Twin boom pushers

[macboffin]

For all twin boom pusher lovers, heres a sizeable one.All glass/kevlar/CF/epoxy construction.powered by 38 h.p. Norton Wankel rotary engine, for the Canadian Army. 14 ft span. I produced this one in Texas about ten years ago.

[zik]

Nice bird macboffin!

What kind of payload could it carry and at what speed?

[macboffin]

Nice bird macboffin!

What kind of payload could it carry and at what speed?
Measured level flight max speed at 1200 ft ASL was 135 kts.
Typical payload including fuel 72 pounds ; typical cameras.sensors weights around 22 pounds.

[Unterhausen]

that's a nice looking plane. Why all the control surfaces?

[macboffin]

that's a nice looking plane. Why all the control surfaces? The wing has ailerons and flaps, flaps in two parts either side of the booms, to lower landing speeds and aid recovery into constricted spaces. Ony one fin had a rudder, that was enough for adequate control.
The elevater was in two parts, dual redundancy in case of possible servo or wiring problems, since a vital control surface.Each half seperately driven.

[Unterhausen]

that's interesting. Does the boom split in half? It looks like the wing will split.

[macboffin]

The boom and fin are integral. The wing comes apart in the middle, two loose square tubes join it,the wing is then bolted onto the fuselage top. The tips are also removeable, there were eventually three sizes of tips so as to vary area and aspect ratio dependant upon operating height and increased weights. Multi-pin connectors engaged automatically when wing fitted to fuselage, to supply flap and aileron servos and tip lights , airspeed sensor under starboard wing and angle of attack/yaw sensor under stbd wing. Two different noses could be used, dependant on camera and other sensors used

[AdamKt1]

I wish, I could get it built by myself...

[Maple.hill]

I've got something very much like this on the drawing board at home right now. 2.5m wings. ryobi weed whapper engine. I'm enhoying the building process and i've not even got tot the electonic stage.

Any design tip or trick that you learned (that you'd like to pass on).

[macboffin]

One design point ; you only need one rudder ; which eases construction a little. Make a scale model "chuck glider" from balsa, say about ten fifteen inches span.Working ailerons, rudder, elevater cut out from surface and hinge with stiff paper in slits.Lets you see how pitch, roll, yaw work out.
And of course CG.Since "flat plate" section, model CG will be a tad rearwards of where it should be on the real thing.Assuming the real one about twelve fourteen inch chord, "real" CG will be about two inches further forward. Soft mount the weed whacker! Kinder to airframe and electronics!
A touch of washout will help, say about two degrees.
Tailplane as high as you can, and lifting section ; this saves having to re-trim pitch/ elevater with varying speeds.( More speed, more tail lift ;keeps the nose down ; close throttle, less tail lift, no need to feed in a bit of "up".
Post some pics as it comes along! Mac

[Unterhausen]

I should have made a chuck glider like you said, my CG is too far aft.

How important is it to have the rear landing gear close to the CG? Mine is too far aft.

[CenTexFlyer]

I should have made a chuck glider like you said, my CG is too far aft.

How important is it to have the rear landing gear close to the CG? Mine is too far aft.

The further back the gear is from the CG, the harder it is for the aircraft to rotate off the ground.

I think just about everyone has visited the twin boom design at least once or twice..... Here is what we call the "OMW" plane. Been kicking around for several years now.

Span : Std 80" - Stretch = 100"
Contsruction : Vacformed ABS, EPP, CF
Power : G26
Cruise : 65 mph
AUW : 14 lbs
Cargo : 7 lbs

Flies like a big ol' trainer. Very little interest in this one in either electric or gas.

[Unterhausen]

well, since I have to move my battery forward, I'll have room for my landing gear up where it belongs. I just put it in the most natural place without thinking about the problems rotating.

I'm just building a small electric so I can fly it in more places. Our Sig Kadet is a little too big.

Not sure why people wouldn't be interested in your plane Myron, that's a really common and practical configuration. But it's amusing how much looks can affect people. In my view, if it can fly, it doesn't really matter how it looks.

[Myron]

Hey guys,

Yeah, not much interest in our big gasser.. It has a 24 oz tank and it will probabaly fly for 5+ hours, and carry 5-8 lbs in its huge cargo bay.. Any takers out there at 1500.00 for a ready to fly bird minus the receiver?

Myron
512-731-3154

[Badllarma]

macboffin would you have any full scale plans avalible for the twin boom pusher you built 10 years ago or know of a source to get hold of them?

