Ideas for aero-ing a piano hinge?

[aerohead]

https://ecomodder.com/forum/member-a...speed-aero.jpg

Originally Posted by Talos Woten

Howdy all!

I'm currently designing a nose cone for Champrius. The key to the nose cone will be a variable area inlet for the radiator right at the tip. I've bought these piano hinges:
https://www.amazon.com/dp/B07PP1XXQT
and plan on having a 24" x 3" opening for the inlet, with one hinge on top, and the other on bottom. That will give me 0-72 sq ins which should be enough to cover all cold to hot weather conditions. Viewed from the side, it's basically the leading edge "front" of a triangle whose base is the radiator (though with some more curvature to guide airflow).

Everything I've read says that aero-shaping for radiator inlets is crucial to proper airflow. It's the reason why virtually every grille in the world is inset slightly in some kind of curved bumper / fender. So I want to make piano hinges like little aerofoils / curve them smooth somehow.

Does anyone have any ideas on how to do that?

Keep in mind the main constraint: whatever we do has to be tough. This part will, without doubt, receive more wear and abuse than every other aeromod on the car. Not only does it have to withstand a constant +15-60 lbs per sq ft of pressure above atmospheric, it's going to get peppered by road debris and other crap while driving.

I'd also like to use a common part or material and re-purpose it, rather than having to custom make something myself. To give an example, the rest of the nose cone will be made from a Brute plastic trash can, cut up and attached to an aluminum frame. That has the natural curved shape we want already, and is tough enough to withstand the aero-abuse.

I've thought about slicing a pipe, but not only could I not find a pipe small enough, I couldn't think of a way to adhere it to the hinge. The hinge has holes in it, so we can potentially use screws if needed.

Any thoughts?

In 1963,Walter Korff, chief aerodynamicist for Lockheed Aircraft Company, and designer of the 409-mph Goldenrod LSR Streamliner, published an SAE Paper which included his design recommendation for a cooling inlet, which may have been borrowed from the 1959 Lotus.
Korff recommended that the net opening be as 'wide' as the radiator, 1/6th the radiator height, and the interconnecting, diverging ductwork be at least one radiator height in length.
To eliminate a vena contracta entry loss ( which invisibly chokes off the airflow) all sides of the opening are bell-mouthed. ( I used a 1" radius for Bonneville and highway )
If the 'pin' of the piano hinge in 'inside', mounted 'flat' between flanges of the stationary upper surface, and moving lower surface, with a 'rolled' gap-filler, the moving panel will always be closed off at the top, as a roll-top desk is, while the lower portion modulates the area of the opening.

[Talos Woten]

Originally Posted by aerohead

Korff recommended that the net opening be as 'wide' as the radiator, 1/6th the radiator height, and the interconnecting, diverging ductwork be at least one radiator height in length.
To eliminate a vena contracta entry loss ( which invisibly chokes off the airflow) all sides of the opening are bell-mouthed. ( I used a 1" radius for Bonneville and highway )

Hey aerohead!

Wowsers, thanks for the technical specifics! It turns out that I've reduplicated the wheel here. My radiator is 26" W x 12" H = 312 sq in. I found by experimentation that the lowest inlet I can safely go to is ~ 50 sq in, which lo and behold is 1/6th the height by the width. I was planning on making a 24" x 3" inlet (constrained by the 2ft piano hinge I could find) and then narrowing to around 2 inches = ~ 48 sq in. But I wanted the extra 24 sq in for extreme cases (like I drive through the desert or there is a heat wave or something).

Hmmm... this has inspired me. I'm going to ditch the hinges and go to a different design. What I've really been struggling with is how to make a rounded nose tip just like an airplane. I should stop fuddling around trying to simulate one and just get something close to one. I could probably take a 3" or 4" PVC pipe, cut it in half, and use that as the leading edge. I could probably repurpose the other sections as "wideners" for the bell mouth.

Okay. Thanks a bunch everyone. We can close this thread... I now have a clear vision of what I'm going to do. It's going to be awesome!

