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Author Topic: Wanting feedback on an idea I had while building a P-30 rolled fuselage  (Read 1109 times)
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randoloid
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« on: January 17, 2019, 11:37:07 PM »

I've been hesitant to share this idea -  I'm relatively new to freeflight and while I've never seen anything like this, I am sure that someone must have tried it in the past. 

I was building my Polecat X with a 1/32 rolled fuselage and was concerned that it wouldn't hold up to the stress of a fully wound motor.  I looked over Don Deloach's plan and it mentioned covering the fuse with tissue on the bias (45°)... That made a lot of sense for adding some strength.... 

Of course, I couldn't just follow instructions... My wife says that my personal motto should be anything worth doing is worth overdoing.  I had used carbon caps on my ribs and was amazed at how much rigidity they added... and I thought why not use some carbon wrapped on the same 45° angle as the tissue. 

My first experiment was to use some carbon tow (thread) impregnated with epoxy and wrapped around the fuse.  (Photo attached)  This is yet to be tested but I was so excited about the idea that I'm already building a second fuse that will use the same 1/16 carbon used for the rib caps-  without glue it's only .2 grams.  Not a lot of weight and seems like it would really strengthen the structure.
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TheLurker
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« Reply #1 on: January 18, 2019, 01:35:41 AM »

Accepting I know less than nothing about these things; my first thought was that the carbon spiral is going to be very much more rigid than the balsa tube it is wrapped around so that rather than the tube flexing under load it may break along the line of the spiral.  My second thought was that a second spiral crossing the first might counter this, but of course that would add more weight.

If you can afford the materials and time then some testing to destruction (comparing breaking loads for unreinforced tube, tissue reinforced tube and your rather natty carbon reinforced tube) is probably the only way to find out whether or not the idea is sound.

Of course the foregoing is probably utter tosh and someone who knows better will be along soon to say so.

Lurk.
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RalphS
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« Reply #2 on: January 18, 2019, 08:55:31 AM »

I used a very similar method to build 50 gram rubber model fuselages - a class similar to Open Rubber but with the rubber limited to 50g.  The pictures show the process.  I rolled 1/32" balsa over a 1.5" diameter nylon bar and after joining used carbon tow/epoxy at approx 45 degrees.  The carbon tows were flattened using old VHS tape - a clue there to the date - then I tissue covered the whole thing with lightweight Esaki tissue and dope.  It produced a very strong fuselage albeit a bit bumpy on the outside over the tows. 

My 50g models used 20 strands of 1/8th rubber and were wound to 30 to 40 ounce inches torque to drive a 2 bladed 24" prop. (My P30's flew on 4 strands of 1/8th wound to about 5 ounce inches and in my opinion never needed carbon reinforced fuselages). The 50g class and the preceding open rubber class produced magnificent flying machines with lots of people in the fly-offs and usually ended up with many modellers looking for models downwind as the sun was setting.



 
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jswain
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« Reply #3 on: January 18, 2019, 12:20:02 PM »

.....I was building my Polecat X with a 1/32 rolled fuselage and was concerned that it wouldn't hold up to the stress of a fully wound motor.  I looked over Don Deloach's plan and it mentioned covering the fuse with tissue on the bias (45°)... That made a lot of sense for adding some strength....  

I agree with you that it doesn't seem like it would be strong enough but it really is strong enough in practice
just using tissue on one side.

The amount of torque from a 6 strand/3 loop 1/8" motor isn't all that much for the models i have built and flown.

All my rolled tube P30 models have had tissue doped to one side (the inside) of the 1/32" balsa at a * 90  * degree angle
which helps with 1. the strength and durability of the tube, 2. the forming of the tube during construction due
to direction of tissue shrinkage and 3. allows cleaning out of sprayed rubber lube inside the tube with a damp
paper towel or cotton ball.

