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Author Topic: Boston Observer  (Read 4268 times)
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scigs30
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« on: January 04, 2012, 02:40:54 PM »

I remember back in 1985 seeing a picture of this Bostonian in a Model Airplane Magazine and I always wanted to build it.  The problem is the picture only showed the girl holding the Bostonian with no name of the plane.  I did not know there was plans available for this bird or there was an article about this Bostonian until a thread I read here.  I still have the picture to this day.  So I ordered the magazine and printed the plans and began building.  This was a fast straight forward build and built from the plans.  The only change I made was I did no use 1/16 X 1/32 for some up the up rights like the plans call for, way to weak in my opinion.  I am also not too crazy about the rear fuselage design or the + incidence on the main wing, but oh well.  This is not a build thread since it was pretty straight forward but she was built using all white glue, I hope to have her covered today.  I have to see if I have the tissue I want to use and the wheels are a little too big for me, I think I need to order some 7/8 wheels. The weight so far is 10.5 grams and for some reason the wing is 15 7/8 long and not 16 inches long, that is just how it is designed and it says it on the plans.
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craig h
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« Reply #1 on: January 04, 2012, 06:05:58 PM »

Nice bones...if it were me..I would make some wheels by cross gaining some 1/32 balsa with aluminum tubing for the axles..very easy to do and save you some bucks for something else. Hope to see some pic's of her covered.
Enjoy..
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scigs30
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« Reply #2 on: January 06, 2012, 11:42:51 PM »

Sorry, But I think my wheel making days are over. This was a fast, easy and fun build and cannot wait to fly her on Sunday. I used Esaki tissue pre shrunk twice to prevents warps and applied it with 50/50 white glue and water.  I doped the tissue first then put it on the tail surfaces to prevent warpage.
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Mr Blue Sky
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« Reply #3 on: January 07, 2012, 04:41:52 AM »

What a pretty aeroplane! It's not often that I see a design that I want to build and the Observer has gone to the very TOP of my list. One of your posts says that you will scan the plan. If you have please send me a copy, thanks.

Tony.
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craig h
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« Reply #4 on: January 07, 2012, 09:09:08 AM »

Very nice....hope you do make the plans available..and hope we see some pic's of it flying..
 Great job..have fun!
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scigs30
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« Reply #5 on: January 07, 2012, 10:59:47 AM »

I am still working on the scanning the plans.  She is being flown tomorrow and I will get some pictures.
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RolandD6
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« Reply #6 on: January 07, 2012, 02:38:10 PM »

I agree with Tony. It is a pretty aeroplane that begs to be built. It is not often a sport (yeah I know, 'Contest') design appeals to me but the Boston Observer does. It has all the usual bits-n-pieces but there is something about the proportions.

Paul
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scigs30
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« Reply #7 on: January 15, 2012, 06:41:25 PM »

I still have to scan the plans, but I did get a chance to flyer her today.  She flew great. Also here is a picture of my Comet Piper Cub flying.
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OZPAF
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« Reply #8 on: January 15, 2012, 08:40:22 PM »

I really enjoy your flying shots.Great little model and your looks very impressive.
Happy Flying
John
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Mr Blue Sky
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« Reply #9 on: January 16, 2012, 03:52:02 AM »

I'm glad somebody is getting to fly. It's a frosty Monday morning, I have a pinched nerve in my shoulder and the sight of your Observer doing her thing make me feel a whole load better. I am hoping to build a Bostonian for the indoor meet at Impington in March. I spend most of the day on the door taking money and answering questions and I hope to be flying this time. The Observer could be a candidate although there are a couple of others I like as well. Your Cub looks a bit special, is it the Coupe version?

Happy landings,
Tony.
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scigs30
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« Reply #10 on: January 17, 2012, 01:23:50 PM »

I posted the plans in the Plans section.
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Dave Andreski
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« Reply #11 on: January 19, 2012, 10:35:27 AM »

Scigs,
Thanks for the great photos and thanks for sharing the "Boston Observer" plan.
Dave Andreski
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« Reply #12 on: January 19, 2012, 11:42:55 AM »

Nice job Scigs.

Randy Randolph had a knack for designing nice looking airplanes.
I notice the plan top view shows a rather aggressive curve in the fuselage sides from the wing leading edge to the nose block.  It looks like you used a more direct, straight line.  Did you simply "crack" the lower longeron, for the taper to the noseblock?
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Mr Blue Sky
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« Reply #13 on: January 21, 2012, 03:16:32 AM »

Thanks for scanning the plan Sgigs. It's time for me to start cutting wood.

