Twin-engine planes or single tanks, which is better?

[Reg Braithwaite]

Interesting logic and conclusions.

Re: "Twin engine planes are faster...." I did not know that.

Let's not confuse things with facts! But checking Wikipedia, I find that a Cessna 205 has a single 300bhp engine and cruises at 142 knots. It seems typcal for a high-wing, fixed gear aircraft. Whereas the Cessna 400 and Mooney Acclaim are both designed specifically for high performance, and cruise at 220+ knots on 310bhp for the 400 and 280bhp for the Acclaim.

The Cessna 402C , on the other hand, has two 325Bhp engines, and its maximum speed is listed at 230 knots.

So... yes you can have a fast single engine plane. And go faster than some twins, just as a Honda CRX from 1985 will zip past a school bus.

 

[F106A]

....I find that a Cessna 205 has a single 300bhp engine and cruises at 142 knots. It seems typcal for a high-wing, fixed gear aircraft.

So... yes you can have a fast single engine plane. And go faster than some twins.

Ah, GA, aka "bug-smashers", "little airplanes." Now I see your point of reference. That 142K cruise, which "seems typical for a high-wing, fixed gear aircraft," is pretty impressive.

The ancient C205 had 300HP and cruised at 142K? I did not know that. (I don't think Clyde did either.) I would've guessed 260/138. Or so.

And I thought I'd heard of some singles going faster than twins.

 

[DA Aquamaster]

A pressurized and turbo charged single can indeed achieve pretty impressive true air speeds and ground speeds at altitude.

A turbocharged and intercooled C206 is a contender for the primary "win the lottery" airplane as it has a good combination of load hauling ability, short field performance, cruise speed, and maintence cost (fixed gear and if turbo normalized and intercooled, very good mechanical relaibility).

The safety records of twins versus singles is illuminating as well given that singles have better safetey records nearly across the board. As indicated above when your only engine quits, the question is not do you make an emergency landing but rather where do you make the landing. And stall speeds are almost always slower, so the crash is more surviveable even if the landing goes badly.

In short, I don't think the analogy is all that great and I am firmly in the pony is a parachute camp.

However, you could compare overhead (cave/wreck/deco) diving with flight in intrument conditions in a light twin. In that case not having to land in the event of an engine failure is very nice in much the same way that having a back up reg is nice if the primary fails in a cave. At the same time, in cave diving the redundant equipment is not enough without proper planning, gas management and currency in instrument and emergency procedues. The same can be said for a light twin in IMC. If the terrain you are over is higher than the engine out ceiling for your current load, density altitude, etc, and or if you are rusty flying singel engine in IMC, you are still screwed and the extra engine just extends the glide to what ends up being a higher velocity crash site.

 

[TSandM]

I think where the analogy breaks down is that in the majority of failure modes in double tanks, you are functionally the same as you were to begin with, after the failure has been dealt with. In otherwords, you retain access to all of your gas, and have a working regulator. Only in the event of a tank or manifold o-ring failure or burst disc going are you reduced to half the gas supply you began with. This is different from a twin engine airplane, which with one engine out, is NOT the airplane you started with at all.

Double tanks are used to allow very large reserves and to permit some redundancy (true redundancy, as pointed out in the first paragraph) in the face of failures. You do pay a price in additional failure points, and certainly in doubled maintenance.

Ponies are parachutes; doubles, you're actually using and doing your dive planning with all the gas you take down with you.

 

[gcbryan]

The only analogy is that both (doubles and twin engines) are more expensive to maintain and more complex to operate. Otherwise there is no analogy at all.

Doubles aren't really more dangerous. Twin engines are statistically speaking as has been mentioned...higher stall speed, reduced flying capabilities at failure from both lift and dynamic instability at the instant of failure (greater lift on one wing).

 

[Nemrod]

Didn't the F105 have a single engine?

Among the fastest civilian aircraft you can buy (new) today are the Cessna Citation X (M.92, twin jet) and the Cessna 400 piston single (235 knots--fixed gear). The only way to go faster in practical terms is to purchase an ex-military aircraft or join the military. The Mooney Aclaim single is slightly faster than the Cessna 400 but it is retractable and it too is a single engine. The PT6 powered Cessna 208 Caravan single turbo prop is one of the most reliable aircraft made. Most of the crap you guys buy overnight delievery probably at some point ride on a 208.

I just don't see any real analogy between diving anf flying.

N

 

[sclakediver]

Check out the T-34C (turbo mentor) for a real high performance single. It's not pressurized but exceeds 300mph and I think the G-limit is +4.5 -2.5. They are a pain to work on, but I'd love to fly one.

 

[Thalassamania]

When my Dad was in the Army Air Corps he trained on B-24s. He tells a story about being a bit overwhelmed buy all the gauges and switches and asking his flight instructor, "I don't know how you can fly this thing." To which his instructor replied, "because I can't get one with five engines."

 

[MikeRDar]

As both a pilot and diver, this has been a great read. I'm currently a far more professional and experienced pilot than diver, but I'm working to rapidly make up the difference, and I'm struck regularly by the similarities between the two. While I could certainly point out differences, I think the fundamental nature of flying and diving have very much in common.

Both are about man venturing somewhere he could not normally go via technology created specifically for that purpose. The venture is not always simple, and requires the diver or aviator to train for some period of time before he can safely carry out the activity. He must learn the equipment, how to operate it and maintain it, and he must learn the fundamental sciences and skills that will keep him alive in his new, fluid environment. When everything is going well, his training is generally sufficient to enjoy the trip and make it safely back home. But when equipment fails, or the environment becomes hazardous, with unexpected dangers, the quality and skills of the man and his machines are quickly revealed.
To some degree, there is always danger involved in the activity. That's why everyone needs at least some basic training to participate. But there are a vast array of recreational, professional, and scientific endeavors that can take place in these different worlds, and some of these require more capable and complex equipment to not only enable the activity in the first place, but to mitigate the higher risk associated with that activity. The more dangerous environments, such as taking twins/a twin into a low visibility situation, require more advanced training and skills to operate the additional equipment and still accomplish the objective with some relative degree of safety. Thus you eventually develop a full spectrum of participants, from those too new to operate the equipment by themselves, to those who are regular recreational participants within the bounds of their training, to those who professionally or personally push the limits of modern capabilities, with the best and sharpest training, the most advanced cutting edge technology, and the greatest goals yet undertaken by man in that field.

And before I get it from all sides, my wife is also an active diver, and I use "man" only in the grandest sense of the word, a la Neil Armstrong, and "he" only to save keystrokes.

 

[RJP]

Most small planes you see have a single engine. Twin-engine planes are faster and offer some redundancy: if one engine quits, the pilot can continue to fly on the other engine. This can be handy if there isn't a safe place to land within the immediate glide radius of the aircraft.

I'll stick with a three-hole configuration, thanks...

With 4,500nm range and cruising speed of +450ktas even if TWO of the engines fail we can still find a place to land just about anywhere within the continental US, and probably be home in time for dinner.