iron eagel

I am building a Sig Something Extra one of the many mods I intend to make is to fair the wing into the fuselage. It is my understanding that this will reduce the drag that is caused when you normally have with a square joint to the fuselage.

Your opinions/suggestions...
One consideration I am thinking of using is to raise the AOA of the faring at the fuselage. I am of the understanding because of the built in washout of an SE wing that tip stalls are not an issue anyhow, but this just would be an enhancement to that design, not to mention it would look good. I also intended to round of the lower part of the fuselage as another improvement to reduce drag. The aircraft will have a full cowl over an inverted engine mount as well as the vertical and horizontal stabs having airfoil shapes and no flying wires.

Why you may ask, just to have a SE that has a clean look.

da Rock

Interesting ideas, all.

There isn't going to be much room for fairings. To get a significant savings in drag from them would require they be decently large. But heck, whatever you can do is going to look kewl.

If you are interested in reducing drag, then lose the stab stiffeners. Those and the landing gear create more drag than the entire fuselage. They basically double what the fuselage creates. Oh wait, I just reread your post and you're planning that. Excellent.... Losing the flying wires is an excellent drag reduction move. Also, while you're doing the extra work, take some time and simply round the LE of the gear struts and taper the TE of same, and you'll have some drag reduction. And if drag reduction matters, then do NOT leave the wheelpants off.

You might consider placing the engine sideways. It just might give better ground handling and a cheekpiece cowling is about as low drag as possible for realistic looking cowls. Frontal area matters and sideways does that well.

You've got some good ideas. That's the beauty of this hobby. If you can think it, you can probably do it.

da Rock

I've not seen that the airplane has built in washout. And I've not seen one to know, but it's picture looks like it's a straight taper wing. Those things naturally stall from the fuselage out anyway. And it looks like a symmetrical airfoil. You do not want to mechanically twist a symmetrical airfoil. The Tower specifications don't mention washout. That'd make sense, if it is a straight taper and symmetrical.

They do mention using the ailerons as flaperons. I really don't think anyone would want to do that with a tapered wing. So that also suggests it's a straight wing.

I really like your idea about airfoiling the stab/elevator and fin/rudder. Just looking at the airplane just now..... It looks pretty, but the bracing on the tail ruins it for me. It's like fingernails on a blackboard to me. It's a cheap way to strengthen something that should have been designed better. In real life, it's usually a cheaper way to build. Or done when cantilever is beyond the ability of the mfg or the workforce.

Looking forward to some construction pictures.............

BMatthews

Iron Eagle, the SE is a full on aerobatic model. As such you really don't want to alter the wing incidence setup from the 0-0-0 setup it has already. At least you don't want to do this if you wish to retain the traits that it was designed to have.

As for the fairing go ahead if you're after it for looks. But really drag with such a model isn't a big deal. The typical size of the engine for aerobatics makes any such drag a total non issue. And if you're after speed then this is not the model you should be building since the surfaces are wide enough that if you try to go that fast it's going to flutter and destroy itself.

iron eagel

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...

After looking through the manual and at the plans again I am trying to figure out where I gotten the idea that the wing had washout....

Tall Paul

Don't remove the tail bracing wires!
The structure is poor back there.
The wing as built on the plan comes off the board with built-in washin.
And the suggested c.g. is way conservative.. 25%.. most fliers move it way back from there.
SIG took no notice of the difference in airfoil thickness between the root and tip when laying out the construction instructions.
When asked to explain, they came up with 'it improves "decoupling" ".. whatever that might mean.
I doubt wing root fairings will accomplish anything worthwhile at the speeds and manuvers the SE does.

BMatthews

Well, if you're looking for a warbird trainer that sort of doubles as a sport model then I'd say you'll get a lot of results doing what you're planning. It's still an odd choice of model given the SE's original intended flying style but what the hey. Have at 'er and all the best.

