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Yet another Sig Something Extra Build - 11/18/2007 10:15:45 PM   
iron eagel



Posts: 1137
Joined: 7/15/2004
From: Middleboro, MA, USA
Status: offline 		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?


_____________________________

The Wrights never crashed, they only had hard landings. I 've had some hard landings myself. AMA EAA AOPA revver #185
       Post #: 1

RE: Yet another Sig Something Extra Build - 11/18/2007 11:23:10 PM   
reincarnate



Posts: 765
Joined: 10/1/2006
From: Columbia City, IN, USA
Status: offline 		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.

_____________________________

Are the wheels supposed to fall off when you land? No? How about the engine?

(in reply to iron eagel)
       Post #: 2

RE: Yet another Sig Something Extra Build - 11/19/2007 2:51:02 AM   
iron eagel



Posts: 1137
Joined: 7/15/2004
From: Middleboro, MA, USA
Status: offline 		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.

_____________________________

The Wrights never crashed, they only had hard landings. I 've had some hard landings myself. AMA EAA AOPA revver #185

(in reply to reincarnate)
       Post #: 3

RE: Yet another Sig Something Extra Build - 12/1/2007 5:49:25 AM   
iron eagel



Posts: 1137
Joined: 7/15/2004
From: Middleboro, MA, USA
Status: offline 		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.


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_____________________________

The Wrights never crashed, they only had hard landings. I 've had some hard landings myself. AMA EAA AOPA revver #185

(in reply to iron eagel)
       Post #: 4

RE: Yet another Sig Something Extra Build - 12/6/2007 5:52:11 AM   
iron eagel



Posts: 1137
Joined: 7/15/2004
From: Middleboro, MA, USA
Status: offline 		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.

Attachments
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_____________________________

The Wrights never crashed, they only had hard landings. I 've had some hard landings myself. AMA EAA AOPA revver #185

(in reply to iron eagel)
       Post #: 5

RE: Yet another Sig Something Extra Build - 12/6/2007 6:16:07 AM   
alex7403


 

Posts: 550
Joined: 6/29/2004
From: New york, NY, USA
Status: offline 		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


< Message edited by alex7403 -- 12/6/2007 7:04:11 AM >

_____________________________

measure twice cut once, again i cant believe i didnt learn it yet....

(in reply to iron eagel)
       Post #: 6

RE: Yet another Sig Something Extra Build - 12/6/2007 6:33:59 AM   
David Cutler



Posts: 2163
Joined: 9/13/2002
From: Los Angeles, CA, USA
Status: offline
quote:

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.


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

(in reply to alex7403)
       Post #: 7

RE: Yet another Sig Something Extra Build - 12/7/2007 1:36:18 AM   
iron eagel



Posts: 1137
Joined: 7/15/2004
From: Middleboro, MA, USA
Status: offline 		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...

_____________________________

The Wrights never crashed, they only had hard landings. I 've had some hard landings myself. AMA EAA AOPA revver #185

(in reply to David Cutler)
       Post #: 8

RE: Yet another Sig Something Extra Build - 12/7/2007 1:52:26 AM   
David Cutler



Posts: 2163
Joined: 9/13/2002
From: Los Angeles, CA, USA
Status: offline

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.

(in reply to iron eagel)
       Post #: 9

RE: Yet another Sig Something Extra Build - 12/7/2007 2:43:15 AM   
alex7403


 

Posts: 550
Joined: 6/29/2004
From: New york, NY, USA
Status: offline 		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


< Message edited by alex7403 -- 12/7/2007 2:53:51 AM >

_____________________________

measure twice cut once, again i cant believe i didnt learn it yet....

(in reply to iron eagel)
       Post #: 10

RE: Yet another Sig Something Extra Build - 12/7/2007 5:37:31 AM   
alex7403


 

Posts: 550
Joined: 6/29/2004
From: New york, NY, USA
Status: offline 		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...

< Message edited by alex7403 -- 12/7/2007 5:59:52 AM >

_____________________________

measure twice cut once, again i cant believe i didnt learn it yet....

(in reply to David Cutler)
       Post #: 11

RE: Yet another Sig Something Extra Build - 12/7/2007 7:51:19 AM   
iron eagel



Posts: 1137
Joined: 7/15/2004
From: Middleboro, MA, USA
Status: offline 		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...

< Message edited by iron eagel -- 12/7/2007 8:05:45 AM >

_____________________________

The Wrights never crashed, they only had hard landings. I 've had some hard landings myself. AMA EAA AOPA revver #185

(in reply to alex7403)
       Post #: 12

RE: Yet another Sig Something Extra Build - 12/8/2007 5:44:23 AM   
iron eagel



Posts: 1137
Joined: 7/15/2004
From: Middleboro, MA, USA
Status: offline 		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.

_____________________________

The Wrights never crashed, they only had hard landings. I 've had some hard landings myself. AMA EAA AOPA revver #185

(in reply to iron eagel)