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Hey... for you guys who model WWI biplanes... can you tell me what's wrong with this propeller?

 

Cropped1_zpsd22b9fea.jpg

 

Cropped2_zps83072e6d.jpg

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My first response is that it's a great looking propeller! If your question is serious, and there is supposed to be something 'wrong", I have three observations.

 

First, in the second pic the prop looks bent. It's hard to tell, because of the angle of the photo AND the laminations, both of which may be causing a trick of the eye. If the prop is not bent backwards on one end, then...

 

It may be on backwards. Most props turn counter-clockwise as viewed from the front. I do not know if this airplane is a exception to that. If it's not, the leading edges of the blade are set to turn clockwise, which may be inaccurate. This is merely a WAG on my part....

 

From an artistic standpoint, most WWI laminated props look best with at least 5-7 laminations, and the four visible are also uneven in thickness. Again, this is merely a layman's observation, with NO idea as to what would be "accurate".

 

If it were on my model, I'd be proud, regardless of any faults, real or perceived!

 

GIL :smiley16:

Edited by ghodges

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I am not a WWI model aircraft specialist, but as an instructor and pilot I can talk to the look of your propeller. There are three major discrepancies. The laminations are straight when seen from the front. The taper of the tips are backwards, and the blades appear to be a consistent thickness and angle across the length of the blade.

 

Beware!- Technical explanations to follow:

 

The lamination in a propeller are there because carving a propeller from a single piece of wood does not yield as strong a propeller as a laminated piece. Wood is stronger across the grain than it is parallel to the grain. If you lay up the propeller with the grains running in different direction it gives the propeller greater strength from forces acting in a lot of different directions and it is less likely to shatter. This is the same reason that when you look at carbon fiber it has layers running in different directions. Thus even if a propeller is made of all the same wood(which they almost never are) you will see the laminations because of the difference of grain direction.

 

The shape of the propeller varies significantly from the inside to the tip. This is for two reasons. Because of centripetal force the inner part of the propeller is subjected to greater forces than the outer, the inner part of the propeller will be thicker than at the tip. Second is the relative motion to the air, the part of the blade near the center of the propeller is moving in the rotational plane slower then the tip(The circumference of the rotation 1' from the center is less that the circumference 3' from the center but both are making a rotation in the same time).

 

There is a term called the mean aerodynamic cord. This is a hypothetical line that is the average line from the front to the back of an airfoil that represents the average relative thickness of the blade . The difference between that line and the relative direction of the wind is called the angle of attack. The angle of attack is critical to determining how much lift an airfoil develops. In a wing, this angle can be relatively constant because the wing is generally traveling through the air at the same speed across the length of the wing. In a propeller because rotational speed, the inner part of the prop is traveling at a relatively slower speed than the tip, to create an even amount of lift across the length of the blade the angle of attack must be higher toward the center and almost flat at the tip. In other words the blade has a twist to it. It is because of this variation that the laminations appear to have a curve when viewed from the front.

 

Last is the taper of the tip. Because the propeller is an airfoil, the front is going to be thicker than the trailing edge. Thus the radius of the taper at the tip is smaller at the front and longer at the rear. In other words there is a longer gentler curve on the back side of the blade just like the wing of a Spitfire.

 

Yea, I know, you asked what time it is, and I told you how to build a clock!Probably way the heck too much information but hopefully this helps.

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Okay... time to reply. PeteJ's detailed description of a laminated propeller is priceless.Gil's observations are right on, and Eric provided a link that confirms all of it. The reason I posted this propeller, which, by the way, is NOT mine, is that this is the propeller on a Wingnut Wings Rumpler (late) that was voted First Place in the Biplane category, Best Aircraft of the entire show, AND won the theme award for World War One.. at the recently completed IPMS/USA National Convention in Hampton, VA.

 

Now please, I do not have anything against the builder (a guy from Williamsburg, VA), but this plane should have never made it past the first pass, and the judges of this category, for some inexplicable reason could not see how poorly done this propeller was. That it received three awards, two of which were specialty awards, is nothing short of perplexing! I'm sorry, but this Rumpler was not only NOT the best aircraft, it wasn't even the best Rumpler at the show. The Rumpler in a Hangar, which won the Michael L. Fritz award for excellence in WWI aircraft modeling, was a better build. See the photos and judge for yourself. Also some photos of other WWI planes in this category that the judges somehow overlooked. I had one modeler tell me that if the judging is going to be this inept, it will make attending the Nationals undesireable.