[aerohead]

I catch ---- for saying it, but your nose is probably already 'saturated.' There's a point where further modification will cease to deliver any additional drag reduction.
If this canopy graphic shows, you'll see that there's no Cd difference between the 'blunt' and more aircraft nose-like bubble canopy.
https://ecomodder.com/forum/showthre...rag-28206.html

[Talos Woten]

Originally Posted by aerohead

I catch ---- for saying it, but your nose is probably already 'saturated.' There's a point where further modification will cease to deliver any additional drag reduction.
If this canopy graphic shows, you'll see that there's no Cd difference between the 'blunt' and more aircraft nose-like bubble canopy.
https://ecomodder.com/forum/showthre...rag-28206.html

Ahh. If we are talking about abstract contiguous contours used as noses, then I completely agree with you that there are a wide range of different shapes that produce effectively equivalent drag.

But, if we are talking about real world cars, there is tremendous opportunity for improvement. The lead order of drag near the nose of a vehicle is the airflow through the radiator system. That has several distinct opportunities to decrease power loss:
1) The air inlet (say, reducing pressure / area that forces work over)
2) The radiator itself (say, by decreasing pressure drop / friction across it)
3) The airflow pathway (say, by using smooth ducting both in and out)
4) The air outlet (say, by matching steady state vector velocity and pressure)

Moreover, both theoretical calculations and actual mods racers make show this improvement is in excess of +20% fuel economy. That's equivalent to a well made and designed boat tail.

So I must disagree that the nose is already "saturated." It seems to me that you've mistaken the ideal airflow around a contour with the reality of airflow through a radiator. That's a big mess because air is being extracted, its properties changed, and then reinjected into the airflow through the vehicle envelope. Which further means comparisons to contours with sealed envelopes fails to capture the complexity of what's actually going on.

But the proof is in the pudding. I'll mod up the nose, post the results, and then we can see whether it was actually worth doing or not. Sound reasonable?

[freebeard]

Sound reasonable?

It's Ecomodder's ambit.

[samwichse]

Originally Posted by Talos Woten

I also looked into trying to get an actual wooden airfoil, like for a model airplane or somesuch. But they are all made out of balsa wood and I don't know if that will be able to withstand the conditions.

Many sailboats are built balsa-core. Fiberglass over balsa sandwich. The one I sail on is almost 50 years old and built this way. You just have to take care of any cracks/water entry.

But if you're worried, you could get a foamie's airfoil and glass it.

[aerohead]

Originally Posted by Talos Woten

Ahh. If we are talking about abstract contiguous contours used as noses, then I completely agree with you that there are a wide range of different shapes that produce effectively equivalent drag.

But, if we are talking about real world cars, there is tremendous opportunity for improvement. The lead order of drag near the nose of a vehicle is the airflow through the radiator system. That has several distinct opportunities to decrease power loss:
1) The air inlet (say, reducing pressure / area that forces work over)
2) The radiator itself (say, by decreasing pressure drop / friction across it)
3) The airflow pathway (say, by using smooth ducting both in and out)
4) The air outlet (say, by matching steady state vector velocity and pressure)

Moreover, both theoretical calculations and actual mods racers make show this improvement is in excess of +20% fuel economy. That's equivalent to a well made and designed boat tail.

So I must disagree that the nose is already "saturated." It seems to me that you've mistaken the ideal airflow around a contour with the reality of airflow through a radiator. That's a big mess because air is being extracted, its properties changed, and then reinjected into the airflow through the vehicle envelope. Which further means comparisons to contours with sealed envelopes fails to capture the complexity of what's actually going on.

But the proof is in the pudding. I'll mod up the nose, post the results, and then we can see whether it was actually worth doing or not. Sound reasonable?

