1/2 scale warbirds

Discussion in 'Warbirds / Warbird Replicas' started by BBerson, Nov 5, 2019.

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  1. Nov 5, 2019 #1

    BBerson

    BBerson

    BBerson

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    Bingelis letter to 1/2 scale warbird designers:



    1/2 SCALE PROBLEMS

    We will move on to another subject which is of concern and I would like to share with you a letter from Tony Bingelis. This letter is as the result of our observation over the years of some activities within our amateur built movement. This particular incident involves a Vfc scale Focke-Wulf 190 replica of a WWII German fighter which, after some 15 to 20 minutes of a staggering first flight after purchase and attempted ferry flight to New York the day after our 1979 Oshkosh Convention, ended in a near tragic crash. The mile drive in Red One with

    son, Tom, and the ball of fire and smoke that erupted from the corn field will never be forgotten. Nor will the run through 10 foot high corn with the fire extinguisher to find the pilot thrown clear of the fire but severely injured. This was indeed a miracle. A 230 pound pilot, parachute, tie-downs, baggage, fuel and oil came to about one half the empty weight of the aircraft. After months in Mercy Hospital in Oshkosh he is home recovering — a very fortunate and wiser person . . . but let's share our views with Tony.

    Dear Paul:
    I'm sorry that I was unable to respond to your letter of September 12, 1979 before this. In the letter you expressed your dismay over the tragic record being developed by small scale replica aircraft and asked for my comments on the subject. I do have an opinion on the matter and perhaps it is very much like your own. At any rate, I, too, feel very strongly that these small scale war replicas are marginal aircraft at best and could be deadly instruments in the hands of low time pleasure pilots. I did not know of the Focke- Wulf 190 accident until I read your letter.

    Some months ago I talked with an individual about the airplane. The workmanship was not outstanding but appeared to be airworthy. I said the usual nice things about one's aircraft but I believe he told me he purchased the aircraft from someone else out of state. The airplane looked fast with its retractable gear and war paint and I asked about the performance. The owner told me that it was too heavy and it didn't do too well on its 100 hp engine. As a matter of fact he said his cruise speed was something like 120-125 mph. I somehow had expected to hear 150-160, at least. He said the climb was sorry and was quite disappointed with the aircraft.

    Another thing that bothers me about all this is the general revelation given me by the letters I re- ceive. People who are totally uninformed of aircraft design, aircraft construction and the realities of aero- dynamic principles, blissfully write and ask why they can't use a different or bigger engine, change the gear to a retractable or tricycle installation, add spoilers or two or three feet to the span . . . or cut the span by a like amount. A recent letter received from a gent who wrote and told me that he didn't like any of the designs he saw and he was going to build his own de- sign but he didn't know where the landing gear should be.

    A lot of builders write me because they can't get information from the designer of the aircraft. And I can understand why. Some of the changes proposed ab- solutely have no merit or logic. If it is a single seater why can't the builder add another seat or another en- gine? Another doesn't like wood construction and wants to change it to an all-metal job. Tell me what changes I should make, they add.

    Finally, everybody that weighs over 200 pounds

    and/or stands 6 feet tall wants to build the smallest airplane he can find. These big guys seem to have a built-in craving for small aircraft. As you know, this really is a dangerous craving. Most of these low- powered designs are operating on the verge anyway . . . add a 245 pound pilot and you have a fused bomb ready to go off aerodynamically or structurally.

    As you know, aerodynamic laws don't work the way the lay mind thinks. For example, doubling the horse- power doesn't double the speed. Four seat, store bought aircraft with full gas on board cannot carry four people. Cutting the span to increase speed by reducing drag will usually do so ... straight down on the final turn.

    These 1/2 scale replicas. Builders say that is just the right size and don't worry about the distorted scale effect necessary to accommodate an oversized pilot. Shouldn't the pilot be 1/2 scale too? Let's see, that would make him three feet tall right? How about the en- gine, according to scale shouldn't it have at least a 600 to 1000 hp mill up front? How could anyone ever expect such a 1/2 scale aircraft to perform safely on a mere 60 hp VW or even a "powerful" 100 hp?

