FLYING THE OV-10 (BY JOE SCHEIL)

The Bronco sat in a Chino hangar that once housed P-51 Mustangs in the process of being restored to flight. Only 20 years removed from the Mustang and Mitchell, the market changes that brought this OV-10 along with seven more to Chino are perhaps emblematic of the huge shifts occurring in the Warbird world. Is it time for “modern” Warbirds to disrupt the marketplace? And this Bronco is a disruption — in every way! The passage of time and the words of journalists have taught generations of enthusiasts to identify with the song of the Merlin and the roar of big radials. This angular warplane makes a sound similar to Mitsubishi MU-2s and Grumman S-2T fire-bombers — and for good reason since the OV-10 is fitted with Garrett T-76G-420/421 turbines, the military designation for the Garrett TPE-331 fixed-shaft turboprop powerplant. For Warbird readers of Air Classics, we haven’t really discussed turboprops.

So, what is a turboprop and why do they exist? A turboprop is a jet engine that turns a propeller through a gearbox integral to the engine. They run on Jet A and are nearly totally reliable, capable of being on an aircraft for thousands of hours, and needing nothing more than minor adjustments when flown by conscientious pilots. The starting and operational use of such engines is simpler than reciprocating engines, they have much more power for their size and can maintain that power to far higher altitudes than piston engines. They burn perhaps twice the amount of fuel in a direct comparison but the benefits outweigh the fuel costs to operators that can afford turbine power. The first military turboprops showed up late in WWII, giving turbine propeller-driven aircraft a very quick power delivery compared to the first generation of pure turbojet warplanes whose delayed throttle response was more than worrying to military planners. Military turboprops were never designed with efficiency at the forefront, so they can be thirsty but the ease of maintenance and available power is why they replaced the pistons. Turboprops have a history of very few shutdowns or engine failures. To understand turboprop effectiveness, one has to look at the numbers built. The TPE-331 in the OV-10 was designed for the military as the T-76 and was expected to be used initially in helicopters. It was created by Garrett AiResearch as a 575 shaft horsepower engine and was not scaled down from a larger engine, which was the practice of the time. This turboprop has been used in 24 fixed-wing aircraft as the primary engine while being retrofitted to 13 more designs since 1965 by Garrett and then Honeywell after 1999. An incredible 13,500 have been built. Considering that number is really important. This engine has been with us for 56 years and that roughly translates to just 250 engines delivered per year. The TPE-331/T-76 generally requires a fuel injector nozzle cleaning every 400 hours, an 1800 hour hot section inspection, and a 5600 hour time between overhauls. These engines simply don’t wear out! The Pratt & Whitney Canada PT-6 deserves mention since 51,000 units have been made and used in many more aircraft along with non-flying applications. The Garrett is considered a little “finer” and it is purely an aircraft engine and always has been. PT-6 applications run across many different types of machines and that fleet is noteworthy in logging OVER 400 MILLION flight hours, and with a shutdown rate of one per 651,126 flight hours. The less common TPE-331 has 122 million flight hours — a staggering 9037 hours per engine so far. The turboprop is in many ways the “ultimate” powerplant for subsonic aircraft and its reliability, weight, and power delivery numbers are unmatched. But they make noise — and lots of it. Where you come from often dictates what you like, and my first turboprop was a Piper Cheyenne LS-400 powered with the superlative TPE-331-14GR engines.

Photo Credit: Air Classics Magazine

Currently, the OV-10s being operated by the Philippine Air Force are the only Broncos still
flying combat missions. These planes, which were mainly airframes donated by Thailand,
operate on a regular basis against ISIS forces in remote jungle areas of the island nation.
The aircraft are supported by the American government but they may become available as
newer aircraft are funneled to the Philippines and the OV-10 Squadron is keeping a close
eye on the machines.

