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http://ecomodder.com/forum/attachmen...1&d=1300384305 I used a cheap and old CAD program to layout the shape of a template that has the curvature of the side skirts to the tail. It turns out that the template shape can be estimated by drawing a straight line, then indenting the line by 5/8" in the middle to form an ellipse. This elliptical shape was then transferred to a large piece of foam, to form the template. The foam dimensions are: 2" x 8" x 42" The template is cut with a hacksaw blade, then sanded smooth so it "looks" consistent in curvature. I have yet to layout and make a template for the curvature from the top of the glass to the tail. This is a picture of the tail light socket. It shows what we have to work with regarding sheet metal. http://ecomodder.com/forum/attachmen...1&d=1276301037 This is a view showing where the trunk lid stops are. When the rear plastic bumper shroud comes, these stops will need to be replicated. http://ecomodder.com/forum/attachmen...1&d=1276301037 A wood block is being fashioned using a hacksaw blade into the compound shape required to fit against the sheet metal of the light socket. http://ecomodder.com/forum/attachmen...1&d=1276301037 The wood blocks are fitted tightly against the shape of the socket sheet metal. Thickened epoxy resin was added to the wood pieces to mimic the exact shape of the sheet metal. Grease was used as a mold release to get the pieces back off after hardening. The reason for the tight fit on the sheet metal will be apparent later on... http://ecomodder.com/forum/attachmen...1&d=1276301037 Jim. |
Can't wait to see some more updates. been wanting to do this to my insight for a while though I don't have the funds/time at the moment.
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The next picture shows the rear end of the car with the plastic bumper guard removed. This is down by the rear of the tire skirt.
http://ecomodder.com/forum/attachmen...1&d=1276653422 This shows that the rear air vents are actually protected by one way valves, made in a soft rubber material. Every time the trunk or door is shut, the vent valve opens briefly to relieve the cabin pressure. http://ecomodder.com/forum/attachmen...1&d=1276653422 Here is another chunk of wood that has been added to attach the previously separate pieces of wood. http://ecomodder.com/forum/attachmen...1&d=1276653422 This shows the rear of the wheel well guard. This will have to be attached to the rear extension at some point. http://ecomodder.com/forum/attachmen...1&d=1276653422 This picture shows many more blocks added to create a solid support in the tail light area. http://ecomodder.com/forum/attachmen...1&d=1276653422 Here's another view with the back hatch open. http://ecomodder.com/forum/attachmen...1&d=1276653422 This picture shows probably the most important feature of the mounting block: Smooth surfaces in which to mount the block assembly to the car when the time comes. All the attachment points are placed in areas where the sheet metal is naturally stronger based on the inherent curvature of the tail light socket. This is the most critical mounting point in the entire tail extension project. If this area looses adhesion, the entire tail will try to fall away from the car. http://ecomodder.com/forum/attachmen...1&d=1276653422 I'm planning on using silicone adhesive to hold this assembly to the tail light socket. This will accomplish two things: 1) Hold the assembly tightly to the sheet metal 2) Allow the assembly to be "pried" from the car, and the stock tail light returned to it's location, if need be. Anyone have any other ideas for strong, yet removable adhesives? Jim. |
You're right, that will be the point that's under the most stress in a crosswind, when hitting a pothole, or just supporting the weight of the extension.
