Dude builds his own frkn P-38

[CAP1]

Imo you don't need engines that big as I doubt the guy rides his P38 at 350mph  

wouldn't modern 400hp engines do the job ?

chevy crate motors.

as much as i like fords, those chevy motors will never die.

 they offer decent power, and not overly heavy...........

[Mace2004]

What I've always wondered about these sort of accounts is, if you scale down an aircraft, does the same aerodynamics apply?
 
 I do know for a fact that an increase or decrease in scale requires a lot higher adjustment in power since the overall volume is affected at a much higher rate than just the scale... but what about the aerodynamics? The wind-tunnel testings would obviously mean that the way the air flows around the aircraft doesn't change with scale... but what I'm talking about is, if one changes the scale of a plane, but cannot exactly adjust the weight accordingly (due to problems like limited engine choices..) - wouldn't this mean the plane needs some sort of adjustments to the design to compensate for it?

Airflow around the aircraft DOES change with scale, that's what Reynolds Numbers are about. Say you build a 1/4 scale Mustang wing, the boundary layer thickness, stall AOA, laminar flow, separation point and drag will all be different because while the air is the same (i.e., same density) the wing is smaller.  I'd guess that in building the 75% P38 the designer probably chose a more appropriate wing than simply scaling the actual wing down.

[Wmaker]

But then, it isn't big enough, either.

Are you saying that the Falconer V-12 doesn't generate enough HP to power 75% replica of a P-38?

[Captain Virgil Hilts]

Are you saying that the Falconer V-12 doesn't generate enough HP to power 75% replica of a P-38?

A P-38 had two 1710 cubic inch engines producing 1750HP each. Falconer's engine does not produce 75% of that, it does not even produce anything close to 1000 HP. The ideal engine would be based on a big block with a bore of about 4.6" and stroke of about 4.5" to 4.75", not a small block with a bore of 4.125" and 3.75".

[CAP1]

A P-38 had two 1710 cubic inch engines producing 1750HP each. Falconer's engine does not produce 75% of that, it does not even produce anything close to 1000 HP. The ideal engine would be based on a big block with a bore of about 4.6" and stroke of about 4.5" to 4.75", not a small block with a bore of 4.125" and 3.75".

that's kind of what i was mentioning earlier. i thought there was a mustang kit that was designed around a big block chevy crate engine.
 if these engines power a kit stang, then they could reliably handle a homebuilt 38......and the muuuusiiicccc they'd make.............<drooling>

[Jabberwock]

A P-38 had two 1710 cubic inch engines producing 1750HP each. Falconer's engine does not produce 75% of that, it does not even produce anything close to 1000 HP. The ideal engine would be based on a big block with a bore of about 4.6" and stroke of about 4.5" to 4.75", not a small block with a bore of 4.125" and 3.75".

The P-38 started with the V-1710s producing just 1,090 hp, and didn't get 1,750 hp engines until the introduction of the L operating on higher octane fuels.

The Falconer V12 is credited with a peak hp of 811 @ 5,700 rpm, or just a sniff under 75% of the power of the early Allisons.

I wouldn't want such a high revving engine, but it could work on a 75% replica.

[Wmaker]

A P-38 had two 1710 cubic inch engines producing 1750HP each. Falconer's engine does not produce 75% of that, it does not even produce anything close to 1000 HP. The ideal engine would be based on a big block with a bore of about 4.6" and stroke of about 4.5" to 4.75", not a small block with a bore of 4.125" and 3.75".

First of all, the weight of the plane doesn't change proportionally with the scale nor does the power need to. With 75% of the original P-38's power, a 3/4 scale replica would be ridiculously overpowered compared to the original no matter what (sensible) way it would be constructed. Second, in terms of power to weight, these kind of 3/4 replicas range from significantly overpowered (Thundermustang) to hopelessly underpowered (Loehle Spitfire) compared to the original, while still retaining fairly good scale appearance. Obviously the high performance examples will be more expensive and fun but they still are all "75%-replicas".

