My attempt to answer my questions that I asked at the beginning of this thread.
( 1 ) From checking around on the internet I understand the first (approximately) 12 aircraft were classified as model G-21, which had according to Grumman's first add, about what they called The Grumman "G-21" Amphibian, which appeared in the Aero Digest, Jan. to June, 1937 edition on page 68, of March, it states: Gross weight: 7500 lbs., Engines: Pratt & Whitney Wasp Junior R-985, rated 400 h.p.
The G-21A came with an increase of 500 lbs. giving it a gross weight of 8000 lbs., 50 more horsepower for a total of 450 hp per engine. I have also seen a lengthened hull and minor hull design change, listed with the G-21A, did it come with anything else, compared to the G-21?
According to Fred Knight's "The Grumman Amphibians", the rear or aft of the step of the hull was increased in length by 4½ in. or (11.43 cm. for the metric people) to reduce spray control on water landings & take-offs. This was first accomplished by fitting wooden blocks to the step and on June 3, 1937's test flight, solved the problem. The first goose c/n 1001 was brought back in and the step on the hull was re-modelled accordingly. All subsequent G-21's had the remodelled step incorporated during production.
So as I read it, there was no difference between the G-21 and the G-21A when it comes to the lengthened hull, as both had the same hull/step design.
The G-21A's had a redesigned tail wheel, compared to the G-21, but it is not stated what the change was.
As to the G-21A, Fred Knight further states: "With up-rated 450hp Wasp Junior SB-2 engines and a gross weight increased from 7,500 to 8,000 lbs." Earlier in his book he stated: "Among the safety factors highlighted in early advertising for the Goose was the use of "proven & dependable" Pratt & Whitney engines of 400hp each. This rating was based on the use of 80 octane fuel. Some literature quoted a 450hp rating but this only referred to a take-off rating when 87 octane was used. He also states the engines were Wasp Junior SB engines". These would have been on the G-21.
A little confused here, were they to use 87 octane fuel to get the 450hp rating or was there an actual engine modification to get the extra 50hp, such as timing/spark, carburetor, increase RPM, etc.?, he does not state that.
He states the G-21 had "Wasp Junior SB engines" and the G-21A had "Wasp Junior SB-2 engines" I suppose Pratt & Whitney through the Federal Aviation Agency, could have upgraded the rating of their engine for the 50hp. increase or maybe the SB engines only produced 400hp and the SB-2 engines produced 450hp.
Now after typing that, I dug around in my Grumman files (they need to be put into some type of order) and found a .pdf file entitled "G-21A Erection & Maintenance Manual", dated February 1, 1938. In this file it states:
Engine Data
Engines (2) Wasp Jr. "S.B." Pratt & Whitney
Type Radial Air Cooled - 9 Cylinders
Horsepower & RPM Take-Off 450 at 2300 with 87 Octane
400 at 2200 with 80 Octane
Maximum Horsepower for Continuous 400 at 2200 (Up to 5000 ft. Operation - Critical Altitude)
Cruising Horsepower (Recommended) 300 at 2000 rpm
So I'm really no farther ahead on this one as to the difference between the 400hp & the 450hp rating of the engines except for the extra 100 RPM and the difference between 80 & 87 octane fuel.
I also understand that a number of the first 12 aircraft were upgraded to G-21A specs. before leaving the factory and some were returned to the factory for the upgrade. Does anyone know the numbers of the 12 that were upgraded and the number that were not upgraded?
Well Fred Knight states, "The twelfth and last "Grey Goose" came off the line as a G-21A Goose". These improvements were approved on Feb. 5, 1938, also under ATC 654, and during 1938, all 11 G-21's, with maybe the exception of c/ns 1009, 1010 and 1011 which had been exported , were modified to G-21A standard."
Ok, he said "maybe the exception of c/ns 1009, 1010 and 1011" but then in Appendix 1, page 310 he states: "c/n 1011 - Built as a G-21 and ordered August 1937 by John Shaffer Phipps New York, N.Y., with BoS Nov. 26, 1937. Regd. to Phipps as NC1294 Nov. 29, 1937 and uprated to G-21A standard in 1938" Since c/n 1011 was not exported but c/n 1008 was, I think Fred Knight might have made a mistake by saying "c/ns 1009, 1010 and 1011" and it should have read c/ns 1008, 1009 and 1010. Further more he states c/n 1008 was delivered to Asiatic Petroleum, New York, on October 25, 1937, crated and shipped to Sydney, Australia, arriving there on December 26, 1937. He also states that Goose c/n 1012 was the first converted G-21A at the factory and it went out on December 9, 1937.
So to answer my own question, it looks like only three were not uprated to the G-21A specifications, c/ns 1008, 1009 & 1010. BANG - the gavel has fallen…….case closed.
The question of: "What is the difference between a Mark I and Mark II ?", will have to wait for awhile as I try and sort out some of this new info, hey at least it gives me something to do.
Dennis