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Author Topic: Nieuport 11 Bebe - Build  (Read 28777 times)
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Rich Moore
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« Reply #425 on: March 12, 2017, 06:50:01 PM »

Wings next for covering, but I keep finding reasons to put it off. I've just spent a bit of time adding some slots for the struts to engage with. Upper wing now has a 10mm balsa strip on wing underside from le to aileron break and is laminated to hold the undercamber. The lower wing gets away with a 6mm wide strip (to the upper surface of the wing - obvs), as it edges onto a rib. I still need to add some sheet reinforcement to the lower wing root bay to prevent damage here. Then I just need to do it. I'll use the contact adhesive for the wings. This model will look odd covered in clear film.

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Rich Moore
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« Reply #426 on: March 13, 2017, 05:29:10 PM »

One of my wheels just fell down the back of the fridge. Not the easiest of places to get to and it's a bit grubby back there, but with a bit of poking around with a length of carbon fibre tubing, I got it out - phew!
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Rich Moore
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« Reply #427 on: March 14, 2017, 01:39:17 PM »

In the past, I've made the flying prop to the scale diameter. On this one, I'm thinking to increase the prop to 15", using the attached blank proportions. This blank gives a blade angle of 33.77 degrees at 75% radius from the centre, which, according to a chart I have (Hepcat's, I think) would give it a pitch/ diameter ratio of about 1.55, which is coarser than I normally make them. Does this sound like a good idea - please shout at me if not.
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ironmike
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« Reply #428 on: March 16, 2017, 11:16:35 AM »

Rich
My experience flying the DR-1 is that your
pitch may be a bit much. Prop on my buddies
Dr-1 is around 1:1
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vintagemike
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« Reply #429 on: March 16, 2017, 02:04:38 PM »

That prop block looks suspiciously like a certain Mr Hipperson,s Senator prop blank to me, definitely a bit high on pitch for what you want
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billdennis747
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« Reply #430 on: March 16, 2017, 02:43:28 PM »

I agree. I used that block on my Jungmann and it wasn't very good:
https://www.youtube.com/watch?v=7gGRqfjDPIc
Things improved greatly with a plastic prop of lower pitch
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Rich Moore
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« Reply #431 on: March 16, 2017, 03:40:24 PM »

Yep, my gut feeling is that it is too coarse, hence the asking. It is indeed Mr Hipperson's Senator block, and thinking about it, is designed for a different type of performance from the one I'm looking for. With multiple confirmation that it isn't really the tool for the job I'll re-think it and use a block for a finer pitch. I think plastic props typically have p/d's of 1 or even less, but I don't want to use a plastic prop if I can carve a wooden one that works. I haven't carved a prop with this fine a pitch before - maybe that is where I've been going wrong! Thanks for the input everyone.
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Rich Moore
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« Reply #432 on: March 17, 2017, 03:19:41 PM »

I have been playing around with props and pitch etc and modified the previous blank to provide a pitch/ diameter of 1.1 at 55% radius. The pitch reduces towards the tip and is 0.9 at 75% radius. I have drawn the blank and attached it below. I have compared this to a large plastic prop I bought for my Dr1 (though never tried due to the work required to install it), which has pitch/diameter ratio of approximately 1.0, so they are similar, except the block will produce a prop with wider blades. This feels more 'right', but I hope I'm not over compensating and taking it too far the other way...
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Prosper
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« Reply #433 on: March 21, 2017, 08:13:41 AM »

Hi Rich, fascinating viewing as usual. Such a big prop is way out of my size range, so the bigger Reynold's number will make it behave differently to any prop I've made. My guess is that 0.9 at 75% is erring towards too fine, but it's erring in the failsafe direction. IMO plastic props are made with very fine pitches because to be commercially successful they have to cater for everything, however heavy or draggy.

I would have thought that for any flying model where duration is desirable, what's wanted is a prop that operates at its best lift-to-drag ratio at the very same airspeed at which the whole model has its best L/D, pretty much. That's probably an impossible combination to find unless you have a wind tunnel handy. But trial-and-error can get you in the right neck of the woods. Is there time for you to make a variable-pitch test  prop of some sort, even if it has flat blades with little or no twist?

