General Skymaster Info & Tips For Buyers

[Ernie Martin]

If you are a fairly new user of this forum, the following points will help you navigate and obtain faster results.

For general information about Skymasters please do a Search before posting a question. The matter has probably been addressed before and it's already here. You will find that the Search feature (on the top dark blue line) might get you both a quicker answer and a greater number of opinions.

If you are considering buying a Skymaster read this first. It not only tells you what to look for before you buy, but covers the different models and even operating costs. Two points in brief. First, Skymasters can be purchased cheaply, but a number of people who have bought them over the years were not financially able to maintain them right so they got run down. Buy one of these and you have a major expense getting them up to snuff and large recurring costs thereafter. That's one of the reasons Skymasters developed for a time a reputation for costly maintenance, but the reputation is unwarranted, and if you buy one that's been properly maintained the costs are comparable to other twins. Second, a Skymaster is designed to be, and can be, safer than conventional twins. But only if you treat it for what it is -- a complex, high-performance, retractable-gear, variable-speed-prop twin -- and if you maintain it properly, and if you do thorough pre-flights, and if you stay proficient. Regrettably, because the aircraft is very forgiving and easy to fly compared to a conventional twin, too many pilots don't do this. They cut corners on maintenance or think they can just get in and fly, and you find an unusually large number of accidents -- like simple fuel starvation or landing gear problems -- because pilots did not give the aircraft the attention it deserves.

We hope you find the site enjoyable and informative.

Ernie

[captbilly]

I didn't see much info on the P model in the link so I though I would add some info specifically on the Pressurized skymaster. I owned one for about 5 years and overall I really enjoyed the plane, but there are some things you should know as well as some incorrect info floating around about the P model skymaster.

Performance: The factory claim of 205 knots at 20,000 ft. and 75% power seems right on to me. I generally ran closer to 65% but saw about 200k true. I have heard that the Riley intercooled models will cruise at close to 220 at 20,000ft. but I can not confirm this. Fuel burn for me always seemed to average 30GPH even though I was running 65% power and the fuel flow gauge showed closer to 20-25 GPH. The engines did not run hot in either climb or cruise and I virtually always cruised with the cowl flaps closed. The engine had a tendency to miss when cruising at 20,000. Some people claim that the missing is caused by some sort of vapor lock, but others think it is due to the unpressurized magnetos arcing. I know that many people have switched to pressurized mags but I do not know if this cured the problem. I am fairly sure that the certified ceiling limit of 20,000 feet was related to the mags because the turbo skymaster (which came with pressurized mags) does not have a 20,000 limit. In addition the P210, which uses an identical pressure differential of 3.2 psi, has a limit of FL230, so the cabin pressure would not seem to be the issue.

All P models are 5 seat aircraft due to having only a single door. FAA requirements specify a second emergency exit for more than 5 passengers, but the P 337 has only the main cabin door. In reality most P337 owners leave out the 5th seat because with it in place there is virtually no baggage space, and getting in and out of the 5th seat is quite difficult for a normal sized adult. I would call the 5th seat a reasonable place for a child on a short trip, but that's all.

IFR range of the 1973 models with 125 gallons is about 3 hours realistically. With an average fuel burn of 30 gph you end up with about 35 gallons reserve at the end of a 3 hour flight, so figure a realistic 600 mile range for the 1973 model and 750-800 miles for the later models with 150 gallons of fuel. For VFR range add 150- 200 miles if you fly at 65% and close to 20,000 ft.

Maintainence for a pressurised Skymaster is about the same as any other pressurized twin. The cost of engine overhauls has much more to do with number of cylinders than it does with the size of those cylinders. The TSIO360d in the P model skymaster has all of the same turbos, manifold pressure controls, fuel injection system and other accessories as any other turbo 6 cylinder, so overhauls will cost nearly the same as a TSIO 540. Obviously there are differences between models but a fuel system overhaul or turbo overhaul on a 360cuin engine is pretty much the same as on a 540cuin engine. A cylinder costs pretty much the same regardless of size, so any 6 cylinder will set you back about 50% more than a 4. The pressurization system, landing gear, wings, control surfaces, etc. of the skymaster, require the same attention and cost as any other pressurized plane, so figure on paying a similar amount to maintain a skymaster as you would a 340 or 414.

