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Author Topic: New Model - for OS15FP  (Read 7698 times)
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glidermaster
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« on: November 12, 2009, 03:52:04 PM »

I am about to get cracking on a new model - not that I need one, but.....................

Anyway, I was contemplating high thrust line (HTL) a while back - but I've abandoned that idea, and instead I will build a Mk.2 of my 'Semislo' design - you can check out Mk.1 on page 2 of the 'Power Models' thread. Mk.1 has proven quite a good model.

I have made a series of small tweaks to the design;
1) - I have pushed the span up a little.
2) - I have made the tail a little bit bigger (as a percentage of wing area).
3) - I am intrigued by Brian Eggleston's airfoil work on bunting F1A gliders, so I have tweaked the leading edge profile of the airfoil to make it slightly more symmetrical in character
4) - Something I've been thinking about for a while, I'm going to build the wing 'All Washed Out'.

On that last point, the right tip will have 2mm washout, the left 5mm. The right inner will have 1.5mm washout from root to tip break, and the left inner 4mm (I am reviewing these numbers still - before starting to stick stuff together).

A little look at the plan.

John
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New Model - for OS15FP
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glidermaster
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« Reply #1 on: November 12, 2009, 03:56:12 PM »

Apologies for the ropey picture - I'll try a different file format.

The plan shows a hard tank, but I'm thinking seriously about a bladder tank for this one. It will have pressure, so I guess I won't be flying it in Slow Open if I make any trips to the UK in the future.

John
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Re: New Model - for OS15FP
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glidermaster
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« Reply #2 on: November 12, 2009, 08:23:59 PM »

Ok this is embarrassing, I've done this many times in the past - one more try for a decent picture.
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gossie
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« Reply #3 on: November 12, 2009, 08:41:43 PM »

We get the idea. Smiley
Looking forward to seeing the build.
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glidermaster
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« Reply #4 on: October 06, 2010, 01:54:37 AM »

I've done very little building this year for various reasons, but I have made a bit of progress with this model - namely the wing and tail.

Both surfaces are 'D box' structures, that is to say they have sheet balsa from the leading edge back to the main spars, top and bottom, and the top and bottom flanges of the main spar are joined with vertical grain balsa webs forming a very stiff closed cell in the front of the wing.

I selected some nice 1/16" sheet for the D box, which is a little thick for a modest size model such as this, and I sanded it thinner it in a simple jig. This consists of a 4 ft. long off-cut of 1/2" ply sanded nice and smooth, to which were epoxied 2 long rails 5" apart of 0.045" aluminium sheet picked from the scrap bin at work. The sheet balsa is held between the rails and sanded with a long block flipping over from time to time, until contact is made with the aluminium. It is a simple process, but actually takes quite a long time, and produces much mess.

John
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glidermaster
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« Reply #5 on: October 06, 2010, 09:27:57 AM »

I tried something new to me on this wing; I built it 'tip-to-tip' meaning I built one wing tip, then jigged it to the right dihedral angle, and built the inner panel right onto it, then the other inner panel, then the last tip. I usually build the whole thing flat, then put in the dihedral (polyhedral). The 'tip-to-tip' system works well, I like it!

I built onto the lower D box sheeting, with no warps built in, then added the webs into the spars. I set the required warps when I added the top sheeting, and formed the close cell at the front of the wing.

One more little detail - there are no spar flanges in the tips, other than little tapered stubs at the tip joint. In other words the tips are just the sheeting and the webs.
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RobinB
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« Reply #6 on: October 07, 2010, 08:18:49 AM »

Very timely for me that you've put this up, John.

I'm about to start on a 430 sq.in. Semislo-inspired wing, so I'll be following this with interest.

First question (probably the first of many!): What weight / grain is your D box sheeting?

Robin
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glidermaster
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« Reply #7 on: October 07, 2010, 11:30:19 AM »

I typically use A or B grain for sheet surfaces, and I think the wood I used on this model is about 5lb/cu.ft.

John
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glidermaster
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« Reply #8 on: October 11, 2010, 08:33:46 PM »

The wing and tail are done ready to cover.

The tail is almost the same construction as the wing - 1/32" sheet for the D box.

A good meaty centre dihedral brace in the wing from hard balsa. Typical 'Buskell' construction!

John
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RobinB
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« Reply #9 on: October 12, 2010, 05:57:12 AM »

Nice-looking wing, John.
Did you web between the sheeting on the tips?

Robin
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glidermaster
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« Reply #10 on: October 12, 2010, 11:26:12 AM »

Yes, Robin.
The tips only have stub spars extending 2 ribs bays from the tip joint. The rest of the tip is just sheeting and webs, which maintains the closed (torsion) cell philosophy.

Started covering last night - heavyweight modelspan for the wings, lightweight for the tail. Similar to the Trad Lad Vintage FAI model, I 'doped' the wood frames with water based acrylic sanding sealer (2 coats - rubbed down) and put the tissue on dry with glue stick on the open structure areas, and will allow it to sit a least 24 hrs before water spraying. The tissue over the sheeting is 'doped' on with more sanding sealer.

I actually only use real dope to seal/shrink the tissue on the open structure areas.

Note that I think this method inferior to the 'all dope' method, but the exposure to dope fumes (which I really don't like) is very much reduced. The Trad Lad wing has much more undercamber than this model, and the glue stick attached tissue held fast on the undercambered surface when water shrunk and properly doped.
John
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Scottl0413
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« Reply #11 on: November 04, 2010, 09:32:46 AM »

John, how's the build coming along on your new plane? Inquiring minds want to know!!

