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Four-Engine Grumman Goose

Wed Mar 08, 2017 11:56 pm

I had never heard of this. There were two converted by McKinnon in 1958-59 with Lycoming GSO-480 engines, 340 hp. ... NtkZh1tuuM:

Re: Four-Engine Grumman Goose

Sun Mar 12, 2017 3:54 pm

I kept looking at it thinking the picture was photoshopped.

Re: Four-Engine Grumman Goose

Thu Mar 16, 2017 7:07 pm

Nope, they were real - just not real successful.

First one started off as a Grumman model JRF-6B serial no. 1147
Converted by McKinnon in 1957-1958 to become "McKinnon G-21C serial no. 1201"
In 1960, McKinnon re-converted it by adding a 36-inch extension to the foward baggage area to include 4 passenger seats and two additional windows on each side plus 12-inch extensions to the elevators and horizontal stabs to compensate for the extra weight up front. As such it officially became "McKinnon G-21D serial no. 1251."

Here it is after the addition of the longer nose in June 1960:


In 1965 he started removing the four 340 hp Lycoming GSO-480-B2D6 geared, supercharged, flat piston engines and replaced them with just two 550 shp PT6A-20 turbine engines in special canted nacelles right up against each side of the fuselage so that there was no stub wing inboard of the nacelles. An engineer at Stanford with whom he consulted claimed it would reduce turbulence over the wing plus keep prop wash from the good engine flowing over the vertical fin and rudder if the other engine conked out. In conjunction with the mod, McKinnon got approval for STC SA1320WE in early 1968 at which point the airplane was re-certified with a new Standard CoA. As such, McKinnon considered it to be a G-21D "Hybrid".

Here it is in its last configuration as a G-21D "Hybrid" turboprop:


The second and last "real" model G-21C started off as a US Navy model JRF-5, Grumman serial no. B-78 and USN Bu. no. 37825. It was eventually transferred to the USCG as their serial no. 7825 and it was stationed at Barbers Point, HI. After being declared surplus, it first went to the Honolulu Department of Public Instruction (maybe for vocational training on aircraft maintenance?) as N5623V. McKinnon bought it from them, started converting it in 1959, sold it to the Wamser family of Milwaukee, WI and registered it as N3459C, and when completed later in 1959 it was re-registered as "McKinnon G-21C serial no. 1202".

Early in 1967, McKinnon bought it back from the Wamser family, refurbished it, and turned around and sold it to the government of East Pakistan to use and a VIP transport (almost their own "Air Force One") where it became AP-AUY.

Here it is at London's Gatwick Airport in Sept. 1967 on its way to East Pakistan for the first time:


After the civil war in the early 1970's East Pakistan became Bangladesh and McKinnon G-21C serial no. 1202 became S2-AAD. It remained in Bangladesh for the rest of its "life" flying first as their Air Forces' VIP transport and later with the national flying club which was started by the former air force pilot who flew it previously. It was left derelict from about 1980 onward and was finally scrapped in 2011 as noted here:

McKinnon later built two more Goose conversions which he called models "G-21C 'Hybrid'" too because they never had the four Lycoming piston engines as required by his type certificate no. 4A24 Section I, but instead he claimed to have simultaneously converted them using STC SA1320WE again to have the two 550 shp PT6A-20 turbine engines. In spite of that fact, they never really qualified as models "G-21C" because they were missing internal structural reinforcements that allowed the "real" models G-21C to have gross weights of 12,499 lbs whereas the two non-conforming so-called G-21C "Hybrid" variants were re-certified up to only 10,500 lbs.

They were given serial nos. 1203 and 1204; as CF-BCI serial no. 1203 was later "upgraded" per the model G-21G master drawing list by someone else in Canada and they falsely claimed that made it an actual "McKinnon G-21G" but McKinnon never "built" or certified it as such; it later ended up with Pen Air in Alaska as N660PA but crashed near Dutch Harbor in 1996, killing the pilot and lone passenger on board.

Serial no. 1204 was registered as N642 with the Bureau of Land Management in Alaska even before its conversion and it went back to them for many years. It was declared surplus and sold to a civilian owner in 1991 and when he died in 2006 or so, it was eventually sold in 2009 to Doug DeVries in Kenmore, WA (dba Vectored Solutions LLC of Everett, WA.) He has been restoring it and again "upgrading" it (IMHO "illegally" without permission from the current TC holder*) according to their Facebook page supposedly to be another 12,500 lb. model G-21G - and also installing co-pilot's brakes in it per STC SA2317WE again without permission from the current owner; *ref. 14 CFR 21.6(a)(1) and (2) and 91.403(d).

Re: Four-Engine Grumman Goose

Sat Mar 18, 2017 11:52 am

I sure have any insight regarding that particular STC mod, but I learned the hard way how problematic an STC can be after it has been out for a few years. The real owner kind of fades off in the distance and if you lose the paperwork you can be stuck with a problem you can't solve.

Of course, there is a lot of integrity required regarding STC's. The classic is the STC that allows the use of autogas. Two identical airplanes and the only thing that makes one legal for autogas and not the other is they paid for the STC. It's a big temptation to cheat.
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