iron eagel

I am about to start the build of a Sig Something Extra, during which I plan on making several modifications.
The first one is to build the Horizontal Stab and Vertical fin as airfoils and eliminate the guy wire supports. With the flat slab surfaces I can see where they may be needed to stiffen up the tail feathers. I feel that I can build fairly ridged airfoils that should not require the additional support of the guy wires and eliminate some drag in the process.

Do you think that they are needed when using the airfoil shaped surfaces? Your thoughts/advice?

After having read several of build threads here I am going to increase the size of the rudder and elevators. As far as the rudder I am thinking of adding about 3/4 to a inch to the overall width. Now for the elevators I am thinking along a 10/15 % enlargement of area. Using both a larger counterbalance and a bit more depth. Your thoughts/advice?

I am also going to eliminate the cheeks and use a full cowl with an inverted engine mounting. The exhaust of the engine heat will be located near the leading edge of the wing. One of the major reasons for the cowl is both to reduce the drag and to increase the frontal area for better Knife Edge performance. Your thoughts/advice?

Also I plan to to add fairings to the wing fuselage joint area. For this I was thinking of using 1/2 to 3/4 inch radius. And add about 3/4 of an inch to each wing by adding horner style wingtips, the thought here is to reduce the chance for aileron flutter,as well as reduce the chance of tip stalls at lower airspeeds.
Your thoughts/advice?

reincarnate

Post your pictures. This is one of my projects this winter also. Sounds like you are doing about the same as I want to on mine.

iron eagel

I intend to post photos when it hits the bench this coming week. I have tomorrow off and will probably going to start on it then, unless the weather is nice enough to go flying.

iron eagel

Well tonight I actually started work in earnest. The first thing that hit me as I was separating the plywood ribs from their sheets and labeling them was the weight. W1, W1A and W2 were very heavy in my hand. I set them aside and continued to separate the rest of the balsa ribs from the sheet. After I glued up the spars with their doublers I pulled out the digital scale and weighed the plywood parts. They weighed a total of 4.8 Oz. Now I am doing a lot of modifications to this plane one of them being that it will be sheathed, and then finished using carbon fiber veil applied and then finished with dope. By doing so I hope to gain some strength without adding a lot of weight to the finished airframe.
It is going to have hard points on the fuse for carrying both payload and weight, one reason is for utility purposes and the other to work on my skills flying a plane with high wing loading.
Now with this having been said we go back to the weight thing. I want to maintain the flying weight target of this plane at the design range of 4 to 4.5 lbs. That is a total weight less fuel and payloads, so I have a 64-72 oz. range. The engine I am going to use (OS 55ax weighs a total of 18.6 oz. So let’s take that right off the top that give me 45.4 to 53.4 oz left for the airframe, servos, receiver, landing gear, and battery. So now if we look at that 4.8 oz we can see that that is roughly 10% of my total remaining weight.
I figure I can lose some of the “slab of wood� by adding some lighting holes to the ribs. So I marked them off tonight and will drill them in the morning on the drill press.

iron eagel

Know the old adage measure twice cut once?
Well save myself some problems by just doing that...
Had I just drilled out the hole as I intended I would have just missed the hole for the wing dowel used to prevent the wing from turning about the Spar Rod. Also by double checking it gave me some time to map out a better idea for reducing weight of the components.

Alex7403

Paul congrats for the new project.

In my opinion, don’t drill too many holes because a hole is a point of stress concentration, from my experience drilling holes for weight loss is a lot of work for a very small gain.

Alex

David Cutler

I 100% agree, especially in the two ribs that hold the mounting tube and are therefore very high stress points. Take weight of the tips, for instance, by all means. There is at least as much meat to take off there and they are not points of high stress. It will also have the effect of reducing the interia when rolling which can't be a bad thing.