Scott
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glidermaster
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« Reply #12 on: November 04, 2010, 10:56:43 AM »

Kind of slow, Scott (but thanks for asking!).

I have made some progress covering the wing and tail, but it's been very busy at work, so modelling time has been at something of a premium for the last few weeks.

John
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glidermaster
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« Reply #13 on: March 01, 2011, 05:32:44 PM »

Not much modeling time for me this Winter, and not much going on in the Power Models section here, either.

However, I have done a little work on the fuselage and the necessary hardware for this model.

The fuselage is a simple box of 1/8" sides and 3/16" top and bottom with 1/8" triangular longerons. Plenty of section thickness to allow shaping to a pleasing final cross section.

John
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glidermaster
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« Reply #14 on: March 01, 2011, 05:33:57 PM »

The tank is sheet brass. Crankcase pressure and flood off for this one.
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glidermaster
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« Reply #15 on: March 01, 2011, 05:37:45 PM »

I have had my first crack at making a scroll type timer.

The clockwork movement is an old Autoknips vane regulated type, and I made the scroll and disk on the lathe. Compared to Seeligs etc the scroll is a bit large and crude, but screw thread turning is a new experience for me, and my lathe is so old that changing the settings is a fairly major undertaking involving removing/replacing several gear wheels.
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« Reply #16 on: March 04, 2011, 06:04:18 PM »

Those OS FP motors make excellent freeflight engines! They are lightweight, cheap and powerful. I have been flying an OS FP .25 on the front of a Star Seeker from Flying Models for several years and have done very well with it -- I won AB Classic over some really good fliers and really hot airplanes at the Empire State Champs in 2009; I placed second this year. I have an OS FP .40 in my Class C classic model, which is a modified version of Bob Stalick's Hot Lumber design. However, it's too much power for the 600 sq. inch model, so I am downgrading to an FP .35 which bolts right in. The FP .40 is going to go into either a Pilfered Pearl 710 or a Satellite 780.

Nice design John!

Thermals, Simon
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« Reply #17 on: March 15, 2011, 12:44:16 PM »

Hi John,
I'm thinking of building a SLOP model with an OS15 fp, your model is most interesting. The aspect ratio looks very high for a lock down power model (approx 8.75 just from measuring my computer screen). Presumably the model will still transition ok etc?  What actual wing area is the model? I can't see too many obvious dims on the plan. Presumably the weight will come out around 15 oz? maybe a bit lighter? The stab looks a bit smaller than some models as well. Looks nice though, certainly prettier than, say, Dave Clarkson's layout Wink
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glidermaster
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« Reply #18 on: March 15, 2011, 03:34:16 PM »

Hi Adam,
There's always an element of doubt in a new design, I guess.............. but I just love designing models.

This model is a little bigger than a Mk.1 version I built in '02 and which is pictured on pg.2 of the 'Power Models' thread. Mk.1 flies well, and transition is usually good. I guess we'll see if it can handle a bit more aspect ratio.

This one (mk.2) is only 15 sq.ins bigger in the wing (375) and another 8 or so in the tail (now 100 sq ins). I will be a bit disappointed if the weight comes out over 14 oz. - i.e. I think it will be a little lighter than the mk.1.

I think the OS15FP is a great engine - perfect for SLOP.

John
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« Reply #19 on: March 16, 2011, 07:12:38 AM »

John, I'm impressed that you're aiming for 14 oz. - that metal motor mount must be lighter than it looks!

I'm guessing you have to fit the tank in before you fit that mount to the fus? Neat looking setup, though.

I'm looking forward to the rest of the timer work, as I have some Monks timers that I've yet to make up the arm assemblies for
and I'd like to see how you do yours.

Robin
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« Reply #20 on: March 25, 2011, 01:51:28 PM »

Timer Arms
10 thou brass sheet
39 thou music wire and brass tube to fit.

The pics pretty much show the rest - the hinge flap and brass tube are soldered together. The timer face plate is 25 thou 7075-T6 alu. As you can see, I screw the hinges to the faceplate with 10BA screws. When it's all fitted I scuff up the face plate surface, clean it and glue the hinges on with epoxy, just cinching down with the screws. When it's dry, dress off the screws flush with the underneath of the faceplate, then centre punch the screw end for a little 'rivet' effect. I haven't had one come off yet, but they can be 'recycled' if need be, without too much bother.

John
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« Reply #21 on: March 26, 2011, 04:31:30 AM »

Aaaaaahhh..... bend the wires to line up with the disc AFTERWARDS!

I've done it the other way around before, and it got really tricky trying to fix the arm to the faceplate in absolutely exactly the right position.

(It usually resulted in some slight re-bending / adjustment, so I might as well have left the bending until afterwards anyway!)

Thanks, John

Robin
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glidermaster
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« Reply #22 on: March 26, 2011, 01:10:35 PM »

Finished timer pic attached.

When I eventually get this model into the air I'll be using instant DT, so both arms will be coming out of the disc window. Later a little bending of the DT arm will allow it to engage the scroll.

You've got it Robin, leave the arm overlength until later. Actually I need to replace the DT arm, it's not quite long enough!

On/Off is internal - and not made yet.

John
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« Reply #23 on: March 26, 2011, 06:22:14 PM »

Good stuff JB. Smiley
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« Reply #24 on: March 27, 2011, 12:24:45 AM »

Quote
I'll be using instant DT,

Hopefully a couple of seconds delay? I just hate to see wings break off as the engine quits ..... :'(
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