fixing clanks' holes/jeep tj help

[baldlobo]

Originally Posted by aerohead

typically,compressibility effects are not encountered in automobiles until above 250 mph.
Pressure differentials will cause lift whether a function of velocity or separation/turbulence.

yup, i know; what i said was in reference to what someone else said.

yes, but both of those are normally produced more over top of a vehicle, then under; are they not?, so lift is not an increase in pressure under a vehicle but a loss of pressure over top of the vehicle.(even without a skinned under carriage)

where as an air dam is used more to equalize the pressures bottom to top(along with decreasing cd due to not hitting control arms and other low hanging parts)

[housedir]

great!

[aerohead]

Originally Posted by baldlobo

yup, i know; what i said was in reference to what someone else said.

yes, but both of those are normally produced more over top of a vehicle, then under; are they not?, so lift is not an increase in pressure under a vehicle but a loss of pressure over top of the vehicle.(even without a skinned under carriage)

where as an air dam is used more to equalize the pressures bottom to top(along with decreasing cd due to not hitting control arms and other low hanging parts)

*On most modern vehicles there won't be any flow separation until somewhere in the rear so typically it's not an issue for front lift.
*The JEEP may have separation in the cowl area as well on top of the roof,downstream of the A-pillars.Both these locations would produce lift.
*The undercarriage of the JEEP would register one of the highest drags for production vehicles.Air attacking from ahead would encounter a torture-chamber of assorted mechanical obstructions,creating much turbulence.The turbulence makes it impossible for kinetic energy to be converted back into static pressure behind in the wake which raises the pressure drag.
*The airdam forces air to go over,around,or below the dam,capturing an inverted pool of dead air between the bottom of the dam and bottom of vehicle.This 'pool' of air travels along with the vehicle with 'active' air moving unobstructed below it to the rear,and beside the vehicle in a straight path with no circulation.
*By increasing the velocity of the active air under the vehicle,it's static pressure is reduced which helps retard lift.
*The air under the vehicle can never be as 'active' as air on the sides or top due to interference with the road boundary,but the airdam can help 'optimize'
conditions,even with a perfectly smooth belly pan.
*ANY lift is induced drag,and the engine will have to burn more fuel to overcome it.
*Since Dr.Alberto Morelli's Pininfarina CNR 'banana' car of 1978,it's been possible to design zero-lift automobiles with excellent directional stability.

[baldlobo]

Originally Posted by aerohead

*On most modern vehicles there won't be any flow separation until somewhere in the rear so typically it's not an issue for front lift.

i agree

*The JEEP may have separation in the cowl area as well on top of the roof,downstream of the A-pillars.Both these locations would produce lift.

past the A-pillar, yes; the cowl area, probably has a dead spot bigger then a normal car's due to the windshields steep incline but it's not before the front axle(weight distribution is 60/40 or so;2500lbs/1500lbs). smaller pockets of instability probably are around the hood hold downs.

*The undercarriage of the JEEP would register one of the highest drags for production vehicles.Air attacking from ahead would encounter a torture-chamber of assorted mechanical obstructions,creating much turbulence.The turbulence makes it impossible for kinetic energy to be converted back into static pressure behind in the wake which raises the pressure drag.

yes; steering linkage, track bar, control arms, drive shaft(that's just the front). But that's why the skid plate cover's about 80-90%(what it's not covering is the steering linkage ends, knuckles, springs, and roll bar end links) of the front end allowing for the dead space between it and the gas tank.

all components of the rear suspension are in board of the frame

*The airdam forces air to go over,around,or below the dam,capturing an inverted pool of dead air between the bottom of the dam and bottom of vehicle.This 'pool' of air travels along with the vehicle with 'active' air moving unobstructed below it to the rear,and beside the vehicle in a straight path with no circulation.

yes, my skid plate is pointed downward; unobstructed airflow yes

*By increasing the velocity of the active air under the vehicle,it's static pressure is reduced which helps retard lift.

already said that earlier to sven; it's part of bernoulii's principle

*The air under the vehicle can never be as 'active' as air on the sides or top due to interference with the road boundary,but the airdam can help 'optimize'
conditions,even with a perfectly smooth belly pan.

yes

*ANY lift is induced drag,and the engine will have to burn more fuel to overcome it.

yes, along with the big parachute of a wake the jeep is pulling behind it.

*Since Dr.Alberto Morelli's Pininfarina CNR 'banana' car of 1978,it's been possible to design zero-lift automobiles with excellent directional stability.

yes, within what a manufacture originally designed it for; at a certain point flow separation will happen, just probably not reached by joe q public.

as for the sides the hood channeling air to the sides, 3.25" fender flares, side steps, door hinges, and mirrors help to produce big wakes along each side.

[aerohead]

Much to do,but many gains to be made.'could be a lot of fun doin' it.
17.97 is pretty good isn't it? Seems like you could get into mid-twenties without straining.
Did you see the tricked out Cherokee vs Prius coast test with Stunt Busters video?
There's a lot of low-hanging fruit out there.

[baldlobo]

yes, considering it's all city; epa rating is 14 city. currently hoping for 19.5mpg(400km on 14gals(54-55l)) on the current tank.

yes, i did; i think they over did it.

i bought some airtabs, yet to put them on; but due to the vents on the back of the hardtop, i only think top of the hardtop and bottom of the gastank can be done with them.

[baldlobo]

haven't updated in a while, so here are some pictures.

front skid plate(aka air dam)



fish eye mirrors help


moved my intake temp sensor


and doing some testing on airtabs(top and bottom)



last trip mpg was 23.4mpg

cheers

[baldlobo]

ok a couple of points

1. i think the temp sensor placement is giving more accurate mpg vs. it's original placement in the the manifold(also getting heat soaked)

2. If you have a lead footed SO don't put airtabs on any vehicle(used 1/8th of a tank for 20km); gub(gas until brake) driving sucks fuel.

3. i think the airtabs might be helping with png(60-25kph vs 60-20kph, same 300m google says 18secs)