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Old Aug 12, 2014, 05:18 AM
I like real wooden aeroplanes!
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Build Log
Bill Winter's "Airknocker" for AMPLAN Build Off - finished and flown

Well, having been responsible for floating the idea for this build off, I need an entry.

The range of choice is bewildering, so I compiled a short list on which models appeared which represented the cream of U.S. designers. It was:

Duet (Strader)
Hummingbird (Plecan)
Infant Sportster (Winter)
Navigator (McGovern)
Gasser (Willard)
Sportwagon (Smith)
Strutz Aircrate (Strader)
Breezy (Willard)
Miss America R/C (Winter)
Airtrails Sportster (Shereshaw)
Airknocker (Winter)

Two of these models I had already built in the distant single channel days, The Miss America R/C (TD 049) and the Gasser (Cox Special 15 - Wheeee!) and the rest are just designs that I find attractive for one reason or another.

Finally I whittled the list down to the Sportwagon and the Airknocker. I selected the Airknocker mainly as it is a simpler build and, with the Avro Avian still to be finished and a couple of O/D projects bubbling under, building time may be at a premium, but also because it is one of those models that, since I first saw it when I bought the Flying Models magazine back in the sixties, just appeals to me.

My version will be of course electric and RET, but other than the essential changes to the nose end structure and the addition of an elevator I intend to curb my natural desire to make structural alterations and build it "as per" with perhaps just a touch of lightening here and there. Indeed I will be very surprised if my electric version doesn't come out considerably lighter than the 28-32 ounces quoted for the original.

No work other than printing out the tiled plan and sticking it together until September 1st, meantime for those who don't know it here is a jpeg of the drawing
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Old Aug 12, 2014, 09:43 AM
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This is a great choice, you will really enjoy this model.
After building an Airknocker per plan and flying it, I would advise to follow Bill Winter's design intent and fly yours rudder-only, especially since it'll have electric propusion. This model absolutely does not need an elevator.
I've always found that rudder-only models make the most beautiful take-offs and touch-and-goes with judicious use of the throttle. The same applies to turns where a bit of throttle up keeps turns flat and pretty.
As far as power goes, the Boll Aero 1.8cc engine turns a 9x4 prop at 7500 rpm, which is just enough power for the 810 gram weight of my example.
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Old Aug 12, 2014, 09:59 AM
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What's the British expression?....."Spoiled for choice"? it's tough to whittle down a long list, but I think you've picked a good one, SD.
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Old Aug 12, 2014, 10:31 AM
I like real wooden aeroplanes!
Sundancer's Avatar
South-west France
Joined Sep 2007
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Originally Posted by JMP_blackfoot View Post
This is a great choice, you will really enjoy this model.
After building an Airknocker per plan and flying it, I would advise to follow Bill Winter's design intent and fly yours rudder-only, especially since it'll have electric propusion. This model absolutely does not need an elevator.
I've always found that rudder-only models make the most beautiful take-offs and touch-and-goes with judicious use of the throttle. The same applies to turns where a bit of throttle up keeps turns flat and pretty.
As far as power goes, the Boll Aero 1.8cc engine turns a 9x4 prop at 7500 rpm, which is just enough power for the 810 gram weight of my example.
Nice looking Airknocker JMP. Sorry though, I won't be following your advice on going rudder only, I've reached the advanced age where I like an easy life and given my tight and tree surrounded flying field I definitely want pitch control.

Interested to see that yours is 29 ounces, in the middle of the designers 28-32 ounces. I'm hoping mine will be closer to 24 ounces and am planning on using a 120 watt outrunner which should be plenty at 80 watts/pound.
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Old Aug 12, 2014, 07:23 PM
I'd rather be flying.....
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I have hiding somewhere a copy of the original AirKnocker article.... I can scan it if desired.

Excellent choice - You can't go wrong with Bill Winter designs !

JMP - wonderful model !

Best Regards,

Jeff
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Old Aug 13, 2014, 02:15 AM
I like real wooden aeroplanes!
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Originally Posted by JeffMac View Post
I have hiding somewhere a copy of the original AirKnocker article.... I can scan it if desired.

Excellent choice - You can't go wrong with Bill Winter designs !

JMP - wonderful model !

Best Regards,

Jeff
Thanks Jeff but Ray (RFJ) who seems to have absolutely all the model magazines which ever existed kindly emailed me a scan a few days ago.