    Outside of that, it's difficult explaining to each budding builder/designer that building or changing an aircraft design is not like modifying a motorcycle or dune buggy or even an automobile. Up in the air things are different and gravity never takes a holiday. I am often tempted to fluff off letters and questions of the nature under discussion but somebody has to tell them . . . alert them . . . of the difficulties, the consequences. Even the reasons why they cannot or should not do what they are thinking.

    Designers catch hell. The minute a design is finalized, here comes a builder who wants to know if he can use a 180 hp instead of a 125. I told this to one builder and he said, "Well, why didn't he design it for a 180 in the first place?" I told him that if the designer had any such inclinations he would have done so but he didn't. Then too, if the design was approved for 180, along would come builders who would bug the designer for information regarding the installation of a 200 hp or 300 hp engine. A buyer of plans has not a license to harass the designer or expect any more after buying his plans than to be informed of manda- tory changes.

    Well, this is ranging far and wide on the subject but I don't know how to limit the issue. Years ago, builders compensated the lack of sufficient power by building larger and lighter aircraft. This 1/2 scale fever runs counter to that logic and as a result is getting a lot of people in trouble. Almost every article I write has a safety thought or remark in it somewhere.

    I wonder if you couldn't get all this before the builders with an article or two by Al Backstrom. He is a good engineer and understands the layman's at- titudes. He might explain the problems of scale ef- fect and Reynolds numbers so that even I could under- stand. Of course, no single article will solve the prob- lem any more than will 100 articles in sequence. Many people will never get the word and many don't want it in the first place. This is a difficult letter to write, Paul, because I didn't know where I was going with the subject . . . and typing a letter without the op- portunity of editing it makes it even more difficult. At any rate, perhaps somewhere in this rambling you may find something of use to you.

    Congratulations on a fine job done by all at Tulla- homa. If man ever conquered the elements, the EAA did just that and in the end had a very successful Fly-In, weather notwithstanding. Thanks for the op- portunity to air these thoughts.

    Adios, Amigo Tony Bingelis

    4 JANUARY 1980
     
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  2. Nov 5, 2019 #2

    crusty old aviator

    crusty old aviator

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    Years ago, I painted a WAR FW-190 for a guy, Luftwaffe #71 dark green. I liked the color so much, I painted my ‘80 Toyota pickup that color. Anyway, he scared himself one too many times flying that girl, and she was built light and he weighed about 160 pounds, so she ended up decorating the roof of a German restaurant...
     
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  3. Nov 5, 2019 #3

    nicknack

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    Just caught sight of this thread. Somewhere in my collections I have an article by Marcel Jurca about what he considers a suitable size for replicas and required HP and wing loadings. I will try to find it and upload it.

    I recall the recommendation of no less than 2/3 scale, 160 to 200hp and 3/4 being most practical.
     
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  4. Nov 5, 2019 #4

    Riggerrob

    Riggerrob

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    Few amateurs understand all the problems with scaling down replica airplanes.

    First is the 'square law' meaning that half the wing span results in 1/4 the wing area.

    Secondly, volume and weight decrease by the cube … or they should. Meaning that 1/2 scale replicas can only carry a tiny fraction of the fuel. guns, etc. as original warbirds.

    Thirdly, many of the originals were difficult to fly. They required the fast reflexes of 19-year-old pilots and precisely monitoring airspeeds, temperatures, etc. Plenty of warbirds crashed during the 1940s, 1950s and 1960s because they required far more skill than the average private pilot. Some originals had nasty stall characteristics. Both the FW-190 and Grumman Hellcat stalled viciously with flaps up, but tamed down considerably after flaps were lowered.
    World War One airplanes were notorious for being tail-heavy and difficult to recover from spins. One of the few successful sellers of World War One replica airplane kits is Robert Baslee who starts with the original outline, but soon moves engines, seats, wheels, etc. to make them handle more like docile Piper Cubs. Then he compares tail volume, stability margins, etc. with modern airplanes before finalizing drawings. On close inspection, many of Baslee's replicas have noses that are longer than scale, larger control surfaces, etc.

    Scaling down cockpits is the greatest challenge. Start by considering that the originals were flown by skinny 19-year-old pilots. Many (e.g. Spitfire and Me-109) were considered cramped for their day.
    I stand 6 feet tall and weighed 190 pounds but when I sat in the cockpit of a War Aircraft Replicas 1/2 scale replica of a Hawker Sea Fury. It was cramped with a bomber jacket, leaving no room for a pilot emergency parachute. Forget about bailing out if it caught fire!

