In-Line Twin Concept Plane

Model undergoing testing in X-Plane environment with front engine feathered.


The basis of the argument is one of economics,

        A) Traditional- Single 180HP certified aircraft engine retails for approximately $30k.
        B) Proposal- 2 Rotax Snowmobile (or auto) engines producing 100HP each cost $5k total

and economics has a direct effect on public saftey bacause:

Author's Concept Plane

3 View of author's concept of inline tandem- "Cat-Dog Plane" named after the cartoon character with 2 heads.
Shown with 2 80HP Rotax Sno-Mo Engines.
Back to back seating for superior CG management and leg room.


Conditions:  3,000 MSL, 50% Fuel, Solo, 80HP Engines
Top Speed: 195MPH
Single Engine- Full Feathering: 130MPH
Single Engine- Fixed Pitch: 90MPH

Length: 25'
Wingspan: 33'
Power: 2 x Inline Cylinder, 80HP each
Empty Weight: 1070 LBS
Max Weight: 1750 LBS

Brief Statistics Lesson:
If you take the loss of power in an engine in flight to be a random process of uniform distribution with probability P, then for a single engine plane the probability of being without power is simply P, but for a twin it becomes P2.

So to plug in some sample numbers for the people who hate algebra, if we take the probablility of loss of power in an engine during a particular flight P to be 1/1,000 then for a twin your odds are (1/1,000)*(1/1,000)=1/1,000,000, those are the kind of odds I like.

Basically the idea is that you don't put all your eggs in one basket.

Therefore, if you have a particularly safe arrangement, you can use particularly ordinary power plants.

Q: With 2 engines, aren't your odds of losing an engine twice as likely?
A:  As some might note, the probability of losing AN engine in a twin is double (2P), but for a suitably (and affordably) powered twin this is not a major catastrophy.

Q: If you lose one engine in a twin, won't the other one "just carry you to the scene of the accident"?
A: Below a certain airspeed, and particularly at low altitudes, it can be dangerious, but this is exclusively a problem of the left/right traditional twin.  This design flys at 130MPH on one engine.

Q: Won't 2 engines cost twice as much?
A: No, they're approximately half size of the single, and can be less specialized single ignition types because of the robust nature of the in-line twin configuration.  Engine price is roughly proportional to rated power for a particular make.

Q: The twin engine aircraft I'm familiar with cannot climb on a single engine, the examples given of twins that have this ability are hot-rods and not representative of the typical twins mere mortals can afford to fly.
A: First off, an inline twin doen't require hard rudder (and drag) to counteract uneven thrust.  Second, get used to flying hot-rods, when engines cost $5K instead of $30k and up, you can afford to power your plane with the appropriate amount of power for safe operation.

Q: Aren't most incidents due to pilot error.
A: Yes, but why punish the safe pilots with a less safe mechanical system.  Lose of engine power rates a close second.

Q: For a particular displacement Rotax aero engine, why is the sled engine more powerful?
A: Many reasons, not the least of which being that because the penalty is so high for failure in a single engine aircraft application, they tend to derate the power (and thus your aircraft performance) in an effort ro retain some reliability.

Raise awareness in the general aviation public of the advantages of the inline twin configuration to drive new product development with regulatory relief in the form of:
1) In regards to pilot licensing, petition FAA to count the number of thrust lines rather than the number of engines.  Would allow single engine pilots to fly in-line twins such as the Cessna 337 with just a type checkout like any other new aircraft.  This being done to reflect the particular training requied to handle the most serious issue in tradition twin engine aircraft: yaw moment induced by loss of power on one side, especially at low airspeeds.
2) Petition FAA to allow for longer (2x?) intervals between mandatory service/inspection for aircraft using in-line twin configuration due to robust operation of inline twin configuration.
3) Petition FAA to allow otherwise compliant twin aircraft with a single line of thrust (but 2 engines) to be part of the new "Sport" aircraft classification.
4) And regarding Sport classification, remove top speed limitation, the stall speed requirement is sufficient; if someone can build a wing with low speed stall characteristic and high top speed, then we'd all like to have it.