Like I said above, the 640hp Falconer powered 3/4-scale Thundermustang has significantly better powerloading at gross weight compared to the original P-51D. Thundermustang's gross weight is roughly 27,5% of the original's gross weight. Using similar construction methonds we could roughly assume that the 75%-scale Falconer powered P-38 would have a gross weight around ~30% of the original's. That would put the grossweight around 5300lbs. With 2x640hp the 75% P-38 would have a power to weight ratio of ~4.1lbs/hp. Even with the 1750hp WEP setting the original P-38J comes out at ~5lbs/hp.

So yes, I think Falconers would be plenty regarding the power output.

Lastly, here's a link where they are building roughly 73% scale P-38 replica kits which are meant to be powered with 425hp GM V-8s...
http://www.aeroplanemonthly.co.uk/news/Selfbuild_P38_Lightning_replica_news_195526.html

[Captain Virgil Hilts]

You assume too many things not in evidence. It is not necessarily true that a 3/4 scale P-38 would be 1/3 the weight of the original. If it were built purely of composites, and didn't carry too much fuel, sure, it could be light.

Further, the engines you speak of produce their power at a much higher RPM, where they cannot be run for long periods of time without being rebuilt at very short intervals.

The Falconer is merely 1 and 1/2 400 cubic inch small block Chevy engines, it's nothing special at all, I've seen it run, and I've seen it apart. At just over 800HP, they're operating at just over 1.3 HP per cubic inch. At that power level, they'll require serious work in about 8 hours or less.

A big block based engine would be far superior. It would require less RPM, and make far more torque. It will run far longer between overhauls, and far longer before replacement as well. The smaller engine I suggested would be about 900 cubic inches, and could make over 1HP per cubic inch with ease, at 5000 RPM or less. Even better, it would easily exceed 1000 foot pounds of torque even at 3000 RPM (I have a 427 small block Ford on the dyno now that makes 500 foot pounds at 3000 RPM, and it's no where near as good a a big block Chevy of the same size), meaning it could run for a very long time.

Having 30 years of experience building high performance automotive engines, and even some Allison experience as well, I'll pass on putting my arse and an expensive aircraft at risk by pushing engines that hard. It's one thing to do it in a boat, where you just have to get a tow, it's far different in an aircraft, where you have to find a place to put it down safely.

[Wmaker]

You assume too many things not in evidence. It is not necessarily true that a 3/4 scale P-38 would be 1/3 the weight of the original. If it were built purely of composites, and didn't carry too much fuel, sure, it could be light.

I assumed too many things? I didn't claim 75% scale replica needs 75% of the original power. Without actually desinging the said aircraft it's of course hard to give an accurate weight to the pound but I really don't see how my guestimate was unrealistic.

Further, the engines you speak of produce their power at a much higher RPM, where they cannot be run for long periods of time without being rebuilt at very short intervals. The Falconer is merely 1 and 1/2 400 cubic inch small block Chevy engines, it's nothing special at all, I've seen it run, and I've seen it apart. At just over 800HP, they're operating at just over 1.3 HP per cubic inch. At that power level, they'll require serious work in about 8 hours or less.

The argument wasn't about how costly these engines would to maintain. The argument was weather or not the Falconer put out enough power to propel a 75% scale P-38 replica. You claimed the engine needs 75% of the original power, which isn't even remotely the case. Also, if you go back and read my post you'll note that I wasn't talking about one putting out 800hp. I was talking about the version used in the Thundermustang producing 640hp@4500 RPM.

A big block based engine would be far superior. It would require less RPM, and make far more torque. It will run far longer between overhauls, and far longer before replacement as well. The smaller engine I suggested would be about 900 cubic inches, and could make over 1HP per cubic inch with ease, at 5000 RPM or less. Even better, it would easily exceed 1000 foot pounds of torque even at 3000 RPM (I have a 427 small block Ford on the dyno now that makes 500 foot pounds at 3000 RPM, and it's no where near as good a a big block Chevy of the same size), meaning it could run for a very long time.