Do you plan to add some kind of access door to get at the hatch switch and lock cylinder? If so, you could use the same door to drive screws through the extension and into sheet metal. I don't know of any adhesives I'd trust with this job. It might be easier to drive wood screws through the sheet metal and into the tail extension from the inside. The rear bulkhead carpet would hide the evidence, too. |
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The goal is to keep the car as stock as possible when making any of these changes, so they can more easily be undone if necessary. So there will be a hatch that opens to the rear of the car and gain access to the normal hatchback and key-lock. Unless someone has any other ideas, the plan is to use silicone caulk to create a tight fitting assembly into the tail light socket area that is held in with various screws. The wood screws are mounted almost 90° to the normal force direction, and that should keep these fasteners in "shear" more than in "tension". This orientation will minimize the possibility of simply pulling the fastener right through the sheet metal under high force. I do like your idea of getting more sheet metal involved though. It makes sense to look at options that would mount a 2x4 piece of lumber sideways across the sheet metal that runs under the rear hatch glass in the area where the top of the plastic bumper guard ran. If the wood in the tail light socket area were to come loose, at least the long 2x4 wood would hopefully give enough support to still keep the extension attached to the car. Jim. |
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Robert,
Your comments about getting good mechanical strength on the upper portion of the tail extension caused me to decide to beef up the mounting system dramatically. This also means that the extension will not be used for trunk space, as you shall see in later photos that access to the "trunk" will be limited due to the beefy mounting system. This first picture shows one way of getting more mechanical strength from thin sheet metal. The Insight is designed to be lightweight, and this also applies the sheet metal in the rear of the car. Unfortunately, this also means that attempting to mount a lever arm off the back of the car means possible trouble if not done carefully. The panels are thin enough that they easily "oil-can" when pushed in various locations. Because of this, any place there are transitions in the sheet metal, the ribbing causes the panel to be stronger in that location. We have to utilize this feature when mounting strengtheners to the car. To this end, the back of the Insight is going to be beefed up to allow adequate mounting strength for the tail extension. http://ecomodder.com/forum/attachmen...1&d=1276905944 Here is another view of a way to strengthen the sheet metal. Any place were there are creases in the sheet metal, this is also an area where lumber can be used to aid in the stiffness of the assembly. http://ecomodder.com/forum/attachmen...1&d=1276905944 This shows the reverse side of the mounting lumber, and shows how smooth the finish is here. This was done by mixing thick epoxy and adding to the back side of the lumber and attaching it to the car and allowing to setup. Grease was used as a mold release, and even then, some areas stuck and had to be carefully pried apart after the epoxy setup. http://ecomodder.com/forum/attachmen...1&d=1276905944 This shows reinforcements being added to this "tab", which will later be used as one of the main structures to hold the tail extension. http://ecomodder.com/forum/attachmen...1&d=1276905944 This picture shows the embedded 5/8 inch fastener that was epoxied in place for good strength. This 5/8 threaded rod was drilled and tapped with a 1/4-20 thread for later attaching to a 5 inch long bolt. http://ecomodder.com/forum/attachmen...1&d=1276905944 Jim. |
I'm taking notes and planning my own boattail construction in my head. There are large areas at the back of the Insight that have little structure, but there's pretty good stiffness around the perimeter of the hatch.
I think I will unbolt the center bumper cover retainer and attach the frame of my tail extension there. I will also get the bumper rebar involved. A few pieces of aluminium angle attached to those two components should be plenty to support a 3' long cargo floor with a 150lb weight capacity. This sturdy cargo area will give me plenty of rigid attachment points for the frame of the tail extension. That lower piece of lumber looks like it's designed to fit under the original bumper cover. I take it that allows you to use lots of fasteners and never worry about how to remove it from the car? |
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As usual, your observational powers are correct. Yes, the lower lumber is slowly being prepared to be "semi-permanently" mounted on the car with silicone adhesive. Several days ago, the wood was trimmed here and there to fit under the bumper cover. By using silicone adhesive, IF NECESSARY, it can still be removed, but will take a lot of digging/prying with a plaster knife. The wood will be prepared for "permanent" mounting by drilling more through holes and mounting with lots of wood screws. Jim. |
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Is it possible to sketch up something as to what you are thinking here? I'm having a hard time visualizing some of what you are saying. I can imagine someone removing the aluminum bumper and attaching beams to the same points were the bumper used to be, but would also imagine that this support would act somewhat like a diving board and flex up/down over bumps in the road, especially if it were 3 feet long. This flex would then mean that the normal gap between the extension and existing bodywork at the tail would need to be larger to accommodate the movement. Maybe you have something else in mind to make the assembly more rigid? Jim. |
This appears to be one of those threads that will get very interesting, very quickly. Keep up the great work, and I look forward to more pictures. I am fascinated at the usage of lumber in the construction of aero mods.
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I will definitely be leaving all of the original crash structure in place, including the bumper rebar. Instead of removing it that bar, I'm going to drill into it and attach a three foot long cargo floor, framed in 0.125"x1" Al L-channel. Interestingly, the bumper rebar is already at the end of a three foot long "diving board" of aluminium honeycomb, so a three foot extension would make a six foot cantilevered beam. To add rigidity to it, I will make a few triangles between it and the strong location just above your center lumber, where Honda has provided three threaded holes in strong sheet metal.
