The Cessna OE-2: a mishmash military model

In 1954, just after the cessation of hostilities in the Korean war, the Marines wanted an improved model of Cessna’s L-19 Army Liaison/Observation airplane (the Navy/Marine designation for the L-19 aircraft was the OE-1).

The new one would have more protection for the crew and higher cruise performance while maintaining the L-19’s excellent takeoff and landing capability. The Marines only wanted a few of these good airplanes, and they were willing to pay–quite a bit more–for them.

Cessna L-19 Bird dog

Cessna’s simple but tough L-19 was the starting point for the OE-2.

I don’t specifically remember the contractual arrangement (as an engineer I probably wasn’t advised), but it went something like this: build an airplane that meets our specification and certificate it to Civil Air Regulations, and we’ll buy 25 of them. In this regard it was deemed to be an upgraded version of the L-19, and in our terms a derivative of it–a new airplane using an existing airplane as a design base.

The normal expectation is that the pair will have some common major components. We started our project with the development model designation M321 (the L-19 was our development model M305–and was already in production when I joined Cessna in the fall of 1951).

The Model 321, which would become the OE-2, thus was to be, like the L-19, a military airplane designed to commercial flight characteristic criteria–with one difference in the order of things, mentioned below. The 305/L-19 had won a fly-off competition against several rivals in the spring of 1950, and by plan its production would proceed after having that already winning configuration certificated.

As an aside, that award based on the fly-off was contested because Cessna had ignored a limit on the horsepower the competing airplanes’ engines were allowed to have. Cessna knew the takeoff (and landing) performance desired (600 feet over a 50 foot obstacle) couldn’t be met with that small an engine.

The award was made to Cessna despite that deviation from the rules. That may have been because the Korean war started just a little later in 1950 and the Army needed immediate replacements for its aging WWII ragwing L-4s and L-5s, and implementing the already flying, and better performing, Cessna 305 was a quick way to do that.

My summertime job in 1951, just before joining Cessna, was building replacement wings for that same L-5, then still in service in Korea. The job was with a small aircraft company in Wichita, called Rawdon Brothers, located on an airport they operated literally across the street from (my) soon to be rival Beechcraft.

The L-19 was the Army’s first all-metal liaison aircraft and was expected to be longer lived than those airplanes it replaced. I seemed to be establishing, with the ancient L-5 and the nascent OE-2, a broad familiarity with this type of airplane. My involvement with the L-19 itself was in between my quite different work on those two other quite different liaison airplanes, and happened around 1952-53. It consisted of some minor contributions to an XL-19 project trying out two turboprop engines for the Army’s then current version (which project was not very successful, overall, though one turbine-engine version set an altitude record for its weight class).

Cessna 180

The OE-2 featured the Cessna 180 wing.

Back to the OE-2 story, the 321 agreement was different in two respects. There was no competition because the project was a model change to the L-19/OE-1, and the production contract award was to be made only after the configuration was designed, flown and certificated. It wasn’t as sure a thing as having won a fly-off, but on the other hand there wasn’t any immediate competition to worry about either.

What we had to worry about was meeting that specification for the desired improvements. I remember more about the “hardware” requirement for added shielding against enemy fire–armor plating and flak curtains–than the numerics of the performance upgrades, which in any case were going to be more difficult to achieve with those heavy additions to the fuselage structure and the enhanced protective measures.

What was pretty obvious was that we would need an even bigger engine, and while the L-19 had a fixed pitch prop selected for takeoff requirements (and with it the necessity to just accept a compromised cruise capability), the speed upgrade for the 321 demanded a constant speed prop that would serve both takeoff and cruise needs. But to assure that takeoff performance was maintained we elected to increase the diameter of the propeller and gear the engine to reduce propeller operating RPM’s for all flight conditions.

With the higher horsepower and larger prop, it was felt necessary to have a more efficient straight-edged and high-aspect ratio empennage, rather than the old elliptical type left over from the 170 (and 190) era and incorporated on the L-19. (I also designed–maybe guessed at is a better description–a good sized dorsal fin we felt was needed for the OE-2 configuration, as well.)

