The production T-37 “Tweet” serves up an enduring mystery

In very early 1952, I was an undergraduate working part time in Cessna’s Flight Test, Aerodynamics and Preliminary Design Group when a request for proposal for the TX came in from the Air Force. The TX was to be the first, that is the primary, trainer in a series of three new trainers which would finish with the TZ, a supersonic one.

While there were many options included for the TX configuration, the Air Force favored a side-by-side cockpit, for more personal communication between student and instructor, and specified particular turbojet and turboprop engines that the government would supply if the bidder chose one of them for their submittal.

Cessna's XT-37 jet
Cessna’s XT-37 twin jet trainer first flew in 1954.

At that time, Cessna had no divisions so such an undertaking would be handled by our own aerodynamics and preliminary design sections and would be quite a departure from airplanes like the 170, L-19, 180, 195 and 310 which we had or were developing. And wide, diverse competition from companies like Beechcraft, North American and Temco was expected.

Management decided to enter the competition anyway, and I was immediately put on full time in order to work on the proposal. That still fit with my education goals since at Wichita University, in the Air Capital of the World, Aero Engineering classes were offered only at night so we could work in the industry during days.

We started the proposal work with an internal competition of configurations with single and twin engine versions using the powerplants the Air Force said they would supply. We settled on a twin with jet engines, placed inboard so as to minimize engine out problems for the novice students, and fleshed out the design and prepared a five-volume technical description for submittal in the formal competition. We were so short-handed that I was chosen to completely author two of the volumes, concerned with stability and control, and did a major part of the analysis for a third, but did not write any of that related text.

If our submittal were selected, it would be the first on-purpose jet trainer design ever for the U.S., since existing ones were adaptation of operational jets, like the T-33 derived from the F-80. About six months after we submitted our proposal, we were awarded the contract to build and test the prototype XT-37s. Readers will likely know that the supersonic TZ became the T-38, but for some reason there never was a TY, and I’m not sure what its role was supposed to be.

In 1952, Cessna’s general aviation airplane design and production activity was at the Pawnee Plant on the east side of Wichita. It was to become the Commercial Airplane Division and in 1953 a new division, the Military Airplane Division, for the T-37 contracts, was initially placed in another facility on the west side of town, the Prospect Plant (later expanded into the Wallace Plant constructed on Wichita’s adjacent Mid Continent Airport).

Prospect had been devoted to and continued to do subcontract work for Boeing. (XT-37 flight operations were thus out of a large, leased hangar at Mid Continent till the Wallace plant was first opened.) Our own Chief of Flight Test, Aerodynamics and Preliminary Design was chosen to be the Chief Engineer for the new independent Military division, and the engineering staff was made up of selected transfers from Pawnee plus a lot of new hires.

I wasn’t selected to be transferred, and my old boss, the new Chief Engineer, told me that in the bargaining for internal talent he traded me for two structures engineers. That seemed to me like about the right balance – one aerodynamicist for two structural analysts.

T-37 interior
The T-37 was built to be a trainer from the start, so it featured side-by-side seating.

So I missed out on almost the first two years of work on the T-37, which was OK because during that time we did some challenging and successful things at the Commercial Division in bringing the 180 and 310 into production, plus one off-the-shelf military airplane, the OE-2 (for the Marines), the initial design and wind tunnel testing of the M620, the initial design and testing for the 172 (preceded by the 170C) and a little later the 182.

In addition we did some boundary layer control flight research for the Navy with each a substantially modified 170 and L-19, and tested turboprop versions of the L-19 for the Army. I was involved in each of these projects in one discipline and extent or another, except the 182. By the way, my contributions to the T-37 proposal were acknowledged and my wife was invited to the ceremonial first flight of the airplane (our commercial first flights were more discreet, if not downright secretive), but I worked all that day on the other side of town.

But then my chance came to join the Military Division when its Chief of Aerodynamics was promoted to Chief Technical Engineer and I took his place. There was still much development work to do on the T-37, which finally was successfully Qualified, the Air Force term for Certificated, and demonstrated emphatically that our efforts had resulted in a uniquely good all-around airplane.

But I want to focus on a period when that development work was finished and production units of the T-37 were being delivered in quantity. We, of course, did production flight tests on completed units, and the Air Force did a random flight check on some, too.