Although.... if I was looking for a warbird trainer I think I'd look at doing a sort of "Stand Way Off and Squint Scale" (SWOSS ) model that uses a more or less warbird layout. Picking a sport or pattern sort of model and adding a big scale sort of looking fuselage wouldn't be that hard to do. Something like a SWOSS Skyraider would actually be a bit cool. And the fuselage would be big enough to stick a camera into. Meh... just a thought.

A few years back a local guy had a Sig Kadet that he'd built up with a lot of experimental metal work details that he wanted to use on a quarter scale model later on. The Kadet came out at 10 lbs... [X(] so he added an extra rib bay on each side. It didn't help much, I think I heard that he got something like 10 to 20 flights out of it before the odds called in the debt. But something similar but lighter and with gobs of washout and perhaps the Selig 8035 airfoil to help out would be an interesting heavy trainer.

iron eagel

I noticed that there are issues with the structure of the tail, that is why I plan to replace both the horizontal and vertical stabs with airfoil shapes, fully sheathed (1/32 inch), and using composites for the spars to stiffen them as well as allow for more ridged mounting to the fuselage. As an additional note, I intend to sheath the plane and use carbon fiber veil applied with dope for the finish.

I thought it had wash-in but when I looked at the manual, I did not come across mention of it.

Thanks for the hint about the COG I will have to keep that in mind.

Gee, I thought that putting fairings would be a big plus, given that thick wing sticking out of the fuselage would cause a lot of disturbed airflow along the rear portion of the fuselage. Oh well, I guess I will just have to do it because it will look good, hopefully without screwing up the design, or performance to much...

I have got to find out how this would improve "decoupling"....

iron eagel

Bruce,
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.

BMatthews

IR, I'm sure you'll learn something from the effort. It's an odd model to do that with as it's totally out of character for that sort of design but if you've already got it then go for it.

As for your Mustang I'm sorry to hear about the loss. It sounds like you may not have let it accelerate downward to restore flying speed before pulling up the nose or that perhaps you pulled up too hard and re-stalled the wing. Just guessing based on your description.....

da Rock

da Rock

It sounds like a kewl project. It's amazing how much more interest you have in an airplane you change than one you buy and fly. We got us a great hobby, don't we.

I think it'll work well to get back your touch, but don't expect it to be much of a warbird trainer. That wing is nothing like one that'd be on your average warbird.

And after noticing in the pictures that it looks like a low aspect ratio, fully symmetrical design, and hearing that it builds with washout.... and that the airfoil thickness changes from root to tip, but the designers didn't seem to notice..... and they suggest flaperons to help make the landings safer......... that sucker ought to be an amazing learning experience.

Tall Paul

The SE is nothing more than a cobbled up SIG FAZER. Uses the same wing, with no sweep where the FAZER has a straight trailing edge with leading edge sweep.
I guess the modifiers couldn't finger out how to put the wing joining tube in the FAZER wing.
I built up the kit, sweeping the wing ala FAZER, and built a profile fuselage version at the same time.
Both flew fine.
The roll rate on an SE is awesome!
Make absolutely positive the aft wing anti-rotation dowel is GLUED in place!
One of the SEs at the field was landed with extreme difficulty.... "interference" was blamed. when I pointed out to the owner and the flier that the right wing was not held by the dowel, and with aileron deflection became a very LARGE wingeron! Which of course would roll the plane -opposite- the commanded direction.
Seems the builder missed the instruction to glue that dowel in place. And it vibrated out of the right wing into the fuselage, with most of it in the left wing.

iron eagel

Thanks guys!
Guess it is time to get started on building....

iron eagel

The cowl arrangement will add approximately 16 inches in side area to the fuselage, most of which is ahead of the stock COG. While I am fairly sure this will make the KE performance much better I am concerned this may affect spiral stability. Although adding more rudder area should negate this (I hope).

da Rock

Don't sweat it. The improvement in aerodynamics is going to be well worth whatever MIGHT happen to the spiral stability. And if you do notice something, it's dead simple to add area to the rudder or fin. And it's easy to test the additions since you can simply tape card stock back there and fly.

