MT Only: Air frames in COACC

[atpollard]

Question, Don.

In the COACC, under Fixed-Wing Aircraft Design on page 32, the weights for Airframe per Metric Ton of Final Aircraft Weight are as follows.

TL 4 (assume should be 5) Simple 0.01 or 10 Kilograms.
TL 6 Fast Subsonic 0.05 or 50 Kilograms
TL 6 Transonic 0.10 or 100 Kilograms
TL 6 Supersonic 0.20 or 200 Kilograms
TK 6 Hypersonic 0.30 or 300 Kilograms

Are those the correct figures?

The reason that I ask is that the following is taken from US Navy Bureau of Aeronautics Airplane Characteristic Charts.

F4F-4 had an empty weight of 5895 pounds, and a loaded weight of 8762 pounds. Applying the 0.01 figure would give the F4F-F an airframe weight of 87.62 pounds.

The PB4Y-2 Privateer patrol bomber, a single tail version of the B-24 Liberator, shows an empty weight of 37,464 pounds and a max take-off weight of 64,000 pounds. Applying the 0.01 figure would give the Privateer an airframe weight of 640 pounds.

The F9F-2 Panther jet fighter shows an empty weight of 9303 pounds and a max take-off weight, land air field only, of 19,494 pounds. Applying the 0.05 factor for fast transonic aircraft, gives the Panther an airframe weight of 974.7 pounds.

I have the data for US Air Force fighters and bomber for the Post-War period up to 1973, with in some case the cost for each major aircraft component. The weights get a bit closer with the later aircraft with the 0.30 figure, but the early ones are maybe just a bit "strange".

If you want, I could get out my books on civil aircraft to for comparison, but based on the R4D-5 Skytrain, the Navy's version of the DC-3, those are going to be as bad. The Skytrain shows an empty weight of 17,057 pounds and a max take-off weight of 29,000. Applying the 0.01 figure, as the DC-3 flew for the first time in 1935, would give the airframe weight as 290 pounds.

Edit Note: I have information on 1920s airships and also early helicopters if you want it. Those airframe weights for early ones are strange as well. Then there is also the case of massive differences in performance between aircraft using the same power plant. I assume that you do not want information on those.

Good questions ... moved to its own topic to keep the errata thread clean.

One small nitpick is that a TL 4 'simple airframe' would probably be intended for WW1 era biplanes, WW2 Liaison aircraft and perhaps the TL 6 'Piper Cub' type aircraft.

So the DC-3, for example, is probably 'fast subsonic' and 'x 0.05' from your list making it a 1450 pound airframe for a 29,000 pound aircraft.

[EDIT: Ignore this, I was thinking of aircraft more like the F9F]
Is the F4F more 'transonic' for 8762 lbs x 0.1 = 876 lb airframe?
[END EDIT]

But the question is still valid and the topic is interesting to a gearhead like me.

 

[atpollard]

I don't think that COACC handles WW2 aircraft particularly well.
They are a strange case falling at the transition between TLs.
Biplanes are a better fit for TL 5 and Jet fighters fit TL 6.

The WW2 aircraft were actually a pretty short lived transition technology.
You might want to look at creating a TL5 fast subsonic airframe to deal with aviation in the 1940's and 1950's.

 

[Timerover51]

I don't think that COACC handles WW2 aircraft particularly well.
They are a strange case falling at the transition between TLs.
Biplanes are a better fit for TL 5 and Jet fighters fit TL 6.

The WW2 aircraft were actually a pretty short lived transition technology.
You might want to look at creating a TL5 fast subsonic airframe to deal with aviation in the 1940's and 1950's.

Hmmm, given that only ONE WW2-era aircraft ever cracked 500 mph, a souped-up P-47 with one monstrous engine, which would be at best 0.75 Mach, I am not sure than any WW2 piston-engine aircraft would qualify as Fast Subsonic. The P-38 did have compressability problems in high-speed dives, but they were restricted to certain areas of the airframe.

The MegaTraveller book has TL 4 at circa 1900, TL 5 at circa 1930, and TL 6 at circa 1950. That would put WW1 aircraft sort of under TL 4, WW-2 aircraft under TL 5, and jets under TL 6.

About 1930, the all-metal monoplane with retractable landing gear was beginning to appear, leading to WW2 types of aircraft.