Let me pause, though, and explain that there were several difficulties with the government-furnished jet engines, and it was easy to call them government-furnished engine problems. One was a very loud, high-pitched whine that came out of the inlets of the engines, which Air Force ground and flight crews identified with a dog whistle, and gave the airplane the endearing, and enduring, nickname of the Tweet. (We actually did a project with vanes with sound-absorbing material surfaces in the inlets that reduced the noise to a tolerable level, but lowered the pressure of the air going to the engines and compromised their performance – and the Air Force, thank goodness for them facilitating unusual nicknames, didn’t think the cost increment and performance degradation with the vanes installed was worth the sound reduction achieved.)

Continuing the historical storyline I just interrupted, at this time of volume delivery of production airplanes, we in engineering were more engaged in finding new missions for the T-37, a very economical airplane to buy and fly, and we wanted to use as much as possible of it in these new configurations. It seems incredible now, and remembering that the engines were GFE, that we sold an airplane that could maneuver like a century series fighter and fly at three-fourths the speed of sound at 35,000 feet for only $80,000. There has been a lot of inflation since then.

Cessna A-37
Cessna went on to produce the A-37, an attack version of the T-37 that saw action in Vietnam.

We emphasized two quite different uses, both for the military – one in which we plucked out the T-37’s cockpit and inboard engines and replaced them with a pressurized four place cabin and more powerful engines to provide a small, cost effective VIP transport. Everything else in the model was original T-37 structure, to which we added wing tip tanks to hold the extra fuel needed for cross-country cruising. This idea was pursued with the Air Force for several years without success.

Then, during my time, we did the initial design, and modest testing, of a light attack version of the airplane with external stores of armaments under the wings, higher thrust engines, and more fuel, again contained in tip tanks. This one ultimately became the A-37 (with variations).

For those who know from another article of my concerns about tip tanks on the 310, understand that I was an advocate for them on these two airplanes, because the extra fuel had to go somewhere and we wanted to save as much as possible of the T-37 unchanged. The tanks for these missions differed in that the ones for the VIP transport had a fuel dumping capability, and for the light attack plane they were instead wholly droppable for quick escape capability in combat.

In addition to trying to expand T-37 missions, we entered the competition for an Army target missile, for which funding was then delayed for a couple of years, by which time the Division had found other interests. And I probably should mention a very important non-airplane project: the design and manufacture of the Minuteman Intermediate Range Ballistic Missile’s huge over-the-road Transporter-erector for the assembled, ready-to-fire weapon, which was concurrent with these others undertakings, and definitely was another major draw on our engineering resources and time.

But we were producing Qualified T-37s and some former experimental test pilots were now production test pilots. One day, one thoughtful one of these came to me and said he believed that some of the airplanes became slightly unstable longitudinally at a certain high speed corner of the flight envelope. I said that was impossible because that was precisely one of the conditions tested in Qualification, and the stability was excellent.

He reluctantly accepted that, but came back a couple of days later and said he was even more certain of this anomaly – which would mean that at least some production airplanes acted differently than the prototypes did, as well as different than the production airplanes the Air Force used to confirm the Qualification.

I told him we would provide him with a handheld force gauge with which he could obtain data to show if this deviation really occurred. It did, on about one out of three airplanes! This was not a safety of flight issue, so we gave hand utilized force gauges to all production test pilots to get further statistics and identify the “bad” airplanes. We then did exhaustive measuring of both these bad ones and good ones for dimensions, contours, and even control cable tensions with the intention of finding and fixing the problem.

But we, perhaps because our measuring skills were inadequate, couldn’t find any difference between the “good” and “bad” airplanes. So we began exchanging ailerons and elevators between good and bad ones, and retesting and still no definitive explanation was forthcoming, as incidences of instability were more or less random.

Cessna 407 prototype
Cessna even considered making a VIP version of the T-37, called the Cessna 407.

At this point everyone got kind of paranoid and someone suggested that the ratio of bad-to-good airplanes was about the same as the ratio of units completed on second shift to those completed on first shift, and those lunkheads on second shift must be doing something wrong. That theory was also tested and found wrong.

I was amazed that with all the activity on production airplanes, and the many inspectors, plant reps, and test pilots from the Air Force present, they weren’t curious about what was going on. In our favor, the routine flight checks by Air Force pilots had resulted in no reporting of this problem. And by now we had a large number of T-37s being used daily in the field, and there were no complaints about this flight characteristic.