If I was making a prop - even a giant one like you're making - I would try to get the blades good and thin. P'raps outdoor rubber duration people who are used to big props will tell me that's wrong, but I'd need a bit of convincing.

Stephen.
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Rich Moore
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« Reply #434 on: March 21, 2017, 09:09:12 AM »

Hi Stephen, thanks for your input. I might just carve a couple - one as shown, one with maybe p/d of 1.0/ 1.1. The set up allows easy swapping of props, and I don't mind building a collection of  them as I don't think this'll be my last big 'un. An adjustable pitch prop would be sensible for experimental purposes, so I'll give that some thought.
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RalphS
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« Reply #435 on: March 21, 2017, 09:54:27 AM »

John Barker's (Hepcat) Prop Picker program would give a better than guessing clue to pitch, etc., along the lines of Prosper's list of variables.  I haven't seen John on here for a day or two.  Perhaps Yak52 might comment if he has John's program. 
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Rich Moore
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« Reply #436 on: March 21, 2017, 02:54:56 PM »

I have had a search for John's prop picker, but all the links I found seem to be broken. I know this would be helpful, but I'm not sure I should be let loose with calcliashuns. Stephen (Prosper) has initiated the 'cunning plan' cogs and I have just glued up some laminated prop blades that need a couple of days to dry in their fixture (15 degrees on a fat pipe sort of thing). I'll try and use these for an adjustable pitch prop. In my head I have some 9mm aluminium tube, some hardwood dowel, a hardwood carved hub, plus a few 2mm machine screws...
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Prosper
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« Reply #437 on: March 21, 2017, 05:00:54 PM »

Waiter Go, Rich. The prop/motor combination has such a profound effect on model performance that I'm sure it's worth the experiment if time allows. I have Hepcat's Prop Picker; if you'd like a copy PM me. My only doubt as to its utility in your case is that it requires a L/D (lift-to-drag ratio) value for the model to be entered. I wouldn't even like to guess at an L/D for your model.  You can establish a rough L/D by gliding your model at the speed you think it'll fly at, from a known height, and measure the ground distance it covers before landing. By the time you're ready to do this it may be just as well to get on with flying it, and use your experience and the wingloading to guide you as to whether its performance seems significantly less good than expected. If it is then changing prop pitch and/or motor length/thickness can make a beeg difference - at least that's what I've found over time.

Just my tuppence worth.

Stephen.
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Rich Moore
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« Reply #438 on: March 21, 2017, 05:10:21 PM »

Thanks Stephen. I haven't got time to mess about too much before I must fly it in anger, so I'll settle for flight in the first instance - I need to finish building it before anything else! However, from flight, I can work on better and then, hopefully, best. I've taken the carrot regarding an adjustable prop though, as this may speed that process up.
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Yak 52
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« Reply #439 on: March 21, 2017, 06:16:45 PM »

Sorry - late to this party  Smiley

My experience with Prop Picker has been with commercial props and using it to size motors (for which it is excellent) but as Prosper mentions you need an idea of the models L/D and also some context with John's T/To thrust value output.

If I were you Rich I'd just make the biggest prop that fits at a sensible pitch (not too high on a bipe?) and wind 'er up  Grin
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Rich Moore
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« Reply #440 on: April 25, 2017, 03:08:59 PM »

I'm warming up to dusting this thing off...
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Rich Moore
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« Reply #441 on: May 06, 2017, 06:00:59 PM »

Some progress this evening but...rant alert!!

The wings had a couple of coats of toluene diluted contact adhesive a couple of evenings ago, and tonight I have been using a household iron to attach the mylar. Although I've managed to get reasonable results, I can't say I've taken to it very well. In fact it's been driving me potty. Perhaps I need to give the contact adhesive more time to cure, but the mylar only has to look at the carbon leading/ trailing edges and it sticks fast. I've had to rip off a couple of pieces and start again and the bloody stuff just clings to my hands like it's some kind of joke. I have got very close to losing my rag this evening!

