P337 Baggage Door

[aknott]

I'm considering a P337 as my next aircraft. The lack of a baggage door concerns me a little. Has anyone here fitted the RT Aerospace baggage door to a P337? If so, what do you think of it?

Thanks

Andrew

[SkyKing]

Andrew,

I wasn't even aware that RT Aerospace offered such a mod for the P337, but I wouldn't even consider it. Have you looked at the Cessna parts manual for the P337? If you haven't, get a copy and look carefully at the structure... you'd definitely be weakening the pressure vessel. In addition fuel lines and valves from the right tank transit this area. I've never heard of anyone doing this mod and I think you'd be talking a VERY expensive proposition.

Perhaps you should consider the turbo version which has the baggage door already installed plus a six-seat interior if you're that concerned about 'baggage'. Any of the rear 4-seats can be removed as needed.

You'll find that most of the 1973 through 1975 P337's are equipped with a four place interior and a fold-up second row seat that folds against the pilot side of the fuselage which allows easy access from the air stair to the rear of the airplane... it's not that big a deal. In 1976 through 1980 P-models, Cessna went to a floating second-row seating arrangement, where the seats float on side rails. In this case the seats can be stowed against the rear firewall, or placed anywhere in between and each seat folds forward to access the rear, or you can remove the entire assembly. And you can also place smaller items under the seats as well, perhaps up to about six or seven inches in height.

Our '77 P-model has a fifth seat which is great for kids or smaller persons, but I certainly wouldn't want to take a trip seated in it as it would be quite cramped. For a youngster it's just the ticket though, with the opposite side of the aircraft available for stacking your baggage if needs be. So far in our three years we've never had a problem with loading the airplane. You just have to be creative! Besides, just how much 'baggage' do you need to carry... that is the question, and another is how often do you fly with four people?

You said you were considering the P337 as your 'next' airplane. What are you flying now?

SkyKing

[Bob Cook]

Skyking et al

Not only is it scary it is expensive. I agree with you Skyking... it would be scary..
Pod only if you need extra baggage space. You would be suprized what I carry with four people. Should send you a picture or two.
A straight Turbo would be better if you need to carry luggage, or better yet, a DC3.

Bob

[aknott]

The mod is supposedly $9500 installed (it is on their website) and apparently they relocate the fuel lines as part of the process.

They have pictures on their website (I found the link on this site!) and apparently the Mod has been STC'd (though I haven't seen the STC...

What you are saying is that getting luggage into the earler (pre '75) aircraft is easier than the newer models?

I'm currently flying a Trinidad (excellent single BTW). I have never flown a 337 but like the concept of the aircraft. If I could go pressurized it would be ideal. I guess I need to try loading luggage into one myself.

Anyone out there with a P337 in the Dallas area?

Regards

Andrew

[kevin]

Hello Kevin:

To answer your question, I am the Ray Torres from RT Aerospace. I was browsing through your web page yesterday and saw the comments concerning our baggage door mod, which I would like to comment on. I'd appreciate it if you could post this on the message board.

Before getting into the mod I would like to give you some background on myself and my company. I have a degree in Aerospace Engineering and am an FAA Designated Engineering Representative (DER) in structures. My company's main business is providing engineering support for aircraft structural repairs and modifications, primary to the airlines and corporate aircraft. Over the past twenty years we have obtained between 70-80 STC's for our customers.

I bought my first 337 in 1989 and have since owned/overhauled/rebuilt a 1965, 67 and 73 Skymaster. All of the mods I have done on Skymasters (except for the P337 door) were done because I had a personal need for that modification in my aircraft. The ability to sell to mods to other 337 operators has never been my primary intent although it does help to justify
some of the mods.

RT Aerospace has two STC's concerning retrofit of baggage door on 337's. STC SA01344AT installs a baggage door on P337's and STC SA0188AT installs the door on non-pressurized 337's (post 1973).

When I got into the baggage door mods I thought that the response from skymaster owners would be overwhelming since this modification gave access to the back of the airplane which is all but useless without the door. Unfortunately, this hasn't been the case, and except for the two prototype aircraft, no other aircraft have been modified. I can't explain the lack of interest in the mod and I don't feel its the price because in both cases
they were initially priced under cost. The only thing I can acertain from reading the comments on the message board is that people have alot of mis-conceptions and fear about pressurized aircraft. Actually, the only difference between a P337 and a non "P" 337 is one additional frame at the pilots side window and about 20 lbs of tank sealant.

With the regards to our modifications, the pressurized door installation is much more complicated than the non-pressurized, but there is nothing "scary" about the installation. Both installations use the same door, which is a epoxy-glass/carbon fiber layup with a 1" thick nomex honeycomb core. Door dimensions are about an inch smaller than the Cessna installed door on older skymasters. On the P337 installation, the door has a piano hinge along the top edge and a 3-pin overcenter latching mechanism along the other 3 door sides. The door opens up and has a hold open rod to hold the door out of the way when loading. Sealing of the door is accomplished through a blown seal which tees off of the main cabin door installation.