So, although we did some further collection of data, and with our efforts on developing other missions and products in full force, this mysterious and seemingly unsolvable random light instability problem just faded from our concerns. Yes, I, and we were guilty of not ever reporting the problem to the Air Force customer, but the airplane was getting good reviews in the field, and apparently no harm resulted. So not reporting the problem was not intentional, but just sort of extended over time till the matter was completely forgotten. Still I was bothered that we had no explanation for the condition, and that empty box to check off was in the back of my mind for a long time, even after I left Cessna.

Now skip forward several decades, when the company decided to have a congratulatory event for those of us, from all company departments, who had contributed to that very successful T-37, which ultimately served in its original mission for a record breaking 52 years. But they decided to hold the event on the less celebratory 45th anniversary of the first flight of the airplane, because they felt if they waited for the 50th many of us wouldn’t be around anymore.

One of those attending was that test pilot who first brought to my attention the light longitudinal instability problem, who had stayed with Cessna for a few more years. So I asked him if a cause of the problem was ever discovered, fully expecting he would say no. But he said yes, that he was flying in formation with another production T-37 and at that flight condition he noticed a “crinkling” in the elevator of the other plane just when the instability occurred. (To those who read my article here at Air Facts on the 180, you will see a similarity to that light instability at high speed that happened only on the prototype airplane, which had a flimsier elevator than the production models.) He was satisfied that his observation solved the mystery for the production T-37, but I was unfulfilled.

Because why would airplanes with structures built in the same manner on the same tools exhibit this difference? And more importantly why didn’t it show up way back when we switched elevators between supposedly good and bad units? To me, even with his valuable observation of the proximate cause, it was a mystery still unsolved. And I guess it will have to remain so. You’re probably just as dissatisfied with this ending of the story as I am.

53 Comments

  • One would normally question why corrective action was not taken to address the “crinkling” elevator. But having worked in aerospace design and manufacturing for many years, I know it comes down to a cost/ benefit decision. The issue was more than likely determined to be minor from the performance standpoint (I’m not sure I would agree with that viewpoint!) and if fatigue-induced failure was not a concern (doesn’t sound like that was looked into) , no design change would have been mandated.
    None the less, you did a great job and brought an outstanding trainer to the world. A side note….I live next to a former USAF training base in Arizona and was entertained for years by dozens of “Tweets” doing night pattern work.

    • Let me emphasize that there was never a concious decision to ignore the problem – but at the time period of the article our best efforts, though done discreetly, had not disclosed any cause to correct. And as I stated I believed it was not a safety of flight issue,as I felt that it was likely that many airplanes have certain conditions where light instability occurs and does not cause a problem. I always thought, for instance,but never confirmed, that our own M310 would be barely unstable in the low speed, high power take-off configuration (not required to be tested in FAA certification, at least back then), but at a time when the pilot was exerting decisive control. Again, time went on and no new evidence was obtained on the T-37 anomaly,so the problem just disappeared from our concerns.
      Now consider that the T-37 was in production for 20 years, and over a thousand of them ended up in the Air Force inventory, with nary a complaint on this matter as far as I know. So I also don’t know when in the production series the “crinkling” (in the pilots description)was observed or how serious a crinkle it was. This crinkling was seen on new airplanes during production flight tests, and if fatigue would have caused the problem to grow, it might have been more evidenced on twenty year old active units. And finally, if it was caused by a difference in good and bad airplane elevators,why wasn’t that evidenced when we interchanged elevators between good and bad airplanes.
      But I think you are right that if we had asked the Air Force to have us do more research on the cause, they would have said it wouldn’t be worth the cost. We had a lot of good ideas they wouldn’t pay for us to explore.

      • Harry, since changing elevators didn’t effect the elevator crinkling, I suggest a couple of possibilities: A minute difference in the hinge mounting. For example, if there are two hinges on the stabilizer slightly off alinement axially, it will add a bending moment under high forces. My guess is there may have been a stack up effect on tolerances somewhere. Several parts connected with a some within spec but at the high end of spec results in the assembly being out of spec. It only happens to a percentage of the assemblies with the unlucky combination of parts. The stack up can be mechanical like hinge pin and hole diameter and rivet location or in aerodynamic surfaces resulting in a slight difference in flow. Really enjoy your engineering mysteries.

  • I was stationed at Webb AFB, TX, in the mid 70’s and T-37’s were used there. Neat to read about their origins. Thanks!