Your fine with what you have done, whats fun is trying different building techniques without spending a fortune.

have fun, john s.
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gman
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« Reply #4 on: January 18, 2019, 01:05:07 PM »

Ralph S, your BMFA 50g model...I've often fancied a "coupe derived" model to use up some of my surplus wings. It seems that yours might have been in that mould. Do tell us the story.
Gavin
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« Reply #5 on: January 18, 2019, 01:19:09 PM »

Another way to strengthen a P30 body tube is that used by John Kamla of Marie P30 fame.  One of the last ones I saw had an uncovered balsa motor tube. No tissue or anything else I could see. I asked him about it. He said that after rolling he scored the balsa with a pounce wheel so it was covered with small holes. He then spread thin CA glue all over it and let it dry. That's it. The CA stiffened and sealed the wood and resulting weight was about the same as covering with doped tissue. Simple.

I haven't tried it myself but John was an amazing builder and flyer.
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Greg Langelius
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« Reply #6 on: December 23, 2019, 06:54:32 PM »

In essence, the greater portion of the strength will come from the CF.

Now, if one were to wrap an identical strand in the opposite direction, one would have something like a tubular geodetic.

Finish it off with three lengthwise CF stringers, and it Could be very strong. Experiment with thinner strands.

I would begin by spiral wrapping a mandrel with the tissue, then a second layer spiral wrapped in the opposite. Omit the balsa. Follow it up with the above process.

You might have invented something interesting in the process.

Greg
« Last Edit: December 23, 2019, 07:16:56 PM by Greg Langelius » Logged

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RalphS
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« Reply #7 on: December 24, 2019, 11:33:07 AM »

Ralph S, your BMFA 50g model...I've often fancied a "coupe derived" model to use up some of my surplus wings. It seems that yours might have been in that mould. Do tell us the story.

Gavin - Just came across your post.  The reason for building my "geodetic" CF fuselage came from my skinny coupes. 

FF duration models spend all their flight yawing.  The lengthy 50g fuselages using square sections show the drag
effect if you hold them at the wing position and wave them sideways through the air. Pod and boom fuselages seem to
have reduced drag when waved about.  JOD always used diamond fuselages because he thought they moved through the air
better than the generally used square section*. I think the pod and boom is better still.  The method that I used above
resulted in a strong fuselage.  I also combined the winding outside the model technique with the structure with an open rear
end with just a slot for the motor peg tube - very easy to load and change motors. The models used a lot of carbon
in the flying surfaces, allowing thin sections, and flew well.  I found the 50g class a bit silly.  Too easy to max
and an eyesight competition for the fly-off and having to start looking for the damn things just as it was getting dark.

At our club meetings JOD and Hepcat used to try to outdo each other in trying to explain their ideas for contest model
superiority.  At one meeting, Hepcat tried to convince us that twin fin models using square section fuselages allowed the
airflow to be guided down the fuselage in the most effecient manner.  I said, "but they never fly in a straight line"
and that seemed to stop the discussion.  I was gratified to see Hepcat say the same thing in this forum much later on.

The rolled tube with geodetic CF reinforcement is an easy way to make 50g model fuselages and they are tough although my
simple technique doesn't make them too good to look at.

*Morrisets New Look (?) Wake and Le Jump-bis coupe have diamond fuselages. (JOD built his after seeing mine perform well)
and I believe the Jump-bis has recently performed well at the Coupe de Brum contest. Wink

Ralph
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« Reply #8 on: December 24, 2019, 08:29:16 PM »

Greg:
I think you may be onto something by omitting the balsa. It might be a good idea to put light Tyvek over the framework to cut down on air drag a bit.

Ralph:
I think the advantage of diamond fuselages may be that they force you to use a pylon, thereby reducing the interference drag between the fuselage and the wing. Just an idea.


-----------------
I think if I was doing a rolled P-30 fuselage, I might use 3/4 ounce glass and epoxy on the inside. The stuff made for wetting out composites, of course, not glue. The latter gives poor results with fiberglass. Floppy and rough looking. It was only a cowl, though.