It’s worth mentioning here that the L-19 was itself a derivative of the in-production Model 170, initially with the major changes made to the fuselage (starting with the cabin area) to accommodate the observation mission of the airplane. So at this point the OE-2 was to be at least a double derivative airplane.

But with the airplane’s increased weight, and a requirement for more range than the L-19, we just incorporated the existing Model 180 wing right into the OE-2 configuration. However, the flaps were stipulated to be electrically operated, instead of having the manual kind as on the 180, and the fuel tanks were made self sealing. While I think I remember designing a new rectangular shaped (square) empennage for the OE-2, it was at least modeled on the similar configuration of the M180.

So did this make the M321/OE-2 a triple derivative (first from a commercial 170 to a military L-19 and from that to using the somewhat modified M180 wing and an empennage fashioned after that of the M180, too?

Cessna OE-2

The OE-2 was a niche airplane, but quite a performer.

To round this idea out, we may have started the 321 design with the sensible thought of using the L-19 fuselage, but with the higher gross weight, added protection against enemy fire, a cowling modified for a new, and geared, engine and accommodating a different wing and empennage, what was left of this thought?

Reviewing, here’s what we then had with the OE-2:

  • A Marine airplane for combat duty, but built and tested to commercial (general aviation) aircraft design criteria.
  • A derivative of a derivative, but 1) with a somewhat modified wing from still another of our commercial airplanes and again 2) major modifications to the first derivative’s fuselage plus 3) an empennage designed to be like that of the airplane the wing came from.
  • A departure from the contractual procedure from the first derivative military airplane, in that award followed certification instead of certification following the award.

See why I call it a mishmash military model? What was rewarding was that, despite all the conglomeration, the certification process was trouble free–I can’t remember even one problem that came up.

Of course many of our commercial airplanes became military ones, though without much change to them except their designation. Examples are the Cessna 195, 310, 172 and 185 (that last one shortly after my time) which were bought truly “off the shelf.” And a reminder that there is one other, actually more prevalent, system for formal approval of an airplane design for military uses–qualification to military standards. Cessna was required to use that procedure on the twin jet T-37 trainer.

There is one other major departure to mention for the OE-2. Even though it met the Marines’ spec and performed admirably–it was a pretty successful mishmash–they only bought about 25 to 27 of them. That last is a figure that I’ve seen reported, and I don’t know if the prototype is included in it.

It’s the only airplane I worked on that was stated as limited production from the start and stayed that way. (I exclude the M620 which, to my chagrin, never got past the prototype stage.) Incidentally, over the years almost 3500 L-19’s were ultimately built–the production line was closed down and then opened again more than once. Users included three branches of the U.S. military and those of many foreign countries. Only the U.S. Marines flew the OE-2.

So how much better did their OE-2 perform than the L-19? Its level high speed was about 40% better, achieved with 24% higher rated horsepower, and its range almost 50% greater, due to about 15% more usable fuel and much better cruise efficiency. It was opined that the L-19 speed was about right for “observing” missions, but maybe the OE-2 was better for getting out of there and getting further away. And it still could be throttled back and operated efficiently when the mission required it.

But the OE-2 was not well known. At the time of the Vietnam war I saw a photo in Aviation Week of a liaison/observation airplane being used there. The caption under the photo said it was an L-19. Its square tail said it was an OE-2.

19 Comments

  1. Ian says:

    Thanks for another interesting article. The empennage is more like the C185 (& some later C180s).

    • harry clements says:

      I’ve noticed that,too. The M185 came after I left the Commercial Airplane Division, and I don’t know if the OE-2 empennage, or maybe just its dorsal fin, were incorporated on it.

      • Ian says:

        Interesting that the C185 wasn’t produced until the early ’60s…unless the particular OE-2 pictured is a developement of the 185. Wonder when the photo was taken.

        • harry clements says:

          We did the design of the OE-2 in 1954, and since the total production was about 27 airplanes they were produced in 1955 and leaking into 1956.These were produced at the Commercial Airplane Division at the Pawnee Plant. The 185 was started after I had moved to the Military Airplane Division and flown well after the last OE-2 had been produced – but it is possible that aspects of the OE-2 were adopted on the 185, since they were both products of the Pawnee Plant, but I can’t comment because I was not involved at all in the 185.