    Most of the WAR replicas and many 3/4 scale replicas (e.g. Jurca) still needed enlarged canopies to accommodate plump post-war pilots.

    Finally, consider that the WAR series of 1/2 scale replicas were based on Ken Rand's KR series (wood, foam and fibreglass), which were in turn based on the wood and fabric Taylor Monoplane, all small airplanes. Like many cold-molded composites, many builders used too much resin and the completed airframes were heavier than anticipated by the designer.

    While factory-new VW engines were widely available during the 1970s, only the 2 litre versions had enough horsepower for serious performance. VW of Germany quit building flat four engines 50 years ago. Any VW still powering an airplane has hot rod pistons, a thicker crankshaft, etc. Souping-up car engines always reduces reliability. But even souped-up VWs (85 horsepower continuous) were not enough for 1/2 scale WAR replicas, so most were built with (100 horsepower) Continental O-200 engines.

    Ken Rand was not a tall fellow, nor was he fat. Many KR 2s were built by large pilots who can only fly them solo. I can fly a KR2, Quickie 2 or Dragonfly solo, but only small children could fly as passengers. With those small weight margins, it is little wonder that an over-loaded WAR FW-190 stalled as it departed Oshkosh with a full load of camping gear, etc.
     
  5. Nov 5, 2019 #5

    Riggerrob

    Riggerrob

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    Few amateurs understand all the problems with scaling down replica airplanes.

    First is the 'square law' meaning that half the wing span results in 1/4 the wing area.

    Secondly, volume and weight decrease by the cube … or they should. Meaning that 1/2 scale replicas can only carry a tiny fraction of the fuel. guns, etc. as original warbirds.

    Thirdly, many of the originals were difficult to fly. They required the fast reflexes of 19-year-old pilots and precisely monitoring airspeeds, temperatures, etc. Plenty of warbirds crashed during the 1940s, 1950s and 1960s because they required far more skill than the average private pilot. Some originals had nasty stall characteristics. Both the FW-190 and Grumman Hellcat stalled viciously with flaps up, but tamed down considerably after flaps were lowered.
    World War One airplanes were notorious for being tail-heavy and difficult to recover from spins. One of the few successful sellers of World War One replica airplane kits is Robert Baslee who starts with the original outline, but soon moves engines, seats, wheels, etc. to make them handle more like docile Piper Cubs. Then he compares tail volume, stability margins, etc. with modern airplanes before finalizing drawings. On close inspection, many of Baslee's replicas have noses that are longer than scale, larger control surfaces, etc.

    Scaling down cockpits is the greatest challenge. Start by considering that the originals were flown by skinny 19-year-old pilots. Many (e.g. Spitfire and Me-109) were considered cramped for their day.
    I stand 6 feet tall and weighed 190 pounds but when I sat in the cockpit of a War Aircraft Replicas 1/2 scale replica of a Hawker Sea Fury. It was cramped with a bomber jacket, leaving no room for a pilot emergency parachute. Forget about bailing out if it caught fire!

    Most of the WAR replicas and many 3/4 scale replicas (e.g. Jurca) still needed enlarged canopies to accommodate plump post-war pilots.

    Finally, consider that the WAR series of 1/2 scale replicas were based on Ken Rand's KR series (wood, foam and fibreglass), which were in turn based on the wood and fabric Taylor Monoplane, all small airplanes. Like many cold-molded composites, many builders used too much resin and the completed airframes were heavier than anticipated by the designer.

    While factory-new VW engines were widely available during the 1970s, only the 2 litre versions had enough horsepower for serious performance. VW of Germany quit building flat four engines 50 years ago. Any VW still powering an airplane has hot rod pistons, a thicker crankshaft, etc. Souping-up car engines always reduces reliability. But even souped-up VWs (85 horsepower continuous) were not enough for 1/2 scale WAR replicas, so most were built with (100 horsepower) Continental O-200 engines.

    Ken Rand was not a tall fellow, nor was he fat. Many KR 2s were built by large pilots who can only fly them solo. I can fly a KR2, Quickie 2 or Dragonfly solo, but only small children could fly as passengers. With those small weight margins, it is little wonder that an over-loaded WAR FW-190 stalled as it departed Oshkosh with a full load of camping gear, etc.
     
