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Author Topic: Blast tube for Burdov's P30 Pirate  (Read 5043 times)
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Tapio Linkosalo
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« Reply #50 on: September 21, 2010, 02:24:19 PM »

Pirate fuselage tube diameter?
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Tmat
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« Reply #51 on: September 21, 2010, 03:16:49 PM »

Oh yeah, I keep forgetting to measure it.

Sorry Tapio, I'll measure it tonight.

Tony
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« Reply #52 on: September 21, 2010, 04:02:54 PM »

Inside dimension of the aluminum nose ring is 16.1mm/0.628". Nose ring is about .85mm so your working with about a 15.2mm/0.59" clearance inside the motor tube. The GG bobbin with the retaining clip cut off (saves a little width) is 10.2mm. So you have around 3 mm to work with on the side. The other complicating factor is the length of the GG front end. From the back of the nose button to the end of the bobbin in the engaged position is 31.19mm/1.22"". That sticks pretty far in there compared to the hook that come with the kit. And remember the GG does not flex like a crockett hook on the kit prop wire.

Now all of you mathematicians can figure out exactly how many degrees of side/down thrust you can get with the GG in the Pirate motor tube.
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« Reply #53 on: September 21, 2010, 04:10:23 PM »

Thanks for the measurements Derek.

Tony
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Tmat
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« Reply #54 on: September 22, 2010, 02:47:23 PM »

O.k. Tapio,
I took some measurements of my Burdov Kevlar P-30 motor tube:

The over length - 28" (711 mm)
distance from nose ring to motor peg - 19" (482 mm)
Front outside diameter - 0.725" (18.4 mm)
Front inside diameter (of nose ring) - 0.625" (15.8 mm)
Diameter at rear peg - 0.562" (14.27 mm)
Rear diameter - 0.242" (6.14 mm)
Weight (without rear peg) -10.1 grams

Incidentally, it was clearly made on a male mandrel in one step (not bonded at the seam after forming). The inside is smooth with no seam.

I hope this is useful.

Tony
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Tapio Linkosalo
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« Reply #55 on: September 23, 2010, 02:41:57 AM »

Interesting... as from the couple Pirate fuselages that I have seen the seam is so pronounced that I though it was obvious that it was glued afterwards.

Anyway, I think that might be worth trying (laminate the fuselage as "open", then glue the seam), as it would make molding so much easier. Taking these thin-walled P-30 tubes off little-tapering male mandrel is not straightforward, but utmost care needs to be taken to avoid buckling the tube while removing. If the seam was open it would be a breeze to take it off.

Or maybe using a silicone plug in a female mold?
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Tmat
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« Reply #56 on: September 23, 2010, 08:44:22 AM »

I think that gluing the seam afterwards would work just fine. Silicone plug in a 2 part female mold would work, but is certainly more complex.

I've got some G10 fiberglass pre-cured sheet that is 0.005" thick (.127 mm) and have wondered if it couldn't just be wrapped around a form with the seam glued to make a tube. But I'm assuming that the stress at the seam would make the tube go slightly oval?

Tony
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« Reply #57 on: September 23, 2010, 02:03:01 PM »

A lot of the aerospace resins cure at 300-350 fahrenheit. If you used a preheated and mold released bar it should shrink enough to be able to remove the tube. Some of the mold releases really work well! You should have seen some of the molds that we used for uncle sam's parts.
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Dave Sechrist
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« Reply #58 on: September 23, 2010, 03:38:45 PM »

I use a male mandrel covered with waxed paper. Three layers of 1.7 oz. kevlar. Cover this with saran wrap, then thick mylar .020 and hold it down with an ace bandage. My mandrel is .640-.620. A little light twist and it comes right off.
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Tmat
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« Reply #59 on: September 23, 2010, 04:41:38 PM »

Do you have a photo Dave?

That sounds like it would be pretty easy to do.

What is your mandrel made from?

Tony
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Dave Sechrist
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« Reply #60 on: September 23, 2010, 09:23:42 PM »

The mandrel is made of stainless steel. I offset the tail stock on my lathe and ground it with a tool post grinder. I don't have any pics right now. I am getting ready for a contest so I won`t have time to post any photos till next week.
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Tapio Linkosalo
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« Reply #61 on: September 24, 2010, 02:31:57 AM »

Three layers of 1.7 oz /sq yd. = 60 grams / m2 cloth? Is this tube for F1G?

I used to make a couple of P-30 tubes on the tail section of conical F1B mandrel, from a single layer of 90 gram cloth. More recently a Finnish company made P-30 tubes from a single layer of 60 gram cloth, with a layer of (10 gram?) carbon paper for the motor tube part. Three layers of 60 gram is actually what I use for F1B. Or rather, two layers of 80g kevlar or two layers of 60 gram kevlar and one layer of 100g uni-directional carbon (if I want a smooth-sanded and painted motor tube).
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Sunbeamtiger
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« Reply #62 on: September 24, 2010, 08:33:37 AM »

There are some additional photos of the P-30 1/2 tube in action here:

http://picasaweb.google.com/tmathews180/P30Details#

My nephew has gotten the hang of using the 1/2 tube system with the Pirate P-30. You can see him winding and flying in the photos.