In order to satisfy the FAA, the door and latching system was tested/cycled in a mockup frame to ultimate pressure differential. We stopped the testing at over 10,000 cycles with no failures or damage.

The fuselage modification for the P337 aircraft consists of the installation of two stub frames at the door forward and aft edges and an upper and lower jamb. An external doubler is then installed which spans from the aft pressure bulkhead to forward of the main gear frame. Again, in addition to the structural analysis of the modification, the FAA made us test the installation to limit pressure differential. This was done on the ground with an external pressure source. The biggest problem we encountered during this test was not with our installation, but with numerous leaks at the main entry door. I was extremely difficult to reach limit pressure differential. The prototype aircraft was a 1973 P337 so the fuel valves were still up in the wing. Modification of a 76-78 P337 will require relocation of the fuel
valves. In addition the bench seat tracks would have to be modified and the seat aft travel limited due to its proximity to the door area. Probably the best modification for these aircraft would be to remove the bench and install floor track mounted seats as in older skymasters.

The non pressurized installation differs in that the only modification to the fuselage is the addition of a door seal retainer. The added door is hinged on the forward side with two external hinges and a paddle latch on the aft side provides the latching mechanism. This installation is very similar to that installed by Cessna on pre 1973 skymasters.

If any body is interested they can e-mail me and I'll put them in contact with the owners of the two modified aircraft.

By the way, we are in the process of modifying our price list, and the new price for the P337 door installation will probably be in the
$20,000 -25,000.00 range depending on model year.

As I stated before, I'm very impressed with your web page and I hope to be looking at it on a regular basis.

Regards,

Ray Torres
RT Aerospace

Ray's email is rtaero@bellsouth.net. (KM)

[Jim Rainer]

THANK YOU, MR. TORRES. I HAVE ALWAYS WONDERED ABOUT THE BACKGROUND OF RT AEROSPACE - NO WAY TO MAKE A LIVING MODIFYING 337s ONLY! I HAVE CALLED BOTH ABOUT THE GEAR DOOR REMOVAL (MORE ABOUT THIS LATER) AND THE BAGGAGE DOOR FOR MY NORMALLY ASPIRATED '76 337G. GETTING THE BAGGAGE IN/OUT IS EASIER THAN THE EARLY LEARJETS BUT STILL NOT THE BEST SITUATION. I DECIDED THE COST/BENEFIT DIDN'T MEET MY NEEDS (TRAVEL ALONE MOST OF THE TIME.)

WHEN I ASKED WHOEVER ANSWERED MY CALL ABOUT THE GEAR DOORS THE FIRST QUESTION TO ME WAS, "HAVE YOU HAD A GEARUP LANDING YET?" I SAID NO AND THE REST OF THE CONVERSATION WAS ABOUT THE COST SAVINGS WHEN I DO HAVE A GEARUP LANDING WHICH THE PERSON I WAS TALKING TO ASSURED ME WAS GOING TO HAPPEN AND THE MOD WOULD SAVE A LOT IN REPAIR COSTS! NEVERTHELESS, I CONTINUED TO CHECK AROUND WITH OTHERS WHO'D HAD THE MOD DONE (AND ON THE 210 AS WELL) AND AGAIN DECIDED THE COST/BENEFIT DIDN'T PUT IT HIGH ON MY PRIORITY LIST.

IN ANY EVENT, I AM GLAD YOU HAVE PERSONALLY GIVEN US YOUR BACKGROUND AND PHILOSOPHY OF BUSINESS. I'VE STILL GOT THE BAGGAGE AND GEAR DOOR MODS ON MY WISH LIST - MAYBE SOME DAY.

Jim:

The aft gear doors removal mod was done strictly for safety. The intent was to remove the drag associated with the aft clamshell doors when cycling the gear. The concern here was the cycling of the doors during single engine operation. The POH states that aircraft cannot maintain altitude on one engine with doors open. The gear door mod solves this at no penalty in speed or noise.

A secondary benefit to this mod is that you get rid of two actuators and four hydraulic lines, therefore there are less places to spring a leak.

Gear up landings was not a factor in this mod since the strut doors (forward main gear doors) are the ones that take most of the damage unless your doors are hanging open. The strut doors are the ones that are getting hard to find if you do have a gear up landing.

The best solution for a gear up landing (aside from proper maintenance) is a big ADF antenna in the belly or a cargo pod.

Ray Torres

[rick bell]

have your gear door modification, it is great, no sink just pure acceleration. this is a mojor immprovement over the stock model.
thanks rt
rick

[SkyKing]

Ray,

Notwithstanding your excellent no-doors kit for the Skymaster, which we have installed on our '77 P337, I believe William D. Thompson, one of Cessna's lead engineers on the 337 project, would find some exception to your statement that, "... the only difference between a P337 and a non "P" 337 is one additional frame at the pilots side window and about 20 lbs of tank sealant."

In all fairness, that is not quite an accurate summation, as the P337 does have a beefed up airframe with heavier gauge and more numerous bulkheads throughout the cabin structure and a rather monstrous rear firewall, as compared to the other 337's, so as so withstand the high cabin pressure loads, even though the cabin pressure is design limited by sonic venturis installed aft of the turbos which limit the maximum pressurization differential to 3.35 PSI.