Additional truss members will be required to give the desired result. I'll just have to keep adding until it feels rigid enough. Quote:
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Of course, that speed is too low for aero work. My own testing leads me to believe that the baseline fuel economy on my 06 MT is about 95 mpg at 55mph on an interstate round trip circuit. I've pretty much commited to 60 MPH testing, so I still have some testing to do. |
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Last night I did the "metal tap test" where one goes around tapping on the metal to listen for "dead sounding" spots. Those three faster holes that you describe above are not all that solid sounding, but still the best we have to work with in that area of the tail. If you compare that area to where the aluminum bumper protrudes through, the bumper area sounds extremely dead and solid in contrast. I can't imagine not adding some type of reinforcement in the area of the three bolts to increase the stiffness there. Jim. |
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Here's a view of the new mounts below the aluminum bumper, made from 2x4's.
http://ecomodder.com/forum/attachmen...&d=1277692141] The bottom edge of the lumber is cut at the same angle as the under-body smoothing panels. http://ecomodder.com/forum/attachmen...1&d=1277692141 Small spacers were machined from 3/8 inch tubing and are mounted on all four bolts on the lower part of the bumper, due to the high curvature of the bumper in this area. http://ecomodder.com/forum/attachmen...1&d=1277692141 This view shows the spacers on the bolts, and stabilizing wood between the four 2x4's. The stabilizing wood maintains the same spacing between the lumber if removed from the car. This is important, otherwise the bolts and screws that hold the tail extension may not line-up properly. http://ecomodder.com/forum/attachmen...1&d=1277692141 Here the foam is being trimmed away from the muffler pipe as part of the heat control in this area. That's the nice thing about foam; it's easily carved. http://ecomodder.com/forum/attachmen...1&d=1277692141 A thin piece of lumber is machined for thickness and will be used as a spacer later on. The two thicknesses will be cut into two separate spacers. http://ecomodder.com/forum/attachmen...1&d=1277692141 One of the wood spacers is shown in this view, and being glued in place. After the epoxy set's-up, wood screws will make sure it stays put. http://ecomodder.com/forum/attachmen...1&d=1277692141 This shows the spacers being glued in place with epoxy. You can start to see part of the extension taking form. http://ecomodder.com/forum/attachmen...1&d=1277693210 Jim. |
3-Wheeler @ 100 mpg
Jim,I don't know about 100 mpg.
The best single 1-way run at 55-mph in the CRX was 84-mpg.That was downhill with a South-westerly from Cloudcroft,NM,@ 8,600-feet,to Denton @ around 620-feet,over around 565 miles if I remember correctly. I think basjoos has seen north of 90 mpg with AeroCivic.I'd pester him and see If he can give you some real-world prediction for your car. I thought 90-mpg would be reasonable for an Insight,but that was with the full tadpole gap-filled trailer as is in the photo archive.I estimated Cd 0.12 with that rig.And that was based on a 70-mpg baseline from a local businessman who bought a fleet of Insights for his employees. Renault claimed 138-mpg for it's Cd 0.19,approx 18.5 ft-sq.,27-Bhp,1987 Vesta II,at a constant 100 km/h from Paris to Bordeax. It's just hard to know. |
People have already broken 100 mpg on a tank of gas in the insight w/o mods. Its completely doable. :)
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Honda has extremely good quality control from car to car,and on coast-to coast runs with fleets' of cars,they return virtually 'identical' performance. It's hard for me to wrap my brain around a 30-40 + mpg variance between like vehicles. If that's what they can do,it's great,just hard to explain and to design around. |
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Daox is correct. Although even with the under-body smoothing panels, I have not gotten over 100 mpg during "normal" driving. The best I got with the car at 55 mph, was 87 mpg on a 95°F day with my Mom and I in the car, over a stretch of 150 miles or so, on reasonably flat roads. When hypermiling to work, the best on a 33 mile loop was 117 mpg, again on a 95°F day. So, will I get over 100 mpg with the extended tail? We shall see, but I would expect a gain like Metro's. Jim. |
Finally got a change to read through this thread.
