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Old 09-09-2013, 03:14 PM   #81 (permalink)
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Hi there and congrats on your build.

yes it makes me think of the Dymaxion and of the wonderful VW 1....
Another vehicle that I actually own has many similarities it is a Freeway HMV. look it up on Youtube; Fred's Freeway...

May I suggest scratch proof Lexan MR10 for the windshield?
That's what my Freeway has.
For aeration inside the cabin, Cessna pop ups are used on the side.
Mine has 3 wheel drums, but discs are going in front this winter.
It is motivated by a Tecumseh 16HP.
It's a blast to drive but......not to be put in inexperienced driver's hands.
I wish you sucess.

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Old 09-09-2013, 03:17 PM   #82 (permalink)
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Quote:
Originally Posted by Old Mechanic View Post
Most decent engines without powertrain losses will do about 10-16 HP per gallon per hour. This diesel is rated at 180 grams per hour per HP. My Insight would go 40 MPH on .5GPH. 1 horsepower per hour on .5 gallon of fuel sounds very low. A V8 burns .5 GPH idling same as my Insight did going 40 MPH. I guarantee you the Insight did not got 40 MPH on one horsepower.

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That was a typo......... it should have read .5 LB per hour. That would be 12 HP for every gallon per hour............. sorry!

Howard
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Old 09-09-2013, 03:26 PM   #83 (permalink)
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Quote:
Originally Posted by sully06 View Post
Another good engine choice is a diesel motor out of a Themo King refrigeration unit. They are little 4 cyl motors made by Isuzu very economical and reliable. I've seen them put in Bobcats before. I want to say somewhere around 30hp so it wouldn't be very fast.
The Isuzu engine on a thermo king is rated down around 20 HP actually, but the same engine is used in the Isuzu pickup with a different injector pump and puts out somewhere in the neighborhood of 45 if I'm not mistaken. It's been awhile. The pump on these can be turned up to put out about 35 HP ........... It's a small pump, and with the small injectors the economy is phenomenal. Years ago I built two irrigation systems out of these that operated at an unheard of efficiency of 7/10 gallon per hour on a 1/4 mile wheel line. A superb little motor! Before Isuzu they used a Mercedes, and afterward they went to a Yanmar.

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Old 09-09-2013, 03:30 PM   #84 (permalink)
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I puzzled over what you wrote below, and then realized you meant 1/2 lb per hp-hour, not 1/2 gallon per hp-hour.

Many years ago, your figure (1/2 lb/hp-hour) would have been correct. Simple, carbureted engines are still in this range, at peak efficiency. (Of course actual, installed running efficiency is much lower, all the way down to virtually 0% when idling.)

Having designed, built, and used dynamometers, I'd amend your statement to read "Dynomometer operators are infamous for producing bogus numbers." To make any useful sense, BSFC numbers are at the crankshaft, and crankshaft dynos can be reliable and highly-repeatable.

Too many people consider best fuel burn figures to be representative of average fuel burn figures when doing back-of-the-envelope calculations. It is a very rare engine installation that comes remotely close to best fuel burn at 55 mph. Where engines like that in the Prius and original Insight shine is in their ability to produce really good numbers at low hp.

Quote:
Originally Posted by owly View Post
7 horsepower to go 55 mph.
typical internal combustion engine numbers 1/2 gallon per hour per HONEST horsepower...

Horsepower ranges mostly below the 1 HP per .5 gallon range, and very slightly above it........ There is a lot of lying done about horsepower and about fuel consumption per horsepower. If it varies much from that number for an internal combustion gas engine, someone's not telling the truth. Dynomometers are infamous for producing bogus numbers.
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Old 09-09-2013, 03:41 PM   #85 (permalink)
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Congratulations, Old Mech, on your design and progress! It looks great!
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Old 09-09-2013, 03:52 PM   #86 (permalink)
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Roll stability

Kenny's comments are very valid.......... The weight distribution is much too far aft. The optimal weight distribution would probably have the axle right under your butt in this case.
One of the reasons I always get back to rear steering is weight distribution. With the engine in the front and two wheel drive, the passengers can sit further back. The front wheels can be non steering so there are minimal fenders impinging on cabin area, and the wheels can be completely skirted. The rear wheel which would steer can be completely enclosed under the body work.
Rear steer positive stability would be achieved by putting the kingpin axis behind the contact point of the tire, and using positive caster. This would apply a force back to center that would be stronger the more centrifugal force there was, as opposed to trailing, where sideways force would want to push you tighter into the turn. I've been a Buckminster Fuller admirer since the 60's........ so I'm biased toward the Dymaxion. I only wish there was some info about his rear steering geometry available on the web.... Thus far I've had no luck. The downfall of the Dymaxion I believe was the weight distribution.

