[Dave Underwood]

The following is what I know, clearly subject to the idiosyncrasies of specific aircraft:

Some of the reasons I think I need a P337:
I frequently visit short strips (2200' paved with no obstructions, 2500' paved with trees one end, 2900' grass w/ no trees - all less than 1000'MSL elevation.) The bulk of my flying is north of 40deg latitude. I have a 4x/year route that goes south around/thru JFK/LGA, PHL, BWI and DCA and the deviations I get are horrendous. From what I've heard if I can get to 15K or higher I'll get much straighter routing. I've been routed over 150nm off course in a single flight. I won't go out over the water in my single and it does poorly above 12,000'. I'm also sick of picking my way through local summer weather at 9,000-11,000 ft. My wife gets headaches if not on O2 above 10-12K and neither of us are fans of the nosebag.

a) The T and P will give you pretty good performance in and out of short fields. My aircraft is an 1978 FT337GP. The F denotes it was built by Reims and the P denotes is it pressurised. It is a Skymaster II. I am pretty sure the difference between the Skymaster and the II related to equipment. Mine as a II has a full deice, a 400-A Integrated Flight Control System/autopilot, Flight Director, HIS etc.

b) The aircraft is a bit heavy for softer grass fields as you might leave ruts in places. That said, I go in and out of several that are in your length range and shorter without difficulty. Just remember soft field technique. On pavement, the aircraft is great.

c) From my manual, the following are the short field take-off distances listed:

Short Field take-off, paved runway, SL, 20°C, no wind, 1/3 flaps, 2800 rpm, 37 inches, mixtures rich, cowl flaps open
at 4700 lbs – ground roll of 985’ and 1565’ to clear 50 ‘. That was in a new aircraft with perfect technique so add say 20% for margin.
at 4400 lbs – gnd roll of 845’/1345 to clear 50’ plus 20%
The manual suggests adding 15% to the ground rolls if operating on grass. For additional margin make it 25%. Still a very reasonable performer.
The manual also says you can decreases the above figures by 10% for each 11 knots of headwind.

d) On pressurised flight, my experience is that as soon as you are above about 14 or 15 k, you are generally controlled by the high altitude sectors. You are treated differently and direct routing is frequent when you are above 14 k. You certainly don’t get messed around as do when you are at say 6 k trying to go through Boston for example. I always file IFR which also makes a difference. My view is that you are above the rest of the GA folks above 14 k and below the airline traffic so it is pretty quiet territory.

e) The weather above 14 k is still an issue, but sometimes you can see more and TCU avoidance at pilots discretion is always given. A storm scope or radar is mandatory in my view if you intend to fly on those rougher days. I have a storm scope and always get deviations when requested. When things are really bad TCU wise, either don’t fly or go low and stay well clear of rain shafts. I have done trips in the mid-teens, in solid clag with embeddeds and when they are wide apart, no real problem as with the StormScope and a little help from the controllers you can get around them. When they a close together, you do have that butt clenching “I really wish I was somewhere else” moment.

f) 337’s are easy twins so water crossings are much less of an issue.

g) So onto my specific questions. I have searched the site and read 100's of messages, but I still have an unanswered question or two:

1) Re: Cabin temp with pressurization. Can you turn off the pressurization until you're at altitude to keep incoming fresh air temps down? Yes you can turn the pressurisation off, but all that really does is fully open the dump valve on the rear firewall, which does increase the cabin air flow a bit, but won't stop the flow from the pressurisation system. You can direct the incoming airflow off the turbo through its own inter cooler which does help, not much on the ground, but once going, a lot. The way the system work, which makes it fool proof is air flow from the high pressure side of the turbo goes up and over the rear portion of the front engine through a restrictor which controls how much air is taken from the engine side. It then either goes via its inter-cooler or directly in to the cabin air systems by way of the heater and a fan mounted on the firewall. The control is via a pair of dump valves on the rear firewall, one controlled by the on/off switch and the other as the failsafe at 3.35 psi. So sometimes it might feel a bit warm, but generally not bad. I’ve never found the inlet air that warm flying here in the UK, but things are generally cool here. On a hot Florida day, I open the windows and/or leave the upper door open. OK, it might be a bit warm, but as soon as you get airborne, things cool down quite nicely. You can then close the windows and get the pressurisation running.

Can you bypass the pressurization intake and get direct fresh air? No, just by directing airflow through the intercooler is my opinion. OK, you could pull out both dump valves which shuts off all airflow at the firewall, but I figure just having the storm windows open is just as good.

If so, is there any problem with turning pressurization on suddenly at altitude? Yes, it is quite hard on the ears as the plane pressurises up quite quickly. I suppose you could set the altitude controller up high and then crank it down which would be less painful on the ears. That said, I fly with the pressurisation running all the time as it give a more pleasant flight. Buzzing along at 8 k with a 3 or 4 k cabin is nice in my view.

If not, how much above outside air temp do you see the cabin temps during climb-out? Negligible to only slightly warmer once you are airborne. Never measured it.

2) How much do the intercoolers help with incoming cabin air temps? If you can estimate an actual temperature diff in degrees F that would be great.
There are already intercoolers in the cabin inlet air circuit which is really only effective when you are airborne, but an additional intercooler just off the turbo is available as an STC’d unit and I assume that is what you are referring to. Those intercoolers I believe give you about a 6 to 10 degree C drop, but you would have to check with the suppliers for the exact drop and how much you would get at low speeds. I never fancied the additional air scoop. That drop when combined with the drop you get across the cabin air intercooler would be quite significant I would imagine, but only once you are airborne and have good flow through the intercoolers.

3) If you have a P337, what's your actual empty weight? The book empty weight is 3061 lbs for a Skymaster and 3167 lbs for a Skymaster II and the gross weight is 4700 lbs for take-off and 4465 lbs for landing. Mine actually weighs in at 3361 lbs empty, well, as empty as I normally treat it with survival gear, raft etc.

What have you added that bumped it up significantly? There are two or three layers of paint on my aircraft, measuring some 70 plus microns thick. I figure that is where the majority of weight has come from. The Garmin stack is likely a bit lighter than the original ARC Radios, but I also have an ADF, EDM760 and the Stormscope plus some extra antennas and always carry survival gear. The last time it was weighed, the fellow suggested the majority was extra paint, so one day perhaps a strip and repaint will be in order.

What's the lowest empty weight I'm going to realistically find on a P337 without AC? Going to depend on the plane and layers of paint.

What’s the reality? You can carry up to 888 lbs of fuel or with less fuel, almost anything that you can fit in the cabin. With full fuel, I can still carry 451 lbs of me and other stuff. That work great for me.

4) What are the differences between the 73-77 T337G (I think this is the official Cessna code for the early pressurized aircraft) and the 78-80 P337H? For some reason this is tough to find. It's often listed as "minor changes." I have found differences by manufacturing year (seat rails, tanks) but not by model letter.

My parts manual covers all pressurized Skymaster aircraft built from 1973 to 1980. I think the serial numbers tell the story as they are continuous through the entire production run starting in 1973 with serial number P3370001 and going to 1980 with serial number P3370342 which was the final H built. There were not a huge number of big changes through the entire build, but you would have to go and have a good look at the parts manual to confirm that for yourself. The increase in fuel capacity to 148 gals was a good change, but from memory and having just had a fast look, there are not big differences between serial numbers. Lots of small differences, yes, but the basic aircraft is much the same.


I hope that gives you a bit more information.

Blue skies - Dave