Many older Pressurized Skymasters have deteriorated quite badly due to defered maintainence. The problem was that for a while the P skymasters were so cheap that anyone could buy one, but not everyone could afford to properly maintain them. I bought a nice 10 year old P337 for $36,500 in 1983 (about the cost of a couple of good engine overhauls), and some were going for less than the cost of the engine cores. I had an anual inspection that cost me $20,000 (not typical but not insanely high either), so you can imagine what would happen to some P skymasters when the owner was faced with repairs that cost nearly as much as the plane. By the way that $20,000 annual included no engine work, just windows, and airframe stuff. The maintainence of P skymasters has improved as their cost has gone up, and as the cost of fuel has gone up. At $5 or more per gallon the cost to fly a P337 is $150-$200 per hour just for fuel so the rule of doubling the fuel cost to get the actual cost of ownership is much more realistic than it was when I was paying $1 per gallon ($0.50 in Mexico).

Fuel system: The P model has an extremely simple fuel system. From the pilots perspective there are just two tanks, left and right. There is only one filler for each set of tanks (left set right set) so you don't have to watch the line boy to make sure he fills the correct tanks. In flight you simply monitor the fuel level of the left and right tanks (all tanks on one side are measured together) and if you have set very different power settings on the front and rear engines you might have to crossfeed (I never had to crossfeed in all the years I had the plane). The fuel gauge is totally inadequate for anything other than telling you roughly how much fuel you have. It is a tiny little guage that will let you know within perhaps 10 gallons of what you actually have. I would really recommend a good fuel totalizer for some peace of mind when trying to press the range to the max.

Single engine performance: Believe it or not the single engine climb rate and ceiling on the P337 is better than any unmodified piston twin. Some of the Riley and RAM (father and son by the way) Cessnas will climb as well as P skymaster on one engine, but even they will do it with quite a bit of drama and at a higher airspeed and lower climb angle than the P skymaster. The Riley Super Skyrocket P337 with 310hp engines will outperform anything but a turbine powered twin on one engine (especially when considering climb angle). I only had one occasion to actually fly on a single engine, although I practiced it many times. Once I had one of the metal fuel injection lines on the rear engine crack completely in two. The only indication I had of a problem was a sudden large increase in fuel flow. I was so unconcerned about flying on one engine that I elected to shut down the rear engine even though I really didn't know if there was anything seriously wrong (might have just been the guage or line to the gauge). I flew 20 minutes back to my home field with no drama whatever. When I oppened the cowling I saw that fuel had been pouring out all over the tops of the cylinders at high pressure though a completely severed solid steel fuel line. I have no idea how it broke, probably a manufacturing flaw, but it could have been a disaster if I hadn't shut it down.

Engines: I never had any issues with the TSIO360c/d but they do have a low 1400 tbo and it is quite common to not make even 1400. Many people claim that there are extra problems on the rear engine due to overheating, but I have never seen this. The only problem I had was never engine oil leaks from the rear engine. It may have even been simply oil coming from the breather (I had a tendency to keep the engine topped up in oil), but it wreaked havoc on the rear deicing boot. The rubber on those boots muct have been designed in the 1930s becasue it swelled up like latex when it got even a hint of oil on it. The boot is expensive so you don't want to be replacing it every year, I assume there is an answer but I never found it. I don't know what people were doing to the engines on P337s to cause them to need overhauls at 300 or 400 hours, but I saw many P337s that required overhauls at those intervals. At the time I owned the P337 I was a B-52 pilot and used to following strick proceedures so maybe I was more conscientous regarding turbo cooldown, rapid power changes, leaning and cowl flaps, than your typical owner, but whatever the case the engines were trouble free (other then the rear engine oil leak).

Cabin: The cabin in the P337 is about the same as a P210. Certainly not what anyone would call cabin class but a decent 4 person plane with a reasonable amount of baggage. The one issue with the P337 vs. a plane like a 210 or other large single is that they is no room behind the rear seats (if you have all 5 in) Since the engine is behind the seats the only baggage space is in the main cabin. I remember comming back from Mexico with my wife and 2 friends with so much stuff in the cabin that the rear seat passengers had to sit on top of it. The useful load and CG range was great (1500+ lbs) so even with full fuel (750 lbs) you could legally fly with virtually anything you could fit in the cabin. I could not come up with a realistic scenario that would have the plane out of CG range.