On taxi out, the aerobatic guys with their Pitts and Extras stuck fingers in their ears and glowered when you growled by. Remember, you don’t have to use the brakes, you just taxi using “Beta” — or reverse pitch — to slow the bird down. I thought it sounded very satisfying. And with that monster at my fingertips, I was able to climb out of John Wayne Airport every Tuesday and Thursday morning at 0710 at 4500 feet per minute and made FL230 in under six minutes. Simply magic! Slumming a ride in a PT-6 powered King Air, I was underwhelmed. Power to weight in the Cheyenne was six pounds per horsepower, similar to a Mustang. It seemed like the King Air was just a heavy turd. I loved the Garrett. Interestingly this engine came into being as the military Garrett T-76 FIRST and was developed into a fixed-wing aircraft engine with the OV-10 airframe. The Garrett is direct drive; what we call a fixed shaft turbine. That means the JET engine (a small one) is built with a gearbox on the front that is a direct and unbreakable link to the propeller. This is VERY different from a free shaft engine like the PT-6 family, which simply blows on a turbine wheel attached to the propeller. The fixed shaft engine is noisy because the jet engine that is the Garrett propeller runs at only two speeds — different from the civilian three speeds — that are set by the condition levers marked Takeoff and Land, Normal Flight, Fuel Shutoff and Feather and Fuel Shutoff. The High setting on the military OV-10 is for takeoff and landing, critical flight environments that require the best the engine can give and that RPM is 100%. Next is Cruise or “Normal Flight,” which is, believe it or not, 96 to 97% of RPM. That’s it. Civilian Garretts have a “LOW” and “HIGH” speed, which gives the pilot a quieter plane for ground ops. LOW corresponding to 65% to 73% of RPM for ground operations. All Garrett aircraft are considered loud but with a ground idle of 96%, the OV-10 screams. The Garrett is an excellent powerplant though and gives you power NOW. That’s kinda why we talk about the propeller condition lever first, because once set in Normal Flight the propeller governor controls engine speed by adjusting the propeller blade angles to maintain what is desired. The power levers control fuel or torque essentially and gives instant response because the propellers instantly respond to the governors’ adjustments. It seems complicated if you are new, but the operation becomes very intuitive. Designed to be simple, in operation it is. Best of all is the NTS (Negative Torque Sensing) system. This will partially feather a propeller when a lack of power is felt by the engine, thus giving the pilot a lower drag scenario in which to take time to decide to feather the whole way or attempt a restart or correct a problem. Ultimately, for me, the OV-10 is a lot more familiar to walk up to and consider flying because as a corporate and then regional airline pilot, turboprops were the bedrock of the 1990s/early 2000s. Most of us starting out 20 years ago learned our trade in medium bomber-sized airliners with P&W “free shaft” powerplants and while we didn’t have the agility of the OV-10, we had the training of flying the line in all weather with aircraft that had systems and characteristics like the Bronco. So, with that background I really was curious about the OV-10 and how it would perform, as well as feel. Would it be a fun airplane that I would consider as a possible purchase, or fly for someone? Would it have a Warbird feel or would it remind me of a Cheyenne or Aero Commander? In any case, I waited for my OV-10 familiarization flight with great anticipation.