    • My dad was stationed at Webb as an instructor. I remember sitting next to the ‘lake’ near the golf course and watching the Tweety Birds taxi by. Quite the childhood memory.. Hope you’re doing great!

  • I was tweet IP at Williams Air Force Base Arizona and then at Randolph Air Force Base Texas from 1982-1985….it wasn’t my first choice out of pilot training, but I realized when I started flying F-16 in 1985–that it had taught me a thing or two about instrument flying! Great airplane to learn on–I was sorry to see it go. Thanks for the article.

  • I’ll get personal in my response. My grandson finished AF flight training last year and one of the disappointments of my career is that he was about a year or so too late to have flown the Tweet. He didn’t want to be an IP either and is just now starting his first permanent assignment as a C-130 pilot.

  • when I got hired by Boeing/Wichita I did not have a security clearance, so they put me into the old air port building to work on a : “Small Turboprop Executive Transport”. My immediate supervisor was Lloyd Long who had been with Cessna before and was rumored to have been part of the T-37 program. Boeing later lost interest in this program and Lloyd moved on to Beech where he most likely became the father of the King Air.

    Gerhard Opel
    Capt.ret.Transamerica Airlines
    member: United Flying Octogenarians

    • Lloyd was the guy I replaced as Chief of Aero at Cessna’s Military Airplane Division when he was promoted to Chief Technical Engineer, so was my boss. When we undertook proposing on that Army target missile mentioned in the article he went full time promoting it and I took his place as Chief Technical Engineer. He was at that celebration of the 45th anniversary of the first flight of the T-37, since he was definitely part of that program.

  • Richard – Would you please require Mr. Clements not enter the ranks of the deceased until at least two(2) weeks after his absolute last story has been published?

    I’ll spring for the party during the idle two weeks . . .

    Harry,

    Thanks for your stories about ‘prior state of the art’ at Cessna. You’ve made me remember that aerospace history is just great to hear, even if it is a smaller story at first glance than the tale of how North American developed the Mustang. Very cool.

  • I really enjoyed the “behind the scenes” aspect of this article. It IS a little disconcerting that such a problem would be ignored but apparently it was not severe enough to draw attention. However, if I had been the pilot seeing or flying a “crinkled elevator” I think I would have been unable to ignore this issue. At any rate I liked the article and it visited rare territory that I enjoyed very much maybe because I am involved in the design and build of a two place airplane myself…the Thatcher CX5. It’s fun to see that the professional designers also have issues.

  • Thanks for the background and insights, Harry.

    I was fortunate enough to get a T-37 familiarization flight (AKA – morale booster) out of Peterson AFB while attending the USAFA in the mid-1970s. I grew up in Cessna singles, and lusted after 310s, but to me, the Tweet was a Cessna only in its side-by-side cockpit. It was a JET!

    The IPs laughed and said it was more of an energy converter – it converted JP-4 into noise. They even said the C-130 was faster. I don’t know about that, but I know the T-37 taught me that a helmet gets very heavy and an oxygen mask gets pretty loose at the bottom of a loop – something I have not experienced in any other Cessna.

    The Tweet was a hard-working bird which earned its place in history. I imagine there are loads of them out there somewhere, but you don’t see them in the warbird shows. Could that be because they’re just not pretty, in the classical jet fighter sense?

    • Google says the T-37 is faster than the C-130.The Mach limit on the T-37 was set at .7 because at .75 we encountered compressibility effects that caused a trim change.It is subjective as to how serious that was, but max speed was not a big objective for a primary trainer. We did a wind tunnel development of a thinner wing that allowed .1 more in Mach, and still with good low speed characteristics, but the Air Force didn’t see the point in it, and from a mission standpoint I would agree.
      I too am surprised that you only see the airplane in museums, and I still think it is at least cute. The airplane was in production twenty years and in service for 52,so at retirement of the model the newest airplane was 32 years old.That may have something to do with it.

  • Dear Harry,

    Another great article. I have a question for you. Since my earliest flying memories are of flying around in my dad’s ’56 172, I love the straight-tail look on the early Cessnas, like the T-37 and the 310 you’ve written about lately. And when I see the swept vertical tail on the newer versions, I always wonder, as a designer, to what degree is there any concern about pitch change with rudder application when using aft rake in rudder hinge line? I would love to see this point addressed either here or in a future article!

