Skymaster question for the pilots
 

There is a plane that flies over my city with an engine in the front and in the rear that I've recently learned is a Cessna Skymaster. The non-pilot that told me what it was indicated that it was a very safe design in that the two engines were in-line.

I know that a more conventional, side-by-side twin engine plane can be trouble if an engine quits during take off. In fact, the owner of our local airport dies when he lost one engine. So my question is, why hasn't this design become the dominant one?

Stock photo

http://forums.pelicanparts.com/uploa...1200869372.jpg

I'd imagine cost.

lawyers-product liability laws essentially killed innovation in the private aircraft industry. the companies have beenstuck making minor improvements to existing designs for 40 years. the homebuilt/experimental types have been working the way around this.

It is a great design, near centerline thrust given the counter rotating props and excellent performance one engine out.

But, with all designs, there are trade-offs:

- Large tail area (empennage) with complex controls and large drag co-efficient. Design also needs to cool aft engine with inlets, adding to drag.

- Complex fuel system to feed for and aft engines.

- Noise and vibration if engines are not in sync.

- Cabin space can be compromised.

- Rough field landings can be tough without a tail.

I love the Skymaster, however. There have been adaptations, mostly in the experimental aircraft association.

Edit: Not a tremendous amount of cruise performance over a single, mostly in gallons per hour.

They were safer than conventional twins in the air, but lose one of the engines on a take off roll particularly the rear engine you would roll off the runway.
They were easy to handle with one dead at altitude. They felt very under powered and heavy. They have their own center trust only rating. There are also know as the Cessna mix master (Slang). It was not one of my favorite air planes to fly.
the Air force flew them as FAC planes in Vietnam, they were pretty tough.
The Cessna 310 was a much more capable twin in that class.
Cool design that never really took off. IMHO.

any airplane can be dangerous if you don't know it's capabilities and limitations. Most aircraft accidents in general aviation are caused by pilot error, fuel starvation, continued flight into IMC.......

Some information extracted from a recent AOPA Safety Foundation Report;

In the period between 2001 and 2005, the number of
GA accidents has declined by 4.3 percent, while annual
estimated GA flight hours have decreased by over two
million. Overall, the GA accident rate per 100,000 flight
hours continues its decade-long decline, and the AOPA
Air Safety Foundation continues to work for additional
improvements in GA safety.
Here are the highlights of GA accident trends for 2005:
• The accident rates per 100,000 hours for GA aircraft
were 7.20 total and 1.39 fatal.
• Pilot-related accidents accounted for three-quarters
of all accidents (74.9 percent) and 82.9 percent of the
fatal accidents. Total pilot-related accidents in 2005
increased 0.8 percent (to 1,076 from 1,067); fatal pilotrelated
accidents jumped 6.1 percent (to 242 from 228)
compared to 2004.
• Maneuvering flight was the category with the largest
number of pilot-related fatal accidents (80). This category
accounted for one out of three fatal crashes (33.1
percent) in 2005. Maneuvering flight was also the number
one fatal accident category for single-engine fixedgear
aircraft, responsible for over one-third (39.5 percent)
of all SEF fatal accidents.
• Weather accident statistics improved in 2005 over the
previous year, accounting for 4.6 percent of all pilotrelated
accidents and 13.6 percent of fatal accidents.
The majority of fatal weather accidents in single-engine
aircraft resulted from VFR flight into IMC.
• Accidents during personal flying accounted for about
seven out of 10 of all accidents (70.1 percent) and fourfifths
(81.2 percent) of all fatal accidents. Personal flying
accounted for half of GA activity (49.4 percent).
• Accidents are more likely to occur during the day
than at night (7.9 vs. 7.1 accidents per 100,000 hours),
and are also more likely to occur in VMC than IMC
(8.0 vs. 5.0 accidents per 100,000 hours).

The idea isn't totally dead....

http://www.airportjournals.com/Photo.../0701013_5.jpg

This is the Adam A500 which is also being produced as a VLJ or Very Light Jet (using two rear mounted engines)

A couple uncles had a "Huff & Puff" for several years. There usage slowed down to the point that they donated it to a missionary organization in Alaska. Apparently, they are highly prized in that role for getting a pretty heavy load in and out of short, rough strips. They particularly like the 1963 only fixed-gear model 336, because of a higher-lift airfoil. The downside is a slower cruising speed than the 337, with retractable gear and the faster airfoil design.

It could be configured with six seats, leaving no room for baggage, or four seats and a large luggage area where the rear two seats were removed. The other option was the belly pod, like in the above picture, to allow luggage space with all six seats installed.

The "Skymasher" was a design that made the asymetrical thrust issue in an engine-out condition in a light twin a non-issue to the non-professional pilot. To the low time or non-pro pilot moving up to the really high performance craft that have 2 engines, losing a motor in any flight regime is a problem because you need to increase the thrust of the remaining motor to 100% to maintain flight. This will yaw the aircraft into the side of the plane that has lost its thrust, and presents a workload issue that many lowtime pilots cannot succeed in, especially in takeoff mode or in IMC, when the workload is high. More so in single pilot situations, which is how most private planes are operated. This is basically why Cessna produced this design, to capture those pilot/owners that knew they didn't want to deal with the potentially disasterous engine-out problems of the "normal" twin.
A very good friend of mine ironically died in the Skymaster a few years ago, he was a surgeon and a great man. He flew that plane all over North America and Mexico, and died as a result of a heart attack while approaching his home base, 4G6.. He put it down in a small field on a hilltop and skidded into a treeline, mostly intact. Good crash landing, but his heart gave out. He called in on the Unicom and stated he was having a problem and let us know where to find him..