Handling: The USAF used these planes a FACs (Forward Air Control) and those guys beat the heck out of them. The planes were often overloaded so badly that they wouldn't even maintain altitude on one engine. In addition the pilots had come out of pilot training where they flew planes with 6.66 and 7.2 g limits (T-37, T-38), so they were used to yankin and bankin. I have heard that the issues with the wing spar on the 337 came from experience with spar failures on USAF 0-2s, I don't know if this is true but it would make some sense. In any case, since I had spoken to guys who had done some acro in their O-2s (and there was a guy actually doing a routine at airshows in a skymaster at the time) I decided to try it in my P337. Aileron rolls were easy with just a few degrees nose up prior to the start and ending a few degrees nose low. I did not have a G meter so I was unwilling to try a loops but I am sure it would be possible to do one without an over g, but I would very much not recommend it to anyone not extremely familiar with acro in a wide range of aircraft.

[WebMaster]

Thank you,
Great information for the P models.

[Shalimar]

I am the proud owner of P3370196, my second 337 the first was a 65 s/n0028. I am also an A&P/IA and do as much of my own work as I can. The earlier comments on performance are right on, my numbers are close to what was reported. You do need to treat the engines properly including cool down and proper application of power.
The airplane is very difficult to work on. It has numerous systems all crammed into a tiny space so systems must be removed to get at other components needing maintenance. Pressurization brings a whole new level of care requirement when penetrating the pressure bulkhead. Having said that the system itself is pretty much maintenance free. Vibration remains a concern on all Skymasters. Check the rear spinner bulkhead and rear cowling and baffles for cracking. For some obscure reason, Cessna riveted the center floor board access panel on the later models replacing the screwed on system on the earlier aircraft. This add a whole new challenge to routing wires, or even inspecting the landing gear hydraulics. I replaced the rivets with nut plates and screws on an FAA field approval.

A key point which has been made earlier is that all Skymasters are cheap to buy but expensive and time consuming to maintain. A low first cost may mean that the aircraft was not well taken care of. Better to pay a little more and get one that has been taken care of.

Still love the airplane and would (or will) do it again.

[hharney]

Since installing the MT composite props 6 years ago (can't believe I have had them that long) I have notice a significant decrease in vibration related issues. Rear muffler is a good example, I normally figured at least every other annual to repair cracks. I have had none since the MT's. The composite material (primarily beechwood) absorbs the vibrations caused from those lovely Continental engines. With the aluminum blades this vibration is just amplified. Great article on composite props in the new Aviation Consumer. So my suggestion is to balance things to a more extreme measure as much as possible. During engine overhauls or prop overhauls balance is the key. I would have to think that for the P and Turbo models with more exhaust stuff it would be even more important. Bottom line, composite props should be a legitimate option if it comes up on your aircraft. You have to do both front and rear at the same time and that may be a show stopper for most to swallow.

[Shalimar]

Excellent recommendation on the MT Props. For me, however according to the MT website, they are only STC'd through the F model. The later G's and H's are not yet approved under the STC. Since I fly a P337H it doesn't work just yet.
In any case, for anyone doing a pre-buy on any 337, I would suggest checking the rear cowling, engine baffling, spinner and spinner bulkhead for vibration related fatigue cracking. The spinner bulkheads are costly to replace and hard to find. On my earlier 337 (s/n0028) I replaced the rear spinner bulkhead twice due to cracking, I used to joke that i burn 20 gph and get 400 hours per spinner bulkhead.

[hharney]

As far as I know the MT's are now approved for the later model (G&H). Not sure why MT does not indicate this on the website. I know of one G model aircraft with MT's.

[skymstr02]

Yes, MT's are STC'd for the full 337 line, here is a link to the STC:

http://rgl.faa.gov/Regulatory_and_Gu...2?OpenDocument

Application Date:
12/01/1999

Status:
Amended, 05/16/2006

Responsible Office:
ACE-115A Atlanta Aircraft Certification Office Tel: (404) 474-5500