There are a few issues with the prop assembly that I might work on. It's not as easy to install the T hook as I'd like. I will open the hole in the T-hook slightly so that the prop shaft goes on a little easier.

Also, with my Pirate, the nose block kept falling out when the motor had unwound. You can see my solution was to add a small hook and rubber band that holds the noseblock in place. While this does work perfectly, it's a bit fiddly to install with a wound motor. The Pirate comes with a Delrin noseblock that has a slotted flange that engages a small screw in the nose ring. This is supposed to act like a bayonette fitting to hold the noseblock in place. However, mine kept falling out anyways.

It's an issue that I'm not used to as all of my FAI rubber duration models use a rubber motor that is in tension even when relaxed and unwound. Thus the noseblock is held in place by the rubber motor. I suppose that the motor could be braided to keep it under tension, but it would also lose some energy to the braiding turns. I could make the noseblock a tight fit, or make some other simple holder like a spring that engages a pin or something like that.

I'd also prefer a small bobbin on the front rather than a T-hook like what I use on my Coupe (or F1B). The bobbin keeps the motor centered in the fuselage better than a T hook or crocket hook, or S hook or what have you.


Tony,
Sorry I haven't posted recently but I've been falling behind on my daily chores and getting ready for a contest this weekend.

Your pictures are fantastic, looks like I'll be making a half tube this winter for the Pirate. Heck I might as well make one for the F1B's too.

It's funny that you mentioned the nose plug falling out of the Pirate. Mine does the same thing too. It has never happened in flight but it seems to happen when it lands but not everytime.

The other day I fabricated a free wheeling setup for one of the Pirates, I'm still using the Checkz red props on both even though everyone is telling me to go to the silver Peck's. Also learned how to bend 'S' hooks to get away from the crockets but I couldn't make one small enough for the Pirate tube, at least not for my taste. So I'll still be using the usual crocket hook for now.I haven't tried the free wheeler yet due to 15-25mph winds all week so it looks another test & fly at the contest Saturday..... I hate that.

My brother Marty, turned me on to a youtube link for making the 'S' hooks and a simple free wheeling hub. You can find the clips by doing a search for "Merlin2360" on the youtube site. Of course, you being a far better flyer/builder than I the video will be old hat to you.

May the Thermal God always be on your side....Mike in Indy
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Mike Richardson
Tmat
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« Reply #63 on: September 24, 2010, 09:30:22 AM »

Mike, the noseblack fell out of my Pirate in flight a few times. The result is a pretty effective DT! A freewheeler that uses a tension based stop is a good way to prevent that I think. It leaves a few turns on the motor that would keep the noseblock under tension when freewheeling.

I haven't had any time to experiment with the Peck or the re-pitched Gizmo prop on my Pirate. I will eventually though.

Good luck with your half tube fabrication and at the contest!

Tony
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Hepcat
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« Reply #64 on: September 24, 2010, 05:37:19 PM »

Hi Tony
Keeping a noseblock in place.
Reply #42 You did not want to waste energy having braiding turns left on the motor.
Reply #63 You thought a tension stop, retaining some turns on the motor would be good.
Have you a comment to share with us?
John
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Tmat
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« Reply #65 on: September 24, 2010, 09:10:50 PM »

Ahh John, you got me. Turns left on is turns left on regardless of the source. I guess I would prefer the tension stop as I'm too lazy to braid a motor.

Another option is to make the distance between the prop hook and motor peg long enough so that the motor is always under tension. On a new model I could do that, but on an existing model it's not an option. Well, unless I used a shorter motor, which I don't want to do.

Any suggestions John? Grin

Tony
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Tapio Linkosalo
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« Reply #66 on: October 08, 2010, 01:49:27 AM »

Quote
Also, with my Pirate, the nose block kept falling out when the motor had unwound. You can see my solution was to add a small hook and rubber band that holds the noseblock in place. While this does work perfectly, it's a bit fiddly to install with a wound motor. The Pirate comes with a Delrin noseblock that has a slotted flange that engages a small screw in the nose ring. This is supposed to act like a bayonet fitting to hold the noseblock in place. However, mine kept falling out anyways.

The attached picture shows the way that I have been using to hold the noseblock in place on my P-30's for decades. The fuselage has two hooks 180 degrees apart, and the noseblock has another two, halfway to the ones in the fuselage. There is a rubber loop pulling the noseblock onto place. While winding, it simply sits around the fuselage behind the hooks, and when done, I put the prop in place and pull the bands across the hooks in the noseblock. Takes about two seconds to fix. You can also see that I use super-simple freewheel clutch, just the end of prop axis bent 270 degrees so that it catches the flange in the prop. Works like charm. The only caveat is that the motor must be loose to release the clutch, but the current SS rubber is slightly thinner than Tan, so 6 strands of SS is just a perfect motor for my model. KISS!
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Tmat
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« Reply #67 on: October 08, 2010, 09:54:24 AM »

Nice Tapio.

