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Old Jun 19, 2007, 01:26 AM
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The original Flying Pigs Sqd.
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I got a BoT!!!

Back in the days, when I was a wee lad I....... no, no, no, I'm not that old yet.

When I started to look around for something to re-start RC flying, for the shortest time I considered the BoT. It's curves and lines have this "come-hither", classic look. And at 3 meter wingspan you won't loose sight of her quickly. But at that time (2002) there were only kits available. Lacking the skills, time and work area (not to mention the $$$) I set my sights on flying wings to start with instead.

I started with the 48" Unicorn. Added a Filip600Sport and some slopers. I got realy comfortable flying all those. Later I replaced my 48" 'Corn with a 42" version for some wilder yank&bank and some general scaring the heeby jeebiez out of birds, innocent bystanders, and fellow RC'ers. That left my Filip for the more sedate flying. And she just wasn't made for that. The Filip and Unicorn had overlapping flying charasteristics, and I wanted something to realy sit in my easy chair and thermal away.

Fast forward a few years.

Dynaflite came out with an affordable ARF BoT. They even have a short clip of a BoT test gliding here. Reading eagerly the various posts here on RCGroups it was clear there were teething problems. The main spar in the wing's center section had serious problems, and had a tendency to snap under pressure. Apparently in earlier BoT's the grain of the wood of the main spar was vertical instead of horizontal. That makes for a very weak spar that can break at very little pressure. Much has been written on the web about this, but suffice it to say that Dynaflite added in the manual that the BoT was intended for hi-start launches and not (the much more powerfull) winch launch. They also seem to have solved the mainspar problem.
Add to this that I intend to electrify my BoT so I will have no need for a hi-start or winch. My BoT will not be subjected to excesive pressure on the wing during launch.

Offcourse, purists will always say that a "good" BoT is one that is build from a kit. And they are right. There are several realy good kits on the market. One of the better ones seems to be coming from Skybench. Dynaflite also produces a kit, or you can just get the plans and build from scratch. If you do a search here on RCGroups, you will get plenty of links. Don't expect that building from a kit or plan will be cheaper then the ARF version. But you will have the satisfaction of knowing that every piece of wood in that glider has been lovingly shaped, sanded and fitted by you.

But for people like me, who lack the skill, a knowledgeable support group, and build area there's the ARF market. After driving my friend Eli Sayag up the wall with my flowery descriptions, he also wanted a BoT. As he is on friendlier foot with his LHS then I am, he organised our purchase of two Dynaflite BoT's, thus keeping costs at an acceptable level. In the end, the LHS actually ordered 4 BoT's. He probably assumes that after seeing our BoT's in Israel, others will follow. Personally, I think he's right...

Apart from putting a motor in the nose, I will also install spoilers in the wing, and move the elevator servo from the tail to the nose.. But more about that in the following building pages...
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Old Jun 19, 2007, 02:38 AM
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After opening the boxes, and a close inspection I have this to say:
For this amount of money spend, I like it !
There is a thick carton partition along the length of the box, dividing the top & bottom, containing the fuse and bits and pieces in the bottom part, and the three wing panels on top. All parts are in seperate plastic bags and individually taped to the box. You'd have a hard time shaking the box, and loosening any part!
The Monokote covering is not without a wrinkle here and there, but I suspect a touch with my covering iron will take care of that. I expected the rudder to be solid balsa, and had already planned on taking of the covering and making lightening holes. No need! The rudder is build up as well.
The fuse seems pretty good as well. Holding it up against a powerfull light I could not detect any change in the thickness. The front part has a light-ply frame (what seems like) hot glued in place. Contrary to what is written in the manual, the opening in the tail for the elevator servo has a fiberglass cover that you tape in place. All wing hold-down holes are pre-drilled.
The only blemish I could found on the fuse was on the tail part where the fuse extends down to protect the rudder during hard landings. Here the gelcoat seems a bit messy. No matter, I was going to epoxy a strip of carbon here anyway.

And last, but not least, I measured the nose and was very pleased to find I can easily fit my AXI2820/10 with a 40mm Turbo Spinner in there .
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Old Jun 19, 2007, 03:28 AM
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Rene - About the spars/grain direction.