Anytime you punch a hole into the pressure vessel -- especially one the size of a baggage door -- you're just opening up the possibility of more problems down the road, especially since this baggage door mod relies on a 'BLOWN' seal, unlike the main cabin door seal, which is designed with tiny holes spaced around the door frame opening that allow pressurized cabin air to enter into the seal and inflate it against the door molding. (And woe to the A&P mechanic I saw one day trying to patch/fill those small holes --so as to help "improve" the door seal! -- obviously this guy didn't have a clue!)

Obviously, if Cessna felt the needs of its customers would have warranted adding this feature and they could have justified the additional costs, they would have included it in the original design. That they did not speaks of their concern for the integrity of the presure vessel. As you know, an explosive door failure while pressurized was one of Cessna's main concerns, as such an event could suck out the co-pilot, but their final design has resulted in no such event ever happening with the airplane.

As I've remarked before, access to the rear of the airplane -- even across the sliding bench seats in our '77 -- is no big deal. It's even easier with the 1973 through 1975 models. Both variations have their pluses and minuses. Besides, if you're going to carry that much junk, the belly pod is the only way -- or leave it at home!

So, my take is that the integrity of the airframe comes first. If you really need a baggage door, buy a normally aspirated Skymaster or a turbo non-pressurized unit that already has one... and save $25,000 and a lot of heartache if things go wrong, which they will, if Murphy's Law intervenes.

By the way, William D. Thompson, one of Cessna's main Skymaster design engineers, passed away last year. He was 81. Some of his wisdom is preserved on this website under the heading "History".

SkyKing

Dear SkyKing:

At first I wasn't going to respond to your message, but I couldn't let some of your statements go by without commenting.

First of all. I don't think we have any disagreeement in that a pressurized fuselage is a more critical structure than a non-pressurized one. Granted, the air volumes and pressures are much less than what we see in airliners, but still it operates as a pressure vessel and failure of the skin could lead to decompression with possible subsequent damage. But what I tried to explain before is that this was taken into account in design of the baggage door. We didn't just "punch a hole in the pressure vessel" and put a door in its place. The hole as reinforced, and the door design was analyzed, tested and subsequently approved by the FAA. This is the same organization that approved the original Cessna design.

Your statement that I do take exception to is "If Cessna felt the
needs of its customers would have warranted adding this feature and they could have justified the additional costs, they would have included it in the original design" If I understand you right, your saying that if Cessna hasn't done it, it shouldn't be done. Well that pretty much does away with the entire after market mod business. Why did you put our gear door mod on your airplane? Cessna didn't do it. What about all the other after market mods such as Winglets, Tail fairings, Horton Stol, Robinson Stol, Intercoolers, air conditioning, IO 520's, higher gross weights, aux fuel tanks, oil filters, blown seals......etc. Since Cessna didn't do these mods, does that mean that they shouldn't be done? All of these mods, if improperly designed or installed could lead to catastrophic failures.

Again, what I'm trying to say here is that any mod can be done if properly engineered and installed. Cessna isn't the only one that can modify an aircraft.

With regards to my comments concerning the differences in structure between the P337 and non P337, I was referring the the post 1973 aircraft. There's no question that there are major structural differences in the aircraft before 1973 and after 1973. and it is obvious that these changes were made to accomodate the pressurized fuselage. But when comparing a post 1973 pressurized 337 and a post 1973 non pressurized 337, the only differences I've noted is the additional frame where the pilots emergency window use to be. Granted, I haven't gone and miked all the skins, but in the area where we installed the baggage door, the structure is identical and the skin thickness is identical.(except for alot of sealant).

My comments concerning the 337 meant no disrespect to the Cessna design engineers. theres no doubt that the 337 is a major engineering feat, just the mere fact that they put the engines on opposite ends of the fuselage is a major accomplishment, the importance of which is only now being appreciated. I've owned skymaster for the last twelve years and will promote the aircraft whenever possible, but as with any aircraft, its not perfect and there's always room for improvement, and what works for one pilot may not work for the next.

Anyway enough said on this subject.

By the way, I was pretty young at the time, but didn't SkyKing fly a Cessna 310?

Regards,

Ray Torres

[Jim Rainer]

Well said, Ray Torres!! Thank goodness for the after-market mod business because a lot of what gets done by you good folks ends up being done later by the manufacurers, i.e. intercoolers on the P210R, for instance.

Jim Rainer

[rick bell]

i would get the mod, i travel for supplies 1 or 2 times a month and it is really a pain to load and unload (i'm ruining the interior, snagging everything). i just don't want to fly to fl. and hang around for several week, i have the greatest mech. can anyone else preform your mods, like the gear door deletion?

Rick

All our mods can be installed by your local A&P (must have some sheet metal experience). The only mod I don't offer in kit form
is the pressurized baggage door installation due to its complexity.

Our web page @ www.RTAerospace.com has price list showing both installed and kit form price. The list also provides estimated man-hours to install.

Ray Torres