I have always liked BWs models, he was a very practical designer. I built a "Pal Joey" for TD049 and Elmic Compact escapement when the plan appeared as a "freebie" in Aeromodeller in the 60's which flew for years, then another one as a "hot rod" galloping ghost model with a Frog 150R, which didn't last quite as long! Then I built the "Miss America R/C" for rudder/elevator and a TD049 in the 1970's and despite being burdened with the then current heavy radio gear it was a lovely little flier.
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Old Aug 15, 2014, 06:07 AM
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For what it's worth, the C.o.G. on mine is located at 56 mm from the leading edge (fuselage top horizontal).
Be sure to choose pretty hard balsa for the wing main spars or, as I did, splice hard balsa near the root (first 1/4) to softer balsa outwards. With elevator and 120W, you'll stress the wings more than my rudder-only low-powered style of flying.
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Old Aug 15, 2014, 06:29 AM
I like real wooden aeroplanes!
Sundancer's Avatar
South-west France
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Quote:
Originally Posted by JMP_blackfoot View Post
For what it's worth, the C.o.G. on mine is located at 56 mm from the leading edge (fuselage top horizontal).
Be sure to choose pretty hard balsa for the wing main spars or, as I did, splice hard balsa near the root (first 1/4) to softer balsa outwards. With elevator and 120W, you'll stress the wings more than my rudder-only low-powered style of flying.
Thanks for that JMP, it is always useful to have a CG position from a known successful model.

I have already addressed the spar situation. My natural inclination with any O/D wing would be to use top and bottom spars with webbing, but I am trying not to alter this one structurally beyond what is needed for the electric and control surface mods. So I decided to keep the big bottom main spar, but I will make this by laminating 1/4" x 1/8" spruce top and bottom of a 1/4" square balsa, and also fit proper tapered 1/16" ply dihedral braces. Many years of designing wings for line launched thermal soarers have made me very sensitive to both the necessary strength and the need to taper out root stresses properly. I considered using the 1/8" x 1/4" spruce on the inner third only and splicing 1/8" x 1/4" balsa from there out, but I have some very nice, light, spruce so hopefully changes in materials elsewhere will counterbalance the extra weight of the spar (changing the ribs to 1/16" and fuselage sides too, with 1/8" square edging). So I am quite confident that whatever else befalls, at least I won't pull the wings off this one!
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Old Aug 17, 2014, 04:28 PM
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May I ask what prop/motor/battery combination you have in mind?
And, if I may be so bold, will you be scalloping...so to speak???

Gordon
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Old Aug 18, 2014, 02:40 AM
I like real wooden aeroplanes!
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Originally Posted by GeeW View Post
May I ask what prop/motor/battery combination you have in mind?
And, if I may be so bold, will you be scalloping...so to speak???

Gordon
Hi Gordon

I'm planning to use a BRC Hobbies A2212-10T running on a 2S 1300 or 1500 pack which should give about 100 watts on a 8 x 4 or about 120 watts on a 9 x 4.

And - yes, I'll definitely be scalloping! It's not illegal in France
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Old Sep 01, 2014, 04:34 PM
I like real wooden aeroplanes!
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It's September 1st, so here we go!

I've had a pretty non-productive year building-wise for one reason or another, just two models and I can't seem to get on with finishing the Avro Avian, so I have been chomping at the bit to get on with this. It is a simple model and for some reason just appeals. So, as I am up to date with the garden and other chores at present I decided to award myself a full days building, something I haven't done for a while as most of my building is done in fairly short sessions these days. I was interested to see how much I could get done in a concentrated session. The weather helped - nice and sunny but not too hot for the chalet workshop at 22 degrees, and also too windy to be tempted away flying.

I had already scaled up the plans from the 1/4 scale jpeg I had - nothing fancy, just a lot of pencil lines on tracing paper.

The first job was to make the main wing spar; instead of the 1/4" x 1/2" solid balsa on the plan I elected to use some nice light 1/4" x 1/8" spruce laminated each side of a piece of 1/4"square balsa. Once this was clamped up and drying I made a 1/16" ply rib template and produced all the wing ribs and riblets, a process which took less than an hour - who needs laser cut parts?I was using quick drying PVA wood glue so by this time the wing spar was ready for trimming to length and assembling with the two ply dihedral braces. Whilst this was drying I cut out all the bits for the tailplane and built it, resisting the temptation to change the "V" structure to my customary criss-cross, I want to keep this one fairly original.

At this point I discovered I had no 1.1/4" wide trailing edge, so had to laminate two 1" wide with two pieces of 1/4" square. Whilst waiting for this to dry I decided to cut out the fuselage sides only to discover I only had 2 sheets of 3/32" balsa when, due to the depth of the fuselage, four are needed. . I quickly decided to use firm 1/16" of which I have an ample stock, and fit 1/8" square corner longerons and spacers to make up for the thinner sheet.

