Foamboard Spar/Former Experiment

hey friend in this video I'd like to investigate some of the properties qualities strength and durability and ease of construction of a couple of different foam boards spar techniques you'll see here and the main two divisions you'll typically see is in the traditional arm and wing is in vertically stacking two three or more pieces of foam board cut to a certain width gluing them sequentially and then forming the uppers wing surface above them and the other is more typical of the flight test design which uses a vertically oriented foam board strips glued together and then placed inside and the wing formed over that the main things I'd like to know about these two different approaches to the same ultimate outcome of having a spar and former for the wing is to see which one is stronger which one is easier to reproduce and which one is more versatile in the ability to adapt to other needs such as including a carbon fiber spar now this is not in any way meant to be a feud between flight test and experimental airlines I love flight tests they've done a million times more for the community than I have but I can't help but think that more heads are better than one and so that there's probably pros and cons of both of these approaches so let's explore what those are the physics having a spar in normal upright flight are that it must bear a compressive force among the upper portion of the substance of the spar and a tension force along the lower surface here so in this simulated foam board spar here when it's flexed this way the upper half of the spawn board and the paper associated with it is compressed together and the foam board and paper on the bottom is subjected to tension and of course that has a certain amount of flexibility and a certain failure point at which it will fail like this and it fails slightly differently on an edge wise a fashion than on a thickness wise direction now admittedly it's much more intuitive to imagine the i-beam principle of strength in flexion by orienting the foam board vertically like this but we have to take into account that even stacked foam board though it doesn't have the typical i-beam configuration has more paper substance above and below Oh which can bear the respective tension and compression forces what I've done to test this is constructed three simulated models of foam board spars in slightly different designs the first of which I'll just refer to as the EI design which are three stacked sections of foam board one inch wide with a simulated upper and lower wing skin on it and then the second I'll refer to as the flight test design which has the double folded foam board vertically oriented spar which has sort of a more traditional ib m-- orientation and configuration and then a third one is the same however the the spar inside has been covered with extreme packing tape like this now I must be said from the outset that the actual strength of these tests far former models is way less than any wing built with any one of these techniques would be so spoiler alert if you don't wish to watch the whole experiment I'll condense the results in a general sense right here what it appears to be testing each of these three designs is that the overall strength as far as failure is concerned correlates well with just the sheer volume of foam that's involved so the EI type technique of stacking foam has more foam weighs more and just is stronger in a fully built up wing like this thirty inch section of our manned wing the weight differences between these are that the tape covered like flight tests improved design weighs four percent more and the wing and will probably end up being maybe two percent more one percent more in the entire plane and the experimental airlines design weighs 11% more again in the wing and probably something like four or five percent more and when you account for the entire weight of the plane the strength of correlation to that turns out to be that using the flight test vertical spar for more design as the benchmark the tape covering as eight percent strength and the EI type of stacking adds thirty one percent strength before actual failure of just this structure again not the whole wing adjust the experimental setup here and so assessing the failure for example of the EI type which failed at about twenty centimeters that a little bit less than an inch deflection down at 1400 grams that's almost three pounds and that's just for this spar experimental setup once you bring an entire wing into the equation with the additional foam board and structures imagine that something like three times that so that's a 500 gram plane under probably a five or six G turn with the most general conclusion for airplanes with a wingspan under forty inches or one meter where you wish to keep it as light as possible and are not subjecting it to an extreme flight forces or heavy loads to probably recommend the flight test vertical spar for more design as it saves a tiny bit of weight and provides a little bit more space inside the wing for servo mounting although being very slightly harder to construct taking a little bit more diligence in your precision for aircraft with a wingspan of greater than 40 inches or one meter where that are heavily loaded or subjected to greater flight forces I would recommend the experimental airlines design with the stacked foam board like this and seriously consider incorporating a carbon-fiber spar like this eight millimeter carbon fiber tube and this happens to come in one metre 40 inch lengths from radical RC so it's a nice native size to fit inside a wing greater than 40 inches without having to trim the carbon fiber itself and they could reuse this over and over as far as the ease of construction between these two designs they're pretty close and complex ending with a little bit of practice either is quite easy I would have to rate the flight test vertical spar for more design as being slightly more