Somehow I can't find it, but I think someone was talking about wiggling the fuselage back and forth to check the resistance from different fuselage shapes. However, I think this is measuring the moment of inertia as much as it's measuring air drag. For the latter, you'd want to spin at a steady rate or hold at an angle in the wind. If you hold the fuselage perpendicular to the wind, you may get periodic vortex shedding, which I don't think would happen with the fuselage at a shallow angle. I have to admit I'm not entirely sure. Vortex shedding would, I think, be higher drag and might make the model wiggle.
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« Reply #9 on: December 25, 2019, 06:22:52 AM »

First a reply to Ralph, you sent me a very detailed PM about your 50g rubber models at about the time of my query. So, no, you didn't ignore me. Peter Woodhouse had a fine day at the Birmingham Coupe dropping just one of his eight flights (F1G & Vintage Coupe). He made the best fly off of the day with his Jump bis and when I chatted about it he gave all the credit to the work you'd done on the model.

But this original thread was about P30. I've flown them a bit, mainly Alan Bond's "Bondy's P30" out of FFQ.
in my experience a model with a thin 4x1/8th motor like Bondy's and the Polecat needs no strengthening as such in the fuselage tube. I've used soft 1/32 or, better, 1mm. A coat of dope inside and a wrap (spiral's easier) on the outside and its done. I didn't even use ply or ally reinforcement rings at each end, just doubled it with surplus balsa tube and hardened with cyano.

The stronger you make it then the more it weighs....

Gavin
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Greg Langelius
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« Reply #10 on: December 25, 2019, 12:07:59 PM »

Lincoln;

I agree completely. My first try would be with doped tissue. Might the Tyvek add a weight penalty?

I think the doped tissue shrinkage could stress the structure adding rigidity as well as smoother airflow.

In fact, building the truss directly on the mandrel, then adding the tissue on the exterior might be the lighter approach with only a single skin. The surface after shrinking could bring a new esthetic to the concept.

How about heat shrink covering?

It might also bring a turbulator effect to the fuselage structure.

I have no idea whether that might be a pro or a con.

When I design wings, I use a hybrid cracked rib/Rees construction technique because it renders flat surfaces with minimal (no?) sag. No constantly changing curvatures. The angular junctions between the flats could serve as turbulators (again, pro or con?).

Consider that an airfoil with conventional curved ribs is largely fiction due to sag, the actual effective airfoil thickness is almost always going to be thinner than what we THINK is defined by the rib curvature. The airfoil cannot therefore generate a truly smooth airflow; so by going with flat, angled panels, we're really not giving up as much as one might think. Because they are less complex, and the actual tapers are regular, the wing can be thinner, and that should provide better control on overall drag. Lift IS drag. By incorporating it into the structure, we might be able to influence/control lift and drag more directly.

And for something truly unorthodox, how about using Heavy Test Weight Spider Wire fishing line instead of carbon. Cheaper, very strong wound fiber, available in many sporting goods departments. I keep two spools of 80lb test in my car as a survival item. It could be saturated in a resin, then arranged on the mandrel (with release agent applied).

I have no idea if all this would work, but it's outside the box; which is my favorite living realm.

Ralph;

GREAT idea, but...; who says a pylon could only work with a diamond cross section?

Remember, we're all a few steps outside the box right now...

Greg

Aw, Heck; it's the morning of Christmas Day, and now those visions of sugar plums are transforming into shapes on a drafting board...
« Last Edit: December 25, 2019, 12:23:57 PM by Greg Langelius » Logged

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« Reply #11 on: December 25, 2019, 01:16:37 PM »

Gotta admit I don't know how light you can get Tyvek or heat shrink.

I don't really know whether the flats or curved ribs with covering that sags a little would work better. I built an RC glider that used all flat segments except at the leading edge. I imagine the penalties for flat segments would be negligible if the first third was curved sheeting.

I'm guessing Spider Wire would be great IF it can be glued well. Be careful not to cut your hands when applying tension. You can get tow that's quite thin, though, or aramid thread.
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« Reply #12 on: December 25, 2019, 01:18:40 PM »

P.S. I've played,with composites a little, but it doesn't make me an expert.
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« Reply #13 on: December 25, 2019, 01:52:36 PM »

Silly me, it's Terry (007) Bond's P30 not Alan's...

