29 May 1958   first HUK-1 accepted from production ; first flight ??
May-Jun 1958 58-5524 supposed introduction of this H-43A   (formerly a HOK-1)
29 Jul-27 Aug 1958




Flight tests at Bloomfield (Report SMR-474) with H-43A 58-5524 and HOK 129801 (4-fin tail, ventral only) and HOK 125528
11-12 Aug 1958 129801 (Pilot Report 113)  First flight of proto servo tail , ventral only
19 Sep 1958 58-1823 first flight of  first production H-43A
01 Nov 1958 58-1841 first flight of  first production H-43B
14 Dec 1958 58-1842 H-43B  58-1842  crashed  (“Aviation Week”  22 Dec 1958). It was scheduled to participate in an official rollout at Bloomfield, CT on 16 December 1958. The accident  was near the conclusion of a rigging and tracking test flight. Rollout , now with 58-1841, was planned later, because 841 was torn down to be instrumented.
Mar 1959



Kaman Photo 3040-1, 25Mar59 : H-43B 58-1841 with dorsal fins only and new exhaust pipe , and H-43A 58-1823 with 4 fin tail configuration 



From a  two-fin tail  (HOK)   via a three-fin tail  (HOK, HUK)  towards the four-fin empennage  (HOK, H-43A, H-43B:


Development of the tail construction for the HOK-1 and later for the H-43A and B was done over a couple of years, starting in 1953.

With Central fin, with fentral fins mounted on the tail boom, or dorsal fins, or both.


The original , 1953 ,  2-fin tail : 


125528 first acceptance at BradleyFld 28Apr53

HOK-1 125528 , seen here at Bradley Fld, CT during first acceptance on 28 April 1953. The "NAVY" title was later replaced by "Marines"


125528 AviationWeek 11May53 viaMutza

This "Aviation Week"  issue 11 May 1953  photo of 125528  shows the earliest tail configuration. Photo via W. Mutza



125531 nodate53 KamanPhoto NIMilHist

HOK-1  125531   , Kaman Photo , no date, ca1953






The initial 3-fin tail :

The following two pictures show the first stage of the three-fin tail, described as follows by Mr. Rita :  The tail configuration is one of the initial iterations using another of the same fin type with an area of 21.4 sq ft, before ultimately being replaced by the current elongated 37.2 sq ft  version 


129803 tail mod KamanPh scan10049

HOK-1  129803  , Kaman Photo ;  note farrings for Radio equipment


129803 DaytonOH Sep54 MAP photo

HOK-1  129803  , Dayton, OH Sep 1954  ; photo credit MAP


The final three-fin tail, used for all HOK and HUK aircraft :

125530 Kaman photo 30Aug55 1020 1 NIMilHist

HOK-1  125530  , Kaman Photo 1020-1 , 30 Aug 1955 ; note the "Bear Paws"


125531 T53 KamanPh1044 7 NIMilHist 300

HOK 125531 with T53 engine , unknown date,  Kaman Photo 1044-7, col. NIMilHist



Test Aircraft 129801 : 

129801 NEAM73 74 photoSeanCarroll

HOK-1 129801 , Oct 1973 ,  seen on display at the Bradley Museum grounds, with modified tail configuration. Photo taken and provided by Mr. Sean Carroll.

The tail construction in this Oct73 photo (ventral and no dorsal fins) is explained in the following Kaman Report No.113   : 

Kaman Aircraft Corp, Pilot Report No.113 , dated 12 Aug 1958 :

First flight of standard HOK-1 129801 with prototype servo tail installed, dated 11 Aug 1958. Ventral fins installed on the tail booms (no dorsals). Wide tail and no central fins. Second flight on 12 Aug 1958. Both flights by Chief Test Pilot W.A. Newton.

The report ends : "In way of conclusion and without delving into details as to reasons, it is strongly felt that the dorsal fins should be a firm requirement in the "B"  helicopter".   It was also adopted as such for the H-43A.

This tail configuration of 129801 was also mentioned in a Report about flight tests undertaken over the period 29 July-27 Aug 1958. Other participating aircraft were HOK 125528 and H-43A 58-5524, which flew the major portion of the test flights.