    Thanks again for the fascinating writing!

    Bill

    • The swept tails on the commercial models happened after I left that Division, but basically they are for “show” – more modern and speedy looking. The slight amount of sweepback creates a modest reduction of the lift curve slope, which is offset by the center of pressure of the configuration being further back, extending the moment arm for the vertical tail and rudder contribution to yawing moment.This is my subjective assessment, as I never made a numerical analysis myself. I hope that answers your question. Note that the T-37 went on in production for twenty years with its original straight tail configuration.

      • Harry,

        Thanks for the note – actually, what I was referring to was the possible issue of an aft-raked hinge-line on the rudder producing displacement of airflow in the vertical direction in addition to the normal, expected, lateral direction. If this helps: imagine a rudder with an aft-raked hinge-line which is deflecting 90 degrees. Doesn’t such a surface, in this case, produce nearly 100 % upward air deflection? If this is true, then it stands to reason that there would be upward air deflection to some degree with more usual deflections.

        Thanks,

        bp

        • Sorry I misunderstood your question.You are right about the phenomena, but textbooks (at least my old ones)on stability and control ignore it as too small compared to other forces and moments routinely taken into account. I feel sure my colleagues at Cessna ignored it,too. So, I stick to my original assessment – sweepback on the tails of those propeller driven models was a marketing tool – it just looks more modern,sporty and speedy.

  • I flew the T-37 at Moore Air Base in Mission, TX for about half of my primary training. It was a pleasure to sit in an air conditioned bird after sweating in the T-34. On my initial flight my instructor took it up to about. 20k and then said “watch this” as he nosed her over and moved the stick to the side with two fingers. After we spiraled down about 5k he moved the stick back and smoothly leveled her out. I loved that bird !

    • You’re giving me the chance to expound on a couple of things. The original Request for Proposal for the TX did not specify air conditioning, and we didn’t include it in our submitted design because that would add weight and cost. But with our greenhouse side by side cockpit, and since the primary training bases were spread from sunny Texas to sunny Georgia, it was an obvious contract change to add air conditioning.
      The other thing was that the requirement was to simulate the iconic F-86 in most flight characteristics, but still be a plane that novice students could fly. There has been, over the years, a lot of discussion of the Tweet’s spin characteristics, but we had one modification that allowed recovery from a normal spin just by releasing the controls – but the AF didn’t want that but instead wanted a spin and recovery technique that was close to that for a jet fighter of the day.
      I mentioned in another comment that the Mach limitation on the T-37 was for a condition of a trim change occurring, but how serious that trim change was was subjective, so it was thought best to placard to give a .05 spread for concerns of how student pilots would react to that trim change that occurred with no easily visible or detected cause.
      And I always wondered why the requirements for the T-37 emphasized fighter characteristics so much, when many students would go on to fly cargo, transport and bomber airplanes.

    • The only source I know is from “googling” Cessna T-37 and it results, in addition to Wikipedia descriptions and the like, with several advertisements from what I would characterize as used airplane dealers that say they have it or the A-37 for sale.I don’t know how they are acquired, but remember that many foreign countries bought both the T-37 and A-37 and they might be surplused from them. I have the feeling that the US Air Force has not made them available or, if not,whether that would be a departure from surplusing their retired airplanes for sale.

  • I enjoyed this interesting look into the T-37, it’s development, and history. Thank you for that. I would only ask one thing: How is it possible that there were “secretive” flights made of the Tweety Bird considering the whistling noise that the two engines made that could be heard for miles around?? That high pitched whine was enough to make me cover my ears when I wasn’t even NEAR the flight line! Cool little jet, thought; and I think it was something that you strapped on, not got into! Thanks for the insight.

  • My first response was dismissed. I’ll try it again.
    Sorry if I was not clear. The secretive flights were on the first, or perhaps first few, flights of our Commercial Airplane Division models like the 310,170C,172 and 182 for the marketing related purpose of not divulging what we were developing, that might have troubles at first, and in fact we may never offer for sale.Such first/early flights were made at the adjacent air base (M310),and/or on days off, or very early in the morning,and maybe to go to a field at a remote Kansas town for further development(M172).
    The XT-37 first flight, in contrast, was a public relations event to which the media and dignitaries were invited.This kind of exposure might result in the pilot remarking after the flight that the airplane climbed like a homesick angel and flew like a dream, even if he had problems with it.
    As I mentioned the Air Force allowed us to (paid for us to) carry out a successful project to tone down the scream coming out of the government furnished J-69 engine, but decided that the penalties were too great, so instead just let the airplane punish ground crews and bystanders, Air Force or Cessnans, and the local folks, too.