In a conventional light twin, loss of either engine (50% of your thrust) can result in a loss of up to 90% of your performance. I won't get into the details, but a simplified explanation is that performance is a function of EXCESS thrust horsepower, not net thrust horsepower. When one engine goes away, the excess THP remaining is very minimal above and beyond what's necessary to keep the aircraft flying and in some cases, isn't even enough to do that (depends on variables like weight, altitude, aircraft configuration, pilot skill, etc.)

With the Skymaster, the biggest advantage (as has been said) is that if one engine fails, you lose the asymmetrical thrust. However, you are still in trouble - you're STILL losing virtually all of your excess THP and will have highly impaired performance.

For the record, assymetrical thrust is not that big a deal in a conventional light twin if you know what to do (i.e. configure the aircraft for "zero sideslip") and execute according to training. The problem with this is that most non-professionals don't practice single-engine technique enough. Multi-engine rentals (or ownership) is very expensive and the mentality of a lot of the people with enough $$$ to fly them is often "I know what I'm doing", which results in a dangerous combination (an old instructor of mine often correctly quipped that the most dangerous pilot in the world was a doctor who flew twice a year and owned a Baron or a King Air. . .) Lots of factors involved, but the MOST important thing in flying twins is to practice the single-engine technique often so that the remaining engine doesn't "fly you to the crash site".

That said, I always feel more comfortable in a twin than a single. In a single, if the engine quits, you WILL be on the ground in a few minutes inside some defined radius (depends on your glide range). In a twin, you have considerably more options provided you know what the hell you're doing, don't panic and execute properly. It's ultimately all about the training.

There's a reason most commercial aircraft have multiple engines.

I know someone who fits that bill....

I know I don to speak from experience our education, but:
- complex fuel system - why more so than a conventional twin?
- cabin space - isn't this easily remedied with newer designs?

With respect to losing one engine during takeoff, CAN the aircraft take off with just the remaining one?

All certified multi-engine aircraft have to meet a minimum engine out rate-of-climb and takeoff distance. The idea is if you lose an engine on takeoff without room to stop the aircraft, you still have enough power to liftoff, climb out, and return to the airport.

I don't know the Skymaster all that well, but I'd guess that the fuel system issues come from location. A conventional twin has the engines mounted on wing nacelles, and fuel storage in the wings. So it's a simple, short route from the fuel to the engine. The Skymaster has engines front and back, but I assume it still uses a wet wing as most aircraft do. So you have additional issues routing the fuel front and back, as well as balancing the fuel quantity between the wings.

The Skymaster is a neat plane, there's one that flies over my house pretty often. Very unique sound. To add to Paul's (Seahawk) critique, they also had cooling issues with the rear motor.

Jeff's comments are spot on regarding the advantages of centerline thrust, but it comes down to one thing: insurance. It's the reason for the Skymaster, as well as the Adam A500. It's very difficult to get insurance on a twin without a lot of hours in a twin. So if you're wanting to buy, you have to rent until your insurance company is satisfied that you're sufficiently experienced. Without the asymmetric thrust issues of a conventional twin, a centerline thrust twin is a bit more idiot proof, and easier to insure.

Light twins under 6,000 max. gross weight actually don't have to demonstrate a positive rate of climb with the critical engine inoperative. The rule (according to FAR Part 23, certification) is that it has to be determined (usually by demonstration) and the rate of climb OR DESCENT published.

Check the following Advisory Circular for good information on this subject (I used to make this mandatory reading for my multi students back in my CFI days):

http://flight.pr.erau.edu/docs/Aviation%20Reference%20Docs/Other%20FAA%20Documents/01%20Twins.pdf

Page 8 in particular. . .

Thanks Jeff, I've been stuck in part 25 land for a few years now. I'm used to the more stringent regulations.

Yea, I was glad when flying cargo that we flew Chieftains with a max. gross of 7,000#. At least you have a fighting chance that way!

Additional stipulation is Vso of 61 knots or less. Geez. It's been years since I studied this stuff - how soon you forget!

http://www.flightsimaviation.com/data/FARS/part_23-67.html

In Part 23 land, we have a saying: You don't have to worry when an engine fails on a twin, because the other engine is there to take you to the crash site.


My favorite Skymaster story:

I used to do some flying out of Norman Oklahoma. There were a couple of pilot training schools in the area, and one in particular had a large number of foreign students.

One day when the pattern was full, the controller was trying to identify which plane was being flown by a foreigner who was making difficult-to-understand radio contact.

The controller radios: Aircraft calling Norman Tower, are you the Skymaster inbound?

The student radios back: My instructor says that I am doing well, but I do not think I am ready to be the sky master.
:D:D:D




I wonder if sky master one step below sky King??

A good one I heard in the pattern of SMO one day:

ATC: "Cessna XXXX, you were instructed to join left traffic for runway 22, not to overfly the field and enter right traffic. Say intentions"

Long pause

Student pilot with VERY thick accent: "Intentions"

Either that guy was very, very confused or had brass balls the size of basketballs. Never did find out what happened to him. I laughed until my sides hurt over that one though.