RE: Sig Smith Miniplane build
 

Are we talking the same thing hereSemi-Symmetrical Airfoil isn't that symmetrical on the top and semi-flat on the bottom. It is not fully symmetrical. The smith mini is not 100% flat bottom nor is it 100% semi-symmetrical. The bottom of the wind is near flat.

RE: Sig Smith Miniplane build
 

It is cambered on the top and not so cambered on the bottom...it's semi-symmetrical. Not flat bottomed.

Don

RE: Sig Smith Miniplane build
 

Does that fall under the definition of "semi-symetrical"?

RE: Sig Smith Miniplane build
 

No. It is Flat bottom.

Semi-symetrical would be rounded on the bottom from LE to TE, only more shallow than the top curve of the wing.

Webster's Dictionary: symmetry - Balance in form, size and position of parts that are on two sides of an axis.

On a fully symmetrical wing, which isn't the argument here, the lower side of the axis would mirror perfectly the top side. On a Semi-symmtrical wing, the curve on the opposite axis does not match, but fully curved none-the-less. If it has a flat bottom, it is a flat bottom. There is no symmetry.

Semantically, an argument could be tried to define a Clark-Y (I'm stil not sure I defined the Clark-y airfoil properly, but for the sake of this conversation, I'll keep going with it.)airfoil as semi-symmetrical, since the very front 10-15% of the wing is curved. But that doesn't change the fact that the bottom of the wing is 85-90% flat. Hardly enough area to consider a flat bottom wing to almost mirror the top part of the wing. Even most trainer wings are rounded at the leading edge, that does not make them semi-symmetrical, or Clark-Y.

I think I'm causing an issue here. If anyone wishes to define a trainer wing as semi-symmetric, I would proudly offer my services to our country to allow them to keep that right! [8D]

RE: Sig Smith Miniplane build
 

Get out your plans again or look at the picture in post number 5 where it shows the lower wing plan. The datum line that runs from the center of the leading edge to the center of the trailing edge clearly shows negative camber below the datum line. The bottom of the airfoil clearly is not parallel to the datum line either. It's curved.

If the airfoil was flat bottom, the datum line would be on the bottom of the airfoil.

Plus the fact that the designer/manufacturer says it's semi-symmetrical sort of makes the point moot. All semi-symetrical means is the lower camber of the airfoil is not equal to the top camber.

Just sayin'.... it doesn't really matter too much to me, the plane flys great.

Don

RE: Sig Smith Miniplane build
 

I love discussions over insignefent details. OK,Here is a question for you. Looking at Great Planes Dazzler Kit. If you were to cut the wing cordwise and look at its profile you would see that forward of the spars and the wing appears to be symetrical, but aft of the spars the wing's bottom is perfectly flat where the top has a definate curve. So what typwe of wing is it?

hattend, for me your explination fits what I have always known to be true.

Sharpeye

RE: Sig Smith Miniplane build
 

Sharpeye22

I haven't a clue what exact wing you have. Sorry.

RE: Sig Smith Miniplane build
 

wow, i didnt think i would start an arguement over this. I guess as long as it flies good, thats all that matters.

PS
I dont think im too fond of the new fast reply

RE: Sig Smith Miniplane build
 

It probably has no real "name", just semi-symetrical.

RE: Sig Smith Miniplane build
 

"It probably has no real "name", just semi-symetrical"

ZING! http://www.rcuniverse.com/forum/js/f...sn/biggrin.gif

RE: Sig Smith Miniplane build
 

Here's a rib....

RE: Sig Smith Miniplane build
 

Looks semi-symetrical to me

Don

RE: Sig Smith Miniplane build
 

It's time to let it go and move on.

RE: Sig Smith Miniplane build
 

Have ordered a Supertiger G-51 with a Bisson Pitts for my Smith Mini (or soon to be - still in box form). Should be here anyday....construction may start sooner than expected.

RE: Sig Smith Miniplane build
 

rc_wings
It should be a real powerhouse with the ST51. Do you expect to post your progress here? Would be great to see.

RE: Sig Smith Miniplane build
 

Will do Rick. Have found lots of good info and tips here, so will gladly share my progress. It will likely start off slow, but later in the year will ramp up on the build. Can't waste summer in the hobby room building when should be flying. Also just got funding from my "accountant" to renovate the hobby room (yippee....) so it may slow down the progress a bit on the smith.

RE: Sig Smith Miniplane build
 

Well I can't take the pressure anymore and have to start the mini! Engine came in and picked up muffler today. Time to get to work and will keep ya posted on my slow progress.