    • Donn Bohde says:

      Ian, I’ve noticed some photos with the larger empennage of the 185 being referred to as 180s I’ve commented on this in several forums, but each time i’ve been told that the 180 never had the larger tail. you mention that in some later models of the 180 it had the empennage looking like the larger one of the 185. can you provide some detail?
      Thanks!

      • Ian says:

        Hi Donn…Some later K models have the185 empennage…my one (1981) does.
        Rumour has it that if a float kit was factory installed the 185 emp was fitted.

  2. bobm says:

    You mention a geared engine, but the picture looks like a 180 cowling with the Cont E225/O470. What engine was actually used?

    • harry clements says:

      It was a Continental TSO-470-2 rated at @265 HP. Seems like we only used Continental engines at that time, including a Continental built French Artouste I on the XL-19(A) turboprop mentioned in the article. The other XL-19(B) (I believe the Army wanted them designated this way) used a Boeing Model 502 turboprop engine – who remembers that Boeing was in the engine business at one time? It was the (B) model with the Boeing engine that set the altitude record.

  3. Robert Wethington says:

    I worked at Pawnee starting in 1964, and can clarify a couple of things: The M180 and M185 vertical tails were different base numbers although the attach points were the same. That was how the last M180 floatplanes used the M185 vertical. I think I remember that Vietnam “L-19″ actually being a MAP 185 (Military designation U-17). My group leader referred to the 185 vertical as an OE-2 vertical. He also described the M185 as a 180 with all the weak points beefed up. That was the only airplane I know of the had an empty weight less than 1/2 it’s maximum gross weight, meaning it could carry itself, although volume was to small.

    • harry clements says:

      I like your information, because if the M185 empennage was the OE-2 empennage (you only mentioned the vertical), I designed it and didn’t know it – just like by designing the 170C empennage I designed the original 172 empennage and didn’t know it. And all I know about the U-17 is what I’ve read about it, but it was an “off-the-shelf” M185 and Military Assistance Program (MAP) airplane that was “given” to many countries and used in many types of missions (including observation). It was not formally used by any U.S. military service, but I’ve read that U.S. pilots did in fact fly it, I guess secretly.
      Still the OE-2 was in service at the time of the Viet Namese war and I feel sure the photo I saw was it and not a U-17.
      My most vivid memory of the OE-2 empennage was that dorsal fin, because I felt there weren’t proven methods for designing it. My guess for it was a good/lucky one, as it served the purpose in certification and operation.

  4. harry clements says:

    I’m responding to Donn Bohde’s comment of April 13, although commentor Robert Wethington (Comment of April 10) might have better first hand knowledge. I’m quoting William Thompson’s book “Cessna Wings for the World” which states that the larger tail, especially noted by the large dorsal fin, was not only used on the M185 but added to later model 180′s for “commonality” on the production line. My memories of certain things and Bill’s often conflict, but in the absence of something better I think his books are authoritative.

    • Ian says:

      Hi Harry…My 180K (1981) has the 185 tail feathers but serial numbers near it have a ‘normal’ 180 one.
      Rumour has it that if a factory float kit was installed it got the185 empennage although another rumour is that when the last thirty or so came off the line everything that was lying around was used with or without float kit…

  5. Was this the plane that was in the mechanics’ training shop at the Wichita Public Schools’ Vo-Tech / Wichita Area Tech. Coll. Aviation School at Wichita Mid-Continent Airport, in the 1990s?

    There was some kind of Birddog-like Cessna in there, but seemed bigger than the regular L-19/O-1 (though I’m possibly just wrong), and had this big, wierd engine (i think it might have been a small turbo-compound engine — where the exhaust turbine helps turn the crankshaft directly — or a gear-driven supercharger — but not a normal turbocharger, as i recall).

    The plane was reportedly a prototype of a bird that got little or no traction with the military — with the prototype being donanted to the school for tinkering.