Ideally, I want no rubber bands or hooks at all like an F1B. A tension stop would achieve this as would braiding (don't like braiding if I can avoid it). The Gizmo Geezer front end is a tension stop device so maybe I should not worry about losing a few turns for the stop tension. Especially for my nephew as he is underwinding anyways.

Tony
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Tapio Linkosalo
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« Reply #68 on: October 08, 2010, 10:32:50 AM »

You know, for me the P-30 is a low-tech, fun model, and I have no intention to make any such "neat" solutions as in F1B.

One thing I might add: with a motor longer than the fuselage, even with the rubberband, it is possible if not likely that the prop will jump off the fuselage when landing. I have once a friendly guy retrieve the model after such landing, commenting that he had noticed that the prop was missing, tried to look around, but avail. I was biting my lip not to comment that it would have been better that he left the model there so I would have known where to look for the prop, but managed to keep my mouth shut. Anyway, after that event, I have added a small rubberband tightly wrapped around the front end of the motor, and pulled against the prop hook when the prop is installed. This way, even if the prop is released from the motor tube, it is still retained by the motor itself.
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Tmat
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« Reply #69 on: October 08, 2010, 01:42:11 PM »

Fair enough. I get that P-30 is a fun event and so on.

My interest in solutions that are more F1B-like is just because I'm odd that way. Grin And it makes it less likely for me to make a mistake when flying different classes if they are all set-up in a similar way.

Tony
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« Reply #70 on: October 09, 2010, 03:00:23 AM »

Tapio

The picture you posted showed what looked like a spirally wound carbon/kevlar fuselage. Is this one made by Burdov, or is it a home brew by you? I'm interested as I've purchased some carbon/kevlar tape as I want to replicate the marvelous French built coupe fuselages, which are sadly no longer available.

Thanks

Peter
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Tapio Linkosalo
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« Reply #71 on: October 09, 2010, 03:48:34 AM »

The tube is made by company called "Kultasiivet" (Golden wings) here in Finland, it was sold to a new owner a couple of years ago, and I do not know if they still make the tubes. I'll try to find out. The carbon is not wound, but thin carbon paper made in an experimental run by the Finnish company Ahlström. Unfortunately, the material did not turn out to be economically viable. Construction of the tube is 1 layer of carbon paper and 1 layer of 80g/m2 kevlar cloth for the almost cylindrical motor tube section, with only the kevlar extending for the conical tail section (one piece with the front section). Later tubes used glass fibre instead of the kevlar.
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« Reply #72 on: October 09, 2010, 10:06:23 PM »

Hi
I have been lurking and following this thread for some time now with a slightly bemused perplexed feeling wondering what some of the fuss is about.

None of my rubber powered model nose blocks ever fall out either in flight or on the ground, including that on my P30 and none of them have hooks or rubber bands holding them on. They just don't need it. They are simply held in by the friction of the locating block as per 99% of most rubber model plans.

Attached photo NO. 1 shows the back of a P30 nose black with the locating key piece built up from 1/4" by 1/16' strip balsa. It could have been made from 1/4" sheet but I was feeling a bit fancy that day. Attached photo NO.2 shows it from the side. I have a perfectly round locating block on another model and once again that would never fall out. Just make the keying block wide enough and a good tight friction fit (a few coats of dope can help) and it won't fall out.

A tip for for winding tubes: I once again keep it very simple and cheap by making them from polypipe available everywhere in many different diameters. The winding tube for my P30 is made from 11/16" inside diameter polypipe 22" long. The winder end can be heated and then pushed against a hard flat surface to get a nice smooth protective "bell end" and the other end has a slot cut in it to slide onto the motor peg.

Cheers

Algy
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« Reply #73 on: October 13, 2010, 09:05:16 AM »

I hear you Algy. But I'm not sure how I'd accomplish making the noseblock fit snuggly into the turned aluminum nose ring AND still allow room to adjust the thrustline when needed (I'm still trimming my plane). If I had a Gizmo Geezer unit, where the small button containing the shaft has the thrust adjustments then a noseblock could be built around it that fit snuggly into the nose ring.

Flying the Pirate on the weekend I found that I could simply flip the rubber band forward after winding to secure the front end (got the idea from Tapio's description of his method). And after flying the band could be flipped back onto the motor tube. that way I didn't have to remove the rubber band at all. Pretty simple.

Tony
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« Reply #74 on: October 20, 2010, 07:40:50 AM »

I am working on new tube for P30 (balsa A-grain with modelspan ... inner, outer surface glass 25g/m2)

I try to do only glass tube (or kevlar)
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