Gross weight differences O-2 vs. 337

[Morne]

Not that WikiPedia is an infallible source, but it seems like the O-2 had a higher max gross weight than the civilian 337. Wiki claims the O-2 could be as heavy as 5,400 lbs. while the 337B, made in 1967 at the same time, tops out with 4,300 lbs.

So why the difference? Were the O-2s beefed up in some manner versus the civilian version that permitted the higher weight?

[hharney]

The military versions had a special use category therefore the higher GW.

As the development of the 337 progressed the GW increased with model production. The straight 337 in 1965 had a GW of 4200, the B model increased to 4400, the C, D, model to 4500 (T models were restricted to 4400 for landing) and the Turbo E model and F, G, H models increased to 4630 for take off but the 4400 landing remained.

The P model G and H had a take off GW of 4700 and a landing GW of 4465.

There are some GW increase STC's available that allowed some models to increase the take off GW to 5400 but were still restricted to the original landing GW. There are also some proprietary STC GW increases that allowed higher take off and landing GW.

I think this is correct to the best of my research but if anyone has some different information please post it here.

Cheers

[awilps]

Herb is right. The O-2A/M337B, from my limited experience with it, has a type certificated max gross of 4300lbs. Higher weights were possible for takeoff and landing in military use, but I believe the extra weight had to be in the form of jettisonable wing stores. Landings above a certain high weight number also warranted completion of paper work and a special inspection by the military, post landing.

[Mayhemxpc]

As stated below, Skymaster models from straight 337 to 337D increased every year with no (or very slight) changes to the airplane. As it was explained to me at RTC, every year, Cessna was able to demonstrate to the FAA, through the proof of time and testing, that the airplane COULD handle more weight. The manuals were changed each year because the increase in gross weight led to decreased performance at that weight.

The O-2. The O-2B was a stock 337A in USAF Gray. MGW=4200. The O-2A was a very modified 337B, with FAA certification at 4300 lbs. BUT these modifications included heavier wing spars, attach points, landing gear and brakes. ALSO the USAF purchase went from 67 to 69. For model year 68, Cessna gave the civilian C337C a 4400 lbs MGW without any changes in airframe or powerplant. (Am I confusing you yet?) SO...although the basic certified weight for the O-2A was 4300 lb, for military use it was 4400 lbs. WAIT! There is more. Up to 4850 could be carried as long as anything over 4400 was jettisonable stores on the wing. If you weren't carrying anything on the pylons, you could take off at 4600 lbs, but you were limited in G-loading and could not land in excess of 4400. Clear? Too bad, there is one more thing. The performance data for the O-2A includes gross take off weights up to 5000 lbs! (Single engine climb is less than 100 fpm, even at sea level.)

Bottom line: FAA says 4300. The Air Force wasn't bound by that and established limits based on their own testing. Real world: I wouldn't worry if I were a little over 4300. The O-2A can handle it.

[Sapper]

In aviation, I am conservative. The O2 has had a hard life in the military, and in fire spotting. Stress in aluminum is cumulative. In the case of my O2, repair of a bullet hole that required some kind of engineering from Cessna. I will not be exceeding the conservative civilian max gross of 4300#.

[Mayhemxpc]

The question was why there is information showing a different MGW for the O-2A than for the civilian C-337B. I am not advocating flying it beyond the FAA type certificate.

Yes, most of the O-2As have had a hard life. Although the Air Force Flight Manual says no aerobatic maneuvers, there is plenty of evidence that O-2A pilots performed such manuevers and the O-2A weapons delivery manual shows tables for rocket launches at 70 degrees dive! Then there is the issue of avoiding and being hit by enemy fire. It is worth getting to know as much of the history of your plane as you can. Mine, for example (aside from the 14 bullet-hole patches) had extensive work done to the spars and attach points when it came back from SEA -- in fact the whole right wing was replaced. It's post Davis-Monthan life, however, has been more sedate than yours.

All that said, I am very careful with W&B and I do not fly it over the 4300 pound type certificate MGW.

[Morne]

Originally Posted by Sapper

Stress in aluminum is cumulative.

Care to elaborate on that?

[hew]

I have a C337E, MTOW 4440lbs, the TC337E has a MTOW of 4630lbs, the C337F has a MTOW of 4630lbs. Is it possible to increase 4440 lbs to 4630 lbs without modifications. The E & F models were almost identical. The service C337SM65 Service Manual lists the C337E MTOW as 4630 lbs.
What should I use?

[hharney]

A6CE is the law of the land


http://rgl.faa.gov/Regulatory_and_Guidance_Library/rgMakeModel.nsf/0/a036166830d57422862572430067c12b/$FILE/A6CE.pdf

[hew]

I have this email from Owen Bell, "We have an STC program in process which will address your request. Hoping to have finished early in 2015" looks promising.