kqutob

Checking the incidence of a new GSP P-47 50 arf we found a difference of 3 degrees between the main wing and the horizontal stabilizer/elevator. Could this be normal ? Could a plane fly well with such a such a flaw. We tried to ask the manufacturers but no reply .

GSNut

My Feedback: (8)

This could be normal, as the full scale P47 was not intended to fly inverted like a R/C sym. airfoil used on a pattern ship..
You will also probably find that the firewall or the engine should be set to three degrees down thrust. Or somewhat similar. It all depends on the mind set of the designer and the liberties that he takes with airfoils and what his own preferences are.

When you do the full test and trim flights the pros and cons should reveal themselves to you.
There are many good Trim Charts available on RCU and also in Scale R/C Modeler Magazine (now defunct) but Great Planes Model Company has reprinted the one from Scale R/C Modeler. A search should give you more results than enough.

Safebet

My Feedback: (12)

I am a novice. Would you explain to me what incidence is? How it can affect flight in just general terms?

I would appreciate it, thank you.

Jim V

GSNut

My Feedback: (8)

Incidence is the angular difference between the center of the leading edge of the wing or stab and the center of the trailing edge of the same as in relation to a reference line drawn through center length of the fuselage. This line would then reflect the estimated flight atitude of the aircraft.
This line is sometimes called (mistakenly the thrust line).
There is also a reference line called the Ground ref. line which relates to the aircraft while it rests upon its wheels...

Each incidence is an ideal that the designer wishes to promote as a feature to enhance his design.

As there are more ideas concerning incidence in relation to thrust, drag, stall points, inverted flight, washout, washin..and etc.

I would recomend some How to design books on Model Aviation available at most Hobby Shops.
Harry Higleyl I believe has one that comes to mind. Or even a seacrh for, here on the RCU..

jbloom

I have a model that I can trim to fly straight and level at, say, half throttle. When I then give full throttle, it will climb until it stalls or I give down elevator. It's not a tremendously bad thing, as it's controllable with some more trim. But would this be a problem with incidence? This was suggested by one of my club members.

GSNut

My Feedback: (8)

I think that your fellow club member is on the right track!!

However first do you have any down thrust in the engine??

And recheck the Center of Gravity as a tail heavy aircraft acts as you described, to a point also.

You didn't say if it was a high wing or a low wing...in case of a high wing a quick test would be place a popsicle stick shim under the (or raise the) wing trailing edge at the Fuse. and fly again. It may take a couple of times and sticks to get the wing incidence corrected.

In case of a low wing the You will have to remove some of the wing saddle at the trailing edge or shim the front leading edge down to remove incidence.

You should notice a definate change in the power/climb tendency, when you arrive at your ideal incidence a more permanent fix would be in order.

jbloom

Thanks.. now for the rest of the info. It's a low wing .40 size plane. It's CG is 2.5" to 2.8" from the leading edge. At the 2.5" mark, with an empty tank, it's slightly nose heavy. I have noticed that due to a previous crash, the dowel in the leading edge was located slightly above the center line (where the instuctions say it should be). This would drop the leading edge of the wing wouldn't it? I can try the popcicle stick and see if the climb continues. But will also cut off the dowel and relocate it to it's proper position.

There is no down or side thrust to the engine mount. It's flat on the firewall.

GSNut

My Feedback: (8)

Please recheck my advice as to the P. sticks for the low wing as I had it wrong....to kill the climb on the low wing either cut the dowel off and relocate to the orginal location or trim the wing saddle at the trailing edge to remove the positive incidence...

Me bad! I most mess up on that. Sorry..
A bit of down thrust for throttle up may help also.

Jim Messer

My Feedback: (2)

Kquotb:

Here is my two cents for what it is worth. It's not gospel, but it works for me. I have designed at least fifty different models of all descriptions in my lifetime, and these are the three rules that I go by:

1A: The incidence angle for any lifting airfoil like I use, such as the Clark Y: the NACA 2418 and 4410: and the Ritz 23012 are all set at somewhere between 1 and 2 degrees positive, with a target of 1.5 degrees. At incidence angles less than 1 degree, the model can become a handfull and hard to trim. At angles more than 2 degrees, the model can balloon and will not fly as though it were on rails.

1B: If I design a racing type plane, then I set the wing at 1/4 degree positive - although most designers will set this at zero. I don't like zero-zero setups, so I cheat a little.

2: In every case, I know from the airfoil selected, where the center of gravity must be for this airfoil to perform. This is usually between 25 and 30 percent of the wing chord. Then I make sure that the balance point is exactly at that spot before the airplane ever leaves the ground. Every airplane, big and small goes through a balance procedure, and I determine correct balance when an incidence meter on the wing shows between 1 and 2 degrees positive with a full gas tank. I don't rely on eyesight as that can be deceiving.

3: I always make sure there is sufficient power to fly the airplane. This comes from experience. The engine/prop combination must fit the airplane. All engines are set at zero - no downthrust required.

