Duct Duct Go
 

It's been a while since I had an idea that is unquestionable excellent (at least IMHO).

I'll list my sources later, but I've been frustrating myself with the 3D software so I went back to what works, pencil drawing, 5 Megapixel camera, slam the brightness and contrast and reduce in the GIMP. Took about 1/2 hour.

https://ecomodder.com/forum/member-f...oanda-duct.jpg

Pix on request, but off the top

• the Austin Windmobile
• Jetopera
• Dyson Bladeless fan
• my earlier Coanda boat tail
• VW GTI W-12 650

Essentially, this: The exhaust on the flat four consists of four J-tubes joined with a 90 degree elbow. So two upward facing exhausts close behind the rear wheels. These are centered in rerouted cooling air ducts that flow upward on either side of the rear window.

<stainless steel|aluminum>

The rear wing is an aluminum tube bent to shape and then slit end to end somewhere on the inner side TBD. Small wedges are inserted and twisted to part the two edges by a fraction of an inch and then spot welded.

This become a spar for an airfoil. While the tube is perpendicular the leading and trailing edge will be more like Colani or the Porsche 959. I propose a 1/18th scale model next because I have one I don't like the color of.

Good Lord willin' and the creek don't rise, I might have more later.

I really like this look. You must really like that Golf, hey? :)

So how does this help with FE? Does it correct some of the airflow at the rear?

What are your plans for the cooling airflow? I also assume your spare stroker engine because I am unsure which flat 4 motor.

Can't deny it's one of my favorites, but this is a first approximation. I could substitute a Jim Dandy roof rack.

https://i.ebayimg.com/images/i/16263...-1/s-l1000.jpg
https://i.ebayimg.com/images/i/16263...-1/s-l1000.jpg

Piotrsko -- Stock fan and shroud, except instead of dumping air to the rear, it goes into a vertical chimney behind each rear tire. It is entrained by the exhaust and the only exit is from the approx. 8ftx2" plenum who's only exit is a slot that run around the inside of the arc.

Where I need help is determining the relation of the volume of air available vs the cross section of the duct. I think this determines the width of the slot.

I think the stock fan wouldn't be overburdened because the exhaust is 'pulling' on the cooling air. But in my original Coanda boat tail, I specified only cooling air because exhaust is corrosive and nasty.

I have the motor in my Superbeetle but I'm not cutting that up. I'm also hoarding a 36hp case but it's incomplete.

I really like this discussion and concept.
 

I remember reading about how the designers of the Japanese Zero fighter fooled with the exhaust stacks to eek out a few more knots of speed at full throttle.

Also, didn't the Mosquito Fighter Bomber of that same time period use radiator heated air to create forward thrust?

This bears investigation if we are to use ICEs .

Some call it the Meredith effect (P-51) but it was more widespread than that.

https://www.youtube.com/watch?v=9wb5YzVbTNo

My favorite example would be the Graf Zeppelin engine car that was essentially a [piston-driven] high-bypass fan jet.

http://www.histaviation.com/LZ_130_t...as_320x152.jpg
http://www.histaviation.com/LZ_130_Graf_Zeppelin.html

I would think if you know rpm you can estimate fan output based on size of opening, but I think that an approximation of that size would suffice since you ARE reducing it with the exhaust flow. Depends on how high the static pressure of the duct needs to be, but that is so far above my pay grade.......

Can't see any use for the 36 case except for old timey full restos which are gonna be really rare and involve cyphering the case serial number (I think they had one) dual port conversion are so common and cheap anymore.......

forwards thrust
 

I believe that it was the P-51 Mustang which has been reported on with respect to heated, air, coming off the oil cooler producing some thrust.
This couldn't work on a subsonic automobile, as it requires compressibility effects of transonic, or supersonic flow to be present.
The exhaust thrust, I believe, was associated with the Messerschmitt Bf 109 fighter.

I mis-spoke at #6. The FW-190 and similar had engine-driven fans on radial engines, The Meredith effect was passive.