complicated and so far as the diligence needed to make your cuts very straight and cutting out that strip and then scoring through the paper to get it to fold over so that this surface upper and lower are very flat and therefore fit neatly within the wing in a precise way using hot glue it's a little bit more forgiving using CA glue and Gorilla Glue needs to be pretty flat in order to get the upper wing surface to conform nicely over this edge right here the flight test design is of course lighter the experimental airline design uses more foam but these pieces of foam border just sort of slap down one on top of the next the alignment left and right doesn't matter and the upper surface always ends up flat and then the typical recommendation for that design after stacking up your pieces like this and gluing them is to remove the paper from the upper surface like that use a side of a smooth instrument like a utility knife to smooth that down to further curve this surface here so that it fits on the inside of the wing and has a broader surface area to glue to so it's somewhat more forgiving in that sense as far as the interior space for servo mounting which I typically place the servos in this rear compartment here the vertical spar former flight test design I think gives a better outcome depending on where the spar former is mounted now if mounted these both with the rear surface about at the same area so this space is about the same but it wouldn't be too hard to imagine moving this bar form or slightly farther forward depending on your camber of the upper surface of the wing and providing more space behind that spar one other minor consideration in that arena is that when gluing your top skin down onto the upper surface of the former if using the e a flat laid down style there's a broad area of glue and then it tends to accept that curve fairly naturally whereas using a vertically oriented a spa reformer like this be careful when applying hot glue and then attempting to form your wing over the top of that to forcibly as it will tend to crease the wing with very little force like that so you'll end up with a wrinkle on the top simply because there's a much narrower fulcrum here so if you do use the vertical spar for more technique be sure to form that upper surface of your wing first instead of using the spar itself as a fulcrum so get that nice Bend and then gently glue it on here so that it doesn't wrinkle like this the reason for that behavior of course is because the glue heats up the foam on the inner surface of the upper wing skin softens it and just allows them to become much more flexible while it's warm for the first part of the experiment are constructed of foam board former slash spars first of the flight test design with a half-inch wide double stacked a vertically oriented spar like this and the second by the ei technique by stacking one inch wide foam board strips like this three of them actually in the experimental model here to provide the exact same height between each of these models weighed and tested those the baseline flight test design here weighed six grams the modified flight test with the extreme packing tape applied along the outer surfaces of the spar here and here weighed nine grams for a 30 inch section and the experimental airlines weighed 20 grams for a 30 inch section next I tested the amount of force required to flex the spar alone on the vertical axis one centimeter at the center with the fulcrums at the tips of the 30-inch section here and here now I'll pause to say this isn't quite accurate to reflect a 30 inch wingspan technically because the upward force of lift isn't applied at the tips it's applied for a straight on tapered wing mid span here so the upward force applied at the tips is actually double that at the mid-span section and it approaches zero towards the fuselage itself but for experimental purposes I've used a thirty inch section of spar and this actually more simulates a 60 inch wingspan just keep that in mind so for the spar alone without any embellishments as you see here the deflection for one centimeter at the center was 88 grams for the flight test version 140 grams for the taped flight test version and 390 grams for the experimental airlines stacked foam board type next each of these was built into an i-beam type of configuration with a 1-inch strip above and below to represent the upper and lower wing skins now this doesn't take into account the amount of cord or the presence or absence of paper on the inside or outside of the wing otherwise so this is just an apples-to-apples comparison between each of these spar former techniques but adding to at the eye beam element of strength these weighed respectively 24 grams for the standard flight test design 28 grams for the modified flight test design and 36 grams for the experimental Airlines type so you can see that with the additional additional elements of like wing or simulated wing skins like this the portion of weight that the spar itself adds diminishes somewhat so in the naked form of the flight test design versus the EEA design there is a 14 gram difference when considered in the total weight of a 30 inch wingspan five inch cord wing like this of 110 grams becomes a much smaller proportion and in a plane that weighs let's say 500 grams 14 grams doesn't add up to so much so I'm not as concerned about the proportion of weight so far between the flight test and experimental Airlines designs here and then I tested the deflection forces for each of these designs and not surprisingly with the addition of those upper and lower members here it became much stronger and out of caution for breaking the wing structure I deflected only five millimeters and found the deflection needed to flex the flight test design was 560 grams which is very respectable the modified flight test with the tape is 640 grams for five millimeters deflection and of the experimental airlines 600 grams so all fairly close the