 

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Here's some other planes in the same category as the first Rumpler:

 

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DSC_0294_zps50258ee4.jpg

 

DSC_0320_zps9820cc93.jpg

 

DSC_0283_zps69ce4a1e.jpg

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Ahhh Joe....your reply sheds some much needed light on things! Your observations are what a lot of "us" (meaning IPMS types, judges, and viewers in general) hear. Problem is, your observations may or may not be correct.

 

First, the Special Awards, with the exception of Best Aircraft, are not judged, but instead are "picked" by a small committee of people on behalf of the sponsor of that award. Thus, the Mike Fritz award has NO qualifiers except that the few people picking that model like it better than the other WWI entries. It may or may not actually be a better build and does NOT have to place in its category. Another thing to remember is that the Rumpler diorama was not in the same category, nor was it judged against the Rumpler that won in the Biplane category. Thus, you cannot really compare them to one another from a judging standpoint, only in casual observation.

 

Category awards are judged MUCH more stringently, especially at the Nats! I didn't judge the WWI stuff, but in our 2 categories alignment was the item that kicked most things to the curb. A misaligned tire or gear strut seemed to be the most common error; and in talking with fellow judges they seemed to concur that this was a bugaboo in most categories. Now, for the biplanes, add in those extra wings, complex gear struts, wing struts, and other struts, and the odds of finding something misaligned is even greater, not to mention glue blobs at the ends of rigging, sagging rigging, or any other basic criteria most every entry has to surmount. You do not necessarily see those small mistakes when walking by, or taking a pic of a model, especially if the problem is on the bottom of the entry!

 

I understand why you question the results. But, unless one of the judges from that Biplane category steps in here to elaborate on what had what problem, we have to assume that the judges found errors in the basics of the construction and finish on those WWI entries you like better than the Rumpler; or at least found fewer on the Rumpler, pushing it to the top. I'll also repeat myself here: my observations on the prop are guesses! Since the judges didn't see a half-bent blade, I'm thinking the one pic is an optical illusion. As for the laminations and whether it's backward, the laminations are neatly done (accurate or not) and the judges may not have known if it's mounted backwards (and it may not be!) Once the Rumpler placed first, it was eligible to be nominated for Best Aircraft.

 

There were 4 nominations for Best Aircraft: the Rumpler, a 1/48 Fiesler Buzz Bomb, a 1/72 scratchbuilt triplane, and a tricked out 1/48 HobbyBoss Sea Fury. All of the aircraft judges spent 15-20 minutes looking at all 4 of those entries before voting. It took two rounds of voting by the aircraft judges to eliminate the Sea Fury and the Buzz Bomb. The third and final vote between the remaining two was about 2/3 to 1/3 in favor of the Rumpler. It was a solid, if not lopsided decision, with no doubts as to which of the 4 the aircraft judges thought was the best of those nominated.

 

Every year it's always possible to take the judging to task. Many of the entries are VERY close in quality and the difference between a model that gets an award and one that doesn't can be woefully small. That's why we have a reputation for "nitpicking". As long as we retain a 1-2-3 type of contest, and flaw counting is the most prevalent way to eliminate models, the casual observer will always stand in wonder of how the results could have come out like they did. Hope this helps shed a little light on the other side of the contest coin!

 

GIL :smiley16:

Edited by ghodges

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Add to what Gil said above, Judges are human. They sometimes miss things. At any show, including the Nats, the awards are what those judges saw and liked on that day. Different day, different judges, possibly a different result.

