World War II Aircraft New Production

[drgondog]

the radio equipment and IFF was probably 100lbs+/-

Right, but we added most of that back - after removing the fuselage tank, ecept for IFF - but the civilian version today would have a lot lighter radios/radar/rnav combo.. maybe 50 pounds +/- between old/new?

 

[drgondog]

Note in my original post I said civillian "replica". I just realized you might be thinking I was talking about restored real warbirds.

Besides the 1000 pounds of "armament" (should have been more specific) and the back armor, I think that many other lighter components could be included in the plane. See the carbon fiber "Grand Mustang" for an extreme example.

I did think you meant 'restored' not re-designed from ground up to take advantage of composites and remove armament.

If we assume than only the external lines are sacred I would speculate that a really good turbo prop/composite design could be built that is a lot lighter than 1500 pound reduction.

Rivets are a high percentage of bare airframe total weight. If you wanted to reduce the airframe to some ultimate G load capability below 11-12 then even more weight could be extracted from wing and tail structure.

 

[Clay_Allison]

I did think you meant 'restored' not re-designed from ground up to take advantage of composites and remove armament.

If we assume than only the external lines are sacred I would speculate that a really good turbo prop/composite design could be built that is a lot lighter than 1500 pound reduction.

Rivets are a high percentage of bare airframe total weight. If you wanted to reduce the airframe to some ultimate G load capability below 11-12 then even more weight could be extracted from wing and tail structure.

If you used a turboprop, that would be another 1000 pounds right there. Compare the weight of a Merlin to the T-55 used on the "grand mustang".

I worry about preserving the original lines on on the reproductions if you use turboprops, since they were designed to have so much weight forward of the firewall. How do you balance that and make it look the same. Extra fuel tank?

 

[Captain Dunsel]

Just remember one thing when you discuss removing weight. You have to keep the CG where it belongs. There's a saying in R/C models that nose heavy planes my fly poorly, but tail heavy planes only fly once.

CD

 

[drgondog]

If you used a turboprop, that would be another 1000 pounds right there. Compare the weight of a Merlin to the T-55 used on the "grand mustang".

I worry about preserving the original lines on on the reproductions if you use turboprops, since they were designed to have so much weight forward of the firewall. How do you balance that and make it look the same. Extra fuel tank?

I don't know how much a T-55 or PT6A weighs but they would trash the original lines. Where can I find figures for weights and lengths of either engine?

The extra fuse tank when full actually moved the cg too far back. I would be more inclined (for civilian/lower structural design target) to put ballast near tail wheel bulkhead - which would be fixed weight rather than the variable weight of fuel in the fuse tank - and a much larger 'arm' from the cg so the ballast could be much lower weight.

Dunsel is right about aft cg. When cg is too far forward you usually don't have enough H. Stabilizer to get off the ground (or very poorly) in lower speed range.

 

[Clay_Allison]

I don't know how much a T-55 or PT6A weighs but they would trash the original lines. Where can I find figures for weights and lengths of either engine?

The extra fuse tank when full actually moved the cg too far back. I would be more inclined (for civilian/lower structural design target) to put ballast near tail wheel bulkhead - which would be fixed weight rather than the variable weight of fuel in the fuse tank - and a much larger 'arm' from the cg so the ballast could be much lower weight.

Dunsel is right about aft cg. When cg is too far forward you usually don't have enough H. Stabilizer to get off the ground (or very poorly) in lower speed range.

The T-55 weaighs 540 pounds and gives 1450 horses.

As for the CG, that was what the second half of my post was about, you will constantly have to be refiguring how much weight you are taking away and where the CG will go. That's a careful process if you want to make it look like the same plane from 50 feet away.

 

[pbfoot]

The T-55 weaighs 540 pounds and gives 1450 horses.

As for the CG, that was what the second half of my post was about, you will constantly have to be refiguring how much weight you are taking away and where the CG will go. That's a careful process if you want to make it look like the same plane from 50 feet away.

Check out the Piper Pa48 Enforcer with was a Turbo powered P51 designed for possible use in Viet Nam

 

[Clay_Allison]

Check out the Piper Pa48 Enforcer with was a Turbo powered P51 designed for possible use in Viet Nam

well aware of it and its Cavalier ancestry. I hate wingtip tanks though, lol.

 

[Marcel]

Here in the Netherlands, someone is building a real, flying replica of the Fokker G.I. We have several Fokker replica's in Lelystad, like a beautiful F.2 with original engine! This year, the MLM will get a B339 Buffalo replica, don't know if it'll be able to fly, though. So I would say it's very well possible to build an airframe of WWII if the money and dedication is there.

 

[drgondog]

The T-55 weaighs 540 pounds and gives 1450 horses.