Gavin
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Greg Langelius
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« Reply #14 on: June 08, 2020, 12:40:05 PM »

Addressing the yaw issue in fuse design; is a streamer legal for P-30? It might/could serve as a drogue, with modified drag from a drogue.

Greg
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« Reply #15 on: June 08, 2020, 04:29:55 PM »

Missing something Greg, why would you want to add a drogue?
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« Reply #16 on: August 21, 2020, 05:06:20 PM »

Hi Guys:
I’m loving this thread!  Could one of you please recommend
What width and thickness for Carbon fiber Wing rib Cap strips for P30
Type models for Rib balsawood thickness of from 1/32” to 1/16” max.
and a source!
Additionally, what width and thickness would be recommended
for a spiral Wrap of Carbon fiber around a Balsa P30 fuselage.  And
Reinforcement of nose block area and motor peg area?
Sincerely,
Jon B. Shereshaw
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gman
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« Reply #17 on: August 21, 2020, 05:43:51 PM »

Hi Jon,
I'm not sure that this is what you want to hear but...I wouldn't recommend any carbon for a spiral wrap of a rolled balsa fuselage because you don't need it. A 1/32" rolled tube is more than strong enough to take the torsion of a "normal" P30 motor. To reinforce the nose and peg ends then either a short doubler of surplus motor tube or maybe 1/64" ply then a bit of Cyano to harden things off. Tissue inside to stop it splitting or absorbing too much motor lube and outside to make it look nice. It's not easy to get a P30 down to 40g, a a tracker, timer, motor hook, rear peg, bands etc all add up and leave precious little for the actual airframe. It needs to be (just) strong enough and no more. The minimum structure and the lightest Mylar covering. I'm sorry, I'm getting overbearing and I apologise. All success with your P30 but in the words of Colin Chapman of Lotus race car fame "simplicate and add lightness"
Gavin
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« Reply #18 on: August 21, 2020, 06:38:17 PM »

There are two different loads on the tube - compression and torsion. The carbon tow wrap will not have any effect on the compression strength of the tube.

Compression may not be a concern for a P30 tube.
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« Reply #19 on: October 16, 2020, 11:46:36 PM »

Lincoln;





I agree completely. My first try would be with doped tissue. Might the Tyvek add a weight penalty?

I think the doped tissue shrinkage could stress the structure adding rigidity as well as smoother airflow.

In fact, building the truss directly on the mandrel, then adding the tissue on the exterior might be the lighter approach with only a single skin. The surface after shrinking could bring a new esthetic to the concept.

How about heat shrink covering?

It might also bring a turbulator effect to the fuselage structure.

I have no idea whether that might be a pro or a con.

When I design wings, I use a hybrid cracked rib/Rees construction technique because it renders flat surfaces with minimal (no?) sag. No constantly changing curvatures. The angular junctions between the flats could serve as turbulators (again, pro or con?).

Consider that an airfoil with conventional curved ribs is largely fiction due to sag, the actual effective airfoil thickness is almost always going to be thinner than what we THINK is defined by the rib curvature. The airfoil cannot therefore generate a truly smooth airflow; so by going with flat, angled panels, we're really not giving up as much as one might think. Because they are less complex, and the actual tapers are regular, the wing can be thinner, and that should provide better control on overall drag. Lift IS drag. By incorporating it into the structure, we might be able to influence/control lift and drag more directly.

And for something truly unorthodox, how about using Heavy Test Weight Spider Wire fishing line instead of carbon. Cheaper, very strong wound fiber, available in many sporting goods departments. I keep two spools of 80lb test in my car as a survival item. It could be saturated in a resin, then arranged on the mandrel (with release agent applied).

I have no idea if all this would work, but it's outside the box; which is my favorite living realm.

Ralph;

GREAT idea, but...; who says a pylon could only work with a diamond cross section?

Remember, we're all a few steps outside the box right now...

Greg

Aw, Heck; it's the morning of Christmas Day, and now those visions of sugar plums are transforming into shapes on a drafting board...
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