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RE: GIANT SPAD DESIGN! (update w/ pix) - 11/23/2006 7:56 PM   
Villa



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From: Wilson, NC,
Status: offline 		Thanks for the correction ChrisSpad. It is SPADTOTHEBONE. To Pilots12: I agree with what ChrisSpad mentioned about the spar being too weak. I hesitated to mention it before since I am not an expert and this is all a learning process. By adding another piece at the top of the spar you will just about double the strength of the spar. You spar will then have a crossection of an I-Beam which is a very efficient beam. Now that I have opened my mouth let me go further, but do remember I am not an expert. I do acrobatics with my planes and I try to cause them to fail in the air (away from everyone else). All my current SPADS use a double spar, like the DOMINATOR in SPADTOTHEBONE.COM. You may not want to do acrobatics with your plane, but if you lose control (screw up) you may be doing acrobatics trying to recover. At the ends of your center yardstick you have two short pieces to make a LAP JOINT with the outer yardsticks. You need to make a LAP JOINT also with the bottom and top members of your I-Beam crossection. Otherwise you are wasting the top and bottom pieces at the ends. You are doing a good job. Keep us informed.

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RE: GIANT SPAD DESIGN! (update w/ pix) - 11/23/2006 8:40 PM   
Pilots12


 

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Status: offline 		Thanks for the info guys. Office Depot ran out of year sticks, so thats all I have for now. I'm going to add more to the top of the spar to make it the "I" shape like Villas talking about, and maybe even add anotehr spar about an inch apart.

The two sheets of balsa in the middle are going to be where the fuse sections bolt onto the wing. They tested at over 25lbs and didnt snap so that should hold up just fine for that

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RE: GIANT SPAD DESIGN! (update w/ pix) - 11/23/2006 9:27 PM   
ChrisSpad



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Status: offline 		the issue is this: when a plane is climbing, it weighs more than it does staticly. When pilots do aerobatics, they reach 7 or 8 g's - fighters sometimes reach 9+G's. What is a G? the force of gravity. Iow, when a pilot pulls a 5 g turn, if he weighs 200 lbs, it feels like he weighs 1000 lbs. 5G is not an unreal number for an r/c airplane - even one that you fly gently. On a plane that size, i'd not use yardsticks at all. They're just not strong enough. On something that size, you really need something heavier - like 1/4"x1 1 1/2" lathing.

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RE: GIANT SPAD DESIGN! (update w/ pix) - 11/23/2006 11:10 PM   
Pilots12


 

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Status: offline 		Yeah I realize what G's are how how many G's you get when flying. But just climbing your not ever going to reach 5 G's... I fly Cessna and with smooth climbs, your still at 1 G. I know that theres more force on the wing when your climbing but its pushing up, not G's. I'm pretty confident that with double yard stick spars, stand up in the I shape, and not pulling aerobatics this wing should hold up just fine. Plus only being 16 and having a crappy job cooking chicken, I dont have much money to put into this. I dont want to spend more than $200 on this and thats already $70 to get the servos needed for this. Its a cheap build just for the fun of it, if it flies, sweet I'm sure all the guys at the field will gather aroung to take a look at it. If the wing snaps, oh ****, I'll learn something new to use on the next project. I'll try to finish the wing up ASAP and post pix of it before i glue it down and then I'll see hwat you guys think of it. But I feel pretty good about it holding up.

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RE: GIANT SPAD DESIGN! (update w/ pix) - 11/24/2006 1:02 AM   
ChrisSpad



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Status: offline 		just hope that if it does snap, that the 20 lb lawn dart you've just launched isn't aimed at anything or anyone, or 200 bucks will be pocket change compared to the damage you'll be liable for.

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RE: GIANT SPAD DESIGN! (update w/ pix) - 11/24/2006 2:48 AM   
MrGreenSpeed



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Status: offline 		If Your going to take the time to build it, the extra time to build the wing correctly will be worth it and shouldn't add to the cost of the build that much.
Better to be safe than sorry.
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RE: GIANT SPAD DESIGN! (update w/ pix) - 11/24/2006 3:08 AM   
Pilots12


 

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Status: offline 		What else should I do then to reinforce it other than 2 spars, each in the I shape and ribs?

