Twin-VW engine Push-Pull design idea (The "Beetlemaster")

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cluttonfred

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If you *must* have twin booms, do you still need twin rudders? And is a high-wing the only option? The Moskalev SAM-13 low-powered fighter prototype is an intriguing layout offering a more compact package than the Skymaster type and it puts the rudder right in the prop wash for low-speed and ground maneuvering. I could see this working well with motorcycle-style seating, the rear passenger straddling the pilot seat but raised 8-12" for visibility, everything as tight and compact as possible for lowest weight and drag.

sam-13 pic.jpg

sam-13 3-view.jpg

PS--Here's a quick and dirty sketch of what that might look like. Playing around with it, I think side-by-side is the way to go to reduce CG travel with and without a passenger. A narrow cockpit like a VP-2 with a bulged canopy like a Malcolm hood might work well here. Gear left up to the imagination. ;-)

SAM-13 inspiration.jpg
PPS--Of course, looking at that side view, you could also drop the twin booms in favor of a single boom a little lower. I'm just sayin'.... ;-)

single boom.jpg
 
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Nicholette

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Annnnnd.... don't forget the Twin boomed, Edgley Optica, 160HP Lyoming ducted fan. (Free extra thrust! An added advantage of lowish twin booms is you do not have to worry so much about people walking into the prop, although ductiing the fan is another solution.) Hmmm I wonder how difficult it would be to re-engine it with two VW's driving that fan?

 
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Vigilant1

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Gear left up to the imagination. ;-)

View attachment 96864
PPS--Of course, looking at that side view, you could also drop the twin booms in favor of a single boom a little lower. I'm just sayin'.... ;-)

View attachment 96892
But allowing for an adequate rotation angle is our big problem, right? Unless we are going to take off or land really "hot" (5 degree AoA?) or have very long gear, the tail needs to be pretty high at the end of the boom. If the tail surfaces and gear legs are going to be typical size, then to give normal rotation angles the lowest point of the aftmost part of the empenage has to be about 45" above the ground. So if our booms start at the bottom of the pod, they need to angle up. If they start at the wing, they can come straight back.
 
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autoreply

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Thanks for the heads-up Mark!

I was thinking pretty much dead up slap a motor on the front of the Rohr, toss the duct.


View attachment 96588
5minute sketch, with 54" props, VW's fully buried.
That's an interesting line of thought. If we expand on that a little further:

If you increase the span and decrease the chord a few times and add winglets with a rudder you get wings with a fairly small chord allowing to use the Rutan method to make them. Additionally, this allows for flaps which might be a necessity (drag during landing) and allow a smaller and lighter wing.

If you *must* have twin booms, do you still need twin rudders? And is a high-wing the only option? The Moskalev SAM-13 low-powered fighter prototype is an intriguing layout offering a more compact package than the Skymaster type and it puts the rudder right in the prop wash for low-speed and ground maneuvering. I could see this working well with motorcycle-style seating, the rear passenger straddling the pilot seat but raised 8-12" for visibility, everything as tight and compact as possible for lowest weight and drag.
Looks a lot more complicated structurally and in the control system.

Also, using an inverted V-tail, by applying power, the propwash will suck down the elevator, which is a good thing.
 

Hephaestus

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Thanks for the heads-up Mark!


That's an interesting line of thought. If we expand on that a little further:

If you increase the span and decrease the chord a few times and add winglets with a rudder you get wings with a fairly small chord allowing to use the Rutan method to make them. Additionally, this allows for flaps which might be a necessity (drag during landing) and allow a smaller and lighter wing.
Not sure about your area - but around here the XPS factory prefers 10x4x4' blocks of dock foam. Or at least that's the cheapest /cuft picked up from their dock.

I just really like the compact size of that Rohr layout.

Rutan style winglets with split flap style rudders was one option i had pondered. But then keeping it simple and adding some speed brakes ala A-4 off the side of the fuselage keeps wing construction even more simple.
 

Vigilant1

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I was thinking pretty much dead up slap a motor on the front of the Rohr, toss the duct.
View attachment 96588
5minute sketch, with 54" props, VW's fully buried.
That's an interesting line of thought. If we expand on that a little further:

If you increase the span and decrease the chord a few times and add winglets with a rudder you get wings with a fairly small chord allowing to use the Rutan method to make them. Additionally, this allows for flaps which might be a necessity (drag during landing) and allow a smaller and lighter wing.
The longer span would be useful for single engine ops.

And, maybe put an H-stab on top of that fin to take the flying wing voodoo out of the project?
 
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Hephaestus

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The longer span would be useful for single engine ops.

And, maybe put an H-stab on top of that fin to take the flying wing voodoo out of the project?
Really short coupled - but sketches out nice with a v-tail.

No flying wing voodoo - straight up delta :)
 

Vigilant1

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No flying wing voodoo - straight up delta :)
The drawing looks very cool. >If< we want to carry two people and stuff (400 lbs?), enough gas to go someplace (200 lbs?), and two VW engines (360 lbs), and we have the obligatory tires, landing gear, prop, exhaust, engine mount, seats, radio, etc then I don't how we can get the MTOW below about 1500 lbs, even with some pretty aggressive structural efficiencies. Getting a 1500+ lb plane to climb on 75-80 HP requires very low induced drag at climb speed, and the key to that is wingspan.

A short wing could work okay if:
1) Safe flight on one engine isn't a requirement. That's not something I'd want, but maybe somebody would.
or
2) Severely reduced MTOW (e.g 1 seat, small amount of fuel, very light structure).

Some rough numbers: Pops's design has an MTOW of about 1550 lbs and span of 34' (area of 140 sq ft). It would have induced drag in level flight at 60 kts of about 70 lbs. It will safely climb on one engine (and dragging another stopped prop) at altitudes of up to about 6K' MSL.

A plane that weighed the same and had a 25' span (say 8' root cord and 1' tip chord =113 sq ft ) would have level-flight induced drag at 60 kts of about 115 lbs. To match the induced drag of Pops's design, the short-winged plane can't weigh more than about 1200 lbs. It would climb a little better (same excess thrust hoisting less weight), so you could either chop more off the wing or increase weight a >little<. But the additional weight will quickly cut the rate of climb (due to induced drag with that short wing), so it can't be much.

Bigger, stubbier wing? With the wing of a Verhees Delta 2 seat version (approx 18' span, 150 sq ft area), our 1550 lb plane would have induced drag at 60 kts of about 195 lbs. That's worse than the previous delta. Despite the bigger wing area (and resultant lower required cL), the reduced span still dominates the induced drag calculations.

A 1200 MTOW plane with 360 lbs of engine(s) is gonna be a 1 seater, and the airframe will still need to be built quite light.
 
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Hephaestus

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Just for arguments sake and it's better than watching the news.

Original was 180sqft of wing (30' wingspan) 1450lbs dry, 150hp of o320.

That o320 was 300 lbs +/-, so you drop the duct and the fancy prop... You're same ballpark as the 2 VWs.

I'm no engineer - but Al Mooney drew this as an inexpensive composite bird. The focus doesn't appear to be on weight reduction through and through...

Of course there's efficiency to be found, I tossed this out there as the boom discussion seemed to be going on endlessly :)
 
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