Of course it would be superior in terms of reliability, goes without saying. Can you give me a commercial example of such engine you are thinking of? There would also be hard time fitting a bigger engine in a 75% scale engine nacelles and then there's the weight penalty. EDIT/The outside dimensions would be smaller like you said, misread. And the weight would most probably be similar. My point is that The Falconer engine is done and already available./EDIT

I'll pass on putting my arse and an expensive aircraft at risk by pushing engines that hard. It's one thing to do it in a boat, where you just have to get a tow, it's far different in an aircraft, where you have to find a place to put it down safely.

I pretty much agree and would be fairly vary myself. But AFAIK The Falconer has worked well in Thundermustangs and 640hp would be enough, no need to up the power. It just makes a pretty attractive option for a 75% inline engined WWII fighter replica considering its size and weight.

[bravoa8]

Uh-Oh! Looks like this topic needs to be named "Heya there SAPP look at this!"

[Captain Virgil Hilts]

Even the 1HP per cubic inch Falconer needs too many RPM to make that power. The Falconer is sort of neat, sort of cool, and excessively expensive. It's "outstanding features" are that it's a V-12 and well, it's a V-12. And it is way too expensive for anything that it does, other than being a V-12.

A big block based engine will be less than 150 pounds heavier, a only a couple of inches taller, longer, or wider. It would be far smaller than 75% of a V1710 Allison.

As far as what is available commercially goes, if you are not hung up on a V-12, there are 750 cubic inch big block Chevy based V-8 engines out there now, and in fact, a 900 cubic inch version. For the same amount of stress you apply to the Falconer, I can get 250 more HP out of an all aluminum big block Chevy V-8 for about 1/2 the money. An all aluminum 620 can be built for less than $18K, and produce 1000 HP normally aspirated on pump gas. It'll make 650HP at 4000 RPM, and 950 foot pounds of torque at around 2500 RPM. And it weighs LESS than the Falconer.

How much power is necessary depends a great deal on how much performance you expect.

Considering where the engines, the weight, and the power is produced and applied, I'm not convinced a 3/4 scale P-38 will be safe and strong if it weighed 1/3 what the original did. Especially if the goal was to produce performance equal or nearly equal to the original. Sure, if your goal is a ceiling of 25K, a top speed of 300MPH, and limits of 6G positive and 3G negative, with a short range, that might be okay. Personally, for the money I'd want more.

[Stoney]

Even the 1HP per cubic inch Falconer needs too many RPM to make that power. The Falconer is sort of neat, sort of cool, and excessively expensive. It's "outstanding features" are that it's a V-12 and well, it's a V-12. And it is way too expensive for anything that it does, other than being a V-12.

A big block based engine will be less than 150 pounds heavier, a only a couple of inches taller, longer, or wider. It would be far smaller than 75% of a V1710 Allison.

As far as what is available commercially goes, if you are not hung up on a V-12, there are 750 cubic inch big block Chevy based V-8 engines out there now, and in fact, a 900 cubic inch version. For the same amount of stress you apply to the Falconer, I can get 250 more HP out of an all aluminum big block Chevy V-8 for about 1/2 the money. An all aluminum 620 can be built for less than $18K, and produce 1000 HP normally aspirated on pump gas. It'll make 650HP at 4000 RPM, and 950 foot pounds of torque at around 2500 RPM. And it weighs LESS than the Falconer.

How much power is necessary depends a great deal on how much performance you expect.

Considering where the engines, the weight, and the power is produced and applied, I'm not convinced a 3/4 scale P-38 will be safe and strong if it weighed 1/3 what the original did. Especially if the goal was to produce performance equal or nearly equal to the original. Sure, if your goal is a ceiling of 25K, a top speed of 300MPH, and limits of 6G positive and 3G negative, with a short range, that might be okay. Personally, for the money I'd want more.

So, how much would the reduction gears of that big block V8 weigh?  Its not just the engine, its the entire powerplant.  Also, is there a prop out there that could handle that motor?  Regardless, 150 more pounds is a huge difference in an aircraft.  And, 1/3 weight for a 3/4 scale plane is probably about right.  The Thundermustang is a steel frame covered with a carbon fiber/fiberglass skin.