Howard


QUOTE=Kenny;379285]Given a single rear wheel, there is essentially no roll stability at the rear. Since it isn't a 'tilter', the front axle (w/two wheels) provides the only roll stability for the entire vehicle. Also, the 3-wheeled configuration gets complex when suspension is involved because the suspended front axle will allow a given amount of roll, exacerbating the tendency to lean in corners. Just a suggestion, but I would strongly encourage a minimum weight distribution of 65% front/35% rear, and a stiff anti-sway bar on the front. Yes, agreed, keep the mass as low as possible... especially on the rear half of the chassis.

At 500 lbs total, you can probably get away with using bathroom scales under each wheel. This will easily ballpark your weight distribution (given approx. 33% under each wheel). If only one scale is available, just make sure the vehicle is level by using blocks or spacers under the other two wheels when weighing.

-kenny-[/QUOTE]
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Old 09-09-2013, 04:01 PM   #87 (permalink)
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How would the contact behind the kingpin cause it to want to turn further in?

Casters work on this principle already... they always move to center when trailing...

Move the kingpin behind the contact patch of the tire, and it doesn't matter what (reasonable) caster angle you have, the forward momentum is going to cause oversteer as the road friction tries to push the tire further off center, instead of further toward center.

Edited to clarify -

I know that Macpherson strut and any other kinds of steering/suspension use the system that you're talking about, but those systems also use an offset steering angle with positive force on one tire helping the return, due to there being two tires, one always going slightly faster than the other in turns.

Now we've got one tire, trailing a single line on the surface. Don't think it's gonna work out the same way.
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Last edited by Christ; 09-09-2013 at 04:12 PM..
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Old 09-09-2013, 04:02 PM   #88 (permalink)
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Ken:
Having been involved in experimental aviation for many years, I've heard countless wild claims on horsepower....... claims that are NOT borne out in real world performance. And with those exaggerated claims come proportionally exaggerated efficiency claims. I have seen nothing to convince me that real world efficiency is exceeded 1/2 pound per HP hour to any significant extent. There is a standard automotive engineering formula for horsepower versus CFM (actual), which also holds true in real life. That is 1.62 actual CFM of airflow required per brake horsepower. Intake efficiency runs from about 80% to about 80% typically, depending on RPM. I reached almost the identical number doing math based on manufacturer horsepower and torque ratings (deriving HP from torque & RPM using the formula T*R / 5252 = horsepower)........ Needless to say there is a "truth factor" involved here also. Now that they use net HP, it would be difficult to do.

I consider dyno operators to be liars for the most part........using their machines to produce falsely optimistic results for sales purposes..............

H.W.


[QUOTE=Ken Fry;389564]I puzzled over what you wrote below, and then realized you meant 1/2 lb per hp-hour, not 1/2 gallon per hp-hour.

Many years ago, your figure (1/2 lb/hp-hour) would have been correct. Simple, carbureted engines are still in this range, at peak efficiency. (Of course actual, installed running efficiency is much lower, all the way down to virtually 0% when idling.)

Having designed, built, and used dynamometers, I'd amend your statement to read "Dynomometer operators are infamous for producing bogus numbers." To make any useful sense, BSFC numbers are at the crankshaft, and crankshaft dynos can be reliable and highly-repeatable.
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Old 09-09-2013, 04:22 PM   #89 (permalink)
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Model it........... The side force acting on the tire contact point if you are turning to the left will be to the right...... steering out of the turn. Look at a bicycle........... The straighter the forks the snakier the steering. The more rake (bend forward), the more directionally stable. I have one bike you can ride hands off all day long....... another you virtually can't take your hands off at all. Note also that all automotive steering kingpins lean back at the top (positive caster), and the more they lean back, the more directionally stable they are. I've built rear steer vehicles......Reversed trucks with loaders mounted on them, and I can tell you that you have to flip the steering axle around to it's normal orientation when you reverse the machine or you will be chasing it all over the place. Look at the way your tires lean in a turn, and this is obvious without even crawling under to look. The more you tilt your steering axle .... positive caster.... the more the contact patch moves forward relative to the steering axle......... and the more stable it becomes........ front or rear steering.


Quote:
Originally Posted by Christ View Post
How would the contact behind the kingpin cause it to want to turn further in?

Casters work on this principle already... they always move to center when trailing...

Move the kingpin behind the contact patch of the tire, and it doesn't matter what (reasonable) caster angle you have, the forward momentum is going to cause oversteer as the road friction tries to push the tire further off center, instead of further toward center.

Edited to clarify -

I know that Macpherson strut and any other kinds of steering/suspension use the system that you're talking about, but those systems also use an offset steering angle with positive force on one tire helping the return, due to there being two tires, one always going slightly faster than the other in turns.

Now we've got one tire, trailing a single line on the surface. Don't think it's gonna work out the same way.
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Old 09-09-2013, 04:58 PM   #90 (permalink)
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Very impressive. You have to give me a tour one day. I'm not far away you know

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