Tony.
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RolandD6
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« Reply #14 on: August 01, 2013, 08:55:21 AM »

Here is my version of the Observer bostonian.

I have increased the slope, fore & aft, of the cockpit glazing and have also added more diagonal bracing. I incorporated extra bracing because I did not expect much torsional stiffening by the covering.

I did a quick and dirty job of the prop and prop shaft because I did not want to make another nose bearing, preferring to try one I already had on hand. Prop shaft is 0.025" which is possibly a bit too light and the prop itself may not produce enough thrust. Normally I would bend the 'Czech' hook using a jig but I do not yet have one that size so it was bent free hand.

Thrust adjustment is by three 2-56 nylon grub screws shown in the second last image. These are easy to make from 2-56 nylon screws slotted with a razor saw and then cut to length with a blade.

The covering is 7.5gsm Tengujo on the wings and fuselage, 6gsm Tengujo on the tailplane and fin.

All colours and sealing/shrinking was done with various mixtures of the acrylic ink shown in the last image.

The tailplane is coloured with Art Spectrum Orange, the fuselage and fin with Art Spectrum Green and the wings with AERO COLOR red-orange. I had already done the tissue for the fuselage and tail before receiving a suggestion that AERO COLOR may be better because it has a higher pigment density and is also airbrush ready.

I did not go to the trouble of using an airbrush because this model incorporates many experiments with the acrylic finishes and it may have been a total disaster. I used a regular 1/2" golden sable bright (ie. rectangular, artist speak) brush. I think the photos adequately show differences in the quality of finish. There is a particular problem with those nose ribs on the wing. The front spar needs to be full depth to support the covering. The covering did not like the sharp point at the end of each nose rib.

In essence, Tengujo pre-prepared with an acrylic coating is basically a paint/ink film reinforced with a web of wood fibres so it tends to catch on sharp points.

I could talk about the mixtures I used but it may not be of value to people because:

1. Art Spectrum is an Australian brand; and

2. Acrylic resins used in different brands of acrylic products do not behave equally with this technique.

Since completing this model, I have got better/different results with two types of floor polish I can source locally. Future seems to be in that mysterious category of unobtanium. Again I could post some info about them but they are Aussie products and behave differently, even when used as a dope substitute. They both seal and shrink the tissue but the surface quality and transparency differ.

Oh yes, the weight. Finished as you see it without rubber it is bit heavy at 10.76 gm (assuming the last decimal place is believable). I expect airbrushing the colour to be lighter and using one of the floor polishes instead of the clear acrylic medium I used (bottle on the left of the last image) may also be lighter.

Next time. Possibly my DPCM Sopwith Pup project.

Paul
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OZPAF
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« Reply #15 on: August 01, 2013, 06:46:09 PM »

Thats a very neat looking model Paul. I like the colour densit - the green on the fuselage looks great and the red is very bright.
The prop looks like a "yoghurt" one and the hub looks interesting - is that a modified nylon bolt or? I couldn't see your thrustline asjusters actually but can imagine how they work.
Just as a matter of interest - i scaled this plan up to arund 20" and built a propotype "Indoor" RC to fly in a small assembly hall. It weighed 45gms ready to fly and used a GWS 5dx3p prop.
It has a slow floating glide and flies well - although underpowered.
John
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RolandD6
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« Reply #16 on: August 02, 2013, 12:12:07 AM »

Thats a very neat looking model Paul. I like the colour densit - the green on the fuselage looks great and the red is very bright.
The prop looks like a "yoghurt" one and the hub looks interesting - is that a modified nylon bolt or? I couldn't see your thrustline asjusters actually but can imagine how they work.
Just as a matter of interest - i scaled this plan up to arund 20" and built a propotype "Indoor" RC to fly in a small assembly hall. It weighed 45gms ready to fly and used a GWS 5dx3p prop.
It has a slow floating glide and flies well - although underpowered.
John

Thanks for the kind words John

The prime reason for doing all of this development was to end up with a suitable system for covering and finishing indoor scale models with a decorated covering weighing near to that of ordinary doped Esaki. This is why I have been trying to use Tengujo 7.5 & 6 gsm tissue; the problem is that Tengujo is very porous so I needed to find a way of filling those holes without adding much weight. I believe I have managed to achieve that goal, near enough anyway. The next couple of projects should prove the process, one way or another. Earlier work with 9gsm tissue proved to be much heavier if the colour density was too generous.