-David C

iron eagel

Alex and Dave,
I have the same concerns as you regarding removing some of the ply from the root ribs. But if you noticed the markings on the photos above, I have allowed a lot of "meat" to remain adjacent to the high stress areas. Also rather than using monocoat or plastic covering I am going with a fully sheathed wing covered in carbon fiber veil (tissue .02 oz./sq. yd. ) and am looking at that to form a stressed skin to add overall strength to the build. Now you mentioned the area adjacent to the wing tube I have a question about this I did not note any mention about filling the area between the wing tube and spar with shear web or balsa. I would think that you would want to tie the spar as directly as possible to the wing tube possible. I intend to fill this area with webbing anyhow to maximize the bond of the spar to the wing tube. Another critical area you mentioned is the dowel socket, where I am going to use fairings or fillets between the wing and fuselage, the load on this dowel should be reduced by a large percentage (I hope). One other change I am making to the wing is to sub. a 1/4 X 3/8" rear spar/Aileron mount notched to go around the rear of the ribs, instead of the 1/4 X 1/4 butt joined spar/aileron mount called for in the plan.

Now off to the shop to do some actual work...

David Cutler

All good points.

Also, if I remember correctly sheet balse is stuck over the two tip ribs just to finish them off. I see no reason why that shouldn't be left off completely to reduce weight.

-David C.

Alex7403

Hi,

You intend to put there a very strong motor, don’t be worried by weight, it will rocket up.

As for stress, general idea: mechanical stress treated best if you spread it, instead of one point better to spread it onto an area.

Like what fiberglass and epoxy is actually doing is spread it into an area.



Alex

Alex7403

I agree with David all good points.

I was thinking about it….
When I got my first under water fishing arrow rifle, 70 cm, total 6 ft range, I had to try the rifle and all my apartment got damaged, everything got broken a little bit….

Did you get a new drill?

Don’t sweat about the holes, Just keep the drill off the plane.

Just joking, my most usable drills are hand drills because of that reason, most damage happens to my planes by me not while flying.

Alex

P.S. hope i'm just joking, just got my first dremel...

iron eagel

Hi Alex,
Lol. On of my drills weighs about 100 lbs it would mash the thing into toothpicks....

No I did not get a new drill, as a matter of fact the newest is about 15 years old, the oldest is about 80 years old. Although I have a cordless dremel that is only 3 years old, with the right angle adapter it is one neat tool no cord to drag around.
There is an old axiom regarding airplanes in general, "With enough horsepower you can make a brick fly."
Now with the OS 55AX I could push the weight up around 7 pounds or higher and the plane would fly. But by keeping the weight down I will get far better performance out of it.
Any time I build a plane, be it a kit, or my own attempt at design, I have 3 goals, stronger, lighter, faster. That will give me the best performance for a given design. On of the worst parts, for me, being an engineer, I can not ever build anything without trying to improve it. I could build it straight out of the box and it would perform quite nicely give the motor I am using, but I can not resist the urge to tweak it.
I have used fiberglass and epoxy and like what you can do with it, but now given what I want to do in the next few years is to experiment with both wood and composite combos to see what I can come up with....
So bear with me a bit....
This is all a science experiment....


Have you ever looked at this website: http://www.airfieldmodels.com ?

P.S.
I do the worst damage to my planes flying them, done a lot of gopher hunting, so to speak.
Over the years I have found that flying is easy, it is not hitting the ground, that is hard....
And I not even going into dumb things that you can do shooting...

iron eagel

Ok so here is an update:

The original weight of the ribs W1-W2 was 4.8 oz, after drilling out the ribs as drawn they now weigh 3.3 oz. That is a savings of over 31 % in the weight of these 6 components. Originally the weight of the ribs for the wing panels would have been 6.8 oz, now we are looking at the component weight total being 5.5 oz I would not call that insignificant at all. Total time for drilling cutting and sanding was less than ½ an hour, not bad pay back, and just here I have more than compensated for the adding of two HS-81 servos for the flap function on this build.

David Cutler

Flaps?

The wing on a SSE is so efficient it's possible to land at almost zero ground speed with a slight headwind.

It's a real floater if you want it to be. I wouldn't have thought flaps would have any use at all.

-David C.

iron eagel

David,

The quote from below is from the aerodynamics forum regarding this build.
here is the link if you are interested:
http://www.rcuniverse.com/forum/m_6676829/tm.htm

"Bruce,
It is mostly for looks, I know that the overall reduction of drag probably will not be all that much of a change, with the exception of the support wires on the tail. I am not looking for high speed performance, I have a one of Mike Connors' "Screamin Demons" for a high speed bird, just cleaning up the plane a bit. I had hoped that just increasing the AOA of the faring at the wing root would not cause degrading of the overall performance. I intend to use a 3/4 inch radius on the farings from the wing to the fuse.