Have you considered that the increase in side area should not include the side area of the engine. It was already there. So if you've figured the fuselage side area to be 16, then all that 16 sq.in. isn't actually additional.

iron eagel

DA your right I did add the side area of the engine above the carb to that figure and the head area would have already been there. So I am adding around 13 inches to the side area, my concern was that all of that added area is well ahead of the stock COG and may be an issue. I have planed to add about 3 square inches to the rudder already, just from what I have read about the mods others have made to the plane. I was just afraid that adding so much side area forward of the COG might cause some issues in level flight.
I got to stop trying to over think this thing...

da Rock

You know, I've lost count of the number of times guys have maidened models without the cowling. And then after a couple of flights, slapped the sucker on and flown like nothing had changed. You know, the models actually did fly as if nothing had changed. Yeah, the model had been designed (hopefully) with the cowl side area included and removing should increase the lateral stability but........... Lateral stability is an odd creature. Too much is often worse than too little. And none of those guys seemed to suffer from too much. So, taking a leap of faith.....................

Your added area to the aft vertical seems to be a quite sensible and adequate move. So............ If it doesn't work out, please have some compassion for those of us who agreed with you and don't tell us it didn't work.

And how is it possible to overthink model airplanes? We're men. We're supposed to do stuff like that. And what better thing to do while in a conversation with the wife. Actually listening can ruin a man's ability to reason. (matter of fact, she's talking to me right now.....

iron eagel

My major concern with doing this is to enhance the flight characteristics of the plane not to trash what is a basically good design. The Sig SE is a good plane built as it comes out of the box, but being an engineer it is hard for me not to try to tweak it a bit. I know the knife edge performance is lacking and a lot of builders have added fin and rudder in order to improve it, others have used Side Force generators. It seems that the real issue is the amount of side area of the fuselage and short of increasing that everything is a stop gap measure. So I decided to approach it from that direction adding the cowl and a cooling duct to increase the side area of the fuselage, hopefully without a negative impact on the overall design. But I am not an aeronautical engineer and seek the input of others with both more knowledge and experience, as to what the changes I am thinking about will do to the performance. You said “Lateral stability is an odd creature. Too much is often worse than too little.� , and I am a bit aware of this, hence my question. I have included a bit more of the sketch,and one for the rudder, so you can see how the duct for the cooling adds to the side area behind the cowl, along with the added rudder area. The blue shows the fin and rudder as on the plans the red is the added area along with where it will be tapered.

I would rather feel stupid for asking questions about what may be a non issue, than to forge ahead without the input of others and trash the build of this plane.

“And how is it possible to overthink model airplanes? We're men. We're supposed to do stuff like that. And what better thing to do while in a conversation with the wife. Actually listening can ruin a man's ability to reason. (matter of fact, she's talking to me right now..�

Gee, I thought I was the only one to use airplanes as an escape while my wife was talking…


edit to add rudder picture

da Rock

OK, the green in the image below shows just what added side area the cowl is going to add to the existing airplane. Not a lot. All that other stuff that isn't green is already there and works as side area already.

It actually takes a fair amount of additional side area up front to have much affect. Why? Because the rudder/fin side area is usually about twice as far from the neutral point as the up front stuff. Leverage works everywhere there are levers.

I'd bet the farm the increased rudder is going to more than handle whatever effect the front adds to the situation. Truth is, from personal experience, I'd want a bit more increase back there just for the additional power. Especially since the model seems knife edge challenged. PLUS, the new outline just looks better than the original.

I don't remember, can that rudder snap that airplane with just elevator/rudder? Or do you need to hit the ailerons too? If the answer is that the ailerons are needed, then if I were you, I'd double the increase back there.

If that airplane wing is non-tapered, the wing planform is a rectangle, then I wouldn't even begin to worry that the increased rudder area could cause problems.

iron eagel

This is the actual side area the duct is enclosed all the way back to just about the stock COG.