taped flight test designed it slightly the best so far so that's looking pretty promising by comparison an identical length of this 8 millimeter carbon-fiber tube from radical RC for 1 centimeter deflection at the center took 1900 grams compared to the best of the EI design which was 30 390 grams now I'll test the failure strength through each of these spar assemblies measuring the deflection with the vertically oriented ruler here and applying a dispersed force over the midline at 15 inches I'm just going to use a small piece of carbon fiber sheet because I don't want to use something there that's going to unduly crease the paper on the top and skew the results I'm measuring this by pushing down at the center point of the spar measuring half of the force at the scale and of course the other half of the force is borne by this other fulcrum at the other end so whatever measurement I acquire here at the scale I will double it to reflect the force that was actually placed on the center starting at 78 millimeters starting to wrinkle there's where it starts to crush at 660 millimeters so 18 millimeters X we'll do the modified flight test with the tape starting at 80 millimeters also crushes at about 60 millimeters now it's still somewhat intact but wrinkled and deformed finally the EI design starting at 80 millimeters 55 millimeters I got a little wrinkled but it sprung back pretty well so all three designs deformed at about two centimeters so just a little bit short of an inch and the failure modes were a little bit crisper in the flight test designs in that there was a distinct point at which it broke in the EI design it would became more and more mushy as I progressed each of them actually sprung back somewhat to the original form and manifested by just a little wrinkle in the top wrinkle in the top and invisible one in the foamboard spar right there and the flight test design and the same here this one actually wrinkled in a couple of places whereas the taped version only wrinkled directly underneath the upper skin surface right here and the EI design there's a very crisp wrinkle and upper surface there are some very slightly perceptible wrinkles in the upper former and a very slightly perceptible in the upper part of the mid former these are all of the members of the spar which are subject to compression forces and the upper part and then in tension the lower half of the middle one the lower former and the lower skin simulator right here don't seem to have any visible damage the subjective failure modes were a little different between them the flight test design seemed to fail a little bit more crisply there was a noted end point at which it gave way slightly less in the modified taped flight test design and was a much more progressive and spongy and the experimental airlines design it was kind of hard to tell where the end point was as I got down to about three centimeters continued to give less resistance but didn't really buckle in a certain way now that was to measure sort of in flight increasing forces now let's see what would happen maybe in a crash I'll just apply some just brute force of this thing bend it over my thumb and see what happens so that just folds in in one spot creases this bar former in the middle and becomes useless the taped flight test design about the same a little bit more dispersion of the wrinkling in there actually all the parts actually stay together doesn't come unglued anywhere and the ei design that actually broke the foam on the bottom again more tension there and then made one discreet a crease right in the middle all the way through essentially compressing the lower sections as the paper gets compressed together right there I designed the arm and wing removing the paper from the inner surface of the upper wing skin so to provide a smooth curve on the upper surface camber just like all scale aircraft so that the sequential compression of oncoming air and decompression to provide lift over the upper surface of the wing is nice and smooth and it's very attractive and aesthetic the flight test design uses in some ways simpler but in some ways a little harder to execute crease and fold at a number of areas to allow that camber to happen now admittedly at the low Reynolds numbers low air speeds and overpowered airplanes that we use in model aircraft this probably performs 90% or better in relation to the to the smooth arm and wing it probably just doesn't really make that much difference but the aesthetic between these for me is a deal-breaker for this faceted design it just doesn't look quite like a real airfoil to me even though I'm sure it works just fine so in conclusion for heavier and more utility type airplanes like long-range fpv cargo carriers and other kind of more burly planes I'd recommend the flat stacked ei style technique which is also very slightly easier to construct and more forgiving of imprecision and cutting the actual formers themselves it also allows the ability to easily incorporate a spar channel like this if you have a wingspan let's say greater than 40 inches up to 90 inches and you can easily slide a carbon-fiber tube in that spark channel for lighter more park flyer types which are not subjected to heavy loads I would go with the flight test design with the vertically oriented former and spar members which doesn't have the ability to easily incorporate a carbon fiber channel however with wingspans of 45 inches or less and lightly loaded this is probably very strong for most people's needs so I hope that information was a little bit useful for you I like to hear your ideas and experiences too and if you of course have any improvements to either of these designs or new one please do share them with the community and let us know so we can use them ourselves Cheers

Channel: Experimental Airlines

Views: 132,027

Keywords: armin, wing, foamboard, rc, radio control

Id: RSAIZrETzU0

Length: 18min 25sec (1105 seconds)

Published: Sat Feb 20 2016