As for the CG, that was what the second half of my post was about, you will constantly have to be refiguring how much weight you are taking away and where the CG will go. That's a careful process if you want to make it look like the same plane from 50 feet away.

I am curious as to why you seem to think I am not acquainted with airframe design issues?

My comment about the extra fuselage tank as a possible solution (not one easily accepted) is that absent installation data for the T-55 and the ducting, intakes, shaft design and overall length of the engine - there isn't much information to assume that you should consider put a new fuel cell forward of the firewall if the T-55 is lighter than the Merlin)... and adding an extra cell to the fuselage aft of the cg just makes the problem worse.

If the T-55 package is heavier than the Merlin package then either extending the aft fuselage (i.e. like the Fw 190D-9) to move the tail further away is one solution, expanding the fuselage fuel cell or adding aft ballast are other possible solutions.

To keep the same general lines as the Mustang and maintain existing stablity and control parameters you probably would add ballast near the tailwheel area. (much greater moment arm from cg than existing fuel cell - therfore less mass required)

I had in mind that the T-55 installation with ducting, removal of all the radiator/oil cooler/structure aft of the original Mustang cg would probably have approximately the same effect but asked you to provide details as the article I read about the Enforcer was vague on this.

Your info of 540 pounds for T-55 seems low (does that include intake and exhaust ducting, new engine mounts, same center of mass as Merlin, etc) but for the moment I assume it correct.

Assume the T-55 is 1000 pounds lighter than the Merlin as you state, and that the center of mass of the new engine package isn't too much different from Merlin package -

Then one possible solution (not a happy one) is that you have to consider moving the T-55 forward by extending the airframe more forward of the firewall than in the original P-51.

By rough calculation the Merlin at ~ 1650 pounds is ~ 1100 pounds (and 3x the weight) more than your figure for the T-55. That means that the center of mass for the T-55 has to be moved 3x distance from CG in comparison to the distance to the center of mass of the Merlin to compensate for 1/3 the weight. Already a stupid idea

But if you did create room in front of firewall, you do not want to add a fuel cell forward of the cg to compensate for the aft cg issue that installing the lighter engine created. When you burn that fuel you also effectively move the resultant cg aft, and are in a possible world of hurt stability wise.

So, the easier solution is to reject the lighter engine package and stay with Merlin or Allison

Looking at the Enforcer pic, Piper definitely did not extend forward airframe - at least by much. The implication is that either the overall installation of the T-55 resulted in nearly the same weight as the Merlin package or they were able to remove a lot of mass aft of the cg (unlikely) to compensate for lighter engine... or the T-55 is so much shorter that the designers were able to push the center of mass of the engine forward and place ~ 1500 pounds of useful weight foreward of firewall/aft of T-55 (unlikely given exhaust ducting requirements of turbo prop).

What is your theory?

 

[Clay_Allison]

I am curious as to why you seem to think I am not acquainted with airframe design issues?

My comment about the extra fuselage tank as a possible solution (not one easily accepted) is that absent installation data for the T-55 and the ducting, intakes, shaft design and overall length of the engine - there isn't much information to assume that you should consider put a new fuel cell forward of the firewall if the T-55 is lighter than the Merlin)... and adding an extra cell to the fuselage aft of the cg just makes the problem worse.

If the T-55 package is heavier than the Merlin package then either extending the aft fuselage (i.e. like the Fw 190D-9) to move the tail further away is one solution, expanding the fuselage fuel cell or adding aft ballast are other possible solutions.

To keep the same general lines as the Mustang and maintain existing stablity and control parameters you probably would add ballast near the tailwheel area. (much greater moment arm from cg than existing fuel cell - therfore less mass required)

I had in mind that the T-55 installation with ducting, removal of all the radiator/oil cooler/structure aft of the original Mustang cg would probably have approximately the same effect but asked you to provide details as the article I read about the Enforcer was vague on this.

Your info of 540 pounds for T-55 seems low (does that include intake and exhaust ducting, new engine mounts, same center of mass as Merlin, etc) but for the moment I assume it correct.

Assume the T-55 is 1000 pounds lighter than the Merlin as you state, and that the center of mass of the new engine package isn't too much different from Merlin package -

Then one possible solution (not a happy one) is that you have to consider moving the T-55 forward by extending the airframe more forward of the firewall than in the original P-51.

By rough calculation the Merlin at ~ 1650 pounds is ~ 1100 pounds (and 3x the weight) more than your figure for the T-55. That means that the center of mass for the T-55 has to be moved 3x distance from CG in comparison to the distance to the center of mass of the Merlin to compensate for 1/3 the weight. Already a stupid idea

But if you did create room in front of firewall, you do not want to add a fuel cell forward of the cg to compensate for the aft cg issue that installing the lighter engine created. When you burn that fuel you also effectively move the resultant cg aft, and are in a possible world of hurt stability wise.

