To P or not to P, that is the question

[bjherron]

1) Re: Cabin temp with pressurization. Can you turn off the pressurization until you're at altitude to keep incoming fresh air temps down? Can you bypass the pressurization intake and get direct fresh air? If so, is there any problem with turning pressurization on suddenly at altitude? If not, how much above outside air temp do you see the cabin temps during climbout?

Yes, you can turn on pressurization in flight. I wish my 73 T337G Pressurized had AC though. It can get warm at takeoff and landing. It is fine up high. I may try one of those ice coolers.

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.

I don't know, I do not have an IC

3) If you have a P337, what's your actual empty weight? What have you added that bumped it up significantly? What's the lowest empty weight I'm going to realistically find on a P337 without AC?

3172.7 is my empty weight. Full of gas that leaves about 735lb for max takeoff, but landing weight is lower. Also, you have to be inside the arm/moment envelope, which makes it tough to actually use all of that weight.

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.

I have a 73 T337G. I am not sure what the changes are.

[JimC]

bj,

Can I bother you with a few followup questions?

re: Warm during takeoff and landing - What's your latitude where you're based? Where do you do most of your flying?

re: tough to use all 735lb - Do you usually find yourself too far forward or aft of the cg?

Does anyone know if the cg location of the earlier long range tanks is about the same as the later 148 gallon tanks?

Thanks,

Jim

[bjherron]

Jim,
No problem at all. We are based in Michigan. Today we flew from STL to ARB in MI. It was 90 - 95F at both airports. Passengers were sweating on takeoff and landing, but very comfortable at 17,500 where we were cruising with a ground speed of 215-220. Whole trip was just under 2 hours, something that few light twins can do.

The heat is my only complaint, and we're going to order one of those ice coolers next week to make things better. I haven't had the plane long enough to know how it is during winter, but I suspect it will be MUCH better.

For the CG, it's always near the forward edge. But then again I am 6'5 and my instructor is also 6'. Plus we are always flying with full tanks.

I spent a lot of time looking, it's hard to beat this without spending a lot more on the plane and gas.

[James Bennon]

BJ, keep us posted as to your purchase of a "cooler" for your P337G and how it performs. We also have a 73 P337G and have been considering the same purchase.

JB

[JimC]

It seems that a large winter Arctic Air setup weighs about the same (67lbs) as factory A/C. It can be removed when you want the space & weight in winter, but it also needs to be refilled.

For those of you considering the Arctic Air coolers - do you wish you had factory A/C?

http://www.arcticaircooler.com/

[Red Air Rambo]

You might want to price the Riley air conditioner...I don't know about the cost but it works great.

[edasmus]

My 2 cents on the Arctic Air (cooler) air conditioner... I purchased one of the larger ones at Oshkosh a few years ago. It works as advertised, which is to say it does a good job keeping the cabin cool.

The preparation work is the problem. Stopping at the gas station on the way to the airport to buy several large bags of ice, getting it all loaded, lifting 50+ pounds into a sweltering C337 cabin and securing it, and by now one is totally drenched in sweat. Not fun.

Realistically about 45 minutes to an hour of cool air is what you get with my unit. Which will get you up and down assuming it is turned off at altitude. If you have a multi-leg day, a re-load is necessary assuming you can get the ice at the airport you happen to be at and then you get to enjoy that preparation work once again.

I try very hard not to use my unit because of all this and actually have not used it in 2 or 3 years now. If I was really motivated for a particular flight and it was 95 plus degrees, I would probably use it but generally if it is that warm outside, I try to avoid flying. You may not have that option however, so the prep work may be worth it to you.

Good Luck,
Ed

[James Bennon]

Ed. Is there a reason that you don't pump the water out of your Arctic Air and leave the unit in the Plane?

I talked with the people form Arctic Air and they said that if you use block ice you can achieve a longer cooling period. For other purposes we have used frozen water in gallon milk jugs and am considering this if we purchase an Arctic Air unit.

JB

[edasmus]

I suppose not any real reason. I guess it seemed less messy to do the prep work outside the airplane. Otherwise, one would be on his knees dragging dripping bags of ice into the back of the airplane to load the cooler. My airplane is a 73G model with no baggage door. So that means unlatching and raising the bench seat to gain access to the back of the cabin to reach the unit. I do admit to being a bit of a "neat freak." I do not care for clutter in my airplane so if I am not to use the unit, then I do not want it sitting in the plane. It takes up a a fair amount of space back there and is an "eye sore."

Just keep in mind, that the unit requires preparation and that preparation is going to be accomplished one way or the other in 90+ degree heat. Once the work is done, the unit will work as advertised.

Ed

[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

[JimC]

Dave,

Thanks very much for the very thorough answer!

The weight on this particular grass strip shouldn't be a problem, as it's home to a Baron that flies out 2-3 days a week. Immediately after a soaking rain is an issue, of course, but under normal conditions it's solid - I've walked it.

I fly IFR on any trips through busy airspace and get screwed on the east coast anywhere from NYC to the DC area and everywhere in between. I can't remember the last time I flew the full north-south roundtrip without a "stand by to copy amended clearance" at least once.

North of the Massachusetts line, deviations are always given and "cleared direct" is common. On some legs I get handed off to center as low as 7K where there isn't any local approach radar. One other advantage that I just thought of for the P/T model is the MOAs - the local ones go to 17,999. 16K would get me above the bulk of the non-frontal weather as a lot of it is rising off the mountains and doesn't go much over 14K except on the warmest days. 18K gets me above that and all the local MOAs. I'd at least be able to go between some very large gaps in the buildups most days. At the 9-11K altitudes I fly today, I often have to punch through the weakest spot I can find in the late afternoon and fly the long way around the MOAs. I fly with both ADS & XM weather but have had them both fail simultaneously & would like to have onboard radar, although I consider it a luxury.

I will have to get used to the reduced seating & payload, but for most of my trips it won't be an issue. I expect I'd try to keep it fueled at about 100 gallons, which should leave about 700-750 lbs payload and a 450-500nm range - good for 90% of my trips.

Jim

[hharney]

Originally Posted by JimC

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.

So, please - talk me out of a pressurized plane!

Thanks for your help,

Jim C

I would suggest that you read these posts from Dennis Hamblin of Flint Fuel Tanks. There is a post that describes the differences in the wings of P model Skymasters.

http://www.337skymaster.com/messages...earchid=585613

[JimC]

Herb,

That link bring up a "Sorry - no matches" page for me. Do you have another link?

Jim

[James Bennon]

Herb, kind of off subject but do you know of the feasibility of converting the rear seats of a 73 P model from fixed position to sliders?

JB

[hharney]

Originally Posted by JimC

Herb,

That link bring up a "Sorry - no matches" page for me. Do you have another link?

Jim

Try this and click "find all posts by ....."

http://www.337skymaster.com/messages/member.php?u=13445