Scale B&V P111 anyone?

HomeBuiltAirplanes.com

Help Support HomeBuiltAirplanes.com:

Riggerrob

Well-Known Member
Joined
Sep 9, 2014
Messages
1,876
Location
Canada
Good point!

One wag sketched a (ficticious) Grumman Goose with only one engine.
Frankly, that is the simplest way to understand Dr. Richard Vogt's assymmetric airplanes. Think of them as twins with only one engine producing power. Then determine which propeller blade is descending. The descending prop blade pulls harder. The engine with the descending prop blade farthest outboard becomes the "critical" engine ... if one fails. This asysmetry is often called "P factor."

When designing an assymetric single, the descending prop blade should over-lap the center line, to minimize assymetric thrust.
I have sketched a few assymetric light amphibians.
My latest sketches of an ultralight ended up assymetric because I wanted to fold it into an ISO 20 shipping container. Assymetry started with the horizontal tail to simplify folding. Then it was such a hassle cramming the pilot, prop, engine, etc. into a single pod, nacelle, gondola ... less than 8 feet long, that I displaced the engine and tail boom to the left of the pilot. That allowed for a crew pod less than 8 feet long and a simple folding scheme. When seen from the side, the engine partially over-lapped to pilot's legs ... without his toes catching fire.
Hah!
Hah!
I did not overlap the propeller with the pilot for fear that a thrown prop blade might amputate a leg.
Northrop P-61 Black Widow night-fighter crews learned that lesson the hard way during World War 2.

I found assymetric airplanes simpler to balance (fore and aft) than Seabees, Lakes, etc. Assym's can locate the prop anywhere you want (fore and aft) with little worry about interfering with seats, windshields, tail booms, etc. The only limitation is postioning the prop well forward of crew or well aft of crew.
If using a Continental or Lycoming engine, the clock-wise rotating (as seen from the rear) propeller needs to hang off the left leading edge. This puts the descending prop blade on the center line, minimizing P-factor. P-factor explains why many single-engined airplanes need a bit of rudder with full power. It also explains why many twins have a "critical" engine.

Yes, Richard Vogt did design a bizarre variety of assymetric airplanes.
Only his assym' Blohm und Voss 141 made it into production, but it was a short production run (about 40) because its BMW radial engine was needed in FW 190.
 

cluttonfred

Well-Known Member
HBA Supporter
Joined
Feb 13, 2010
Messages
8,115
Location
Fort Walton Beach, Florida, USA
I have long thought that a very simple asymmetric design could be very appealing, basically a conventional monoplane glider layout with the wing offset to one side and an offset tailplane to go with it. Basically imagine this Monnett Moni with the engine mounted in a tractor or pusher nacelle on the wing and a conventional tail with offset horizontal surface. You'd get fantastic visibility over the nose and, if you go with removable outer wing panels and a fixed center section about 7' span with the tailplane sized to match, the whole thing could be hangared in a 20' shipping container.



My latest sketches of an ultralight ended up assymetric because I wanted to fold it into an ISO 20 shipping container. Assymetry started with the horizontal tail to simplify folding. Then it was such a hassle cramming the pilot, prop, engine, etc. into a single pod, nacelle, gondola ... less than 8 feet long, that I displaced the engine and tail boom to the left of the pilot. That allowed for a crew pod less than 8 feet long and a simple folding scheme. When seen from the side, the engine partially over-lapped to pilot's legs ... without his toes catching fire.
 

Riggerrob

Well-Known Member
Joined
Sep 9, 2014
Messages
1,876
Location
Canada
Dear Cluttonfred,
You don't even need to build an assym' horizontal tail. The first version of Blohm und Voss' 141 had a horizontal stabilizer that was symmetric about the center-line/thrust-line of the long boom.
The production version only had an assym' horizontal tail to clear the field of fire for the rear-facing gunner.

A hand full of motor-gliders have been built to your suggested configuration.

Most of my sketches of a BV.141 half-scale replica also follow your suggested configuration with an engine boom 2 feet wide, wing center-section 2 feet wide and a pilot's gondola 2 feet wide. The span of the center section is determined by prop diameter. You want to keep prop-wash clear of the gondola.

A third alternative is the Dornier P222 assym' dive bomber. The pilot and gunner sit BESIDE the engine for improved forward visibility. Dornier's proposal never flew off the drawing board. Hint: Unicraft will cheerfully sell you a 1/72 scale model of Dornier's P.222 dive-bomber proposal.
 

cluttonfred

Well-Known Member
HBA Supporter
Joined
Feb 13, 2010
Messages
8,115
Location
Fort Walton Beach, Florida, USA
In my concept the asymmetric tail was to save having to fold or remove the horizontal tail for towing or storage, so it would follow the same offset and 7' span of the wing center section. Just remove the outer wing panels, hang them on racks in the 20' container, wheel the rest through the doors, and Bob's your uncle.

Among Richard Vogt's Blohm & Voss designs, the BV.178 illustrates the general idea, but with a much shorter span center section, offset tailplane, and not a jet, of course.

1618423485936.png 1618423503592.png 1618423555742.png
 
Last edited:

bifft

Well-Known Member
Joined
Apr 17, 2011
Messages
301
Location
Utah

cluttonfred

Well-Known Member
HBA Supporter
Joined
Feb 13, 2010
Messages
8,115
Location
Fort Walton Beach, Florida, USA
Almost. Topaz put the pilot in a nacelle (pod) and the engine at the front of the fuselage (boom). I was thinking of the pilot at the front of the fuselage and the engine in a nacelle, so the effect would be more like a short-winged sailplane with an auxiliary engine stuck on one wing and then the wing and tailplane offset a little for balance.

Not this...

1618505056014.png

...but this....

HBA concept sketches (17).jpg
This is just a quick sketch, but to give you an idea of scale, the spans of the center section and tailplane are about 7' each and the landing gear (not shown) would also have a track of 7' or less. Overall span with the two removable 8' outer panels is about 23' for about 60 sq ft area, so this is a hot little ship. You could make those outer panels 12' each and untapered for 31' span and 93 sq ft area and meet microlight/LSA limits with the right airfoil.

I was riffing off of Topaz's sketch, so this is probably more asymmetric than would actually be required for what would probably be a lightweight two-stroke or small industrial V-twin engine. In actual practice you would probably use different spans on the outer panels with the centerline of the wing near the pilot's right shoulder. Also, I've shown a pusher to keep the pilot out of the plane of the spinning prop, and in practice I'd probably raise the engine on a pylon above the wing to keep the landing gear short.

Lastly (and then I'll stop making edits to this post!), I would probably want a small ground-adjustable vertical surface like a winglet on the right end tailplane right in the slipstream to trim out any left turning tendency due to the offset thrust line.

 
Last edited:
Top