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Ply/Balsa - 3/24/2002 8:29:11 AM   
Kestrel-RCU


 

Posts: 26
Joined: 3/18/2002
From: Wisconsin
Status: offline 		Could 1/64" ply be used in place of 1/16" balsa sheeting? Would it be lighter and stronger?
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Hummm - 3/24/2002 9:17:14 AM   
dhrider


 

Posts: 22
Joined: 2/25/2002
From: Northglenn, CO, USA
Status: offline 		My samurai is 1/64th ply covered with Oracover. sure beats balsa for me. I dont know if it any lighter but is sure is stonger!!!

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Ply/Balsa - 3/25/2002 7:33:50 AM   
Kestrel-RCU


 

Posts: 26
Joined: 3/18/2002
From: Wisconsin
Status: offline 		Thanks DH. I was pretty sure that it would be stronger. I am considering ways to build the tail planes lighter without sacrificing durability. I did find some weight comparisons but it didn't show any 1/64. And, showed 1/32 as being a lot heavier than 1/16 balsa, but it was a 5 ply.

I have also thought about the possibility of using carbon fiber. ????????

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Balsa - 3/25/2002 8:32:01 AM   
Ollie


 

Posts: 958
Joined: 12/8/2001
From: Punta Gorda, FL
Status: offline 		The range of strength and weight of a balsa part has a range of 5 or 6 to one depending on its density. The lightest conterst balsa only weighs about 4 pounds per cubic foot and ther hardest balsa can weigh as much as 24 pounds per cubic foot. It doesn't mean much to compare balsa of a certain thickness with plywood of a given thickness without specifying the balsa's density.

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Ply/Balsa - 3/25/2002 6:12:47 PM   
Kestrel-RCU


 

Posts: 26
Joined: 3/18/2002
From: Wisconsin
Status: offline 		Is strength sacrificed by using the lighter balsa?

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Balsa Strength - 3/25/2002 6:49:51 PM   
Ollie


 

Posts: 958
Joined: 12/8/2001
From: Punta Gorda, FL
Status: offline 		See:
http://www.uoguelph.ca/~antoon/hobby/sigbal.htm
If you scroll down the page you will see that doubling the density of balsa more than doubles its stiffness and strength. Matching the density of balsa parts to the application is at least as important as using the right size. Serious modelers select their balsa density and grain for each particular application.

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Ply/Balsa - 3/26/2002 12:38:55 AM   
Kestrel-RCU


 

Posts: 26
Joined: 3/18/2002
From: Wisconsin
Status: offline 		Thanks Ollie. I did find a chart that showed that similar info. Would you happen to know of any listings for the 1/64" ply? I found a chart but it didn't list the 1/64"

I am planning the construction of a T tail. Definitely not an area to compromise strength for weight.

I have e-mailed ACP asking if they have a product that could be substituted for the 1/16" balsa skin. Rather expensive stuff though. Not sure if the $ is worth it.

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Ply/Balsa - 3/26/2002 1:48:35 AM   
seafury_fb11



Posts: 236
Joined: 2/22/2002
From: Los Angeles
Status: offline 		Kestrel,
What kind of plane are you building - sailplane? sloper? If it's a sloper, you don't really need to worry so much about a little extra weight. I sheet the wings of all of my slopers with 1/32" ply then glass them with 6oz cloth. I built a high tail (not exactly a t-tail) plane a while back. For the vertical, I and used a foam core sheeted with 1/64" ply, then glassed over that. It is plenty rigid even though it is only about 1/4" wide where the horizontal goes through. I don't get any flutter at all - and this plane hauls.

http://russ.rcplanet.com/slopeships/me262.html

Russ.


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T-Tail weight and Strength - 3/26/2002 4:06:48 AM   
Ollie


 

Posts: 958
Joined: 12/8/2001
From: Punta Gorda, FL
Status: offline 		Often the most highly stressed part of a T-tail is the fuselage just in front of the fin. In a hard landing the inertia of the stab and vertical tail are the culprets. Saving weight (mass) in the tail surfaces means less stress on the fuselage just in front of the fin and lighter turns out to be more survivable.
Also, in a ground loop, the inertia of the tail surfaces torques the tail boom. Unfortunately these loads are hard to quantify and the structure is difficult to design rationally. In cases like these, one falls back on an empirical approach.

Build one and see where it breaks. Then lighten the next one where it doesn't break and beef it up where it does. After a few iterations you will have a design that is refined for the conditions of use.

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Regards, Ollie

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Ply/Balsa - 3/26/2002 6:54:23 AM   
Kestrel-RCU


 

Posts: 26
Joined: 3/18/2002
From: Wisconsin
Status: offline 		Seafury, the model is a Mystery Ship. I have been told by some that it is a decent model and by some that it is a stone! One owner who had an early version claimed its biggest downfall was a heavy tail. It seems that the later models had the wing moved to require less nose weight. Anyway, I like the looks of it, the price was in the budget and it looks like a nice large building project for next winter. So for now I am looking for some things to perhaps improve the model before i start to build. Lightening the tail planes looks like a good place to start.