I managed to get the first wing half on the board before lunch, so immediately afterwards I could tip over the main spar and build the second half onto the first. Whilst this was drying I occupied myself with carving and sanding the tailplane and elevator, quite pleasant sitting out in the sun in front of the workshop to avoid making a mess inside. I also made a 1/16"ply template for the scallops on the wing and tail trailing edge, by which time the wing could come off the plan and I fitted the top centre section sheeting. A break for a cup of tea gave time for this to dry (I was using quick drying "fast grab" PVA for all the building) and then I had another session outside in the sun carving and sanding the wing (with that chunky leading edge there was a lot of carving and sanding to do!) and then fitted the trailing edge ply rubber band protector and the 16 swg wire to the leading edge to perform the same job at the front.

By now it was dinner time, so after a sufficient digestion period I returned to the workshop for another hour which I spent applying the scalloping to the wing trailing edge and elevator (I was glad I had gone to the trouble of making the template, I'm sure that using this and carving in the scallops produced better results than the method suggested by the designer of sanding them in with a round block). That just left time to glue up and pin down the 1/8" balsa fin pieces to dry overnight before retiring to watch University Challenge on TV.

So, complete flying surfaces ready to cover, fuselage sides cut out ready for framing, total building time so far 8 hours. Very satisfying.

The wing weighs 4.3/8 unces/124 grams and the tailplane/elevator i ounce/28 grams.

I doubt the rest will go as quickly once we get into the fiddly bits, but it is a nice start.
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Old Sep 01, 2014, 04:54 PM
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'Fizzin' heck' you're going to be giving our very own Billy Whizz a serious run for his money on this one!
It would have taken me a day to have built the tailplane and maybe cut out (probably badly) a handful of ribs!


A question about the plan if I may. The part labelled 'B' laminated from 1/8" on the plans...what is it???
'D' appears to be the T/E bulkhead, part shown bottom right appears to be the L'E bulkhead or is it the one sort of under the main spar???

Gordon
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Old Sep 01, 2014, 06:14 PM
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Originally Posted by Sundancer View Post
The wing weighs 4.3/8 unces/124 grams and the tailplane/elevator i ounce/28 grams.
You're on your way to a light Airknocker.
FWIW, my finished wing weighs 159 grams and the tailplane 42 grams.
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Old Sep 01, 2014, 11:58 PM
I like real wooden aeroplanes!
Sundancer's Avatar
South-west France
Joined Sep 2007
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Quote:
Originally Posted by GeeW View Post
'Fizzin' heck' you're going to be giving our very own Billy Wizz a serious run for his money on this one!
It would have taken me a day to have built the tailplane and maybe cut out (probably badly) a handful of ribs!


A question about the plan if I may. The part labelled 'B' laminated from 1/8" on the plans...what is it???
'D' appears to be the T/E bulkhead, part shown bottom right appears to be the L'E bulkhead or is it the one sort of under the main spar???

Gordon
Don't worry Gordon, things will slow down now, it is always installation and the other detailed bits that take the time with me, flying surfaces and major airframe components are easy, especially on a structure as straightforward as this.

Fuselage bulkheads; well, that is one of today's jobs and I have to say I puzzled over the plan a bit as it is rather vague around the nose area. From measurements "B" (shown over the nose) is the LE bulkhead, "D" (shown over the fuselage behind the wing TE) is the TE bulkhead and the unlabelled one bottom right is the intermediate one which would have been the escapement mount in the single channel installation. The other two shapes under the fuselage are the front fuselage "floor" and the nose doublers (about which the plan is vague). The firewall isn't shown, but in any case I am having to change things a bit in this area as obviously I have no bearers and will be using a slip-on "bucket" cowling held by magnets over the motor mounted on the re-positioned firewall.
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Old Sep 02, 2014, 12:03 AM
I like real wooden aeroplanes!
Sundancer's Avatar
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Originally Posted by JMP_blackfoot View Post
You're on your way to a light Airknocker.
FWIW, my finished wing weighs 159 grams and the tailplane 42 grams.
Thanks for the weight information JMP. As it will be mylar/tissue covered I would hope the finished weights will be less than yours, which should keep me on target for about 24 ounces. Not that it wouldn't be perfectly OK at 30 ounces, I'm just conditioned to building light from my early days with electrics when the power and radio systems were so much heavier.
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