[Captain Virgil Hilts]

So, how much would the reduction gears of that big block V8 weigh?  Its not just the engine, its the entire powerplant.  Also, is there a prop out there that could handle that motor?  Regardless, 150 more pounds is a huge difference in an aircraft.  And, 1/3 weight for a 3/4 scale plane is probably about right.  The Thundermustang is a steel frame covered with a carbon fiber/fiberglass skin.

A V-8 would not weigh more than the Falconer, it would weigh less. These days, gear boxes are far stronger and weigh far less. Further, since the big block turns fewer RPM, the gear box is less complex, smaller, and has less load on it. I'm sure there is a prop that can handle it.

The Mustang has a single fuselage, with the engine mounted in the normal location. A P-38 would have two fuselages and a nacelle, the wing structure alone would be far different, since all that weight, and all that power, would be way off of the centerline. You're comparing apples and oranges, the entire layout is different, and so is the strength requirement.

[Stoney]

A V-8 would not weigh more than the Falconer, it would weigh less. These days, gear boxes are far stronger and weigh far less. Further, since the big block turns fewer RPM, the gear box is less complex, smaller, and has less load on it. I'm sure there is a prop that can handle it.

The Mustang has a single fuselage, with the engine mounted in the normal location. A P-38 would have two fuselages and a nacelle, the wing structure alone would be far different, since all that weight, and all that power, would be way off of the centerline. You're comparing apples and oranges, the entire layout is different, and so is the strength requirement.

The Thunder Mustang guys had to get a prop custom designed by MT for the Falconer--that kind of development is very expensive.  Further, if a full scale P-38 weighed 13,000 pounds, I better be able to make a 3/4 scale that weighs 4,000 lbs or less--otherwise it'll be a pig.  I bet this guy's P-38 weighs around 2,000 lbs empty.  You build it out of high-strength composites and I'm guessing you could get it down to 1500 lbs, maybe less.

[Wmaker]

Even the 1HP per cubic inch Falconer needs too many RPM to make that power. The Falconer is sort of neat, sort of cool, and excessively expensive. It's "outstanding features" are that it's a V-12 and well, it's a V-12. And it is way too expensive for anything that it does, other than being a V-12.

Again, the argument was about the power out put. Weather it is enough or isn't. And clearly Falconer can put out enough power to power a 75% scale P-38. Falconer V-12 has proven itself in the Thundermustang for aero engine use. It is a ready concept.

As far as what is available commercially goes, if you are not hung up on a V-12, there are 750 cubic inch big block Chevy based V-8 engines out there now, and in fact, a 900 cubic inch version. For the same amount of stress you apply to the Falconer, I can get 250 more HP out of an all aluminum big block Chevy V-8 for about 1/2 the money. An all aluminum 620 can be built for less than $18K, and produce 1000 HP normally aspirated on pump gas. It'll make 650HP at 4000 RPM, and 950 foot pounds of torque at around 2500 RPM. And it weighs LESS than the Falconer.

Does that less than 18k a piece include conversion and testing for aeroengine use, reduction gears and the works for only couple of engines?

How much power is necessary depends a great deal on how much performance you expect.

Exactly. That's why your comment about Falconer not putting out enough HP isn't true.

Considering where the engines, the weight, and the power is produced and applied, I'm not convinced a 3/4 scale P-38 will be safe and strong if it weighed 1/3 what the original did. Especially if the goal was to produce performance equal or nearly equal to the original. Sure, if your goal is a ceiling of 25K, a top speed of 300MPH, and limits of 6G positive and 3G negative, with a short range, that might be okay. Personally, for the money I'd want more.

To match the original's power to weight ratio of 4.95kbs/hp (and this is using the high 1750hp figure), the Falconer 2x640hp powered replica would have to weigh ~6336lbs. So even at that weight the Falconers can keep the power to weight ratio in check. Considering the aspect ratio of the P-38's wing, I think the wing loading would starting to be a problem with 75% scale wing...

Building it to a weight around 30% of the original isn't unrealistic at all.