Great work :thumbup: Looking forward to more updates. |
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it will be hard to sleep until you finish and have a chance to test! With your direct injection engine at high load,and tasty factory Cd,87 mpg sounds very realistic. My hope is that the EFI is smart enough to maintain the great BSFC after streamlining,when the engine will be operating at lower load. The Chrysler Airflow showed a significant gain with its 'long-tail' variant,I have to believe that you'll experience a similar gain.There's just too much data in the public domain now to suggest otherwise. I,along with no doubt many,many others,are rooting for both you and Robert,awaiting the super slinky Insights as they strike Tropos-fear along the highways.:thumbup: |
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I think that though the Insight is not much lower in Cd than the CRX, it has a more efficient engine. |
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CleanMPG, - Garage An authoritative source on fuel economy and hypermiling Scrole down the page to the hybrid section to see the long term logs for several Insights. These folks ARE hypermiling - some actually pulse and glide - and since there is little control of condition and terrain, then the results vary quite a bit. It is just their everyday commute or drive. But these are "tank" averages over a long term. Short distance controlled test runs should deliver significantly better fuel economy(FE) than any of these reported results. FE for the Insight is highly variable and depends greatly on speed, terrain, driving conditions, and operator driving skill(particulary the skill at keeping the engine in lean burn). This is one reason I have gone to so much trouble to find and scope out a 2 way test circuit that is not too hilly and will be repeatable to a high degree. I addressed this earlier, but my baseline FE for my course, in the late spring, is very close to 100MPG at 55 MPH, constant lean burn. 100MPG in warm weather, under test condition is an achievable baseline for aero testing. It could be even better if one has a flat test circuit. |
I may have to do a bit of backtracking on this FE issue:o Right after I posted, I went out and ran a test at 60 MPH target, actually achieving 58 MPH average with the turn-around, and it sure looks like the Insight really hits a wall going from 55 MPH to 60 MPH. The FE dropped from around 100 MPG to about 90 MPG, using the same test course and driving technique. It looks like beyond 55 MPH is a wall of air for the Insight. I hope to make another test drive tomorrow morning to gain more "insight";) I have removed my lower grill block, for state inspection, but that wouldn't seem to explain the rather large difference in FE.
If this is indeed the case, then there is going to be a strong benefit from a good boattail. The CleanMPG data that I referenced above is mostly by hypermilers, including mine ordinarily, though I do not pulse and glide. I simply drive fairly slow and am careful to maintain lean burn. The ordinary hybrid features like autostop and regeneration do help slightly. More to follow |
There's 16% more aero drag at 60mph than at 55mph, and you had an 11% increase in fuel consumption per mile. That sounds about right to me. You don't really hit a wall until lean burn fails at 75mpg, a little over 65mph.
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dropping below 75 mpg above 65 mph sounds like a nice problem to have! Perhaps Steven Chu will turn a glance when the new tails hit the asphalt and the meters turn backwards at the pump.:thumbup: |
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weight......
3-Wheeler, any idea on the weight estimate the extension will add?
i made an aerobed for my truck and i figure it weighed 150#. |
A bit more data. Made another test run of my circuit this morning. At 60 mph (58 with the turnaround) I achieved 90 MPG. Adjusting yesterday's results slightly for traffic, I'm gonna say this thing is closing in on 89-90 MPG at 60mph on my course with my technique. I think that "flatlanders" will do slightly better. Gonna make one more test run, probably Monday.
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At the time, Craig Vetter was in full swing with his WindJammer fairings, which weighed close to 40 lbs. My foam/fiberglass model, which actually covered more of the bike, including riders legs, weighed only 13 lbs. The tail extension on the Insight should weigh less than 30 lbs. Jim. |
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The two tail light mounting brackets are getting "angled" blocks attached to allow through bolts to rest at these angles.
http://ecomodder.com/forum/attachmen...1&d=1279330911 The first piece of foam is attached to one of the supporting embedded wood anchors. I'll have to admit, that this was pretty exciting seeing the very first foam piece in place. http://ecomodder.com/forum/attachmen...1&d=1279330911 Here's the back side of the foam, showing just how the embedded wood block is being supported. http://ecomodder.com/forum/attachmen...1&d=1279330911 Later that night, a picture with the garage door closed, since the mosquitos are out and hungry. The foam has a nice and tight fit against the sheet metal. Way tighter than the normal gaps around the doors and such. http://ecomodder.com/forum/attachmen...1&d=1279330911 Here's another shot several days later. It took about two hours to fit and glue that curved piece on the bottom side of the tail light. It's the piece with the masking tape and duct tape attached. This includes both sides of the car. The block is extremely thin on the back side due to the way the sheet metal is formed in that area. http://ecomodder.com/forum/attachmen...1&d=1279330911 This picture is showing the underside of the bumper area. Lots of foam blocks added here. http://ecomodder.com/forum/attachmen...1&d=1279410742 Those four foam blocks that are added to the bottom of this picture, will create some of the hardest work on the tail extension project. They are so innocent looking