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RE: GIANT SPAD DESIGN! (update w/ pix) - 11/24/2006 3:15 AM   
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Status: offline 		What else can you do? For starters, you should stagger the joint so that the the horizontal bits and the vertical bits don't all break at the same place. Second, 1 inch of overlap is way too little.



A heavier spar as chrispad suggested earilier is great advice.

We're not ganging up on ya, we're all just thinking of the people and property that will be around when that wing fails.

cc

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RE: GIANT SPAD DESIGN! (update w/ pix) - 11/24/2006 3:29 AM   
CTH


 

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Status: offline 		Pilots12 are you planning on using standard size servos? I'll give ya some if you are. I want to see this plane in the air! PM me with what you need.

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RE: GIANT SPAD DESIGN! (update w/ pix) - 11/24/2006 4:03 AM   
Pilots12


 

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Status: offline 		Alright I ll take the short lap joints off and add longer ones, and for the 2nd spar u'll just use two back to back.

CTH, I'm planning on using 7 standard servos.

I've never flown anything of this size before, only 40 and 60 size planes. Would a standard servo be enough for the elevator for something this size and weight?

< Message edited by Pilots12 -- 11/24/2006 4:23 AM >

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RE: GIANT SPAD DESIGN! (update w/ pix) - 11/24/2006 6:36 AM   
batchelc



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Status: offline 		Pilot12:

The spar is no place to save time, money or effort.

I would start by laying the yard sticks horizontal instead of vertical (you may have allready done this). One at the top and one at the bottom. You can add a shear web between them with another yard stick or similar material. Ideally you would find material that has a vertical grain for the shear web. The stresses actually act about 45 degrees to vertical.

You can join the spars at the center several ways. The easiest may be to go and buy some cheap fiberglass resin and fiberglass cloth (~10 for the resin and ~5-10 for the cloth). Unidirectional cloth would be best. Walmart and home depot both sell the bondo brand of resin/cloth. You want the fibers of the cloth running lengthwise on the spar. 3-4 layers should be plenty top and bottom. I would make the cloth 25-30% of the wingspan in length.

If you lay a piece of waxed paper down, put your cloth down and pour your resin down. Then put another piece on top. now spread the resin around to saturate the cloth. You can cut this sandwich with scissors (old but sharp). Peel off one side and stick to your spar. Then peel the other side off. Make sure to work out any air bubbles.

Clean up with acetone. You will want to wear disposable gloves (can be found the in the pharmacy section of some stores).

You can build the whole spar on the building board and then glue it into the wing. Anyone have any cheaper ideas for joining the spars?

I would be happy to answer any questions you have.

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RE: GIANT SPAD DESIGN! (update w/ pix) - 11/24/2006 6:54 PM   
Villa



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Status: offline 		Hi Pilot12. I don't fly giant scale so I cannot advice you on whether a standard servo will work on the elevator. I was hoping that someone with giant scale experience would answer you. Since none have, here is some of my experience. Earlier I referd you to my Flying Lawn-mower. It uses a 46FX engine and weighs about 6.5 pounds. The elevator is in two halfs which also serves as ailerons. Is is called an elevon. Each half has a servo and an electronic mixer does the magic (I don't have computer radios). I started with standard servos but they were being overpowered and one failed and I had a crash. I changed to the next size stronger. I think they are Futaba 3010. This is two servos on a 46 size plane weighing only 6.5 pounds. I assume your elevator will be one piece. You are planning 7 servos which sounds like you may be using two servos on your one piece elevator. Remember this: if one of the two servos fails ( I have had many servos fail) the other servo will not be able to overcome the resulting drag/jam and you will be without an elevator.