I don't know the details of the BoT's spars but the usual construction for a webbed spar is for the top and bottom spars to run with the grain spanwise. The webs between the top and bottom spars are there for a crush load (when the wing bends up or down). They prevent the spar under compression (top one if on tow) from bending at the maximum stress point. In that case the balsa grain should be vertical. Balsa is much stronger for any given load when in compression along the grain. Having the webs outside the spars, it is even more important that the grain be vertical. For highest efficiency, the webs need to be fitted fully in contact with top and bottom spars and to the ribs each side.

I would be surprised if the kit you have is not like that.

It's a pretty aeroplane though! Ideal for sitting on a clifftop in a light breeze, looking out over the water while sipping a cold beer or three.

Here's a pic to show what I mean.

As I say, I don't know thw details of that actual model.
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Old Jun 19, 2007, 04:25 AM
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The covering is not transparent, so I'll see when I open her up to fit the spoilers.
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Old Jun 19, 2007, 04:38 AM
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Quote:
Originally Posted by Tony Oliver
In that case the balsa grain should be vertical. Balsa is much stronger for any given load when in compression along the grain. Having the webs outside the spars, it is even more important that the grain be vertical. For highest efficiency, the webs need to be fitted fully in contact with top and bottom spars and to the ribs each side.
That's correct.
Quote:
I would be surprised if the kit you have is not like that.
Unfortunately the earlier versions were wrong - the grain ran horizontal and the webs were poorly secured and fitted, apparently just hot glued in place. Bad job all around.

Hopefully this has been corrected now that the model is several years old and the problems have been well documented.
Quote:
Originally Posted by Up&Away
The covering is not transparent, so I'll see when I open her up to fit the spoilers.
Let us know what it looks like inside when you open her up. The spoilers are a wise addition.

There is also a big chunk of lead in the nose, but that weight will be offset by your motor/batteries. You may want to keep that servo in the tail. Better/shorter control rod and may/should help balancing.
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Old Jun 19, 2007, 05:08 AM
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Thanks guys. I'll post pics of anything worthwhile, including the spar .

Anyway, getting back to last night. So as not to agravate the wife too much, I started last night on some bits 'n pieces. It should also be noted that I am building two BoT's at once, so I realy need the whole of the table...

The outer wing panels connect to the center with a dihedral brace consisting of two pieces of ply and two pieces of aluminium, epoxied together. Knowing my extraordinairy ability to spread a multitude of different glues anywhere around the house (it sticks to my fingers; glue does, realy!) I strayed slightly from the manual. I glued the ply parts first together with alyphatic glue (after trial fitting) and let that dry under pressure. Then I epoxied the aluminium parts to the ply. Each part seperately, so I wouldn't have two sides of epoxy slathered ply to deal with. All that with regular changing of latex gloves.

Then I made the spoiler blades. 1.5mm Balsa 15cmx4cm each.
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Old Jun 19, 2007, 09:39 AM
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That steel rule looks all wrong!

They are supposed to be covered with blobs of epoxy, smears of wood glue (they show up as black after a day or two), and odd coloured paint splashes.

Looking forward to seeing both flying.

Incidentally, a week ago I decided to look up the meaning of 'aliphatic'. I'm not much wiser as to the effect as far as glues are concerned, but the references I read seem to suggest that it means 'picking up oxygen'. Maybe if the manufacturers changed it to picking up CO2, we would all be more politically acceptable?

On that same stupidly correct theme, the world may be interested to learn that here in the UK, the footplate area of working steam locomotives will be designated 'No Smoking' areas from the 1st of July (Honest, not the 1st April!).

Our government seems to be surprised that we think they are a bunch of dimwits!
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Old Jun 19, 2007, 09:48 AM
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Rene,

The only issue I had with mine (and I really had no problems until my elevator servo failed) was that I think the center section should be glassed over. I cut away the Monokote and laid a layer of 2 oz (I think it was this weight) glass top and bottom out two inches past the centerline. This is the only area I saw that seemed like it could use some beefing up.

One mistake I made was to install the horizonal stab servo in the tail. I would definately add a bellcrank and mount the servo forward.

BTW, I made spoilers quite similar to yours. Believe me, if they're even half that size they'll drop it out of the sky in a flash!