Do these three things, and you will never have to worry if the airplane will fly. There won't be any white knuckle test flights, and the chances of crashing are nil. Your test flight will look like any other ordinary flight. Isn't that what you are looking for?

GSNut

My Feedback: (8)

Hi, Jim!!

Your right on !

Have the same dislike of the zero - zero set up... At trainer speeds the aircraft is always wandering and never seems to grove.

But there are some who seem to like to hold in trim on the stick...and work at flying...
I have a friend who trims to neutral then dials in down trim and then holds with up stick...sez's he likes it that way.

Well to each his own, I guess.

Ed Smith

.

Well, not exactly.

All of our Pylon racers are set up zero, zero, zero. Engine, wing, Tail. They do fly on a rail, both in the straightaway and around the turns. If the airplane was forever "Wandering and hunting" we could never control them at the speeds they go.

Ed S

Ed_Moorman

My Feedback: (1)

As I recall (and it's been a long, long time since I studied any of this) incidence is the angle of some component relative to a reference line, usually a line down the center of the fuselage. Wing incidence, stab incidence and thrust line would both be measured relative to this line. On the wing you reference to the chord line which is from the leading edge to the trailing edge, not the bottom of the wing. Positive incidence is leading edge up on both the wing and stab.

The difference in the wing and stab is called decalage, as I recall again.

Planes that have a lifting airfoil (as opposed to a symmetrical airfoil) tend to climb under full power. Your flat bottom airfoils climb the most, especially a trainer with a .46 at full power. To correct this, you need to change the incidence of the wing, stab or maybe the thrust line. Raising the trailing edge of the wing to lower the wing incidence is easily done on a high wing plane. For years I have recommended 2 popsicle sticks under the TE of a trainer.

Changing the incidence on a low wing plane is difficult unless you have a pattern plane with adjustable wings. Most of the time it isn't worth the trouble unless you really like to experiment. You can use a rat tail file and lengthen the dowel holes to lower the leading edge, then shim the LE down and fill the gap with silicone. This is usually easier than changing the whole wing saddle to raise the TE.

Here is a trick I have used in the past: add a lifting stab. if you will look at the Telemaster designs, they have lifting stabs. The idea being that as speed increases, the flat bottom airfoil causes the plane to want to climb. The lifting stab causes the tail to rise, lowering the nose, countering the climb. The plane tends to fly around tail high at speed, which I have never liked, but it does work. When I used it, I added a small spar on top the stab (1/8-3/16 square), some leading edge half ribs and Monokoted over it.

The idea is to get the elevator trim to about zero at high speed. Fly at full power and trim for leval flight. Land without re-trimming and see what the position of the elevator is. Once it gets to level, you're OK. Fixing incidence and flight characteristics is a lot of cut-and-try work, but if you like aero experimenting and learning about flight, it can be a lot of fun.

GSNut

My Feedback: (8)

Hi, Ed !

Glad you joined in...and I have no problem with Pylon Racers being set up this way. It's the beginers and intermediate flyers that must interpert what goes awry when things don't happen as they should.

I shall leave the Pylon Racers to those who can, I'm too old and short on hand/eye cordination
to fly bullets. Though I still have a couple Midjet Mustangs hung in the shop with the racing Cox .15's still in them. (About 20 Years Dead Now)!! "GO FAST AND TURN LEFT"

Now I just keep them big and below 115 mph if possible, though I probably will exceed that some with my 260 Duellist (2 - ST .90s) when completed. But will have a Second there at all times just in case.

britbrat

And yet another preference -- on shoulder wing & high wing models with flat bottomed airfoils, I prefer about 1 deg of NEGATIVE incidence on the wing, with zero, zero on the thrust line & horiz stab. I find that this results in a beautifully tracking model that has excellent inverted capability.

ballgunner

My Feedback: (1)

Ed Moorman got it right. The difference in the angle of the tail surfaces and the wing is called decalage. With most of the flat bottom airfoils we use they are set on the fuselage flat on the bottom which automatically gives 1 to 1&1/4 degrees of incidence in relation to the thrust line. If you install the engine with down thrust you are increasing the incidence. The line for determining angle of incidence is determined by the line from the center of the leading edge to the trailing edge not along the bottom of a flat bottomed airfoil.

Ernie Misner

If you have a trainer type plane that wants to climb as the throttle is increased, it's fun to mix in a little down elevator as the throttle is opened. (if you have a computer radio with that capability) My experience was that just a tiny bit would do the trick. Any more than that and the plane would want to ballon up when chopping the throttle at high speed.

Ernie

jaka

Hi!
I agree with Ed Smith (being a pylonracer myself) that all low winged sport aircraft having semi symetrical or symetrical airfoils should be set up zero,zero,zero (engine , wing , stab).
It's also vital to understand that a model aircraft should be trimed out at full speed.....always!!
Be it scale or sport doesn't matter.
When we fly our fast pylonracers at full speed (at around 375km/h) we don't stear them all the time....our airplanes are like missiles ...they are trimmed out to go straight as long as you don't do anything.They are infact very easy to fly if you get used to the speed ......

Regards!
Jan K
Sweden