RE: Sig Smith Miniplane build
 

rc_wings

I'll be hanging out on here as you go and I am looking forward to your build. Are you still going with the ST.51? Did you end up with a Bisson muffler?

My "Smith" has been sitting in semi retirement ever since the aileron linkage broke. I am seriously considering pulling it out and doing some mods. One of which would be to put a ST.51 in it simply because I have a new one sitting unused and the OS45FSR that is in my "Smith" is tired. If I get so motivated I will also modify aileron travel and change up my linkages to get some mechanical differential in the ailerons. Along with that, It is so old I will set the plane up and check everything with an incidence meter and realign as neccesary.

RE: Sig Smith Miniplane build
 

Hi Rick,

Yes I did get the ST-51 and the Bisson Pitts. The fit will be close from the fins to the cowl but suspect there will be enough room not to have to cut a hole. My only dilemma now is which way to position the carb. I think if I position the needle down and elongate the holes slightly for the muffler pipes and the needle I may be able to remove the cowl easily without removing anything additional to the prop and spinner. Not too worried at this point but did have me scratching my head last night while positioning the motor different ways looking for the best option. Will know better once the fuse is framed and the cowl can slide on. The linkage may be the problem as it may bump the top of the cowl.

I have to say am really looking forward to this build. I have had the kit for many years but have always had other projects come up before it. I have built quite a few planes from "kit" form, but the last 2-3 years have been rather hectic with work, kids, and life in general (same story for everyone I guess) so reverted to a few electric ARFs. They are nice, but I had almost forgotten the high I get from seeing and flying something that I constructed entirely myself..........until this spring. I have a C.G. Sukhoi which I am ashamed to say was on/off for about 12 years for various reasons. Other projects were completed within so I don't feel too silly (am slow...but not usually THAT slow [:o] ). However, finished the Sukhoi this spring and it turned out amazing...almost worth the 12 year wait :D. Flying it for the first time was a dream, and without ANY trim changes required! Engine still being broken in and working on getting the right prop combo for the Webra 1.20. Needless to say am really anxious to get started and see the SMP take shape. Hopefully fly it next spring...or maybe even earlier.

Back to the SMP - It seems that it has a tendency to pitch up. Some suggestions have been made, but not sure which one may be the best option: Offset the engine down slightly, or change the incidence in the stab? Any recommendations on which would be better and amount required? Or just build it as per plan and compensate as required in flight as most have done???

As for your SMP.....keep us posted on the engine refit and performance as am very interested.

Marko

RE: Sig Smith Miniplane build
 

Usually with a bipe, negative incidence is put into the top wing top compensate for this problem.

RE: Sig Smith Miniplane build
 

Thanks ilikebipes. Have you experimented with the SMP to determine how much negative incidence is required on the top wing?

RE: Sig Smith Miniplane build
 

I have put 1.5 degrees down in my 2 previous Minis. It still wants to climb when you add throttle. (I shouldn't say what I'm about to, but...) I think it is a result of the flat bottom on the wing.

I don 't think that changing the thrustline with the engine will be effective enough.

This airplane flies very well as designed with the .40 2 strokes. I understand the desire to put the ST .51 in it. I'm probabaly going to do the same thing with the Mini I have framed up. But all that torque makes for ground looping nightmares! throttle into it slowly.


Everybody can crucify me for saying it has a flat bottom wing now. [sm=50_50.gif]

RE: Sig Smith Miniplane build
 

Can't find a crucifixion smiley, sorry

Don

RE: Sig Smith Miniplane build
 

So 1.5 neg incidence on the top wing + 2 degrees down thrust should get me closer to the mark?

RE: Sig Smith Miniplane build
 

Ilikebipes,

I’m a big fan of biplanes as well. ;)When you guys had this flat bottom versus semisymmetrical discussion on the previous page I left it alone. I will still leave it alone as to what this plane has. [:o]Everyone has their own opinion.

But I would like to offer a definition of semisymmetrical. We all know symmetrical refers to the top and bottom of the rib being exactly the same. Look up the synonym in “Word” and you will see words like (balanced, even, equal and proportioned). In this case semi means…Almost……partially. If you type semi in “Word” and look at it’s synonyms you will see (half, partially, partly) with the antonym being (fully). So, semisymmetrical in the reference to the rib shape of an airplane wing could be broke down to - - partially proportioned. Or even partly symmetrical could be used as a definition.

Does that mean even though this wing has a flat section in the bottom of the airfoil, can it still be, by definition, a semisymmetrical airfoil?[8D]

Also, I speculate the reason for this flat section being designed into the wing is so the wings will build flat on the table.