I had also thought about adding horner style wingtips, perhaps not that good of a idea...
It's just that those big blunt wingtips do not look all that great, perhaps a better idea is just to make them tapered and leave it at that.

I have started a posting in the kit build forum but have not added to it yet, as I am trying to work out all the details of changes I hope to make. Among the changes planned in addition to those above, Adding 10-15% more rudder area and where the wings will have the wingtips added to the span I wanted to enlarge the horizontal stab and elevator by the same percentage as I am adding to the wing area.

I had thought about cutting down the ailerons at the root and adding flaps, I am not all that concerned about roll response that I will lose by doing this. I also am going to add hard points to the fuse so I could add payloads or weight to the finished airplane. I hope to use this plane as a warbird trainer it has been a long time since I had flow a plane with high wing loading and by adding weight at the COG I could vary the wing loading to get the feel of flying a warbird again without trashing one in the process...

The main reason I had considered mounting the engine inverted within a full cowl and it would be very easy to make the exhaust for the hot air under the main fuse behind the cowl. This exhaust would end right about the LE of the wing, this will add more side area ahead of the COG and should enhance the Knife Edge performance...
A couple of months ago I slammed a thirty year old TF Mustang into the ground. Not even the motor survived I'm not to sure about what happened, it may have been a high speed stall. Lost control and got into a spin up high, stopped the spin and when I tried to pull up the nose came up and the plane continued down nose high till it hit the ground. Hence my wanting to try something else before I trash another old plane still knocking the rust off.

The main reason for the SE is that I have it and it is designed for more performance than a trainer would be. I have a brand new OS 55AX I plan to put in it so power to weight should not be much of an issue.

I hope to keep the basic flying weight as close to the 4 lb figure as possible so as a sport plane it will still perform, and by varying the wing loading I may be able to see how it reacts with more load."[/font]

Perhaps this might give you an idea of the purpose of this build.
Also each year we have a fun fly and this plane would be able to perform all of the events well up to and including the bomb drop, using the hard point mounts for payload.
This year I a going to fly in it rather than CD.....

iron eagel

Well not content with just lighting up the plywood components I also trimmed out the balsa ribs the same way. The end result was I lost another .6 oz total weight savings thus far is now 2.1 oz, 1/8 of a pound reduction thus far. With all of the modifications I plan on the plane, and the fact want to keep the weight as close to the original spec as possible, trimming weight wherever possible is a must.
One of modifications, adding flaps, has two consequences. The first is the added weight of the second servo, and the other is having to relocating the control horn on the aileron closer to the center of the aileron. To center the control horn on the aileron this requires moving it outboard. With that new horn location that also calls for the servo location to move more outboard as well. The result of that is more weight toward the wingtip, which will in turn drastically reduce roll response due to the mass of the servo and force needed to overcome the rules of inertia that come into play. The airplane is a good design and this would clearly degrade it’s performance, not what I really want to do. So if I want to keep the performance of the plane and add the option of flaps I will have to come up with a method of moving the aileron without adding the mass of the servo outboard. Torque rods are out of the question. I could use a bell crank type of setup, but that would add a lot of weight. The solution I came up with is, mount the servos inboard and use pull-pull for the aileron control link to the servo. The components needed for a pull-pull setup are light weight, and I have the added benefit of moving the servo location well inboard from the original location. Cool, this will move more of the major mass closer to the roll axis, that is an improvement.

David Cutler

I'm intrigued.

When are you going to use the flaps?

Also, if you need flaps. why not use the flaperon control in the transmitter?

-David C.

iron eagel

Dave,
I will use the flaps when I adjust the payload weight by three pounds or so to simulate the 30 oz+ wing loading of a warbird, or I want to use the plane when STOL function would be helpful. (Like when you have a spot landing or shortest take off type of competition).
Flaperons while they do work to a degree, also increase the chance of a tip stall, due to the effect of increasing the AOA of the wingtip.

Paul

David Cutler

I agree with your logic, but have to say that a SSE has such an efficient wing that the need for flaps in any circumstance is near to zero. When landing it's such a floater that the problem is getting the thing to leave the sky!

I also reckon increasing the wing loading to the extent that it will tip stall will create a situation where it will have the aerodynamics of a brick! I have never had a model that exhibits such a lack of tip stalling or snapping when you don't want it to.

