S-3B as an air tanker?

S-3B air tanker proposal
A design for converting the S-3B into an air tanker, by Argon ST, a subsidiary of The Boeing Company.

The concept of converting the S-3B into an air tanker has been floating around for a while, so let’s explore it a little.

In 1975 the U.S. Navy replaced the S-2 with the jet engine powered S-3A. The S-2 is still being used today by CAL FIRE after the agency replaced the piston engines with turboprops and renamed it the S-2T.

Most of the  S-3As, 119 of the 188 that were built between 1974 and 1978, were modified in the mid- to late 1980s with updated avionics, radar, and missile capability, and an updated name — S-3B.

S-3Bs Davis Monthan AFB
S-3Bs at Davis Monthan AFB

Since they were retired in 2009, over 100 S-3Bs have been stored in the desert. According to an engineering analysis by Argon ST, a subsidiary of The Boeing Company, an S-3B converted into an air tanker could carry up to 2,000 gallons of retardant, would have a maximum speed of 450 KIAS (518 mph), a drop speed of 125 to 135 KIAS (144 – 155 mph), with retardant coverage levels from 0.5 to 8. The engineering analysis for tanking the S-3B was sponsored by NASA and is available at no cost to the USFS.

The S-2T used by CAL FIRE has a 1,200-gallon retardant tank and a maximum speed of 235 KIAS (270 mph).

A speedy air tanker with those specifications would make a pretty good initial attack resource. One of our readers suggested that the federal land management agencies could pick up 100 of them and outfit 40 with tanks. Many of us will remember when the U.S. Forest Service had significant initial attack capability from both the ground and the air.

Typos, let us know, and please keep in mind the commenting ground rules before you post a comment.

19 thoughts on “S-3B as an air tanker?”

  1. Smart money would be on boosting the numbers on what we have that works…AND investing in UAV technology to find the future of fire fighting in the wild lands.

  2. Looks like I was typing when Bean posted….C-2 would be interesting as well. Too bad about the load limits for both aircraft, that doesn’t bode all that well as a solution airframe.

    1. Danny,

      I think there is a way the S-3 might do the job. I’d pick it over the C-2 because of the S-3’s higher structural load design limits. Besides, the C-2A requires a center wing replacement to extend its service life.

      If the S-3 was able to very rapidly jettison its load of retardant in the event of a single engine loss on takeoff and the brakes were improved, the single engine climb restriction would not be a factor and its payload would only be constrained by critical field length requirements. I expect at that point, it could carry a respectable payload.

  3. I have no access to any NATOPS data on the E-2, but a quick internet search shows some numbers that would lean towards it being feasible out of the shorter runways. I have always thought it was a good looking bird as well with a similar mission in some ways to the S-2, and bears a similar pedigree to the S-2 in regards to strength, durability and construction. Since the E-2 is still being built and supported, one could argue that it would be a beneficial platform to invest some R&D in. Not sure on the specifics, but I’ve read that the D models with FADEC are able to produce 5450shp single engine to meet the Navy climb mins. Size wise, it ought to fit in most reload pits that accommodate an S-2, or possibly an S-3. Hoser has been quoted in saying that he firmly believes that the S-2T will still be airworthy in another 23 years, and given Cal Fire’s Mx program and record, there’s not too much doubt there. I’m sure Cal Fire has looked at the airplane, and is thinking ahead to what’s next. I have heard the -14GR cores are becoming harder to find……and are worth a pretty penny!

  4. I’ve poured over the Argon report, as well as the Cal Fire Pilots newsletter archives that include some great additional information and discussion about the S-3 as an air tanker, even as a replacement for the S-2. For all the above mentioned reasons, it’s still a program that would have to address several significant issues to be feasible from longer runways at lower density altitudes, not to mention Cal Fire as an airplane capable of operationing out of the “bread & butter” air attack bases (Grass Valley, Columbia, etc.) with their shorter runways and density altitudes in the 6k on a normal afternoon @ fire-thirty.

    I’ve always thought the E-2 Hawkeye has been an overlooked, or not even mentioned aircraft that could serve quite well in this capacity. 5100SHP turboprops, similar profile to the S-2, albeit a little bigger in regards to wingspan, length etc. If the radome was removed…..aerodynamically this would have to be taken into consideration of course, but as I understand it, that the lift created from the dome only offsets its weight, so as long as there weren’t any penalties for removal, it’d be a wash performance-wise……all the heavy mission avionics and crew stations taken out, and a similar sized (in regards to the S-3) retardant tank installed, it’d seem to be a formidable platform. Not sure on all the specific data concerning balanced field length, single engine climb etc, but it’s still an airframe being produced and supported by Northrop Grumman, with plenty of airframes in AMARG, and has many of the same qualities of the S-2 that make it such a perfect initial attack air tanker. The FOD issues of the S-3 (not to mention no reversers on the aircraft) go away with a turboprop. Brakes, not sure, but you see E-2 get down and stopped in some pretty impressive distances. Max T.O. is around 57,000, so talking apples to apples as far as the S-3 is concerned. Obviously a design that works well for the Navy, and seems to be an aircraft that shouldn’t be overlooked for this roll. Love to hear what Bean and others would say about this, I’m sure I’m missing a lot of info and potential drawbacks, but even in talking with several Cal Fire pilots, this aircraft has never come up.