  • Thanks! Lots of good memories concerning the T-37. I worked in Periodic Maint. at Reese AFB in Lubbock, Tx from Mar. 62 though Dec. 63.
    On the trim pad we wore “Mickey Mouse” ears filled with caulking compound plus our Military issued “ear plugs”! After several hours running up the tweets, when I climbed into my 52 Dodge, the only way I knew the car was running was by looking at the gauge’s spool up! LOL The VA Hosp. says I have a hearing loss “right at the J-69 level”. Anyway, it was great and fairly easy plane to work on. Roll under it with a “creeper” for the fuel pump. Easy access to the “hell hole” where all the “fluids” connections were put for easy observation and inspection. Engine change was only a two man (sometimes one man) operation. Good thing that the Air Force had QC “Quality Control” to follow behind us new airman checking on our work. I learned a lot on the T-37. Jan.64 I was transferred to Misawa AFB in Misawa, Japan, Land of the Rising Sun and Cherry Blossoms. Worked mainly F-101 Voodoo’s (Overhaul and Flightline) plus “trim pad” but did some work on F-100 and F-102 when needed. Shipped out to Vietnam with the 45th TFS working on RF101C photo birds. Also a great airplane but a real step up maint. wise. Supersonic, twin J-57’s, up off the ground maint. Ladder’s and work stands, drag chutes, etc. Became a civilian in 1966, joined Piedmont Airlines/US Airways. Retired in 1996. Private Pilots Lic. in 1967. Now retired and enjoying life at age 71. Flying for me, all started with the T-37 in West Texas. Land of Tex-Mex food and Chicken Fried Steak. Thanks for the memories! Now living in Roanoke, Va. Beautiful place! Merry Christmas to all and to all Good Night! Joe

    • Our design objective for the proposal for the TX was to keep the airplane small and accessible. That was not my direct concern except to support that goal with accomodating aerodynamics. One of our Cessna ground crew demonstrated changing an engine in less than 20 minutes (I suppose they practiced for that). Another little known experiment was to have one AF pilot training class start their flying with the T-37 – the average time to solo in the airplane was less than eight hours, which I thought was remarkable and I expected the Air force to continue with that. But I don’t know what the washout rate was, and they soon bought another Cessna product, the 172/T-41 for initial, I think screening, flying which I presumed saved money.

  • I think the first best day of my life was soloing the T-37. My IP, Capt. Kirby Cannon, climbed out and just walked over to the side of the taxiway there at Laughlin AFB, TX, after saying, “Take her up and get in the pattern and do some touch and go’s, and come on in after while and we’ll discuss it.” The air conditioning was good at altitude, but not as cool as needed when you stayed down in the hot, humid air at traffic pattern altitude. Very forgiving aircraft; very nice to fly. Went on to C-141s and C-130s after my class of 1968-H graduated. I’m drawing up a set of 3-view line drawings for the Tweet that I hope will be better than the ones on the web.

    Thanks for all the inside history on this great little plane, Harry!

    Jim Johnson

  • I was in class 67F at Laughlin AFB, then a Tweet IP at Randolph AFB in San Antonio 1967-71, accumulating about 1500 hours. Cessna’s T-37 was a great trainer. I still use those principles instructing today, although I have added taildragger skills for the C120. Thanks to the 122 dB scream of the J69, I now wear hearing aids, but I recall many really great teaching stories! Such as the student that got us into an inverted spin after botching a conventional recovery. It had nothing to do with his wife being full term pregnant!

  • Harry,
    great reading on the T-37 – thanks for the effort to make this inside information accessible to the rest of us.
    Questions:
    1.) what can you recall about the competitors entries in the T-37 competition. What did they do right and what appeared too weak to be competitive?
    2.) Was the J-69 a Continetal CAE built version of the Turbomeca engine?
    3.) Where do the configuration parallels between the T-37 and the Morane Saulnier MS-760 4-place fit in the big picture. Beechcraft never got any traction with efforts to market the PARIS Jet. I chuckle when I now see the MS-760’s showing up over here and being remarketed.