TC Number -- Make -- Model:
A2CE -- Cessna Aircraft Company, The -- 336
A6CE -- Cessna Aircraft Company, The -- 337
A6CE -- Cessna Aircraft Company, The -- 337A
A6CE -- Cessna Aircraft Company, The -- 337B
A6CE -- Cessna Aircraft Company, The -- 337C
A6CE -- Cessna Aircraft Company, The -- 337D
A6CE -- Cessna Aircraft Company, The -- 337E
A6CE -- Cessna Aircraft Company, The -- 337F
A6CE -- Cessna Aircraft Company, The -- 337G
A6CE -- Cessna Aircraft Company, The -- 337H
A6CE -- Cessna Aircraft Company, The -- M337B

APPLICABLE MODELS: Model Number
Serial Numbers
336
633,636, 336-001 through 336-0195
337
337-0002 through 337-0239
337A (USAF 02B)
337-0240 through 337-0525 (except 337-0306 & 337-0470)
337B
337-0001, 337-0470, 337-0526 through 337-0755 (except 337-0569)
337C
337-0756 through 337-0978
337D
337-0979 through 337-1193
M337B (USAF 02A)
337-M0001 through 337-M0476
337E
33701194 through 33701316
337F
33701317 through 33701462 and 33700306 (except 33701449)
337G
33701463 through 33701815 and 33701449
337H
33701816 through 33701950 (except 33701920 and 33701923 through 33701927)

Folks, I'm back like a bad cold sore . . . just can't get rid of me.

I'm in the midst of getting the old girl back in the air, and need a starter for the front engine on my 1966 337A. I did a message search for "starter" and only found a discussion from 2002 about Lamar starters. Obviously, a lot has changed since then.

Does anyone have any recent experience replacing a starter on these birds and whether the light weight starters are a viable option these days, and if so, which one(s)?

Thanks,

Keven
________
Herbal vaporizers

[Shalimar]

Is the starter missing or is it non-functioning? If it doesn't work then I would send it out for overhaul. If it is missing then I would look at Sky-Tec light weight starters. I had one on my 65 337 rear engine and it worked well. I believe that the model number that you want is a C24ST5, Aircraft Spruce has them for $567.00. A couple of other thoughts: Sacramento Sky Ranch has some interesting comments on the light weight starter. Apparently they don't work well for repetitive starts (20 or more per day). Also, with a light weight starter you cannot rotate the prop backwards. I would recommend staying away from Kelly Aerospace starters (or any Kelly product for that matter) Perhaps others on this site can comment otherwise, but my experience with Kelly stuff has not been great.
Good Luck and get this back in the air!

I believe that my starter got smoked by a line guy with aux power. He plugged it in, I hit my stareter, and smoke came out of the cowling. Both ends of the starter cable were melted, and burnt smelling fluid was running out of the starter. Oh, what a great feeling that is! Any way, one of the field windings looks like black, runny, silly putty! Have taken it to be overhauled, but they are having a difficult time finding parts any more. So, I'm looking at other options.

When you say that you can't rotate the prop in the opposite direction with a light weight starter, do you mean at all? If not, how do you time the mag or do any maintenance requiring such an action?

Any problems with the light weight starters actually turning the engine? I've got two on my Twin Comanche, and sometimes it seems like they have to muster every amp of energy just to barely swing the prop. Never had a failure, but it sure is different from every other plane I've flown with regular starters.

Any other comments are welcome.

Thanks for your input.

Keven
________
Vodun (voodoo) forums

[Shalimar]

I had no trouble with starting using a light weight starter, it spun the rear engine just fine. With respect to counter-rotating the engine you can do it but it is very resistant. It felt to me that I was trying to make it do something that it did not want to do and I was concerned with putting undue stress on the gear train. Perhaps someone else on this blog can shed more light on this. It did make mag timing and compression testing more of a challenge.
All that said, I am surprised that parts for a heavy weight starter are hard to find. There are a lot of heavy weights still out there! Suggest that you contact Cessna Pilots Association (if you are a member, and it's worthwhile) and see if they can shed some light on this.
Good luck

[hharney]

Keven
I bought a reman couple of years ago for the front engine and it was in stock, next day it was in. I can't see why there would be a problem getting parts or just go with a reman.

Getting the 337 ready for that trip to Idaho?

[VLJ Guy]

Thank you to all
I appreciate the information and the insight.
Gary

[edasmus]

If you are an AOPA member you can access all kinds of info on how to buy an aircraft on their web-site, aopa.org. On the front page click the "Aircraft and Ownership" tab which will lead you to all the info I could imagine one would need.

Ed