Pilot12, you are 16 years and I am 70. So what. You have received a lot of negative input to your project. I sure hope you don't get discouraged. I'm a retired design engineer. I love to design my planes, especially on the computer. You seem to enjoy that also. Don't let any of this discourage you. Why don't you build a few more proven designs and get more experience under your belt. The Canard plane you see to the left is one I designed and fly every day. The detailed drawings are on this site at

http://www.rcuniverse.com/forum/m_3580825/anchors_3580825/mpage_1/key_canard/anchor/tm.htm#3580825

I tend to build a little stronger that most. Maybe it is because I have the advantage of over 100 crashes in more that 30 years. Hope to hear more from you.

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RE: GIANT SPAD DESIGN! (update w/ pix) - 11/24/2006 8:00 PM   
Omaha_RC_Flyer



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quote:

ORIGINAL: Pilots12

What else should I do then to reinforce it other than 2 spars, each in the I shape and ribs?


Not to rain on your parade, or discourage your enthusiasm, but I would strongly consider replacing your spar, with one like I built for my Triple DPS. http://www.rcuniverse.com/forum/fb.asp?m=3585156 I used three pieces of 1/4" pine 74" long, epoxied together, to make it. I would hate to see all your work, end up crashing, or hurting someone, due to a spar failure. The yardsticks will not cut it, especially the way you have them pieced together. My Triple DPS is 19.5 lbs., yardsticks for a spar, was completely out of the question, when I designed it.

Later,
Omaha

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RE: GIANT SPAD DESIGN! (update w/ pix) - 11/24/2006 8:36 PM   
Pilots12


 

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Status: offline 		What about two double spars like this from yardsticks....



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RE: GIANT SPAD DESIGN! (update w/ pix) - 11/24/2006 9:04 PM   
batchelc



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Status: offline 		Your idea of adding a second shear web will add some strength, but not in the area thats needed. See my other drawing. The tension and compression loads are the concern. If you were to do anything you could add more mass on the horizontals, not the vertical.

You should build a test spar for some real-world experience. Just build the 2 piece spar and hang some weights on either side. You can hang the weights 1/2 way out to be conservative. For a 20# model you should build to 1.5 times the design load. So for 3.8 G's (same as your Cessna) that's 5.7g's or 114#. Divide by 2 to get 57# per side. Now make sure that the spar holds that for 3 seconds. You can hang dumb-bell weights or similar. Make sure to hang the same on each side.

Now you can see that this is quite a load for some yard sticks. By contrast a 5# model would only have 28.5#. Divide by 2 for 14.25# per side.

If the wing is going to fail it is likely that your joint at the root will fail.

You may want to look at your local home improvement store and go with metal or good pine/spruce like someone suggested. You may find strip wood in the trim section.

Chris


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RE: GIANT SPAD DESIGN! (update w/ pix) - 11/24/2006 9:40 PM   
Pilots12


 

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Status: offline 		Maybe I can use a wide peice of pine for the horizontal part of the SPAR and use the thickness of 3 yardsticks for the vertical part. This wing is going to come out heavy, I'm already looking at around 8lbs for the wing alone!

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RE: GIANT SPAD DESIGN! (update w/ pix) - 11/24/2006 9:47 PM   
batchelc



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Status: offline 		The verticle doesn't need to be that strong. The major stresses are on the horizontal top and bottom. The most stress is going to be in the center section. The verticle will add to stiffness of the wing.

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RE: GIANT SPAD DESIGN! (update w/ pix) - 11/24/2006 10:40 PM   
Omaha_RC_Flyer



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quote:

ORIGINAL: Pilots12

Maybe I can use a wide peice of pine for the horizontal part of the SPAR and use the thickness of 3 yardsticks for the vertical part. This wing is going to come out heavy, I'm already looking at around 8lbs for the wing alone!


Where is all the weight coming from? My Triple DPS wing is only 4 lbs. RTF with 3 Servos, Horns, and Push rods installed. RNAF (2 mil top with a 4 mil bottom) 76" wingspan with a 16" chord , with 4 mil flap, and ailerons.