    1. Hi ,i read what ya typed,maybe the E2 would be better,but i asked about this plane many years back and was told the tail would have to be changed.true? untrue?..i dont know…i do have a question though Danny…are you saying the Hawkeye might,or would be able to get off from places like grass valley,columbia,sonoma?…if so..that would be the better aircraft..no?…cides i like the E2’s looks more..lol.Dave

    2. Navy has a carrier cargo version of the E-2. [no dome] called the C-2. Also has rear cargo door approved for inflight use at 140-150 Kts.

      Empty weight 35,340. Max field take off weight 60,000. Max field landing weight 52,323.

      At a 4000MSL field and 80F, Single engine takeoff requirements limit max gross weight to approx 52,000. Figure 1/2 fuel 6000# and that allows approx 1200 gal of retardant.

      Issues?
      2.0 G limit. Same as converted passenger airline aircraft. Operating an airframe that wasn’t designed for tactical flying.

      CFL with 52,000 gross weight at 4000 MSL, 80 deg F, no wind requires approx 10,000 runway. Like all Navy carrier aircraft, a different set of brakes would help for land based ops. Not exactly a Grass Valley airplane.

      The C-2 has 4 vertical stabilizers and three rudders for directional stability/ control. There might be some stability design considerations with a tanker version.

      Data from C-2A NATOPS Chapter 28

  5. if this is to be IA,why does it have to have 2000gals? CalFire S2T’s are supposed to carry 1200 gals,but the maximum load allowed (from what ive read,and was told by both Norm Cook,from aero union ,and Joe Satrapa “Hoser” T88 this season it seems)is that they are only allowed a 1100 gallon load and hoser seems to prefer a combat load,800 gallons from what i gather,so if they use much less,again a loader at GV ATB told me common load is 1000 gals,then why worry about the heavier 2000 gal load?..and why does a base for this plane have to be at places like Grass Valley,4350ft, or Columbia? whats wrong with places like Lincoln with a 6000ft runway? or Chico,mcclellan,atwater,all currant reload centers.and all are as close to where california’s fire happen as any of the smaller ATBs used by CalFire,now i understand the S3B is being looked at for fire areas nation wide (world wide?),but California i know…not so much bout dem ferrin places like Nevada or Oregon…ha

  6. Max gross takeoff weight for the S-3B is 52,500#. Critical field length with no wind is approx 9,500 ft. for a 4000 MSL field at 80 degrees F. However …

    With an 80 degree F day from a 4000 MSL field, the max gross takeoff weight goes down to approx 36,000 to enable single engine takeoff. [A 16,500 lb payload reduction]

    Depending on who you believe about real aircraft zero fuel weight in a tanker configuration and how much fuel is onboard, there just isn’t much payload for high density altitude operations. Maybe a 1000 gal payload for the 80F 4000MSL field example unless you count on instant jettison capability.

    To improve single engine takeoff characteristics would require higher thrust engines. Better brakes are required to reduce the critical field length. It needs a considerable weight reduction program to improve payload characteristics. Low mounted engines pretty much require operations from FOD free fields.

    T/O and Single engine data from the S-3B NATOPS manual chapter 31 and 32.

    1. Great information, Bean, thanks.

      I wonder how much the weight of the aircraft could be reduced if it were stripped of all of the hardware that is not necessary for air tanker missions. That’s no doubt covered in the study that was done by Argon ST, which I have not seen in its entirety. And I’m thinking that a 2,000-gallon tank, with retardant, would weigh around 20,000 to 22,000 pounds.

  7. I’ve read the Argon Study, and I believe it addresses the brake issue. With the speed and range of the S-3b, it can be stationed at larger bases. To me it seems like an ideal initial attack tanker, and I bet the USFS can get several of them for the price of a C-130.

    Just out of curiosity, what made you bring up the Viking again?

    1. If the brakes are still an issue, keep in mind that the S-3B primarily operated from carriers and landed in a couple of hundred feet, so all we have to do is install some arresting cables on the short runways and use the tail hook. Brakes are over-rated.

      (kidding, of course! 🙂 )

  8. Why not check with Lockheed and see what the cost would be to reman with a COD fuselage like they proposed to the NAVY and put a completely inclosed gravity tank in it.

    1. Well, since Lockheed’s proposal was to completely scrap the entire fuselage, keeping only the empennage, wings, and flight controls, I’d be willing to bet that their price tag would be quite high. Especially with the low volume of aircraft that would actually be modified for firefighting. Not only that, but to modify an entire fleet would take a decade from now at the pace Uncle Sam works. Might as well buy an all-new airplane.

      You’d be better off with cost effective bolt-on upgrades like carbon brakes and new engines to shorten the critical field length, throw in some avionics upgrades, and settle for whatever internal tank capacity you can get with the existing airframe.

  9. If I’m not mistaken, another study of some type was done that showed the S-3’s takeoff performance and ramp weights were of greater concern than the proposed payload.

    1. Thanks, Trevor. I don’t know about the ramp weight, but here’s a passage from the 1995-1996 National Air Tanker Study:

      Aircraft Compatibility with Airtanker Bases
      The E-2C, S-3, A-6, A-10, and B-747-200B all were compatible with less than 45% of the base locations. The major reason for this incompatibility was the requirement to meet accelerate and stop (critical field length) within the paved portion of the airport runway.

      There is an upgraded engine available, the TF-34. I don’t know if that would fix the takeoff issue at the shorter air fields.

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