  6. Nov 5, 2019 #6

    ScaleBirdsScott

    ScaleBirdsScott

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    Building a 1/2 scale replica is totally possible but it depends on the nature of the word "replica" and the nature of 1/2 scale and the nature of the aircraft.

    The specific approach of the WAR composite type aircraft is one example of an approach. There's other approaches. Painting all replica-ish type aircraft with the same brush or using the same parameters/rules of thumb seems to make a lot of assumptions on what replica, scale, and mission all entail.

    Clearly, there's capable aircraft that share the general rough proportions of what you might call a WWII-era fighter plane (of which there are many variances on shape/size in reality) and yet do nothing to try and look like anything but themselves. So, starting with that premise, what wings do those planes have? What areas, proportions, power, weights, etc? Then dress it up a bit.

    Trying to just take a big fighter plane and scale it down past about 75% is the wrong approach. At 50-70% it is about designing a sport plane and then go through the steps to make it look right.

    There's nothing wrong with a 5-700lb single-seat monoplane with 80-100hp to fly around and be fun with the proper wing. There's nothing inherently wrong about that sport plane looking like a replica.
     
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  7. Nov 5, 2019 #7

    radfordc

    radfordc

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    Well said!
     
  8. Nov 5, 2019 #8

    Wanttaja

    Wanttaja

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    If you get something that vaguely looks like a plane from that era, sometimes the paint is all you need. Some Fly Babies illustrate....
    [​IMG]
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    Ron Wanttaja
     
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  9. Nov 5, 2019 #9

    plncraze

    plncraze

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    John Isaacs started with airplanes which were "close" in size when he did his replicas. This have a basis for design so he was not starting from nothing.
     
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  10. Nov 5, 2019 #10

    ScaleBirdsScott

    ScaleBirdsScott

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    I really dig the Fly Baby, wish there was a well-done kit for it.

    Still, there's a sort of leap of effort between painting a bona-fide sportplane in a military livery for warbird appeal, and then actually going through the work to fully transform the contours and details and fairings to specifically call to the design of a historic piece.

    It's something that consumes my mind pretty-much every day, for better or worse.
     
  11. Nov 6, 2019 #11

    Wanttaja

    Wanttaja

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    But think of the opportunity to warp history.

    About 15 years ago, a Fly Baby owner in Great Britain got the idea to make slight cosmetic changes to his bird to make it look "kinda" like a Junkers CL1 trench strafer from WWI.

    Now...if you do a Google image search for "Junkers CL1", most of the hits are Fly Babies. :)
    [​IMG]
    There's an outfit that sells ready-to-fly RC models of the Junkers CL1.
    [​IMG]

    http://www.airtekhobbies.com/seagull5500005.html

    Yep...it's the Fly Baby version.

    Ron "Resistance is Futile" Wanttaja
     
  12. Nov 6, 2019 #12

    Flitzer

    Flitzer

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    Well I agree with most of what's been written on this subject.

    Personally, purely when appraising such a type 'up close and personal' when parked on the turf, I consider 88% scale as about as small as one should go for a scaled down 'fighter' type, although 75% can work for a biplane.

    Low wing monoplanes with relatively short undercarriages will always look 'toylike' up close, since the observer is looking down at them, whereas a real Spitfire or Lavochkin 5FN, Fokker D.XXI or what have you, despite their relatively small size, still loomed over their crews standing alongside. So it depends how close your want to approach 'reality'. This is quite apart from the associated handling and control characteristics of an aircraft of lower mass which might have lightning fast control responses compared with the full size.

    For biplanes or parasol types, something like 75% scale is probably the lowest cut-off for down-sizing. This is not especially due to potential handling difficulties, after all a Pitts is pretty small and hundreds are flying. But at least with a a high enough upper plane and a long enough undercarriage, standing next to such a 'replica' one can be persuaded of its authenticity.

    The Flitzer series represent, for the most part, the physically smallest sporting biplanes flying successfully on the modest power of a VW, so a fighter-type based around that will exhibit the desired handling and performance one would look for in a small 'replica' biplane fighter. For example, one Flitzer evolution, based on the more compact Flitzer Meteor, is the PV-6 Stormcock, which itself is loosely-based on the Blackburn Lincock of 1928, a light interceptor type and one of the best British Aerobatic aeroplanes in existence prior to WW2.