Later,
Omaha

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RE: GIANT SPAD DESIGN! (update w/ pix) - 11/25/2006 1:02 AM   
Pilots12


 

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Status: offline 		Hi, this is Pilots12 friend who he is building it with. I happened to have some Oak laying around and had my uncle make me some pieces 1/4" x 8' long and they really dont weigh all that much more then pine and should be stronger. We will probably make our spar like the one omaha showed us in his previous post and keep the old spar in there. Overall the plane is shaping up nicely and we will be sure to post some more pix before finishing it. Thanks for the advice

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RE: GIANT SPAD DESIGN! (update w/ pix) - 11/25/2006 4:33 AM   
Pilots12


 

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quote:

ORIGINAL: Omaha_RC_Flyer


quote:

ORIGINAL: Pilots12

Maybe I can use a wide peice of pine for the horizontal part of the SPAR and use the thickness of 3 yardsticks for the vertical part. This wing is going to come out heavy, I'm already looking at around 8lbs for the wing alone!


Where is all the weight coming from? My Triple DPS wing is only 4 lbs. RTF with 3 Servos, Horns, and Push rods installed. RNAF (2 mil top with a 4 mil bottom) 76" wingspan with a 16" chord , with 4 mil flap, and ailerons.

Later,
Omaha


The whole wing is 4mm coro folded over to make the top. Then i picked up some home depot sign, same as the election signs that are 4mm coro and glued those to the bottom to add some strengh to it and the ailerons are on those home depot signs. So like 20sq ft of 4mm coro plus the spars and support for the bolt on fuse. I think I might end up taking the home depot signs off and just leave an inch for the ailerons to connect to the wing.



here you can see the home depot signs but i dont think there needed since the spar will support it.

< Message edited by Pilots12 -- 11/25/2006 4:35 AM >

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RE: GIANT SPAD DESIGN! (update w/ pix) - 11/25/2006 6:06 PM   
Omaha_RC_Flyer



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quote:

ORIGINAL: Pilots12

I dont want to spend more than $200 on this and thats already $70 to get the servos needed for this.


How many servos do you plan on using? Have you thought about redundancy? That is the reason I have 11 servos, 2 receivers, and 2 batteries in my Triple DPS. If a servo goes bad on my 19.5 lbs. plane during flight, I can still land it safely (i.e. split elevators, dual rudders, dual ailerons, etc...) .


Later,
Omaha

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RE: GIANT SPAD DESIGN! (update w/ pix) - 11/25/2006 6:19 PM   
Villa



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Status: offline 		Pilot12. You are right, those home depot signs add no strength. They only add weight, which reduces the strenght of your wing.

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RE: GIANT SPAD DESIGN! (update w/ pix) - 11/25/2006 6:56 PM   
Villa



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Status: offline 		Pilot12. If you still insist on building a Giant Spad plane I suggest you check out the Biguns! (Large Scale SPADS) at


http://spadworld.net/forum/ Lot of good information there. Generally speaking, you will not see detailed information on failures. Take that with a grain of salt.

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RE: GIANT SPAD DESIGN! (update w/ pix) - 11/25/2006 9:52 PM   
Pilots12


 

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Status: offline 		Omaha, I plan to use 1 rx with 6 or 7 servos. if I use 7 I'm looking at 2 for the elevator or 6 with a high torque servo for the elevator.

I just rebuilt the whole spar, and tested it by lifting 50lbs with it. it holds up great no problem with the weight. I also took the Home Depot signs out, and am going to buy some 2mm coro to use for the top of the wing for smoother airflow. The 4mm has a crease in it now and it makes a sharp angle at the top of the spar. I'll get pix later today and also start a post on spadworld with them.

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RE: GIANT SPAD DESIGN! (update w/ pix) - 11/26/2006 2:40 AM   
Pilots12


 

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Status: offline 		new spar. The vertical part is 2 yardsticks staggered back to back and 1/4" x 8' oak for the horizontals.



we put screws through all the joints for more strengh


65lbs and it doesnt even bend. I can lean all my weight on this for a few secs and still have it support me.


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