    Keep writing – I promise to keep reading
    thanks
    Hans

    • As a new entrant to aviation – I was still an undergraduate when we did the proposal for the T-37 – and uncertain about Cessna’s agressiveness on this and some other projects, I thought North American would be the primary rival, after all they had dominated U.S. military trainers for decades. I never saw their entry, and I imagine our claims would have seemed ridiculous for a company with Cessna’s limited experience – but I realized later that our chances of making them were probably better than North American’s because we were not limited by internal history. I’m thinking of our plan for first flight in 18 months – which took 24 – but they (NA)probably planned for 24 months and would have taken 36.I only have insight to two other competitor’s airplanes, Beechcraft and Temco.
      I think the Temco TT-1 (if I remember the designation), a tandem single engine configuration, was a non-starter. And the surprise was a Beech design I found in the archives of a friend that looked so much like our proposal I wondered if they had a spy in our place. I don’t know why they didn’t propose it.I think their derivation of the MS-760 was a good one, but your guess is as good as mine as to why it never prospered in either configuration.
      Yes the J-69 was Continental’s continuation of the Turbomeca engine. One of the unrecognized hitches is that the models for the protoype airplanes were so different than those for production that we encountered problems, for instance due to their higher thrust and lower idling speed, that we thought either solved or non-existant – in particular stall warning buffet, which disappeared at high thrust and was unbearably strong at idle thrust with the production engines.

  • Harry,
    Thanks for your great article on the T-37. Why has the design of the engines in the wing root gone away? Nobody seems to favor that anymore on twin jets and it seems like a very good design in terms of eliminating asymmetric thrust with one engine out.
    Regards,
    Peter

    • You have identified the reason that we chose to have the wing root location for the engines – assymetric thrust with one engine out. We thought that to be doubly important on a primary,but jet, trainer, in which, depending on the class, the students had little or no flying experience. That gave some inherant problems, like how do you design “light” spar carry through structures, which must go around the engines. That also complicated engine change procedures, which we wanted to be quick. We elected to enhance the engine out aspect by placing the engines well inboard and contending with a curved duct from air inlet to engine face (that didn’t eliminate the intake “scream”, unfortunately). It also made the engine exhaust exit into the area of the horizontal tail which, as mentioned in a prior comment, gave us a problem with the production engines that had higher thrust and lower idle speed than the protoype engines – and complicated obtaining appropriate stall warning buffet in various conditions. We still thought we made the right choice.

      • Thanks Harry. My fantasy is to re-engine the T-37 or A-37B with Williams FJ44 engines for a quieter and more fuel efficient machine, with the same great handling!

      • I am a collector of USAF aircraft and live near the former Reese AFB so was naturally attracted to the Tweet and Talons as subjects. Of course many had been sold overseas or crashed before I got started (1976) so am missing many serial numbers. Do you know of anyone who photographed the jets when manufactured or a source of my missing Tweets?? Thanks

  • Hello everyone, I have the fortune of working on one of the two remaining T-37’s in the United States. The one I maintain is based in Waukesha, WI and we finally made a flight today after a three and a half year hiatus.
    The airplane is a very nice piece of machinery and although it presents its challenges, it is fun to work on.
    I believe we are planning on taking it to EAA airVenture this year.

    I really enjoyed reading this article and I am always looking for information on the Tweet!

    Sam

    • Hi Sam,

      I had the distinct pleasure of being the last qualified T-37 pilot in the U.S. Air Force. After I flew the final student training sortie at Sheppard AFB in June, 2009, I took the last jet to the aircraft bone yard in Tucson, AZ about a month later. Furthermore, I continued to fly them (after their retirement) at Davis-Monthan AFB through July of 2010, on Functional Check Flight test sorties in preparation for their sale to Colombia. I ended up with about 2,600 hours in the aircraft, 1.3 at a time. I loved that bird!

  • Mr. Clements,
    I am writing a book on post WWII trainers and I read your article on the T-37 with great interest. I know that the T-37 evolved from Cessna’s successful response to a 1952 RFP under the TX program, and I understand that eight other companies responded. Do you have any information on the unsuccessful proposals? Also, William Thompson account in “Wings For The World II” suggests that the RFP did not specify an engine configuration (p.37). Was a turbine required or could a recip be proposed under the TX spec.?

