think it has a lot to do with keeping the fuse. centre line in line with the line of flight. Probably determined to be at cruising speed. Line of flight would be the least drag. I've seen a few planes flying set at 0 incidence and they look like they're flying up hill. I imagine wing loading has a lot to do with it too. Remember seeing movies of B 17s flying in formation and looking out the windscreen at the guy next to you and seeing the wing incidence of his plane. Mind you he's carrying a few tons of bombs. Just a few observations.
Gord

fredsedno

Nah, I,m not the sharpest tack.
Never heard of the Brunton you mention,however, I did spend 42 yrs.manufacturing& assisting in tooling Boeing,Grumman, G.E.,Utica Forge,Pratt&Whitney, etc. Routinely worked to 5 decimal places. Sine of 1*[.01745] was obtained from Wolf&Phelps Machinists Hand Book.
As was stated above, .018 is plenty close enough.

Yup,not the sharpest tack[me],Fredsedno

beepee

Mike,

It does change the angle relative to the h stab if it is already mounted. My point is that flight characteristics are controlled more by the relative angles of the wing and h stab (and engine too, for that matter), than the wing to fuselage. That is, when we are only talking about 1 deg or so of variance.

Bedford

da Rock

The angle the wing is attached to the fuselage is called the incidence angle. The angle of the wing to the airflow that the wing assumes to carry it's load is called the angle of attack.

The wing is going to assume whatever AOA it needs to carry it's load. The tail is going to play very little part in that. It's incidence angle will play no part other than to establish the tails AOA. The tail incidence is usually built in. When the tail is moved to it's AOA the pilot will have to trim the elevator to give whatever he wants at that point. The elevator will either be straight back or not. Depends on how well the designer did his math.

If the tail's incidence isn't perfect and the tails AOA winds up off a bit, some elevator trim is needed. And the tail still works perfectly at it's primary job but usually creates more drag than it could have. The wing is going to demand a certain amount of effort from the tail no matter how the tail does it.

Trimming the excess drag out of a tail is done by changing it's incidence. What results is the tail flying with less drag, so the airplane has less drag and it's a bit faster then. When it's faster, the wing will fly with slightly less AOA. It's locked to the fuselage, so the fuselage will fly with (usually) less AOA. It's not much change and not easily seen from the ground. Larger commercial airplanes often have trimmable stabs. Look closely at where the stabs meet the fuselages on the big birds. You'll see the marks on the fuselage sides. Big commercial airplanes fly with greatly varied loads and fuel consumption (drag) matters a lot. They also design those birds to be able to configure for the least drag for special situations like takeoffs. Trim the tail for a takeoff AOA and the takeoff and climbout acceleration is better. And that matters to them.

When a model flies around with the fuselage obviously not level, the way to get the fuselage level in cruise is to change the incidence of the wing to the fuselage. If the problem can be seen from the ground, it's not going to be solved just cleaning up the tail. The wing has chosen it's AOA based on the load. Cleaning up the tail does change the load somewhat, but not by much. The wing is in control and chooses it's AOA to suit the load. And that AOA has pitched the fuselage. Fix the wing's incidence to the fuselage and the airplane flies with it's fuselage better aligned and what happens then. The fixed stab's incidence just might bring the stab's AOA into better alignment and you don't need the elevator trim. And you get less drag. And the fuselage's AOA is better and you get less drag. The engine has less to pull and the airspeed comes up. With more airspeed, the wing needs less AOA and danged if the fuselage isn't flying tail high now........ But it's not enough to see from the ground. And if you were an experienced designer, you'd have expected all that and worked out the incidences better for the fix.

incidence is one thing
angle of attack is another

beepee

da Rock,

You are quite right about wing incidence and angle of attack, but you missed the critical relationship of relative incidence (wing and stab) to pitch stability. If the angle of attack of the wing in flight is greater than the angle of attack of the stab you have positive pitch stability. There are other variables involved, of course, but this is the primary influence. Changing the relative incidence has a significant impact on stability, and because these relative angles are usually quite small, a 1 degree variance can make a very noticable difference.

Bedford

da Rock

Actually, I didn't miss, just didn't write out an entire chapter covering everything about the subject. Which is almost out of character for me, as I've been told time and again.

And that post really was only meant to bring about the proper use of the two terms, incidence and AOA. Not to cover everything about pitch stability.

BTW, the wing and tail can have identical incidence angles and that stab will experience a different AOA simply from the downwash. So relative incidence is most certainly relative.