    I attempted to attach an image representing how the completed machine would look but fir some reason it failed to upload. Spanning 17' 6" it intended for the direct-drive Verner 5Si 83 hp. radial turning close to a 2 metre propeller. The Lincock itself spanned a little over 22', so the Stormcock is around 80% scale. However, the PV-6 is a much simplified machine, based closely on Flitzer design features and is not intended as a true replica in any sense; rather to convey the style and character of some of the prototype fighter biplanes on the inter-war period.
     
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  13. Nov 7, 2019 #13

    crusty old aviator

    crusty old aviator

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    My 3/4 scale Curtiss Hawk P6E was designed and built by Joe Locasto in Santa Clara, CA. He said that he should have gone with 70% or 80% because that 5% required a LOT of additional arithmetic! Her Olds 215 engine, stroked up with an Olds 300 crankshaft, fits well inside the cowling without having to disrupt the original lines, but the cockpit certainly is cozy. Oh, you bet she’s painted up to look like she’s based out of Selfridge in the early 30’s (snowy owls).
     
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  14. Nov 7, 2019 #14

    Riggerrob

    Riggerrob

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    Scalebirdscott,

    Your post number 6 was spot-on!

    A second approach is the Loehle 5151. It started as an ultra-light with very light wood and fabric construction, but they still managed to make the silhouette a reasonable approximation of a P-51 Mustang.

    A third approach is the Silence Twister, a semi-scale Spitfire replica. This little composite kitplane is so pretty that I would paint it in a simple colour scheme, like a single colour photo-recon Spitfire. Single-seat Twisters fly graceful aerobatics with 100 hp Rotax engines.

    I have made dozens of sketches of DG Mosquito and Blohm & Voss 141 replicas, concluding that exactly 1/2 scale means tight cockpits. Shoulders are pressed hard against wing spars as you struggle to keep rudder pedals aft of the propeller arc(s). Even original Mosquitos were tight fits with two crew. A group of Frenchmen actually completed a Mosquito replica, but they had to enlarge the canopy to fit two crew.
     
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  15. Nov 7, 2019 #15

    ScaleBirdsScott

    ScaleBirdsScott

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    Any pictures of the 3/4 Curtiss? Big fan of the Hawk in all guises.
     
  16. Nov 8, 2019 #16

    TMann

    TMann

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    We had a guy in our EAA Chapter 80 (Ralph Rosnick) that was trying to cobble together enough P6E parts for a restoration project. He took what he had and fabricated the rest.
    You can see the end product in the EAA Museum.
    He would machine the parts he couldn't find and then sandblast them to give the appearance that they had been cast as was the case on the original.
     
  17. Nov 8, 2019 #17

    crusty old aviator

    crusty old aviator

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    upload_2019-11-8_11-35-40.png
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    Here's Joe, about 30 years ago. He started this project in the early 70's. The wheel pants are made from spun aluminum, front & rear, welded together, then cut vertically in half and holes cut for the tire, axle support, etc.

    I read Ralph's book, Hawk Safari, and many of his photos have proven useful in this project. EAA was kind enough to put his girl on their website as one of their museum aircraft that you can take a virtual cockpit tour of.
     
  18. Nov 8, 2019 #18

    TMann

    TMann

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    I was riding with the guy that does the Timeless Voices for EAA and we got to talking about the Hawk.
    He stated that the Hawk was insured for the most bucks of all the planes in the museum.
    Quite a tribute.
     
  19. Nov 9, 2019 #19

    crusty old aviator

    crusty old aviator

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    If you read Ralph’s book, you gain quite an appreciation for just how unlikely it is that his replica was completed and flew: she’s worth more than whatever EAA is willing to insure her for.
    One of the passages from Ralph’s book that stuck with me was his take on the sole surviving P6E on display at Wright-Pat: those Purdue students really cobbled her together.
     
  20. Nov 9, 2019 #20

    Tiger Tim

    Tiger Tim

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    I would think the viability of a half scale warbird just depends on the size of the full-scale. You may have to start amputating limbs to fit in a half size Me-109 but a 50% scale Douglas B-19 would be nearly the size of a DC-6!
     

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