redesigning the landing gear might cause other problems too. for example, the DR-1s face-plant problem could've been fixed by moving the gear forward but then the lightly built aft fuselage would have to carry more weight on landings.


dave

Well rounded wingtips on a constant chord wing were found in wind tunnel tests to reduce minimum drag by about 5%, and induced drag by about half as much as the best form of taper, which was found to be about 70%, after factoring out the increase in aspect ratio resulting from removing area from the tip. The tip form was composed of two semi-ellipses, with about twice as much area removed from the trailing edge as from the leading edge, with the trailing edge tip curve extending inward on the span by about one chord.

The negatively raked wingtips of some WW1 airplanes were found to be particularly bad - a simple rectangular tip performed better.

This is "as close as makes no never mind" true representation of a rounded wingtip, constructed using full-scale practices by Charlie Richards.
The wing tip bow is as seen a single piece, with only two smaller ribs needed to continue the shape, and two struts to maintain the bow under the pressure of the covering.
All the ribs are hand-layed up, with each gusset.. the compression strut is to scale..
A marvelous piece of work.
For the flying version, Charlie did most of it the same way, but of sturdier material.
This one is slowly disintegrating over the years..

Which Wing tips?- on a model -pretty hard to beat NO tip at all.
Why?
you save weight
An old full scale builder told me " just smooth it off " .
If you are building a scale model - do it so it looks scale.
Otherwise - just end it.
Full scale - well that's a case by case thing-

The Dr-! (and similar rotary motored planes) had too much of the mass of the equipment in the plane mounted directly over the fulcrum of the axle.. that's a long moment arm which makes overturning sooooooo easy!
My Dr-1 finishes most landings upside down!
There's no mass behind the c.g. to prevent the tail from tipping up.
Takeoffs are also a problem, requiring up elevator to prevent the tipping, but also demanding its release ASAP to prevent a tip-stall takeoff!

Paul, that Stearman wing is a thing of beauty! Is this one just for show? I'd like my next scale model (most likely either the Albatros BII or CVII) to have an "as close as makes no never mind" wing structure though I'd be willing to accept non-scale ribs (but with scale airfoils in a scale location) for the sake of greater strength. I might build a few "test ribs" to see how strong the laticed and gusseted version are compared with a solid (thin) ply one with lightening holes.

BTW, one reason I'm looking at the CVII is that it had a relatively long nose moment compared to most of the WWI aircraft. It also has the fun funky engine up front!

Chicken and egg. It ain't a perfect world, the Great War itself presenting evidence sufficient of this and mankind's penchant for illogic and enacting stupidity.

Implementation of undercarriage production and design was aleady a fait accompli, reinforced by fixed ideas and resistance to change as is typical of our species. if one might use the Microsoft analogy. Not only is it easier to come up with perpetual patches than redesign a flawed OS from the ground up, but the fact that one has to accomodate legacy apps and deal with economic and emotional resistance to change during the process is self-determining and restrictive of the ideal process.

So you could say it was partially due to convention, with the usual human resistance to new ideas and change. Even if one could overcome those social and political barriers, where else would you place the undercarriage? On those relatively fragile lower wing structures? Almost universally, undercarriages on scout and recon types were narrow track centred on the fuselage.

Secondly, the narrow track undercarriage issue compounded by no brakes simply make an aircraft more susceptible. The major factor in terms of probability was relative pilot inexperience.

Perhaps, but you've moved back into that armchair, grabbed a coffee, turned the air conditioning on and are thinking about it without the pressures and constraints of the time.

As I flip through Janes it occurs to me from my observation of wingtip design that pure prejudicial preference and aesthetics at the whim of the individual designer heavily influenced tip design. ie: Most Fokkers had squarish tips Dr.1, D.7, D.8 etc. Albatross eg: III & V, Halberstadt and Pfalz went for taper. etc..etc..

As can be seen in the Spitfire and Me109 designs, the high narrow track undercarriage implemented due to structural issues again presented a problem with ground handling 20 years later. It was quickly abandoned in other types, but never addressed in those particular designs. Reason in my view? As needs must - also known as pressure of production triage.

Re tip design.

As it turned out, early during WW2, the rounded tip was very much in vogue. Elliptical made an appearance, but was less popular not least at a guess due to production issues? Examples (primary Marks) of rounded tips Hurricanes, Spitfire II & V & IX, Whirlwind, Mosquito and from the US, P-38, P-39, P-40, P-47, Jap - Zero, Tony, German - Bf 109. Later, as both excess horsepower and overall speeds increased the squared off tip very much came back into vogue.

Today, in an era where fuel economy is everything, the taper supported by induced drag reducing tips is common on everything from gliders through lighties and airliners.