As far as I know everybody is adding a lot to the rudder, many I have seen use large counterbalances also. I had hoped that by adding to the side area ahead of the COG would be enough to improve the knife edge. Perhaps I should add a lot more rudder than I have already.

AS far as the snap with elevator/rudder I do not know I have not flown one myself, yet.
Perhaps Tall Paul could answer that question he has had several by the looks of it...

It is a tapered wing that is why I am concerned. Stock it has a real fast roll, although I have cut down the ailerons so it may not be as responsive in roll. Although I am setting up the ailerons on pull/pull so I can mount the servos 8 inches further inboard than stock to make the wing tips lighter, and keeping the most mass close in to the roll axis of the plane.

perhaps this view will help

da Rock

The actual side area of the airplane without the fairing and duct would be what's in the included picture. When I first looked I thought you had a pipe in there so I included one. The more I look, the less I think you have a pipe on the original. No big deal, what is important is that lots of those airplanes are setup with the engines sticking up and some with them down. Either way, the side area of the engine is side area and does what side area does. And in that area, you're really not adding a heck of a lot more side area with the cowling around the engine. Yes, the duct will be adding side area, but it's in an area behind the engine that would see a heck of a lot of disrupted air without the duct there.

BTW, lots of speed models of all types ran streamlined cowls up to engine's head. They went straight back about about twice as far as they went forward. They disrupted the air appreciably less than the dirty engine shape and were very sufficient at what they did. Nobody chose to extend them with a duct. I'll see if I can find a picture or two of my old models that used those cowls.

I would suggest that the duct isn't needed unless you plan to use a pipe or muffler. And suggest the duct isn't needed even with a pipe. And mention that enhancing the cooling of an engine can be a bag of worms. If you have too effective a negative pressure at the exhaust, it is entirely possible that the engine will run too cool. And will give you fits because of that. Make sure to keep the ratio of intake to exhaust around 1.5:1 no matter what the rear of the cowl/duct looks like.

OK, tapered matters. It probably will snap nicely. And it's stall characteristics would play against a loss of lateral stability. But my experience is that it won't be much. And my feeling is that your cowling isn't going to be anything like a yaw stability problem.

I'm really looking forward to hearing how this works out. These discussions offer almost as much learning and fun as doing maidens on other guys airplanes.

iron eagel

Thanks for the input da...
The fun thing about this hobby is what you can learn about aerodynamics in the pursuit of building the "perfect" airplane...
And over the past years, I have learned a lot from reading this forum.


I have the cooling intake exhaust ratio set up at a 1.4:1 ratio as per the section of Andy Lennon's book that talked about cowls.
One comment he made was about the Hawker Hurricane cooling setup and how it was designed to add thrust while in flight. That and some of the examples he used suggested that you might be able to design a setup, where as best as I grasp it you have a thermal engine. Hmm interesting.... That is why when you look at the side view of the ducting a pipe springs to mind, or perhaps a rocket combustion chamber and nozzle. Yea I know really a reach...
With the four stroke it would be very easy to pipe it with off the shelf components. The stock exhaust could be easily modified to be piped, and to be honest with you I am still bouncing back and forth on which engine to use. I have an OS 70 four stroke, and an OS MAX 55AX, they both are almost identical in weight, size and performance, and it would be neat to really go full out to make it look as sleek as possible. All this not for speed but but having a very clean airframe to get the best flight time out of a tank. Not to mention having a plane that looks cool, a really nice fun fly maxed out. Why just because you can do it....
And given the broad envelope I want the plane to be able to fly in, a neat experiment if nothing else.
I'll be sure to give a report on the results...

P.S.
I am going to see if I can get one of our more experienced pilots do the maiden. lol

da Rock

Hmmmmm......

Where exactly is Middleboro

iron eagel

About a 45 min ride south of Boston, near Cape Cod, or 10 minutes from King Field (KTAN) Taunton MA. Almost due west of Plymouth and the rock...