129801 SeanCarroll BradleyMuseum Jun Jul74 sm

HOK  129801 with Mr. Sean Carroll at Bradley Museum ground   Jun-Jul 1974 

Mr. Rita's comment : Diagonal braces like that shown in the picture were used for a number of test related purposes ranging from safety considerations  such as providing for test purposes an added measure of rollover protection for the fuselage crew compartment in the event of an incident as well as configurational assessments in the development testing of the HOK for obtaining vibratory airframe flight test data to help in defining the necessarystructural interface between the lower cockpit tray area and basic fuselage structure.

As to why it was remounted in the aircraft when given to BradleyMuseum, I can only surmise that it might have also been last used to provide comparison vibration data for a/c 129800 which was involved in Vibration reduction at the time. Usually, at the end of a contract, when an aircraft is disposed of by the Government, all sorts of bits and pieces associated with it's use, and paid for by the Government, go with it. 

Never the less, It's not the brace that ends up as the subject, but that of the Cabin Door Sill Gusset, primarily with it's configurational necessity, removal for the HUK and H-43A fuselage configurations and lastly the H-43B and it's current configuration of necessity. 

The HOK as designed has a large cabin door capability such that the extended lower tub area is the primary forward structure with minimum loads carried by the forward cockpit canopy frames and pilot's overhead roof. However; while adequate structurally, initial cockpit and pilot station vibration data indicated that an increase was required in it's flexural stiffness for minimum cockpit and crew station vibration levels. While  it's obstruction was not an issue for the  Marine's HOK  mission, it needed to be re-considered in light of the HUK and extended SAR and Plane Guard requirements. Shortly after the HOK Carrier Evaluation Program (05 May-06 Jul 1956) with two modified aircraft with wide doors,  a Kaman Engineering Change Proposal (ECP), titled "Removal of Cabin Door Sill Gusset", dated 27 Aug 1956 was approved for both a block change for subsequent HOK-1 orders( a/c s/n series 139xxx and above) and it's addition to the list of ECP's and changes approved for Model HOK-1 helicopter as part of the detail specification for the HUK helicopter.


The 4-fin tail for the H-43A :

129839 N298B Anacostia Apr58 EBay2014

HOK-1  N298B  (is supposed to be BuNo 129839)  at Anacostia  April 1958  , photo gained from EBay2014 auction 



585524 06Apr59 KamanP 2703 1 NIMilHist

H-43A  58-5524  (which is supposed to be a HOK-1, BuNo unknown - who knows, maybe the same N298B or 129839 seen at left)   -

May-June 1958 timeframe    Kaman Photo 2703-1   


The initial 4-fin tail for the H-43B :

581841 03Apr59 KamanPh 2791 3 NIMilHist

H-43B  58-1841 , most probably 13 Dec 1958 , Kaman Photo 2791-3  ,

ventral fins only


581841 RonDupasColl Internet

H-43B  58-1841 , most probably 13 Dec 1958 ,

photo taken from Internet , Ron Dupas Collection      ventral fins only


581841 testing 15Dec58 KamanPh 2810 8

H-43B  58-1841 , tiedown testing ,  Kaman Photo 2810-8 , dated  15 Dec 1958 ,  ventral fins only

Mr. Rita recalls :  Since I was directly involved in the flight test instrumentation with 1841 at the time, I can verify the configuration of both the H-43B and H-43A aircraft at the time. However, I am not sure of the exact date when the specific configurational changes were made to the H-43B, but I do know that the ventrals were an interference problem during the tie-down testing phase for personnel when entering or exiting the H-43B from the rear, particularly with fire fighting gear and other equipment like with  oscillograph data magazines. Note also in the picture the bar added between the outbboard fins to prevent running into the ventrals. Note the sticks at the top of the outboard fin which were used to determine rotor blade to fin clearances and, although for monitoring and safety considerations associated with rotor dynamic behavior during the ground test, they would ultimately provide the initial clearance data for removal of the ventrals and installation of the dorsal configuration shown in the March 25th photo, here below

581823 81841 Bloomfield 25Mar59 KamanPh3040 EBay

H-43B 58-1841 with  dorsal and no ventral fins  and H-43A 58-1823 at Bloomfield, CT  ; Kaman Photo 3040-1  25 Mar 1959  (photo from EBay16 auction)


Mr. Rita : with respect to the tail pipe configurations, the short "Sugar" scoop used during the HOK 125531/T-53 development program was the same configuration used for the first flight in mid December 1958 and during the tie-down test, after which it was replaced with an extended  straight long pipe section to prevent the up-ward oriented exhast gases from affecting the rotor's flow characteristics and contributing to adverse rotor induced airframe vibrations as well as diverting the exit gases to obtain a thrust benefit to help offset the added tail pipe's weight penalty on the aircraft's C.G. and an added longitudinal cyclic control benefit.