I think that if you look at the picture that taul pall posted, you will see what looks like a simple light weight structure. A rounded structure CAN take a blow from any direction and disperse the load into the greater structure. It does offer better aerodynamics than a rectangular wing, it does hold up to the shrinking fabric covering better with less weight. With the rather pathetic engines of the era, weight was critical

This style of construction pictured by Paul has anti-compression struts, and positive and negative drag cables that are diagonal between the spars. Biplanes also allow bracing against the second wing which add strength again without much weight gain, albeit with loads of drag. A number of WW1 designs were not even true biplanes, with the lower wing used only to brace the upper wing. I believe the term was seqi-plane or something like that, where the lower wing has less than 50% of the area of the upper wing.

Sesquiplane. The Nieuport 17 and Albatross D.V being two famous and classic period examples from the opposing sides.

Tall Paul's opine doesn't rate much with me. I've seen how he stacks his car.'

Anyone who considers that they can ignore completely the reason most probable which is immediately obvious to experienced pilots in favour of some idealistic nonsense attributing it to development of aerodynamic design doesn't present as knowing anything worthwhile about flying, even less about human behaviour and the pragmatism behind all three aspects typically influencing the outcome of the subject under discussion.

As to the ability of the rounded structure being able to deflect the energy from a blow, and better still not to hang up on or rotate around upon striking an object including the poor ******* holding the wingtip - this has already been stated and is a prime example of why it offers optimum tip shape to minimise the catastrophic consequences of a tip strike resulting into a ground loop or worse. Of course aerodynamics or manufacture could have been an influence, but pilot survival rated a lot higher than aircraft longevity in terms of priority...and in an environment where attrition meant that machines were't designed like a Boeing to last in service for 20 years. You're not building a piece of furnitutre either. Though replacing machines was a logistical nightmare for the Germans, replacing pilots was even worse. Once that cadre of experience is gone, it becomes literally lambs to the slaughter! And I'm talking about the flying off and on the ground part, not engaging the enemy.

Sigrun, the fact that Fokker didn't use the rounded/tapered tips and Albatros, Rumpler, LFV and others did is more likely explained by the fact that Fokker made single bay fighters while the others did mostly 2-3 bay 2-seaters. I would imagine the likelihood of ground loop increased proportionately with wing span. Sure this shape also is to be found on some fighters but I'd guess it was already to be found of that company's 2-seater designs.

As far as the designers making "pilot survivability" their primary design objective, I think you're overstading that case a bit. I still belief that the primary design considerations were those needed to win the Adlershoff competitions (and thus military production contracts): speed (primarily a matter of horsepower and the engine dictated much of the rest of the design), climb rate, and flight characteristics -- in the case of a fighter this meant maneuverably (i.e. "squirrlely but flyable") and in the case of an observer stable enough to fly over long flights but with enough maneuverabilty to get out of trouble. I also believe that reducing drag became more and more a conscious design goal towards the end of the war (compare the Albatros CV with the Albatros BI and II).

BTW, you state that they weren't "building a piece of furniture" -- well, actually that's what a good number of the workemen in the Albatros factories had been doing before the war! And that goes a lot way towards explaining the skilled woodwork and beautiful natural finishes on those monocoque fuselages.

[8D] Thats a good point abufletcher, and at the risk of being stereotyped as an air conditioned, chair sitting, coffee sipper by Sigrun...... weren't the Germans also doing wind tunnel and aerodynamic testing on models of various Aircraft? I believe if you research it you'll find they were.....and albeit a primitive attempt at making improvements, I'm sure some of their discoveries there influnced some design decisions. Now I'm not saying I know for sure that this inspired rounded wingtips any more than the practical field reasons cited above, which seem very logical and probable as well.....but then none of us know for sure!......never will.

ZZ.

Ok,I guess It's time for me to chime-in here and straighten-out all of you![sm=bananahead.gif]After getting my master's degree in aerodynamic engineering from the prostegeious university of TLAR back in 1964,I have come to the conclusion that rounded wing tips were a combination of all of the above!Aeroplanes back then were still in there infantcy-they were still learning.As for the ground loop thing,take a look at the wing tips of the Sopwith aircraft---especially the beloved "PUP".This plane was trully loved by it's pilots!!!No other plane that I know of at the time had such a reputation.It got that rep. due to the fact that it was a VERY user friendly bird to fly!Also it could manuver very well and was reasonably successful as a fighter during the period.It was,however,a little low on firepower-only 1 gun.Of course,By adding the second gun and the additional amo increased the weight and therefore required more power(can you say-"vishous-circle")The other plane that comes to mind is the Russian Mig 3.This fighter was feared by the Luftwaffa and orders were given to---avoid engageing the thing at all costs at high altitude!It also had very little firepower compared to most other fighters of the time.BTW,Since the Mig 3 was designed years before the famous P51,one has no choice but to come to the conclusion that it most definitely must have influnced the engineers at North American Aviation,due to the fact that they designed the Mustang in such a very short length of time!Just look at the Mig and the Mustang and it should be obvious.As you can see by now,I'm no expert,but this subject just got me going.