Really interested in this design for a future project. :)

[macboffin]

Twin boom pusher. Herewith 3 view drawing. Construction was Fibrelam, glass/Kevlar/ carbon fiber, produced from moulds for fuselage, wing tips, and some other components. Power was the Norton NR 71 air-cooled Wankel-type engine, 38 HP, 8500 revs, 28 inch Punctilio prop. Engine weight 23 lbs.
Stressed + 6G, -4G. I guess thats enough for starters!

[macboffin]

Angle of attack sensor under port wing, airspeed sensor under stbd wing.
Rudder on port fin only,(one is enough.) Fins integral to booms, (two bolt fitting) two bolts in each fin to attach tailplane, wings have sliding pair of joiner part-spars, tips of different spans to cater for low/higher altitude and differing loads, several different nose assemblies with differing sensor packages.

[kd7ost]

Macboffin,

How do you attach the booms to the wings on an aircraft like that?

Dan

[macboffin]

Macboffin,

How do you attach the booms to the wings on an aircraft like that?

Dan Front end of the booms followed the upper profile of the wing.
The rear spar had substantial doublers out as far as the boom attachment point, two bolts through the booms went into trapped nuts in the spars. The booms were triangular section basically, from quarter-inch Fiberlam sheet,
(Glass skinned honey comb sandwich material). Multi-pin plugs/sockets at the interface points served the tail group servos and lighting.

[kd7ost]

Thanks for the info. Was the wing built up from wood then?

Dan

[macboffin]

Hi Dan, no, the wing was mainly from Fiberlam, it's a sheet material comes in different thicknesses and face materials, it's a honeycomb core with usually glass faces, the honeycomb core looks similar to a real bee's honeycomb,hexagonal cells, made from Nomex paper.Can also be got with ali or carbon fiber faces, and there is a variety with ali honeycomb core also. Thicknesses from 1/8" up to two inches. Aircraft galleys, airsteps, floors are made from it. It stands very high point loadings,( high heeled shoes in a Jumbo's floors dor instance). Fastenings by way of proprietary ali or steel inserts ; or epoxy it. Tough stuff, you need a high speed router to cut cleanly, with carbide blades. Very very light material, worth the hassle.
We used it for ribs, built-up spars, etc.Fuselage via a mould with glass/Kevlar skin, layer of the honeycomb material, another skin to make a sandwich,vac-bagged in the mould. Quite a few light planes are built like this, including small jets. Super material. I think Hexcel Corporation supplies in the States.
No wood at all in the plane.

[dalbert02]

I was at a car accident once where parts of the race car were made of this material. It was a Formula (Indy?) style car and the part I held was part of the floor board. The section was about 3 feet by one foot and about 1" thick. It weighed nothing! Well, at least if felt that way. :) It was aluminum honey comb covered with carbon fiber. I have seen parts of the Lancair homebuilt aircraft use the Nomex honeycomb and carbon fiber and it too was incredibly strong and light. Very interesting stuff! Thanks Mac. Your posts are always interesting and educational. :)
-dave

[kd7ost]

Yes,

Thanks for the information macboffin. It sounds like its not a home shop, layman process.

Dan

[macboffin]

The sheet material is "home-workable", a bandsaw will cut it, the technique is to use masking tape where you are going to cut, which prevents the cut edges fraying out. With the 1/4" sheet you can cut with a Stanley knife, renewing the blade every ten inches or so. It blunts blades very fast!
You can bend it by cutting a strip of facing material,(Cut through thickness of face only,not into core) and pull the strip off, (you'll need a pair of pliers, it's well bonded to the honeycomb core) run a bead of epoxy along the area, then bend , wipe the spare epoxy off, and hold to the angle until the epoxy sets.Then epoxy a strip of glass tape into the corner. If you remove a wider strip, the material can be doubled back on itself ; good technique for cockpit coaming edges, "Instant longeron" etc. The fuselage of the "Shadow" kit-built two seat light aircraft is built by this "cut and fold" method.
By the way, you have to clean any surfaces to be bonded with acetone or similar to ensure a good bond.

[Gary Mortimer]

I want one please Macboffin!!!

Can I send a postal order!!

Is this the aircraft that you mentioned was sent to South Africa in another place??

[fly_asmara]

Macboffin,

Well done! Thats a really nice looking plane! Have you flown her? How did she fly?


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fly_asmara

[macboffin]

I want one please Macboffin!!!

Can I send a postal order!!

Is this the aircraft that you mentioned was sent to South Africa in another place?? No, it went to the Canadian Army ; about ten years ago.
Bearing in mind it was all-moulded epoxy/Kevlar/glass/carbon fiber, had a Norton Wankel engine 40HP, the postal order would be in the order of 6 figures!

[macboffin]

Macboffin,

Well done! Thats a really nice looking plane! Have you flown her? How did she fly?


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fly_asmara It flew very well ; for all I know, it's still flying!