:( P-51 Mustang, P-38 Lightning. :(

aerohead -- Thanks for giving this your attention. I'm looking at a die-cast scale model and it looks like a [no more than] 4" inverted U-shape leading edge for an airfoil.

Given, say, 250cfs of flow (25 times 10x) through the duct what should it's area be? I'd address the slot opening later.

I'm comparing a minimalist vertical hoop with something more like the Bird of Prey:

https://nationalinterest.org/sites/d...s/boeing_0.jpghttps://nationalinterest.org/sites/d...s/boeing_0.jpg

I think it could have an angled intake throat if the plenum is fed from the quarter-points instead of the ends.

The opening sketch is very interesting.

Would it operate at the aero-template profile in cross-section or be better suited to operating in free air and larger than the envelope?

One major concern would be corrosive effects of automobile exhaust on the materials.

With that much mass/surface area I can see this being all titanium although perhaps there are some high temperature plastics that are carbon based that I don't know about.

.................................................. ...................

The FW-190 video was amazing, even though I only watched the first half before many of the heavy charts came out.

It touched on "ram-air" intake only being effective on automobiles +80mph, first time I've heard that claim.

The air-intake being post fan and internal begs the question of why Porsche didn't do this on the air-cooled 911 models. Seems like an easy way to semi-supercharger/blower one's engine if there is already a powerful fan running.

On the older 911's like my car (1977), it would be pretty easy to cut a hole or slot into the cooling fans fiberglass ducting shroud and close loop it to the CIS airbox located just above it.

I thought you might like it.

I specified stainless steel and aluminum but I agree the corrosive effects are a problem. I wanted cooling air only with the Coanda boat tail, but then there was that discussion of exhaust driven cooling and I succumbed to peer pressure. :)

I don't know if the airflow available would support that large a duct. Since the boundary layer makes it half-way down the back window unassisted the final duct might not be much larger that the engine compartment lid. Mimicking the Bird of Prey, it might stretch from out to out on the fenders and be no higher that the beltline.

Sounds to me that the infamous displaced hinge on the engine hood is ideal for the inlet opening.

I have heard that CFM is thought to be 1200 through this fan, but I'm probably wrong.

There are duct sizing calculators for HVAC available online and tables available on ICBO diy house plan sites, although they may not do airspeed.

I'd heard 1500. IIRC the Porsche fan came with anywhere from 5 to 11 blades.

I'm looking at through the rear fenders at the same hinge line. The whole assembly could reverse-alligator from a new hinge line in the rear apron.

Might be more efficient to reverse cooling flow through the engine than duct it through the wheel wells, say perhaps with an underbody engine scoop. Couple of standard vent boxes joined at the fan inlet, couple of circumference vents on the doghouse ducting to the exit hole......

I believe you know the redline was supposedly 3600 rpm and everything was based on that. Porsches, being a later variant could spin much faster have different numbers. The bug street racers I knew were getting a reliable (?) 300 horse at 6 grand which would have floated stocker valves into the pistons.

Valve float = shift point. :)

Your reversed flow needs a pic. A 3D printed fan with reversed pitch?

What I've been thinking the last few days is a supplemental fan driven off the lower crank pulley with a belt drive to raise it's location (then into the bladeless duct of course).

Whoa! Type III aluminum scroll fan and the squirrel cage.

An old thread in Pelican Parts explored this, everyone agreed that with the exhaust pipes under the car pre-heating the cooling air this would be a bad idea.

One would have to flip the engine upside down to get around this I suppose.

Also the design of the fan cooling shroud is very specific and directional, another complete redesign there.

[citation needed]

http://cdn7.bigcommerce.com/s-sclwyu...=2&imbypass=on
http://cdn7.bigcommerce.com/s-sclwyu...1519343140.jpg

Dune buggy exhaust would work with a heat-pump heater out of a Leaf?

