Talk:Martin JRM Mars

Recient use?

Was there an article showing one dropping water last week (July/August 2024) in Colorado? 99.185.73.8 (talk) 02:29, 5 August 2024 (UTC)

Gross Weight?

The use of the “Gross Weight” label in the specifications is incorrect; the 90000lb value is more likely to be the Useful Load. TechViking (talk) 15:21, 31 August 2024 (UTC)

Resolve as part of a complete overhaul of the Specifications- see MTOW vs Engines discussion below. TechViking (talk) 14:55, 3 September 2024 (UTC)

MTOW vs Engine Type

There are discrepancies in the Maximum Takeoff Weight (MTOW) in the specifications for the JRM-3 Mars. Is the MTOW 165,000lb with the 2,500hp Wright R-3350 Duplex-Cyclone engines, or just with the 3,000hp Pratt & Whitney R-4360 Wasp Major.

In the specifications section, the sited source [4, Jane’s Fighting Aircraft of WWII p.244] provides the JRM-1 model specifications with MTOW of 145,000lb with Wright R-3350-18 2200hp engines, but does not include the JRM-2 or JRM-3 models.

In the Variants section, the reference [38] for the JRM-2 and a subsequent link from that page only mentions an increased MTOW but not by how much. However, the 165,000lb value is supported by the January 2009 issue of Aviation History : “The JRM-2’s increased power permitted a takeoff weight of 165,000 pounds and added more than 10,000 pounds to its useful load.” That same paragraph implies that the increased MTOW for the subsequent JRM-3 variant is linked to the R-4360 and, in a later paragraph, that a lower limit for the water bomber with the R-3350 applies: “The decision to switch to R-3350 engines, and accept the resultant reduction in payload, was likely due to long-term maintenance considerations.” The Aviation History article also states that, for the JRM-1, “the installation of 2,500-hp R-3350-24W engines, plus new four-bladed propellers, boosted takeoff weight to 148,500 pounds.” This differs from the 145,000lb listed from other sources. Unfortunately the web version of this article does not list its sources.

Finally, the other source [48] sited in the Specifications section for the JRM-3 is from Coulson Aviation for the water bomber conversion, but it lists 162,000lb MTOW with the 2,500hp R-3350-24WA. Note: the original source link is dead but the web archive PDF is still valid.

So, should the MTOW for the JRM-3 water bomber conversion with the R-3350-24WA engines be 145,000lb, 148,500lb, 162,000lb or 165,000lb?

Should there be a separate specifications section for “Civilian Use/Water Bomber”, and the original military JRM-3 specifications be edited to indicate the R-4360-4T engine with the 165,000lb MTOW? TechViking (talk) 17:34, 31 August 2024 (UTC)

It is a mess. I believe the Jane's variant described is the JRM-1, others have inserted JRM-3/fire bomber specs along the way (this occurs in many other aircraft articles). The specs should only relate to the variant in parentheses in the section header and, preferably, all come from one cited source. The convention is for only one set of specs per aircraft article per project guidelines. The water bomber specs have been included in its section, they have also been duplicated there. The specs PDF from Coulson Aviation is not complete and at Featured Article level they would most likely be removed as would links to the company as they're advertising 'pilot experiences'.

Since both aircraft have been donated to museums, that last point is kinda redundant.--Sturmvogel 66 (talk) 10:12, 2 September 2024 (UTC)

We could enter all the specs from Jane's which would simplify the specs section and be correct at the same time, there might be a more comprehensive specs source from specialised publications about the Mars. Nimbus (Cumulus nimbus floats by) 07:23, 1 September 2024 (UTC)

The specifications in Jane’s (Bridgman, 1946) covers the XPB2M-1 prototype and the JRM-1 initial production model. I concur that, until a definitive source for the JRM-2 and JRM-3 variants are found, the Specifications section should be for the JRM-1. The other data from the various sources could remain in the Variants section. I think it likely that the Aviation History publication did have access to reliable source data, but that would need to be verified by someone with access to the original. TechViking (talk) 13:42, 1 September 2024 (UTC)

I've just tried to amend the specs using Jane's but there is no performance data apart from weights. When these specs were added both sources and mixed data was input by an editor who is now indefinitely blocked. I would hope somewhere that there is a specialist publication on the Mars, in the meantime the problem has been noted and, if desired, the information from Jane's could be retained which would leave a sparse specs section. Nimbus (Cumulus nimbus floats by) 14:57, 1 September 2024 (UTC)

I've got Ginter's book on the aircraft. I'll add whatever it has once I have a chance to read through it.--Sturmvogel 66 (talk) 19:47, 1 September 2024 (UTC)

Great! Hopefully that can be a definitive source for the converted water bomber type. TechViking (talk) 15:07, 2 September 2024 (UTC)

Ginter has fairly complete stats for the JRM-1 and -2 and states that the Navy converted all of the existing aircraft to the -3 version which had the R-3350-24WA engines and Curtiss electric 16' 8" 4-bladed propellers. Given that the MTOW of the -2 increased to 165,000 lbs (20,000 lbs over the -1), something more had to be done to account for all the additional weight since dimensions were identical as were fuel and oil capacity. The book doesn't much cover the water bomber modifications, but does note that "loaded weight" for the Mars was 148,500 lbs when comparing it with other possible conversion candidates. Ginter's later book should cover that in more detail, but it's important to remember that there were two different versions of the Mars converted into water bombers, although the sole -2 was destroyed in a hurricane after only a single fire season of work. So for the actual specs of the JRM-3 water bombers, if we can find them, I'd suggest that we use those of the -1 conversions as they're the only ones still in existence.--Sturmvogel 66 (talk) 18:47, 2 September 2024 (UTC)

There isn't a copy available to borrow outside of Canada and I not interested enough to invest $65 in a hard copy.--Sturmvogel 66 (talk) 18:53, 2 September 2024 (UTC)

The JRM-1 flight manual is available for free download, I waded through it last night. Its dimensions are rounded but it has tables of precise performance data. Combined with the Jane's source the specs section could be completed. Nimbus (Cumulus nimbus floats by) 11:03, 3 September 2024 (UTC)

That’s a good find. Yes, between that and the web archive of Jane’s, I agree that the specifications can be edited to detail the JRM-1 model, and Ginter’s can be used to improve the description of the JRM-2 in the variants section.

More details for the JRM-3/water bomber may also be available through the BC Aviation Museum when the Hawaii Mars exhibit officially opens to the public at the end of the month. I’ll keep an eye on that. TechViking (talk) 14:53, 3 September 2024 (UTC)

Sorry, but I think I missed something. What’s available to borrow in Canada? I am in Canada and could try to get access to it. TechViking (talk) 14:48, 3 September 2024 (UTC)

This book: Coulson, Wayne and Steve Ginter. The Mighty Martin Mars: From 1945 US Navy Transport to 21st Century, Initial Attack Firefighting. Port Alberni, British Columbia, Canada: Half Moon Bay Publications, 2009. ISBN 978-0-9812987-0-2--Sturmvogel 66 (talk) 15:28, 3 September 2024 (UTC)