    • harry clements says:

      I have a nominee if it was really bigger than the L-19: Cessna’s development Model 308. I only know about it because I used to pass by it in Cessna’s boneyard daily on my way to work in the Experimental Hangar – and it was flown before I joined the company. It is covered in William Thompson’s book “Cessna Wings for the World”, but the version on twins and miscellaneous protoypes. It was developed because of a request for proposal from the Army for a 4 to 6 place airplane to be an ambulance, light cargo, and observation airplane. It is stated that it had a Lycoming GSO-580 supercharged 8-cylinder 375 HP engine.The other feature was a square empennage.Apparently it didn’t demonstrate well, got no traction and the DeHavilland Beaver got the job.
      There was one other mostly complete airplane in that boneyard, but Thompson didn’t include it in his book. It appeared to be a 190-195 type airplane with a horizontally opposed engine and a tubular steel landing gear. Looked like a model worth pursuing – don’t know why it wasn’t successful.

      • Robert Wethington says:

        The 190/195 with the flat engine and tubular gear was the X-210. That was in either one of Bill Thompson’s books or Cessna’s history written by Jerry Deneau. Scuttlebutt was that it was slower than the radial engine versions, and the engines cost more.

  6. Chuck Bowser says:

    I worked at the Naval Air Test Center, Patuxent River, MD from 1967 to 1974 in the Flight Test Division, Flying Qualities and Performance Branch, Attack Section. While there we conducted a flight test evaluation of the Marine/Cessna O-1C airplane. The OE-2 designation was changed to O-1C.

  7. Mike Weinfurter says:

    Some facts on OE-2′s, 180′, & 185′s;

    The OE-2 was the first Cessna with the large dorsal fin on the square tail, later adapted to the 185, the first production year for it being 1961. The 180′s and 185′s were easily distinguished by the dorsal until Cessna standardized the airframes beginning with the ’65 model year. In ’65, they were the same firewall aft. Now the only visual difference is the small curved scoop at the bottom center of the firewall providing cooling air for the electric fuel pump needed for the 185′s fuel-injected engine.

    25 OE-2′s/O-1C’s(Vietnam era designation) were built for the Marines per The Lovable One-Niner. It’s 265 hp TO-470-2 featured a belt-driven supercharger. They went to VMO-2 & VMO-6 with the surviving aircraft sent to RVN with VMO-2. (Wonder if any are still there?)

    As for OE-2 survivors, There’s one in a Marine Museum on either the east or west coast. It was one of the damaged ones from I believe Camp Pendleton which was made whole for display purposes with some 180 parts. There’s been one rumored to be at an Aviation Tech School maybe in the midwest, but that one has never been located that we know of. Another is in northeast Texas near the coast. It was restored and flown in the mid seventies to early 80′s until being parked. I had the privledge to fly it in ’79 at an airshow when it was part of the Gulf Central Air Force. Learned formation flying that summer in a Birddog with the OE-2 and GCAF’s OY-1. I was either on their wing or them on mine. Finally figured out how by season’s end. Those guys claimed it was heavier, only 40 degrees flaps, but for sure faster doing 170 mph true at 11,000 on 11 gph per them. Described its induction system as a a PS5C bendix lying on it’s side. It was at OSH for at least 2 years. The son of one owner has it, knows what he has, and I heard would like it to go to a museum. The price is WAY up there and he may not want it flown due to rarity. I still have the photos of the day I got to fly it with one of it’s Pilots on board. I have a friend whom was dual-rated in the Marines at Pendleton and flew them in VMO-6. He said the engines seemed to last maybe 400 hours(?).

  8. Hawk Greenway says:

    I have owned a 1965 U17C for 25 years. Started out with an IO-470 engine of 260hp, zinc chromated interior, Float plane V brace, stainless cables, 24V electrical system, and the larger 185 style verticla stabilizer, but no float attachment fittings (it does have “pick me up” rings on top of the wing). Was never delivered to the South Vietnamese army. It is simply registered as a Cessna 185 with the FAA. With a modified engine mount and an IO-520 it has truly been a “normal” 185.

  9. steve noyes says:

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