I guess I need practice - I didn't like tissue covering once but now I enjoy it. I can't wait to get the tissue over the top of this mylar stuff!
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vintagemike
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« Reply #442 on: May 06, 2017, 06:47:32 PM »

Have you tried using a Pritt Stick for attaching mylar? use a fairly new one, they tend to go slimey after a while. You might find its a lot less messy (no smell either) and you get a little bit of "moveabillity"
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Rich Moore
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« Reply #443 on: May 07, 2017, 04:30:50 AM »

Quote
Have you tried using a Pritt Stick for attaching mylar?

No. I have tried pva, which worked quite well and if things don't improve I'll probably revert to that. I thought I had better use contact adhesive as it seemed the 'proper' way to stick it, especially on an under-cambered section. Being a plastic, it makes sense that it needs a solvent adhesive so I am surprised pva sticks it so well, and maybe pritt stick would work. I should test a couple of pieces and do a 'pull off' test to see how strong the bond is.

Where I might come 'unstuck' using pva would be on the undercambered ribs. Sometimes diagonal wrinkles occur alongside the ribs, but with the contact adhesive they are easily removed by easing the mylar along the rib a bit by reheating with the iron. That's probably the main advantage for contact glue - manipulation with heat.

It's me - new technology, new tricks, old man. I'll get there.
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ZK-AUD
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« Reply #444 on: May 07, 2017, 04:43:16 AM »

Mate there's an explanation of covering in film on Mike Woodhouse's site.  Saw it the other day and noted the strategy for removing static - no doubt useful for when I have a go at covering in mylar one day!
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RalphS
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« Reply #445 on: May 07, 2017, 08:54:50 AM »

The wings had a couple of coats of toluene diluted contact adhesive a couple of evenings ago, and tonight I have been using a household iron to attach the mylar.

As a long time user I have only found the need to put more than one coat on heavily under-cambered wing ribs.  One coat is sufficient on all other parts if I have lightly doped and sanded the structure previously.  I have never left the coated surfaces more than about 10-15 minutes.

but the mylar only has to look at the carbon leading/ trailing edges and it sticks fast. 

I would guess that the adhesive needed to be thinner.  I mix it so that it drips off the end of a cocktail stick like a water drop.  The mylar can be repositioned easily with a bit of care.  It should fasten to the LE/TE with slight finger pressure but when reactivated with the iron it will stick.

Practice makes perfect.
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« Reply #446 on: May 07, 2017, 10:36:37 AM »

Just stumbled across video on covering an F1B rudder with Mylar, might be of interest. Here is link:
https://www.youtube.com/watch?v=X3LU789gM3A

Louis
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RalphS
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« Reply #447 on: May 07, 2017, 03:08:15 PM »

Just stumbled across video on covering an F1B rudder with Mylar, might be of interest. Here is link:
https://www.youtube.com/watch?v=X3LU789gM3A
Louis

Excellent video.  Note the small amount of very thin adhesive that he uses.  Looks like thinned contact adhesive as he parks his brush in thinners, otherwise it would go hard.  The iron that he uses is similar in size to the one that I use.  Very sharp blades to cut the overhanging mylar.  The only thing that I didn't like was the trimming done on his legs.  Well worth looking at.  Thanks Louis.
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Rich Moore
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« Reply #448 on: May 07, 2017, 05:03:40 PM »

Thank you all. Again.

I have had wing session #2 this evening and things went a lot better. I put this down, mostly, to an attitude transplant - I sat down in a much better mood to start with, cracked off a nice fresh razor blade and put a different cd in the player. Other than that I think my biggest problem was what Ralph says - that the glue mixture wasn't thin enough, and I was too liberal with it. Plus I have made the mistake of starting with a heavily under cambered wing, which probably isn't the easiest shape to try on a first attempt.

Photos show what I've ended up with. Not too bad, but not professional either. 2nd photo shows the worst of the wrinkles which are behind the leading edge on underside in a couple of bays. I can't iron these out and I think I must lift off from the l/e and pull out, or replace the bays in question.
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« Last Edit: May 07, 2017, 05:15:23 PM by Rich Moore » Logged

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ZK-AUD
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« Reply #449 on: May 07, 2017, 08:00:30 PM »

Reminds me of the guy who fronted up to his psychiatrist just wearing clingfilm - Quack says "I can clearly see you're nuts!"
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