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Simplified version of the classic biplane

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Nigel R28/11/2019 10:54:51
4156 forum posts
698 photos

Hello all

I'm aiming to build an Aeromaster over the coming months (or maybe years, I'm not a fast builder). It's a classic 0.60 size biplane from 1966. It looks just like a full size single place homebuild bipe and reportedly has an lively flight performance.

The original kit version plan is on outerzone here

It's all very nice, but a bit complicated for me. I quite like my airframes a bit simpler. The original was geared up for a kit production and used locking tabs and so on. Wings are banded on. Lots of stringers and fiddly bits on the formers.

In 1978, a nice simplfied version was published in RCM - the Aeromistress. See plan here

That's all very nice, but a bit too much ply for me. I quite like my airframes a bit lighter. However, this version does follow the outline of the original quite faithfully, and adds a very neat cabane arrangement, whereby just one regular nylon bolt attaches the top wing.

In 1980, a scaled down version (from 48" down to 42" ) in 0.40 size was published in RCM - the Airmeister (see plan here).

I also have a Precedent BiFly - the smaller version - which, when I took a ruler to it, turns out to be remarkably close in size and shape to the Aeromaster, just scaled down from 48" to 36".

The Aeromistress, Airmeister and BiFly all capture the aerodynamics of the original Aeromaster,. I'm hoping my effort will do the same, and be a blend of the best bits (at least to me) of all of them.

Edited By Nigel R on 28/11/2019 10:55:37

Nigel R28/11/2019 11:05:24
4156 forum posts
698 photos

I'm currently planning and drawing. No wood cut yet, nothing ordered, just making plans

All opinions on what I'm thinking of doing are welcome!

My current favourite powerplant is an OS 91 Surpass. Just about the best of the rest of the field that isn't Laser. I haven't much experience with the newer OS four strokes but the Surpass era motors always seemed to be a good blend of quality construction, good running characteristics, and reliability.

I could also go with a 61 SF. They're nice lumps of metal too, but I just can't shake the feeling that a two stroke isn't right for this kind of airframe.

So, first question to the field.

Has anyone put a 90 size four stroke into something like a BiFly 48, and if so, did you need to change much to get a good balance with the heavier engine (or was it church roof in the tail)?

My first instinct is to try and keep the prop driver in the designed location, but maybe I could move it forward a bit. I will need to move the firewall back a bit, I think. But also, perhaps the tail could be lengthened a little to compensate for the heavier engine.

PS anyone suggesting I go electric will be made to stand in the naughty corner for a few minutes!

brokenenglish28/11/2019 11:11:12
599 forum posts
30 photos

I prefer Ken Willard's Sporty Forty to all the above.

Former Member28/11/2019 11:16:27
3573 forum posts

[This posting has been removed]

Nigel R28/11/2019 11:20:45
4156 forum posts
698 photos

I guess I kind of am, Tom. It's hard to step too far away from them if I make a "homebuilt style" bipe. I suppose ultimately the only thing that will remain is the outline. Who knows, I might adjust a few things here and there on that, too. Early days yet with this one.

On an engine weight note, the original plan shows a Veco 61, which weighed a big whole 515g including silencer. Considerably lighter than a current 60 with a good double chamber silencer.

Perhaps I need to keep the four stroke back a bit, and leave the prop driver in the "right" place. Relocate firewall to suit. The 0.91 is 640g total, I think.


Edited By Nigel R on 28/11/2019 11:28:34

Former Member28/11/2019 11:26:34
3573 forum posts

[This posting has been removed]

Chris Freeman 328/11/2019 11:36:05
355 forum posts
530 photos

Nice project, the aeromaster was inspired by the Bucker Jungman and has a very good reputation for being a great flying aircraft. I will follow this thread with interest.

Peter Christy28/11/2019 11:39:09
1901 forum posts

Another worth considering is the "Stringalong", by Frank Knowles. Its not on Outerzone, but was a Radio Modeller plan IIRC, in the mid 60's, so might be available from Sarik.

I built two, back in the day, and it was a very nice flyer. I still have the fuselage and tail (wings were damaged in a cross-wind landing on a gusty day!) awaiting restoration! Mine was "adequately" powered by a Webra 61 Blackhead.

Its a lot simpler to build than the Aeromaster!

It was designed for competition aerobatics, and I recall seeing the designer flying one at the Nats around 1966/7 time, though it looks more like a WW1 Fokker!

Should go like a rocket with a 91 up front!

The pictures show my first one (around 1968/9), which was sadly destroyed on its second flight when the brand new Simprop radio suffered a total failure due to poor soldering in the battery pack! The second one used my Bonner Digimite (the radio the SImprop was meant to replace), before eventually being upgraded to a reliable "red box" Sprengbrook radio! I modified both to four inset ailerons instead of the original two strip ailerons on the bottom wing only. One central servo in the bottom wing worked the lot.

The roll rate was quite fast!




Edited By Peter Christy on 28/11/2019 11:41:28

Denis Watkins28/11/2019 11:57:01
4649 forum posts
131 photos

Just for information and comparison Nigel

The Aeromaster does look the business

I know Bipes have loads of drag, but in my view, at 48" is still 8 foot of wing to carry weight

And this size, including my bi-fly, come out a heavy 7.5 - 8lb

BUT my 4ft span bipe goes like a Rocket already on a Saito 62, so what will an OS91 do

Also the 91 is relatively quiet, and a nice motor, and you have one

And 60s are relatively quiet too in 2 stroke

You decide

John Lee28/11/2019 12:12:08
803 forum posts
93 photos

I built an Aeromaster from the Great Planes Kit in the late 70's early 80s & fitted an OS 90FS. It was well matched to the airframe & flew very well indeed.