The configuration of the OV-10 I was to fly was different from the others under restoration at Matt Nightingale’s California Aerofab facility at Chino Airport. Registered N15453, this aircraft was obtained in flying condition from Florida where it had been previously operated by the Department of State. It was built as Bureau of Aeronautics serial 155409 and NAA c/n 305-20, the 29th OV-10 made out of a total of just 360. It had been completed on 22 April 1968 and was immediately sent to Vietnam. It had arrived at Camp Pendleton on 23 April and was listed in Da Nang with VMO-2 on 2 May 1968! Serving in combat for one year, the Bronco was next at Okinawa in 1969 before moving on Kanehoe, Oahu, by 1971. In 1985, the Bronco was converted to an OV-10D and got the long nose and other mods. By 23 April 1993, the OV-10D was in storage at Davis-Monthan with the code PA0002. At some point, the Department of State acquired the old warrior with the civil registration N15453. The DoS OVs were operated by DynCorp and were part of the clandestine Latin American drug Interdiction efforts.  The DoS Broncos still stand out a bit. The DoS removed the fuselage sponsons — the stub wings that housed machine guns — in order to mount the hopper for herbicide spraying. Additionally, the long nose and Kevlar fuselage armor to protect the crew from small arms fire not only shows the military usage but also the equally hazardous anti-drug mission. A wind-driven pump was added along with spray booms that would allow a herbicide or other chemicals to be dispersed. Little has been published on these controversial operations, but it is believed the DoS OVs were in service from 1996 to 2008. Painted black overall with red flashing on the tail, the plane looked not unlike a P-61 Black Widow. Some records have this OV being used by the Policia Nacional de Colombia as PNC-3043, but this could have been a DoS cover. Oddly, the OV then went to the Valiant Air Command but was never flown by that group, just stored and displayed. The OV-10 Squadron and Blue Air Training found N15453 and added it to their fleet. Perhaps because of the aircraft’s Latin American use, it had a very large unit mounted in front of the back seat position. What this meant was that my forward visibility was nil! Sort of like the Spirit of St. Louis, I could look around the box and get some forward visibility but, for my initial flight, I found I wouldn’t really be able to see much forward! Startup and taxi went by quickly as every airplane has its own sequence and cadence, and turboprops come up to temperature quickly. They burn a bunch on the ground, so you want to get the airplane rapidly into the air. My first military turboprop was a surprise for me as there is no sound deadening like I was used to in civilian planes so while I thought the previous turboprops I flew were loud, this was something else entirely! Unlike a recip, the turboprop engine note really doesn’t change — it just is a strident and urgent drone that fills the cockpit. The propeller and reduction gearbox is five feet away from you (on either side) in the back seat and the plexiglass does little to mitigate the sound. Visibility above and below was very good, but the engines and wing prevented any look behind the leading edge of the wing from the back seat. I am sure the visibility in the front seat is excellent. When it was my turn to fly to Bronco, I found the plane has nice flight controls — not beautiful, but nice. The OV is kind of workmanlike in its handling. It does not feel particularly light or heavy and is reasonable to throw around the sky at medium altitudes. Flying the OV, I can’t get away from its history and what the military pilots were doing along with their civil counterparts in the drug war. So, the control input and results seem excellent for what crews needed to be doing — keeping eyes outside, power and speed up, and looking for trouble on the ground. The OV has good visibility in some quadrants for the CAS mission but would not be a great platform to defend from an aerial opponent. The visibility behind the engine wing line is nonexistent! (EDITOR’S NOTE: On the internet, a viewer can watch Venezuelan F-16s shoot down two OV10s on 27 November 1992. The OVs were being operated by a faction loyal to the communist leader Hugo Chavez so Joe’s comments about rear visibility are correct — the OVs didn’t know what hit them as the F-16s shredded them with 20mm cannon fire.) Any turboprop’s energy is always a bit deceiving since the OV’s engines provide all the power (and airflow) over the wings that you seem to need. I bet this one would be able to hang on its propellers fairly well. I read that NASA had played with one, adding lift devices and different props until they got it to be almost like a Storch. This one stalls at around 74. The props always turn at 2000 rpm so the sound of airflow over the airframe is really tough to hear if that’s one of your cues. Trying a lazy 8 just to feel pitch and roll control through a variable speed and load range, you find the onset of speed “heavies” up the controls quite a bit. Sitting around looking at things from an OV perch over a tactical spot is as light as you can imagine, so a nice place to work in normal operations. Approach and landing is a numbers deal. Partial flaps were all I saw although someday I would love to try some full flap arrivals. With great power and response, large flight controls, and nearly indestructible landing gear designed for STOL work, I would bet the OV-10 could make some very interesting arrivals. However, this was not my plane! The interesting nature of the OV and its different feel from the piston Warbirds makes the Bronco worth considering for a variety of reasons. One main item to consider is the fact we are constantly moving away from piston-engine technology along with the ability of pilots to operate tailwheel aircraft (especially large ones), so there is an entirely new market of prospective OV owners — especially pilots that want an aircraft with unique performance as well as looks. Ultimately, I would love to fly the OV on a range or do some air-to-ground work with Blue Air Training. It would be a sensational platform to operate in the air-to-ground role with something to shoot at! So, for a potential Warbird owner wanting a modern and distinctive aircraft with tricycle gear and turbine power along with amazing military history, then the OV-10 would have to be at the very top of the list.