I have seen exhaust systems on sand buggies that wander all over the engine in an effort to get equal length runners. Bugger to replace injectors and plugs, BUT...... ducting does not have to contend with hot air if the inlet is in front of the heat source. Or even a teepee style sand exhaust that would dump exhaust heat into the total exhaust
Backwards rotation cam and the fan now pulls air out of the engine, need to flip the ring gear in the trannie like a reduction bussie, and I do like the squirrel cage idea. I think I get 750 cfm on 1/2 hp squirrel cage fan in my house heater, maybe not. Or you can reverse rotation with a different fan belt scheme, like the serpentines on current cars runs the cooling fan "backwards". Worse case make a backwards fan since they are a brazed assembly.

I think it's doable, not sure it would be worth the effort. Freebeard: have you installed your aero software on your new computer to test your hoop concept?

It was Cd that wanted CFD software tested. ecomodder.com/forum/showthread.php/can-you-test-out-free-cfd-software-39117.html

In my case, I'm watching for someone to implement CFD in the Blender physics engine. I do have Blender 2.92 running, but I've been using it to design geodesic domes.

The potential for CFD is there because Blender has implemented OpenVDB.

The Tepee header is an interesting case. One Coanda nozzle right about the license plate location. It would look like a Breer stinger (the one on the right)

https://ecomodder.com/forum/member-f...ed-stinger.png

Now updating this is something I could do in Blender, if I can find the Beetle model. Hmmmm, an aerospike? Minimal exhaust mixing?

design area
 

I'd have you look at ASHRAE and SMACNA, and consider your duct shape and surface roughness.
Friction 'pumping' losses will be a Reynolds number function, based on how smooth the duct surface walls, at a given flow velocity.
You'll see at SMACNA, that your losses vary remarkably with flow velocity.
You're at 15,000 CFM. Choose a loss factor to establish design velocity. Then dividing your volume by velocity will spit out the area.
It's very conditional.
The smoothest surface has a friction loss coefficient of 0.003 pounds/ sq-ft.
Your design velocity, in feet/minute, will give you your surface area.
I don't have the proper work books with me to go any further. I'll get that for Friday.
On a car, the surface area is approximately 10-X projected frontal area, making a frontal area-based friction drag coefficient = 10 X 0.003 = Cdf 0.03. Total drag, minus 0.03 = approx. pressure drag.
[Dynamic pressure ( 1/2 x rho x velocity-squared ) x Cdf ]= friction drag component.

So that textured aluminum sheet I'm hoarding is right out? Friday is soon enough, I've got other targets for my attention at the moment.

textured
 

The smoother the better, although, if it's a relatively small surface area compared to the overall area of the vehicle, we might not lose sleep over it.

No further progress on this, but I did find this video:

https://www.youtube.com/watch?v=f2UCK3pCFjk

It's all speculative CGI, but it's an interesting concept. For instance it claims 15x thrust, where Jetoptera gets to that with an additional box wing. 10x from Coanda and one level of entrainment?

edit: On the subject of quadcoptera, I've been learning about the Prandtl wing and found a mention of a Prandtl propeller! It would be longer ...but quiet. All the noise comes from the tips.

Not entirely correct. I have long lost the issue, but an article in Racecar Engineering demonstrated this effect in wind tunnel testing for F1 cars. It was very small, but I suppose it could mean the difference between running out of fuel 100 feet before the finish line vs. at the line. For road cars, such gains are statistically very likely impossibly insignificant nonetheless.

Quiet
 

Check out the Vietnam War-era, Lockheed YO-3 'Quiet Star,' battlefield observation plane and its unique, hand-carved propeller. Large diameter, low rpm. Pima Air Museum, near Tucson, Arizona,has a restored example in their collection.
And 'Q-tip' propellers.
Virginia-Class nuclear submarine propulsor ( if you have TOP SECRET clearance )

F1
 

That seems plausible. I'm not sure anymore what maximum velocities are achieved in F1, but Indycars, which are similar, approach transonic speed at Indianapolis Speedway, at least during qualification.
Transonic speed, and its compressibility effects would be a requirement for achieving thrust. It cannot happen in subsonic flow.