Build a Diesel Powered Trike for Speed & MPG

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Discussion Overview

The discussion revolves around the design and construction of a diesel-powered trike aimed at achieving high speeds (approximately 50 mph) and exceptional fuel efficiency (400-500 mpg). Participants explore various aspects of the project, including design considerations, component sourcing, and technical challenges related to aerodynamics and engine performance.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested
  • Experimental/applied

Main Points Raised

  • One participant suggests using a diesel engine for better torque and efficiency compared to smaller gas engines, citing examples of existing small engines that achieve good mileage.
  • Another participant emphasizes the importance of the vehicle's aerodynamics, noting that achieving the desired fuel efficiency hinges on the design of the shell and its drag coefficient.
  • Concerns are raised about the construction of the fiberglass shell, with suggestions for using air tools to expedite the sanding process and ensure a smooth finish.
  • A participant shares their experience with motorcycle construction, recommending sourcing parts from motorcycle junkyards and custom shops, and highlights the need for a comprehensive plan before starting the build.
  • There is discussion about the legal aspects of building a custom vehicle, including obtaining a VIN and ensuring the vehicle meets street-worthy requirements.
  • One participant mentions the potential for DIY solutions for the shell construction, referencing a project that could serve as a guide.
  • Another participant notes the need for a proper respirator when working with fiberglass materials due to health risks associated with the chemicals involved.

Areas of Agreement / Disagreement

Participants generally agree on the feasibility of building a diesel-powered trike but express differing views on the challenges involved, particularly regarding the aerodynamics of the shell and the specifics of engine performance. The discussion remains unresolved with multiple competing ideas about the best approach to achieve the desired speed and fuel efficiency.

Contextual Notes

Participants acknowledge various limitations, including the need for precise calculations regarding engine performance at different RPMs and the impact of drag on fuel efficiency. There are also references to the importance of sourcing appropriate materials and tools for construction, which may vary based on individual circumstances.

lyeinyoureye
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I'm trying to put together something that can go ~50mph, weighs ~150-175lbs, and gets ~400-500mpg. After poking around a bit, I've seen that a few smaller gas engines like Honda's GX22 used on a road bicycle can result in excellent mileage (~300-350mpg) and speed (~30mph) when set up appropriately.
I was thinking about putting together a diesel powered, faired, recumbent trike.
Some sort of amalgamation of this
http://www.wisil.recumbents.com/wisil/wianecki/leaning_trike.htm
this
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&category=11754&item=7521626569&rd=1&ssPageName=WDVW
and these
http://www.velomobile.de/GB/Introduction/introduction.html
would fit the bill.

The only large disadvantage is increased weight, which would be ~150-175lbs. However, the diesel engine and reduced drag should offset that penalty nicely.
Does anyone have any suggestions regarding where I should start and what I should be aware of when attempting to put together something like this?
 
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Cool idea! A vehicle small enough to get great milage but still give you some cover from the rain sounds like a very practical idea. Hope it works out. I take it this is strictly something you'll do for yourself and not as a business, or at least to start. Is that right? Are you in the US?

I built a motorcycle from the ground up. The frame for the bike came from an aftermarket manufacturer (Santee Industries). The frame came with a "manufacturer's statement of origin" which you can then take to your state's DMV to get a title. The frame comes with a number stamped into it which becomes the VIN number. Another way of getting a VIN number is to simply buy an old motorcycle frame from a junk yard and use that VIN number and title. You don't need to actually use the frame, although that's not exactly legal.

From a practical design/manufacturing perspective, it seems to me you're starting more with a motorcycle than with a bike or car. Go to a motorcycle junk yard and get some ideas first, or look online for ideas as you've already done. Also check out custom bike (motorcycle) shops and talk to the folks there for ideas. Bicycle shops would be another area to get some information at. Think about what major components you'll need such as the frame, transmission, drive between tranny and rear end, a rear end, a front end, suspension, brakes, seat, gas tank, etc... You need to put a picture of this together in your mind.

You'll need to be able to make and modify parts with small hand tools, drilling, cutting, welding. It also helps to have access to a machine shop. I found the use of lathes, milling machines and sheet metal bending equipment to be extreamly useful. Just simple things like brackets or mechanisms for controls are typically things you'll need to make or find used and modify.

To me, the cover would be the hard part. Not sure how you go about constructing the fiberglass shell exactly. There must be some premade parts you can buy, or perhaps someone here has some experience with constructing such things.

Focus on the hardest parts first, the parts you're unsure of. Have a plan on how to do them before spending lots of money. To me, the hard parts are the fiberglass cover, the frame, and the legal aspect of making it street worthy. When you feel comfortable about getting past the hard parts, buy or manufacture your frame and start working from there. Also, make sure you have a location to build this. It will probably take a few years, but it will be one of the best educations you can get.

Best of luck!
 
I'm in CA and it'll be for private use. Fortunately I already have a donor motorcycle frame from an old CB650, and insurance is surprisingly cheap, probably because it's a 200cc engine on a trike. I'll need to find out what red tape needs to be cut up, but the biggest hurtles seem to be money and and the shell.
My uncle is an avid DIY'er, he has a very complete shop and should be able to help me with this entire project. Like you stated, the shell seems like the toughest part, but judging from this it too could be a DIY project
http://www.wisil.recumbents.com/wisil/rodero/regrodero.htm
I'll post again once I figure out some of the details and get the ball rolling on this project, thanks for the help!
 
If you uncle has an air compressor of sufficient capacity, then with a dual-action (DA) sander and a linear sander (go visit a local autobody shop, they'll have these tools) and a large supply of sandpaper of coarse grit the shell shouldn't be too bad. Without the air tools, this would be a monster sanding job, even with something easy like the foam. The electric versions just don't compare, with the air tools just keep them oiled and the coarse paper fresh and even the body filler stage goes quickly and you can make some smooth shiny fiberglass parts in very little time.

Oh, and a proper respirator is an absolute must! Make sure its a proper chemical filter and not just some $5 particulate filter - inside the mask you should smell nothing, when you do start to smell chemicals you throw it away. You can get a 3M respirator at an autobody shop and they're only like $20 for a throwaway model, more for ones with replaceable filters. The chemicals are nasty smelling and harmful to the central nervous system if you read the MSDS, use the mask!
 
One quick observation. The efficiency of this hinges on the aerodynamics of the shell...
if I can design it s.t. the engine runs at say, 1-1.5k rpm @ 55mph, then I don't see a problem with getting 400-600mpg. However, if I need to use 3.4hp @ 55mph the maximum efficiency is 263mpg, and the actual probably much less. One advantage is the torque curve of the diesel, it should be making ~6-8 ft/lbs over it's entire rev range, however I'm still not sure if I can build something that will only use 250-400g/hpH @ 55mph.
Apparently, with a drag coefficient of .6, a velomobile (enclosed bicycle in tis cas) can reach ~25mph with the rider expending ~120watts
http://www.adventuresofgreg.com/HPVlog/10-24-04.html
So... I might be able to get away with ~750-1000 watts expended @ 55mph, but it all seems to hinge on the drag coefficient of the shell. :cry:
OTOH, it seems like it is doable, even with human power, the torque of the diesel engine just makes it possible to go up hills...
http://bughouse.neiu.edu/lofiversion/index.php/t1505.html
 
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