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Here we go again! It seems that after every National, some super sleuth finds some picayune error designed to embarrass the builder and once again, attempt to reveal to all the world the manifest incompetence of the judges. It almost always involves some accuracy issue and thereby only ends up embarrassing this year's Sherlock Holmes as it does every year. The National, as every contest under IPMS rules, is a craftsmanship competition. How many times does this have to be said? Propeller shape is an accuracy issue. The rules under which we compete and judge are explicit on this point. Only an absurd deviation from accuracy, such as contra-rotating props on this aircraft, would eliminate this piece from consideration. I would suggest that the modeler who finds that the "inept" judging makes attending the Nationals "undesireable" should indeed stay home. How could he or she hope to compete successfully or, God forbid, judge competently when the rules, plainly stated, are still so incomprehensible to him or her? Nick Filippone, IPMS # 969, Senior National Judge

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And I'm out of popcorn! :m1helmet:

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I didn't take Joe's question to be anything more than an open, honest attempt to get some facts. It's VERY hard for people who build models and go to contests but are only peripherally involved to understand the intricacies of judging. Most entrants do not read any of the rules past the point where it tells them where to enter their model. If you've never judged at an IPMS show, it's hard to understand exactly how minute a mistake can eliminate your model. This is especially true at a show like the IPMS Nats, where you're competing against some of the best builders and more of them!

 

Hopefully, Joe will take this info to his friend who was "so disappointed" and he will hopefully see that you cannot use casual observations in place of three guys who spent an hour or more examining those models with the proverbial fine tooth comb. Perhaps he'll be encouraged to read the judges handbook more closely or even volunteer to judge at a show. Judging is absolutely the best way to learn how to become more competitive and improve your chances at winning!

 

I don't think this was meant as a poke at the judging. I think it was an attempt to learn. Besides, he's not alone! Even we national judges question results all the time. As David mentioned, it's a subjective process and not immune from human error. If you don't ask questions, you can't learn and improve!

 

GIL :smiley16:

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I have to stand by Gil on this one. Yes, the prop is a very poor representation of the real deal but within the rules of IPMS judging, the lamination lines are straight without any bleed through and the prop has a consistent finish without glue or other problems. The ruled do not talk to accurate representation but to skill of build and consistency of finish. There are so many places to go wrong on a WWI biplane that if this was all that was wrong, then the builder did one heck of a job. At least he thought about showing it as a laminated prop. Not trying to judge, just saying...

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Thanks everyone for the great feedback and comments. Well said, by all... even by Senior National Judge Nick, IPMS # 969. As someone who builds WWI biplanes almost exclusively and has won awards for them, locally, regionally and nationally, I guess I allowed my frustratiion with at least this one issue to drive my comments. I attended the Nationals and thought it was a good convention. I thought the quality of the models - all of them - was really impressive. I have some idea what judges face. While I have not judged at the national level (although I have been encouraged to do so), I have judged at model contests locally and regionally. I get it... there will always be issues and judges will always be open to criticism, fair or not. It is the nature of the game. Mr. Filippone's comments, at least in part, seem to betray a frustration of years of dealing with those criticisms. I apologize for offending him. That wasn't my intention. Having said that, judging at the National level has to be held to the highest standard. Anyone judging, from senior judges to new guys, should never feel that they are above scrutiny. Responding that if anyone questions it, they should just stay home, is not the solution, it is part of the problem. My comments and question was not mean-spirited. I simply questioned how such a glaring mistake did not disqualify a certain model. Some of you offered opinions, especially Gil, and I appreciate those observations. I also know the two Rumplers were not in the same category, as Gil pointed out, and I realize that they would not be "competing" against each other. However, they were for the Theme award, and I still maintain the Rumpler in the Hangar was more deserving. Now that might just be my opinion, I understand that, but it was an opinion shared by the Spruce Goose Chapter that sponsors the Michael L. Fritz award. I happened to win that award last year in Denver, and so along with all the previous winners attending this National, we all agreed on that Rumpler. I assure you, we looked closely at all the WWI aircraft in the hall. (So, I guess I did judge at the National level after all.) As some of you may know, Michael L. Fritz award winners make up some the finest WWI aircraft modelers in our country today. It is an award you can only win once in your lifetime, and it is the longest running specialty award to date for IPMS/USA Nationals.

 

Anyway, enough said. Sorry if my questioning this one instance of judging offended anyone. It's good to talk these things out. I am especially appreciative of Gil's comments, insights, help and attitude. I have printed out Pete's amazing detailing of laminated props. Great stuff. Thanks!

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