  • Mr. Clements,

    I am writing a book on post WWII trainers and I read your article on the T-37 with great interest. I know that the T-37 evolved from Cessna’s successful response to the 1952 RFP under the TX program. I think eight other manufacturers responded to the RFP – do you have any information on the unsuccessful responses?
    Thank You,
    Mark Frankel

  • Hello Harry,
    I am impressed with the knowledge and experience so clearly and simply expressed in your article and through the response. I trained at Williams field in 1963, graduating with class 64-E. This month we celebrated our 50th USAF pilot class reunion in Phoenix.
    That being said, I am searching for actual engine and aircraft dB and SPL levels of the T-37A. Can you provide or point me to credible data regarding noise levels of the T-37A? I also flew KC-135A’s (J-57 engines). So far, the aircraft manufacturers and engine manufacturers are holding this information as “proprietary.” Imagine, 50-year-old technology seen as a security threat. I look forward to your reply, especially as I want to establish a “sound” link between active duty military jet engine noise exposure and bilateral hearing loss/tinnitus.

    Love of flying,

    Christopher L Fromkin
    ex-USAF
    Retired TWA

  • Chris: The Dash-One for T-37B said the J-69 had a measured 125 dB on the A Scale… I was a Randolph IP 1967-71, and just this year got two hearing aids due to high freq loss. Contact me at jim72989@mac.com

  • Excellent read! I used to be a T-37 instructor pilot from 1996-1999 in the USAF. I am currently a system safety engineer for Textron Aviation (formerly Beechcraft, now merged with Cessna), on the T-6 trainer. Sounds like engineering practices and management decision-making hasn’t changed in many respects. Not saying that it’s good or bad….just the same!

  • Thank you Harry, for the very important historical information on the T-37. I have been a Cessna fan since the Bamboo Bomber, and Sky King’s 310. My dad was a pilot and after WW2 bought a 120. He taught me to fly in that 120. Later he had a few more planes before he retired from flying, but they were all Cessna. What a wonderful company with such great employees. Thanks to all who have provided a safe airplane for me to fly. I’m now 71 and I still occasionally fly with a friend. It is a shame that government intervention and insurance companies have ruined general aviation. I look forward to more from you, Harry. God bless.

  • I flew in the T 37 in the summer of 1979 as an Air Force cadet from St Thomas College MN. I remember that intro ride very well .I asked the instructor pilot, who I really never saw, because he had his sun shield down, to give me a very spirited ride. Once we got up around, oh maybe 3-4ooo ft in that hot Texas sky(out of Del Rio?) he proceeded to dive , then pull up in a turn( a Silon maneuver from Star Wars perhaps). Well that was something. I had no g suit on and the meter said
    something like 4.5 G’s. It hurt, the pores on my face squirted perspsiration into the shield. It was awesome. A Mexican pilot had a flame out in a t 38 , so we scrambled and I got a few more minutes to dance around in the clouds. A fun day.

  • Gerald, as the last Tweet driver, I flew FCF sorties on the T-37s as we released them from the boneyard for international aircraft sales from 2008 – 2010. With that said, I had access to Tweet row and other areas of AMARG, and wrote down as many serial numbers as I could find. In addition, I photographed each aircraft. It will take some time to dig out those records, as I have since moved, but I will see what I can find for you.

  • I was a T-37 instructor at Webb during the 70s – I had my choice between instructing in the “American” squadron (USAF UPT) or in the “foreign” squadron (Security Assistance Training Program). I chose the SATP squadron because we flew a more interesting syllabus – four-ship formation, day/night VFR navigation and it was more interesting instructing Vietnamese and allied students. The -37 was a great aircraft and was extremely forgiving – we all developed lightning fast reflexes. A fellow IP of mine had a student who confused the words “idle” and “cut-off” so you can let your imagination run with that for a bit. Fun times in West Texas. Loved the Tweet, thanks.

  • My Dad was stationed at Webb AFB during 1966-1967. He ran the radio shop and would sometimes take me to the flight line to watch the T-37s and 38s taxi by. We lived on base and could hear the extra loud F-102 of which there were couple based there when it would take off. Webb was a jet training base that provided flight training to pilots from around the world. Thanks for bringing back some nice Texas memories.

  • could be that the problem was related to harmonics? resonance is a problem that is hard to detect, as it may occur due to several factor coinciding, including the small details during manufacturing? just in assembling, many things may go slightly different, even within tolerances?

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