In general, for WW1 era aircraft, the empty weight would be greater than half of the loaded or max take-off weight of the aircraft, for WW-2 era aircraft, the figure would be about 0.5, and for jets, it depends on the size. Larger aircraft have lower empty weight fractions than smaller jets.

Oh, and the Piper Cub first flew in the 1930s.

I will pull out some of the information on non-rigid and rigid airships that I have and also some for the helicopters, and see about posting it for comparison as well.

I guess that when it comes to design sequences, I would start with some existing aircraft and then reverse design them. From that, see if I could continue to design reasonably accurate additional existing aircraft, and if that is successful, think that I have a somewhat acceptable design sequence.

 

[atpollard]

OOPS on the TLs ... I still think in rough terms of CT cutoffs
TL 3 = 1700-1860
TL 4 = 1860-1900
TL 5 = 1900-1940
TL 6 = 1940+

[OFF TOPIC: I like to stick with the 40 year increments up to TL 10 ... TL 6 = 1940-1980, TL 7 = 1980-2020, TL 8 = 2020-2060 ... Strictly IMTU, but it seems to fit the handheld lasers and flying cars better than the optimistic CT dates.]

Still, even historically, the transition from wood/fabric bodied propeller driven planes to metal body jet aircraft seems to me like a very fast one if, like me, you follow the military/commercial aircraft and exclude the racing aircraft of the late 1920's and early 1930's as a special case (like the later rocket-powered aircraft are a special case rather than a general trend in mainstream aviation).

I look forward to seeing your data.
I am a big fan of airships.

 

[Timerover51]

Greetings, Arthur. Could you give me your email address to send the airship information too?

 

[jec10]

I'm not sure that comparing the total mass of a real-world aircraft with the weight of one step in the design sequence is appropriate. The question should be whether the whole design sequence results in an approximately similar outcome. Does the COACC sequence result in prop fighters at TL6 roughly equivalent to WW2-era fighters in their characteristics?

The example prop fighter on page 13 is Fast Subsonic so I also think you're better using this airframe type rather than Simple.

 

[Timerover51]

I'm not sure that comparing the total mass of a real-world aircraft with the weight of one step in the design sequence is appropriate. The question should be whether the whole design sequence results in an approximately similar outcome. Does the COACC sequence result in prop fighters at TL6 roughly equivalent to WW2-era fighters in their characteristics?

The example prop fighter on page 13 is Fast Subsonic so I also think you're better using this airframe type rather than Simple.

I will have to pull it out and look, however, another issue is that the same engine will give the same performance with similar air frame weight, which is highly questionable, given that the P-40N and the P-51D had the same engine, but had a speed difference on the order of 75 miles an hour.

 

[jec10]

I'm pretty sure the P40N and the P51D did not have the same engine. Perhaps you mean an earlier model of Mustang?

When you compare a P40N to a P51A which did have the same Allison engine then you're looking at about 10mph difference.

Anyway, I don't think COACC was ever intended for recreating all the variety of WW2-era aircraft in exact verisimilitude. It is a 'near enough' system for roleplayers that gives representative results.

I'd suggest you look elsewhere if you want to recreate existing aircraft to that level of detail.

 

[Vargas]

Anyway, I don't think COACC was ever intended for recreating all the variety of WW2-era aircraft in exact verisimilitude. It is a 'near enough' system for roleplayers that gives representative results.

I'd suggest you look elsewhere if you want to recreate existing aircraft to that level of detail.

I'm pretty sure it was never intended to model any era of aircraft with any great level of fidelity. Consider if you will all math and engineering that goes into aircraft design. You can't get that from a few simple tables and formula.

And I had the same problem years ago with the design system, only with 1970s jets.

 

[Timerover51]

I'm pretty sure the P40N and the P51D did not have the same engine. Perhaps you mean an earlier model of Mustang?

When you compare a P40N to a P51A which did have the same Allison engine then you're looking at about 10mph difference.

Anyway, I don't think COACC was ever intended for recreating all the variety of WW2-era aircraft in exact verisimilitude. It is a 'near enough' system for roleplayers that gives representative results.

I'd suggest you look elsewhere if you want to recreate existing aircraft to that level of detail.

Correction, the P-40F and P-40L had the Packard-built Merlin, same as the P-51D. Performance difference was similar. P-40N had a late-war Allison.