Ollie, you are right on in regard to the weak area in front of the fin. Some have said that it is a weak area on the Mystery Ship. I looked one over carefully this past Sat. It doesn't look to be a flaw in the model, but rather the weakest link in the chain inherent to the T-tail design. As you suggest. The one that I looked at had never had a problem in that area. The gentleman is a good pilot so it perhaps never had a hard landing. I was considering a .007 by 1/2" wide strip of carbon fiber on the sides of the fuse in the fin/fuse junction to beef it up without adding a lot of weight.

Hope the weather shapes up pretty soon so I can get out flying. Won't have quite as much time to think up all of this crazy stuff.

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T-Tail Strength - 3/26/2002 7:53:29 AM   
Ollie


 

Posts: 958
Joined: 12/8/2001
From: Punta Gorda, FL
Status: offline 		It's not just the Mystery Ship. Every T-tail model faces the problem.

The area on top of the fuselage comes under severe compression in a hard landing. The compression is a particular problem with fiberous materials like wood and carbon fiber which are much weaker in compression than in tension. The compression is caused by the inertia of the stabilizer and to a lesser degree the inertia of the top of the fin. Anything you do to reduce the mass in this area will pay off bigtime. Minimizing the metal in this area is one measure. Use plastic rather than metal clevices. Keep the threaded rod as short as possible. Replace any hard or medium hard wood with contest balsa. Use the lightest covering film. Every gram saved reduces the inertial loads. Don't do dorky landings.

If you still want to reinforce something, reinforce the top of the fuselage, not the sides. Unidirectional cloth is much stronger in compression than woven cloth.

_____________________________

Regards, Ollie

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Ply/Balsa - 3/26/2002 9:13:21 AM   
Kestrel-RCU


 

Posts: 26
Joined: 3/18/2002
From: Wisconsin
Status: offline 		Thanks Ollie. Very helpful info. I don't have the kit yet but do have the instruciton manual. I believe it says to plank the top of the fuse with 1/8" Balsa running cross grain. Which is common practise. Wouldn't it be stronger under compression if the grain were running lengthwise? At least for a few inches forward of the fin?

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Balsa Properties - 3/26/2002 2:42:11 PM   
Ollie


 

Posts: 958
Joined: 12/8/2001
From: Punta Gorda, FL
Status: offline 		Yes, Balsa is about 17 times stronger in compression with the grain than it is across the grain!

Even so, the leading edge of the fin puts a compression load on the side grain of the top sheeting, no matter which way the grain of the top sheeting runs. You might want to replace the leading edge of the fin and several inches of top sheeting with a single laminated piece of balsa that is bent to conform to the angle between the top sheeting and the leading edge of the fin. This introduces a radius to the outline of the side view. The result is that the bearing loads are transformed into bending loads, for which the balsa is much stronger. So you end up making that area of the structure much stronger at little or no weight penalty but at the cost of building complication.

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Regards, Ollie

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Ply/Balsa - 3/26/2002 6:03:03 PM   
Kestrel-RCU


 

Posts: 26
Joined: 3/18/2002
From: Wisconsin
Status: offline 		I had considered something like the darkened area in this sketch but your method would spread the stress over a larger area forward without adding the extra weight.

Attachments
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T-Tail - 3/27/2002 7:17:46 PM   
MTT



Posts: 561
Joined: 1/18/2002
From: West Chester, OH, USA
Status: offline 		I can confirm that the fuse of the Mystery Ship just in front of the vertical stab is too weak, from own experience. I had a not too hard landing, and the fuse split open just in that area. I have now repaired it with the grain running lenghtwise. Still haven't been able to fly it though.
Another thing with the Mystery Ship : I liked the kit very much, fit of the parts is excellent, instructions are very good, it is a very enjoyable build.
However, I think that the vertical fin is way too weak for that relatively heavy flying tail, so now I am considering either to take the weight penalty and reinforce the vertical fin somehow, or change the whole setup altogether to a conventional tail.
Another thing : The kit comes with a already hollowed out nosecone for balancing the plane, but there is not nearly enough space in the nose cone for the amount of lead required, so you have to find room for more in the fwd part of the fuse, and there is not much space to begin with ! Try to save as much weight on the tail as possible, since the nose is relatively short, and any excess weight on the tail requires a lot of weight up front to balance it.

Michael

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Ply/Balsa - 3/28/2002 9:12:47 AM   
Kestrel-RCU


 

Posts: 26
Joined: 3/18/2002
From: Wisco