...bob
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Old Jun 19, 2007, 03:33 PM
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Not much done today. I had to go to my daughter's school to see her dance.

Despite my serious efforts not to, it appears I have been too generous slopping epoxy about with the dehidral braces. So after some energetic sanding with my PermaGrit sanding block (I am nothing without my PermaGrit. Best investment ever!) and dissapearing in a cloud of cured epoxy, wood and aluminium dust while holding my breath, lots & lots of trial fitting, I got the braces to fit, and epoxied them in place. I also epoxied the anti-rotation pin in place.

And that's all I did tonight!

Eli, this is your wing:
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Old Jun 20, 2007, 01:58 AM
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Oh, and on the issue of servos and the elevator, I will be using two GWS HPX Park servos (19 grams and good for 3Kg torque) both under the wing. The elevator will be activated via a bellcrank. For the spoilers I have two 9grams hexTronik servos.
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Old Jun 20, 2007, 03:55 PM
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Finished now with the dihedral braces for both BoT's, so it's on with the spoilers.

The pics are self explenatory. I had one unpleasant surprise though. In the pictures I saw of someone installing spoilers in his BoT, there were large holes in the ribs. Great, you can get the wiring through those, no problem. But here I have teeny tiny holes! Apart from the obvious (opening up the covering all the way to the wingroot), any ideas for a simple way to get the servo wiring to the center?
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Old Jun 20, 2007, 04:30 PM
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Quote:
Originally Posted by Up&Away
Finished now with the dihedral braces for both BoT's, so it's on with the spoilers.

The pics are self explenatory. I had one unpleasant surprise though. In the pictures I saw of someone installing spoilers in his BoT, there were large holes in the ribs. Great, you can get the wiring through those, no problem. But here I have teeny tiny holes! Apart from the obvious (opening up the covering all the way to the wingroot), any ideas for a simple way to get the servo wiring to the center?
Make the holes larger.
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Old Jun 20, 2007, 04:40 PM
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Try a length of piano wire which is just thick enough to fit the holes (US calls it music wire) to make sure the holes line up. Then make up a cutting tube with a diameter large enough to take the servo wire and its socket ends. The tube also needs to be long enough to allow at least 5 inches (125mm?) more than the length 'root to spoiler box'.If you're happy about making up your own extension leads, then only the servo wire size hole is needed You need to unpick the pins from the 'plug' end of your extension lead. I've only done it once, but it was fairly easy to use brass tube sharpened on the inside with a fine file and given a jagged end - something like a rotary saw blade. Just rotate the tube to cut its way through each rib. You may need to resharpen it a few times depending on the rib material. It also helps to lubricate the tube slightly with candle wax to make it easier as the ribs are pierced.

The piano wire acts as a guide to stop the tube breaking through towards the covering Once the tube breaks through the last rib you can remove the piano wire, feed the extension lead through the tube (or pull it through after tying/taping it to the piano wire).Feed the wire from the spoiler end, or you won't be able to remove the tube! Once it's safely through, reassemble the socket end making sure the pins are in the right order for your servos.

I'm sure there are other ways but this does work even though it's a fiddle around.
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Old Jun 23, 2007, 05:10 PM
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I took your advice Tony! And as usual, it turned out great.

I had a copper tube left over from when I immitated your wingdowel system. With a file I sharpened one end, and inserted a wooden dowel in the other end, so I could insert the tube in my electric drill. Then I measured how far the tube should go, and put some duct tape on the tube. As you said, it is important not too put too much pressure on the tube while it's turning. Otherwise you could break some ribs. Also, I re-sharpened the tube a few times. All in all it took me about 15 minutes to get the job done.

Now all I need to do is get a string through from the underside of the center panel, towards the servos...
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Old Jun 24, 2007, 04:12 PM
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Got home late today, so I didn't get much done.

I made the servo trays for one wing, and I inserted a piece of spring through the holes in the ribs to the middle of the center panel. That was easier than I thought. I inserted the copper tube again, mad a hole in the bottom of the wing's center, and pushed a piece of string from the tip, through the tube to the middle. I fished the string out of the hole with a pair of tweezers.

Tomorrow I hope to do the second wing, and maybe solder some servo wire extensions...
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