With respect to pipes exit configuration, or thrust diverting feature, there were three iterations during the life of the H-43B. The initial shown in the Mar 25th photo (see above) which was primarily to exhaust the gases with the latter two associated with modification to the exit diverter and angle. See Rotor Tips, July 1960 for a discussion of the second configuration (with aircraft 58-1846 in the Dec59 - Jun1960 time frame)  and, lastly, the final all-up H-43B tail and exhaust pipe configurations  (with 58-1849 between Oct1960 to Jun61961.


581846 H43B 164753AC 17May1960

H-43B  58-1846     , Edwards AFB, CA   date  17 May 1960  , USAF Photo 164753AC   (coll. Ragay)  , dorsal and no ventral fins



towards the final 4-fin tail of the H-43B : 


H43B OLD and NEW Tail Jun Aug60 AFFTC Report May61

Original Empennage Configuration (81846) and Modified Empennage Configuration (91548) during Jun-Aug 1960 , AFFTC Report TR-60-21 ,  May61

From this AFFTC REport :

The H-43B Category II/III system evalu­ation tests were conducted jointly with the Air Defense Command to provide an operational and functional evaluation of the Support Sys­tem in a typical base environment. This report covers 340:20 hours of a planned 500 hour test. The test was terminated early because of a succession of rotor blade-to-tail interference in­cidents. Testing of the secondary mission - fire suppression - was delayed due to the blade-to-tail interference problem. 

Aircraft incidents

A series of rotor blade to tail interference inci­dents have occurred. Three rotor to tail interference incidents occurred at Kaman Aircraft Corporation between September 1959 and March 1960.

The fourth incident occurred at AFFTC on 4 April 1960. One of the right rotor blades clipped the top 2 inches from the right rudder and vertical stabilizer assembly while making a nose down slope landing on a 14 degree slope.  

After the incident at the AFFTC, the following events took place:

  1. On 18 April 1960. Stead AFB, Nevada re­ported an accident involving rotor-tail interference while the aircraft was hovering in a crosswind.

          (Ragay : most probably 58-1856)

  1. On 29 April 1960, Stead AFB, Nevada re­ported a second accident invoking rotor-tail inter­ference while the aircraft was in aurorotative flight. 

The AFFTC recommended grounding all H-43B's on a May 1960 because of this problem. 

  1. Rotor-tail interference was experienced at Kaman Aircraft Corporation on 4 May 1960 during a slope landing. 

As a result of these incidents all H-43B's were grounded on 4 May 1960 in accord­ance with T. O. 1H-43B-518. (A 14).

From a Kaman News Release :

The first production H-43B HUSKIE helicopter with a new and improved tail configuration has been delivered to the U. S. Air Force. The first aircraft went to Warren Air Force Base, Cheyenne, Wyoming. (Ragay : 59-1556 was delivered from Kaman on 06 July 1960)

The Kaman Aircraft Corporation, builders of the helicopter, said the new vertical tail surfaces are 14 inches lower than on previous models.

The new tail design eliminates two vertical surfaces located on the upper surface of the stabilizer and reduces the height of the helicopter's two rudders. Surface area is maintained by the addition of two fixed end plates located 20 inches outboard of the rudders.





H-43B 58-1841 survived with the earliest tail configuration (dorsal and no ventral fins , because it never entered service -  since 1962 the aircraft was in use as Ground Instruction Aircraft , assigned to 3750 MSG at Sheppard AFB, TX)

581841 Cresson TX 24Mar2001 coll Ragay HH-43B   on display at Cresson, TX  , photo 24 Mar 2001  (coll. Ragay) 




last update 21/12/2016