So, the easier solution is to reject the lighter engine package and stay with Merlin or Allison

Looking at the Enforcer pic, Piper definitely did not extend forward airframe - at least by much. The implication is that either the overall installation of the T-55 resulted in nearly the same weight as the Merlin package or they were able to remove a lot of mass aft of the cg (unlikely) to compensate for lighter engine... or the T-55 is so much shorter that the designers were able to push the center of mass of the engine forward and place ~ 1500 pounds of useful weight foreward of firewall/aft of T-55 (unlikely given exhaust ducting requirements of turbo prop).

What is your theory?

I know that you know what you're talking about. I was just saying that I wasn't playing "mad scientist" without considering the ramifications. Honestly I was more interested in knowing your theory since I didn't have one, but given what you've told me I'd say the ducting weighed nearly enough to compensate for the engine weights and the lightening aft of the CG took care of a bit more.

BTW. 540 is dry weight, standalone, I couldn't get a number for installed weight.

For another turboprop mustang, check out the carbon fiber Grand Mustang

 

[drgondog]

I know that you know what you're talking about. I was just saying that I wasn't playing "mad scientist" without considering the ramifications. Honestly I was more interested in knowing your theory since I didn't have one, but given what you've told me I'd say the ducting weighed nearly enough to compensate for the engine weights and the lightening aft of the CG took care of a bit more.

BTW. 540 is dry weight, standalone, I couldn't get a number for installed weight.

For another turboprop mustang, check out the carbon fiber Grand Mustang

Clay - the thing that confused me on the first article I read on the Enforcer was a stated gross weight of 14,500+ pounds and I was trying to figure out where they put it!

 

[Clay_Allison]

Clay - the thing that confused me on the first article I read on the Enforcer was a stated gross weight of 14,500+ pounds and I was trying to figure out where they put it!

TURBOKART Here's where I got the weight listing. Also an ad for one for sale claiming the same shipping weight.

 

[drgondog]

TURBOKART Here's where I got the weight listing. Also an ad for one for sale claiming the same shipping weight.

No problem. No desparation required. I make mistakes.

 

[Elvis]

Re: Clay Allison's "Turbokart" link.

I noticed, in the stats at the bottom of the page, for the Lycoming T53-L-13B Turboshaft Engine, that one of the things listed was Compression Ratio ("Compression Ratio: 7.2:1 at 25,600 rpm").

......

How does one achieve a c.r. rating for a turbine engine?
Is this a comparison of atmospheric air pressure to compressed air pressure?

...



Elvis

 

[Clay_Allison]

Re: Clay Allison's "Turbokart" link.

I noticed, in the stats at the bottom of the page, for the Lycoming T53-L-13B Turboshaft Engine, that one of the things listed was Compression Ratio ("Compression Ratio: 7.2:1 at 25,600 rpm").

......

How does one achieve a c.r. rating for a turbine engine?
Is this a comparison of atmospheric air pressure to compressed air pressure?

...



Elvis

No idea. It was the result of a Google search, but like I said there was one for sale that listed the same shipping weight on another site so I had some verification.

 

[drgondog]

Re: Clay Allison's "Turbokart" link.

I noticed, in the stats at the bottom of the page, for the Lycoming T53-L-13B Turboshaft Engine, that one of the things listed was Compression Ratio ("Compression Ratio: 7.2:1 at 25,600 rpm").

......

How does one achieve a c.r. rating for a turbine engine?
Is this a comparison of atmospheric air pressure to compressed air pressure?

...



Elvis

Elvis - the compression ratio is the ratio of the internal, compressed, air pressure at the final stage of turbine blade compression at the combustion chamber - to the ambient air pressure in the freestream in front of the engine.

 

[Elvis]

So its a comparison of atmospheric air pressure to compressed air pressure.

Ok, I thought that had to be it.
Thanks for defining that drgondog....and Clay, sorry if it seemed my question was pointed towards you.
I wasn't neccessarily asking you only, but rather, I was only asking for a definition of that particular stat, as it applies to that particular instance, to whomever could define it.

Thanks again, guys.




Elvis

 

[Hollywood]

If you are looking at Warbird Reproductions Claus Colling @ Flugwerk will build you a Fw190D with Allison power that looks FANTASTIC and just like the original for less than they are asking for the Grand Mustang...........

 

[gjs238]

With unlimitless funds, not only would it be great to build flying replicas, but build them they way we sometimes speculate about in our what-if posts.

Build a P-38 with Merlins.
P-39 with turbocharger, or with Merlin.
Etc.