Anyhow, whatever you do it would be interesting to hear from you when you fly the model.

Please keep us informed!

-David C.

iron eagel

I have a couple of planes that when they stall they just drop the nose. Granted they are high wing trainer types, with constant cord wings, they are not high aspect type of wings, and they are light wing loading.

I have read that, with high aspect wings, flaps will significantly reduce the chance of of a tip stall. According to what I have read flaps raise the AOA at the wing root so that it stalls before the wingtips will, reducing the chance of snap. Most of my older warbird aircraft and some of the scale ones, are in the 30 oz wing load range, and do indeed fly like a brick, and you want to talk about snapping when you don't want them to.

I want this plane to be able to be fly as well as it was designed to, despite the fact that I have a whole myriad of changes I intend to make. I want to be able to adapt the plane for a number of purposes, or payloads but still perform as well as originally designed, if not better, with a bit larger flight envelope. Adding the weight of the cowl, cooling vent, wing fairings, sheathing, and structural upgrades to the fuselage and tail feathers; will be difficult to do not adversely affect the performance because of the added weight.

I intend to post the build and keep it updated until at least the maiden flights, and test have been performed.

pt40crasher

I like the kit mods. I don't know if it worth $100. FWIW, this airplane does not need flaperons or a flap mod. I have to say, I'm not sure if you picked the right model for what you are trying to accomplish. The SSE does not tip stall. This airplane has trainer like wing loading, a very low landing speed, and a totally different airfoil than what you will find in a warbird. There is no shortage of inexpensive warbird ARF's prone to tip stalling that you could buy and equip cheaper than the SSE bash you propose. By all means, do what you want to. I like your design ideas and would like to see the build, but I think there are better ways to learn to fly warbirds. Good luck and I look forward to your build. Here is my 2nd kit build SSE.

[link=http://www.rcuniverse.com/forum/m_5163755/mpage_1/key_2nd%2Cbuild%2Csig/tm.htm]here[/link]

iron eagel

The airfoil is not that close to any used on a warbird but where this is a higher performance airplane I think it will be an interesting experiment. And if the mods work out well for this airplane I can apply them to the new warbirds I intend to build. I had read your post on your SSE build it and others where the reason I bought the kit to start with. Overall it is a well behaved, yet a stellar performer, while still fairly docile if that is what you want. The problem I can not build just a straight kit, I have to try and expand on what it already can do, or enhance the performance if possible. As far as ARF's I just don't feel right flying a plane that I don't build, besides building is as much if not more fun that flying to me anyhow. And lord knows the way I fly R/C I need to enjoy building them or buying lots of ARF's ...

iron eagel

While I was cutting out shear webs last night I was thinking about the overall performance of the plane and what the modifications would have. Overall thus far it should perform about as it would for normal flight, even with the reduced area for the ailerons that would be used for flaps, because of the mass of the servos being moved inboard. But as I thought about the slow speed flight and 3/D type of flight the airplane was designed for. In hover aileron effectiveness would be severely reduced as most of the inboard portion of the aileron that would be in the prop wash, would now be used for flaps. Now the flaps are not needed for the operation of this plane so I will have to give it some serious thought.

Alex7403

hi Paul,

IMO
As for aileron effectiveness maybe we should think in terms of moment on a lever.
Sure the flaps taking surface area from the aileron, but what influence more the movement is the tip of the lever not its root.
What I’m trying to say is that near the root of the wing the aileron not influencing the roll as near the tip of the wing.
My problem was always the fast reaction of the ailerons like it flips upside down with no warning.
It will roll with smaller ailerons too.
Alex

Red B.

If you haven't tried a SSE with flaps you don't know what you are missing. IMHO flaps turns this great aircraft into a spectacular one.
Slow flight is can beridiculously slow, very steep STOL-type landings are a blast and a little bit of crow mixing makes harriers a piece of cake.
As an old time C/L stunt flier I enjoy emulating the F2B stunt pattern with my SSE, the maneuvers are a little bit bigger, but the SSE corners really well with flap elevator coupling.
Try flaps, I can almost guarantee you will like it! I have flown SSE's with and without flap servos in the wings and the difference in roll performance is minimal. With a computer radio it is easy to couple flaps and ailerons to work together as big ailerons.

Without a doubt, the flap equipped SSE is my all time favourite aircraft.