I recall Ken Bings doing a classic kit review at the time which inspired my build. Rather than the usual 'flew straight off the board with a couple of clicks of trim' Ken went into detail of how it reacted during all sorts of manoeuvres such as knife edge to knife edge flicks.

FlyinBrian28/11/2019 12:31:04
677 forum posts
4 photos

I have built at least six Aeromaster bipes, as you may assume I like em. My first was from a plan loaned to me by Ken Binks in the late 60's, I have also built one from the Great Planes Super Aeromaster kit which is basically the same as the original but uses bolt on wings and u/c plus a round cowl.

While the build is lengthy it is not hard.

My current Aeromaster is a bit of a bitsa with a second hand fus, the bottom wing from a previous model and a self built top wing.

I have an unstarted GP Super Aeromaster kit tucked away - Just in case!

I have also had a Stringalong but the AM is a much better aeroplane IMHO

kc28/11/2019 12:49:46
6706 forum posts
173 photos

The original versions used engines like Merco 61 etc which are probably more equivalent to a modern 60 four stroke than a 90. Even a 60 four stroke seems maximum for a 48 inch span bipe!

kc28/11/2019 12:55:37
6706 forum posts
173 photos

The Super Aeromaster is surely the best looking of the lot and the plan is available on Outerzone showing the built up radial cowl. Worth considering?

Anyone wanting a simple bipe should consider the Acrobits which in my opinion flies better than the Renegade bipe (another simple construction but using a wood cabane structure) which I once flew straight after flying my Renegade - my friends Acrobits was just that bit nicer to fly!   Both are about 48 inch and flew well on a modern .40 two stroke. - do you really need more power?

Edited By kc on 28/11/2019 13:13:40

Edited By kc on 28/11/2019 13:14:40

John Lee28/11/2019 13:07:01
803 forum posts
93 photos

The Review is well worth a read, particularly the 'Flying' section at the end.


John Lee28/11/2019 13:07:20
803 forum posts
93 photos


John Lee28/11/2019 13:07:34
803 forum posts
93 photos


Mike T28/11/2019 13:16:40
572 forum posts
35 photos

IMO the Aeromaster looks by far the best of the designs linked in the OP. I'm not sure the Super Aeromaster looks better - the radial cowl looks disproportionately small to me.

If it were me, I'd keep the outlines of the Aeromaster (with possibly a decent sized radial cow) and design-in the simplified structures of the others.

kc28/11/2019 13:42:04
6706 forum posts
173 photos

Biplanes need cabane structures and if you enjoy soldering then it's fun but if you hate soldering.......

.......when planning a redesign consider using dural struts in a similar manner to the Barnstormer etc but using wing bolts instead of rubber bands.

Nigel R28/11/2019 14:04:49
4156 forum posts
698 photos

Thanks all for the interest! I hope I can do it justice with this build.

Chris - the Jungmann and Jungmeister are both great looking bipes in all their forms.

Mike - that's what I'm really aiming for yes

Brian - I'm not planning on that many (at least for now!) - but I'm hoping to keep almost all of the build to regular sport type construction, the real exception will be the cabane area, I think that will need some careful attention.

John - many thanks for posting that review - makes good reading smiley

kc - The Super Aeromaster style cowl is a nice addition to the looks. I could go for that.

Denis - I also have a 70 Surpass, so there is another option on the table; that said, I do like a "sufficient" amount of power. I think the original Veco 0.60 would probably be equivalent to a recent "oversized 0.40" type such as ASP 52, Irvine 53, etc. But then again, back in the '60s a 2 stroke would be allowed to rev much more so than we would do now, and it would be producing a fair bit of go. So perhaps not that different. As to fitting a 0.90 four stroke, I think I would put the power as roughly equivalent to a 0.60 2 stroke.

As a general thing on sizes, most of the 0.40 size bipes I looked at, tended to have longer, thinner wings. The GP Sportster Bipe for instance is the same span (well, very nearly) but has much less area (720sq in) and a much slimmer, lighter fuselage. The Aeromaster is quite a compact airframe, with fairly low aspect ratio wings - it carries a lot of area (about 850sq in) which to me puts it well into the 0.60 size class.

I've just googled the weight of the 61 SF and come up with 540g with no silencer. JE reckon their super quiet silencer is 160g - so that's 700g all up, which on the face of it makes it heavier than the 91 Surpass. The four stroke will definitely swing a bigger, heavier prop. Possibly a heavier mount? I can't see much in it either way, but the 91 will sound a lot better in a bipe.


PS kc I enjoy soldering, it's all good. I'm kitted up with a wire bender and quite happy to bend, bind and get the torch out on the result. What I will need to try and do is reduce the amount of critical dimensions on the cabane wires.

Edited By Nigel R on 28/11/2019 14:06:46

Don Fry28/11/2019 15:19:44
4557 forum posts
54 photos

One area where you can simplify the build is to replace the formers aft of the wings with depron. It makes cutting those stringer formers so much easier, and lighter, and cheaper. Ditto wing ribs.

With regards to engine weight I think you risk madness trying to make the predictions of cause and effect. If you look at the picture of the 1307hrs post, it shows a set of servos that weigh in at a porky 70 grams each. A receiver of that era was also IRO 70 grams, that is probably that big chunk of foam rubber forward of the servos. Now the moment to the CG of that lot, is about the same as the engine CG moment. Modern kit, installing 148 servos from the spares box, and a receiver, 140 grams, tops for weight.

So you might need 140 grams less engine weight to balance, or more using H.V. light gear. But it's all a bit of a philosophical discussion. Build it, be all right on the night,

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