but the shape in this area is very difficult to keep true to the Honda stylist's intentions. http://ecomodder.com/forum/attachmen...1&d=1279330911 Here's a shot of the back side of the foam thus far. Lot's of Elmers Glue back there! http://ecomodder.com/forum/attachmen...1&d=1279331757 Now the assemblage of foam is removed from the car, and you can see the detail of foam shaping that went into each block before being glued. This is the summation of many hours of cutting, fitting, and gluing each individual block. http://ecomodder.com/forum/attachmen...1&d=1279331757 Here is what the underside blocks look like so far. You can see the embedded wood support blocks in the foam here as well. http://ecomodder.com/forum/attachmen...1&d=1279331757 Here's a close-up, showing the many various shaped blocks that make up the assembly. http://ecomodder.com/forum/attachmen...1&d=1279331757 Now fiberglass cloth/resin is added to the back side of this assembly and placed on the car to setup. Notice the Glad Wrap sticking out from behind the foam. This acts as a mold release to keep the epoxy from sticking anywhere on the car. http://ecomodder.com/forum/attachmen...1&d=1279410738 Here's several more blocks added along the rear skirt. http://ecomodder.com/forum/attachmen...1&d=1279411131 This shows the back side of the assembly with the fiberglass and Glad Wrap still attached. http://ecomodder.com/forum/attachmen...1&d=1279562368 Same thing for the lower assembly, and still with mold release attached. http://ecomodder.com/forum/attachmen...1&d=1279410738 This shows the curvature template that will be used extensively in an attempt to maintain proper curvature of the tail extension. http://ecomodder.com/forum/attachmen...1&d=1279332504 This is a "machined" piece of foam, using a "new technique" that was necessary to keep the intended Honda shape just above the rear skirt. http://ecomodder.com/forum/attachmen...1&d=1279562162 This picture shows the new machined foam smoothed out and added to the rest of the foam in this area. The foam template is used to glue each piece and then rechecked several more times to ensure that the angles are correct before allowing the glue to setup. Notice the white filler. These are areas that were over-filed/sanded and had to be filled to bring these surfaces in alignment with the template. The white areas took the most time to ensure they are "straight" and smooth. http://ecomodder.com/forum/attachmen...1&d=1279411344 This is a picture as the car is today. Lot's of hours at this point!! You can see the older fiberglass area and the new panels that were added more recently. http://ecomodder.com/forum/attachmen...1&d=1279411422 The end shot shows the "curvature" of the sheet metal shape just above the rear skirts. This area really takes patience to get right and the convex and concave shapes "look" extremely simple, but actually have compound radii. This takes the most planning and care to keep aligned with the sheet metal shape in this area. http://ecomodder.com/forum/attachmen...1&d=1279410738 These panels have enough foam added now, that more fiberglass will be added to support the back sides of these panels, before other blocks are again added. The masking tape on the car is used to "align" the template in the same direction as the anticipated air flow across these surfaces. This also allows some repeatability in placement of the template each time it is used to glue more blocks behind those already in place. http://ecomodder.com/forum/attachmen...1&d=1279562162 Jim. |
Beautiful work! Now that I'm looking at all of the support/attachment points, I'm wondering how you plan to removed the completed boattail. Do you plan some sort of access hatch on the top or bottom?
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I need a little help from some computer type. I see about half of the pictures, but the last half of the pictures don't come through. I have a little red X where the pictures would be in the text, but no picture. I right click and have a menu that has an option to open the picture, but it doesn't open. I'm running Vista and looking at the forum on Internet Explorer.
Thanks for any help offered! |
its not just you, looking at the errors in my browser it seems they are not transferring from the server correctly.
No clue why. "Resource interpreted as image but transferred with MIME type text/html." |
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Eventually, there will be four embedded pieces of wood on top and four on the bottom. I noticed that about half of the thumbnails are not showing as well, even though they render in full size. I might have to repost those pictures. Done! Had to repost the pictures a second time for some reason! Jim. |
Wow! Thanks for posting the pictures. They show up fine for me.
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You know about using nichrome hotwire to cut extruded polystyrene foam, right?
Also, for lofting good aerodynamic lines and perhaps for skeletal structure, have you considered using PVC pipe and glue? I don't know if standard PVC plumbers glue is compatible with the pink foam you're using, but it would sure be handy if you could use PVC pipe and glue for the skeletal structure, with pink or blue Styrofoam as filler, then sculpt with hotwire and sanding block. Sureform or cheese grater work, too. If extruded styrene foam is not chemically compatible with PVC glue, consider polyurethane foam, which should not be hotwired due to toxic fumes, but which sculpts and sands beautifully. As for using PVC pipe to loft the aero lines, somebody I think on this website had a dual bicycle Porsche 911 depicted: PVC in ~1/2" diameter makes a wonderful lofting tool. All this stuff is cheap and easy from Lowes or Home Depot. Light weight. Somebody else on I think this website did a beautiful motorcycle fairing, with heat-shrinkable Dacron skin and diluted Elmer's glue instead of epoxy. Since the part was non-structural, its strength was fine. Worth a shot for this application? |
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