Achieving opacity is the problem and I am beginning to think that it will be more difficult to achieve with acrylics than it may be by using dope and quality pigmented paint like Floquil. Unfortunately dope and hydrocarbon solvent paints are not desirable materials from my perspective.

The thrustline adjustment device is simple in concept but difficult to make in its current form. It is a metal tube with a PTFE bearing inserted into each end. At the prop end, the insert has a hemispherical rear that nests into a hemispherical cup (the black ring). The bearing at the hook end is top hat shaped. Turning the PTFE to get a snug fit in the tube is not easy. It is a bit like machining stainless steel. A very sharp tool and plunge cutting is needed to avoid the tool pushing the work piece aside.

The blue bit is a piece of BIC ball point pen barrel with three 2-56 tapped holes spaced radially at 120°. The nylon grub screws are in those tapped holes. The white bit inside the blue bit is a short piece of styrene tube that locates in a 5.5mm dia. hole drilled in the balsa nose block.

The prop is a commercial one I purchased from A2Z. See https://www.a2zcorp.us/store/ProductDetailNP.asp?Cguid={DA89125A-F755-4161-BEA2-9D7DADB7CEF3}&ProductID=1922&Category=ModelSupplies:Propeller

I have made props using blades cut from polystyrene cream or yogurt containers. Styrene containers are not so common these days. Polypropylene seems to be becoming the plastic of choice.

Your electric model is big by my standards but is typical of the size flown in Melbourne at this venue: http://www.indooraviation.com/

Most members are R/C fliers but a few like me fly F/F, mostly rubber.

The photos for 26/7/2013 ( http://www.indooraviation.com/photos-from-26-july.html ) were taken in the current and hopefully permanent venue. Some of the others were taken at an earlier venue.

Paul
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korale
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« Reply #17 on: November 19, 2013, 07:36:52 AM »

Paul,

Guess what ? I've been working on an Observer as well, here are the 'bones', weight so far is 5.1 g I'm estimating 9g as final weight.

I've got to get her covered and need to make a prop, look forward to flying yours and mine together
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korale
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« Reply #18 on: January 29, 2014, 05:41:45 AM »

Well I finally got it covered and carved a prop, I decided to try out printing on tissue for the colours, its not perfect but it looks ok. current weight is 9.3g. I need to do some detail work on the prop and then its ready to fly. I tried a couple of test glides and it looked great.

 
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Pete Fardell
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« Reply #19 on: January 29, 2014, 06:25:30 AM »

Looks great! Did you just lightly stick the tissue to paper to print it? It came out really well.
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korale
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« Reply #20 on: January 29, 2014, 06:29:26 AM »

I preshrunk and stuck the tissue around the edges to a sheet of A4 and then printed it.
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RolandD6
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« Reply #21 on: January 29, 2014, 03:44:05 PM »

Much lighter than mine. I have not yet perfected my methods for using acrylic finishes and sealers. More work to be done.

My model flies well but not for very long indoors, primarily because of its weight although the prop may be partly to blame because it needs a hefty bit of rubber. At present I am developing a method (tooling) to help me carve small prop blades accurately. I prefer the style of hub and replaceable blades. I have had success with twisted blades but my modelling associates keep telling me that carved is better so I am doing all of this work to see for myself. The idea behind making tooling is to minimise human error in the creation of a particular design so that the relative merits of different designs are being compared, not differing bumbling efforts at trying to duplicate a particular design freehand.

The next indoor flying day of the VFFS is at Manningham D.I.S.C. on Sunday 17th Feb. The official start time is 1.00 pm but people begin to arrive around 12.30pm. I will not be there because we have a family holiday booked.

You will find D.I.S.C. on Melway map 48 F4.

Paul
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korale
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« Reply #22 on: January 29, 2014, 10:21:48 PM »

Paul,

   I will definitely be there on the 17th, and I might have another model as well.

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RolandD6
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« Reply #23 on: February 04, 2014, 08:09:32 PM »

...
The next indoor flying day of the VFFS is at Manningham D.I.S.C. on Sunday 17th Feb...

Correction: The date should be Sunday 16th February

I hope that no one other than korale is affected by this error.

Paul
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korale
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« Reply #24 on: February 16, 2014, 02:50:16 AM »

Went to Manningham today and managed to get the Observer trimmed out, I think it needs some slightly thicker rubber and I might make a new noseblock. best time I managed was 58 secs.

http://www.youtube.com/watch?v=fN4NStWeBFo

Sorry for the quality of the movie.
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