I was recently trying to follow the S-4 family helicopters history, and compare what Mr Seibel is telling us himself with what one can find on the Internet. And boy, there are significant differences.
I want to know how many airframes there were built and where they ended up. Serial numbers and registrations were nice to have as well.
Looking for that, I actually found 4 different scenarios.
1)
Let's start with the one posted by the page
1000aircraftphotos.com. It says that:
There was S-4 with 108 HP engine registered as N5152. Then (as I understand) another one was built as S-4A with 125 HP engine registered as N5153 and having S/N 2. Then the first ship was re-engined to 125 HP engine and both were acquired by the Army as regs 51-5112 and 51-5113. They were returned to manufacturter (then already Cessna) in 1952. Another ship built in the meantime was S-4B registered as N5154 having S/N 4
So, in total this source says about three airframes. Note also that according to my current knowledge, the picture is not presenting S-4, but S-4A (not sure about the reg)
2)
Info from the book S.Harding "U.S.Army Aircraft since 1947", 1990 (cited
here and on wikipedia article)
It says just about two S-4As being delivered to the Army and the second one (depicted as 51-5113) as being rebuild to the S-4B
3)
I often try to confirm my findings by going through the helicopter registry history aggregated by the grate page of
www.rotorspot.nl
This very source gives an information that is something in between 1) and 2):
There was a S-4 (S/N 1) registered as N5152. Then there was S-4A (S/N 2) registered as N5153. Finally there was another S-4A (S/N 4) registered as N5154 → then type changed to YH-24 and registration to 51-5113 → then type changed again to S-4B and back to original registration - N5154. This adds up to 3 airframes.
4)
Let's now go through what Mr Seibel says. (timestamps to the video in the brackets)
There was a S-4, first certified in April 1950. Immediately after the ceremony of receiving Type Certificate, this very airframe was re-engined to a stronger (125HP) engine (ts: 1:11:58) and the re-certification of the modernised version commenced. In about the same time the Army expressed its interest in the design and ordered two ships (Army, but procurement went through Air Force) The two airframes for the Army were quickly built (ts 1:13:13 and 1:22:40) and delivered in April 1951 (ts 1:28:19). After the evaluation of the Army, the Seibel company came to a though that it cannot be used as a trainer and need to be modified - then they took the very same airframe which served as S-4 and later as S-4A prototypes and modified it to the S-4B standard - but this was never certified (ts: 1:28:41). The S-4B flown for several months after Seibel was acquired by Cessna (on a stock exchange basis, finalised in January 1952)(ts 1:41:00), then Cessna decided to abandon its development and to start from clean sheet design (a bigger one) (ts 1:41:13). The two army helicopters were bought back by Cessna, used in the research program with the Army and later scrapped.
This in total adds up to 3 of the S-4 family airframes. I am not sure about registrations and serials about the S-4B indeed is visible on the video with N5154 registration.