The nose plays only a very minor role in the total aerodynamic drag.( ' Aero is more about the rear of the car than the front.' Freeman Thomas, Director, Strategic Design, Ford Motor Company, Los Angeles Auto Show, 2008 )
The 'ideal' nose was already, fully tested in the 1970s. It's DNA reaches back to 1922.
Very little leading edge radii is required to achieve attached forebody flow.
Once attached flow is achieved, no additional softening will result in additional drag reduction. By definition, the flow is 'saturated'.
The OEM Prius nose is for all intents and purposes, saturated for external flow.
I agree about cooling system drag, but that wasn't the topic.
And since I'm very familiar with the 2008 Prius, my observation would be that, there's no room inside the engine bay with which an ideal 2% racing cooling system could be realized. You want what Dr. Alberto Morelli designed for the CNR 'banana' car, but there's simply no space available. You'd have to move the AC condenser and radiator to the back of the car ( something which has been done for low-drag concept cars [ Ford Probe-IV, GM Precept ]).
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Streamlining can reduce cooling load and radiator size, but not air conditioner load condenser size. And it's preferred to keep heat exchangers in the vicinity of the forward stagnation point.
Heat exchangers are designed for 100% turbulent flow, to achieve optimum heat rejection. They MUST have some degree of flow resistance.( if you have a conventional gas water heater you'll find a turbulator stuck inside its chimney )
You might find a more expensive radiator, made from a more expensive metal, with a higher heat transfer coefficient, which would allow some down-sizing. Porsche has done this.
If the distance from the cooling inlet to the face of the heat exchangers is less than the radiator height, then extending the nose forwards to achieve that distance would be warranted ( I did this on the Chevette, CRX, Dodge pickup, and Toyota pickup ).
This reshaping itself doesn't reduce drag, but does enable cooling drag reduction which does.
I'm going to call you out on the 20% mpg improvement due to a cooling drag reduction. There's got to be some significant context attached to a claim like that.
The worst cooling system recently reported was Cd 0.048 by PhD Joseph Katz, in 2017, on a generic Cd 0.355 SUV. The 'rear surfaces' were Cd 0.085 ( 77% higher! ). Eliminating the cooling system entirely would be a 13.5% drag reduction. On the ancient 1970s metric, you'd only be looking at a 6.7% mpg improvement.
20% would be a Bonneville car, with a sealed nose like the Cd 0.2, HOT ROD Camaro Project Red Hat, using an ice-water bath to survive the long course. Not a 'passenger' car.

[Talos Woten]

Originally Posted by aerohead

Once attached flow is achieved, no additional softening will result in additional drag reduction. By definition, the flow is 'saturated'.

Hmmm... that doesn't jibe with what I know about aerofoils on planes. Longer, thinner aerofoils do reduce drag, up until skin friction begins to dominate. However, real engineering is often about tradeoffs, in material, size, etc. That's why truncated aerofoils are often used; they are a good balance between weight and performance.

Originally Posted by aerohead

I agree about cooling system drag, but that wasn't the topic.

Hehe. Well, that might be what you were thinking, but it's not what I was thinking. I include everything at the front of the car to be part of the nose, including the radiator and wheels.

Originally Posted by aerohead

Heat exchangers are designed for 100% turbulent flow, to achieve optimum heat rejection.

We can also improve thermal exchange by slowing the flow, giving the air mass more time to transfer heat.

Originally Posted by aerohead

I'm going to call you out on the 20% mpg improvement due to a cooling drag reduction.

Oh ho! The race is on! Here's my prediction about how the 20% fuel economy increase is going to breakdown:
~3% Nose re-shaping
~5% Air Curtain
12%+ Radiator rerouting (smaller inlet, ducting, etc.)

I agree with you that (sadly) limited space makes the outlet ducting unfeasible. So I'm going to focus on the inlet duct, which there will be plenty of space for once I extend the nose by 8"+. No change in the location of the radiator.

So... would you be interested in a wager whether I can achieve that? I'm predicting that it will be the +8 mpg from 60-something-ish mpg to just over 70. I'm particularly fond of gentlemen's wagers that involves eating crow. (coughs out old feathers).

[freebeard]

Hehe. Well, that might be what you were thinking, but it's not what I was thinking.

OP's thread OP's rules we're talking specifically about a piano hinge.

[aerohead]

Originally Posted by Talos Woten

Hmmm... that doesn't jibe with what I know about aerofoils on planes. Longer, thinner aerofoils do reduce drag, up until skin friction begins to dominate. However, real engineering is often about tradeoffs, in material, size, etc. That's why truncated aerofoils are often used; they are a good balance between weight and performance.



Hehe. Well, that might be what you were thinking, but it's not what I was thinking. I include everything at the front of the car to be part of the nose, including the radiator and wheels.



We can also improve thermal exchange by slowing the flow, giving the air mass more time to transfer heat.



Oh ho! The race is on! Here's my prediction about how the 20% fuel economy increase is going to breakdown:
~3% Nose re-shaping
~5% Air Curtain
12%+ Radiator rerouting (smaller inlet, ducting, etc.)

I agree with you that (sadly) limited space makes the outlet ducting unfeasible. So I'm going to focus on the inlet duct, which there will be plenty of space for once I extend the nose by 8"+. No change in the location of the radiator.

So... would you be interested in a wager whether I can achieve that? I'm predicting that it will be the +8 mpg from 60-something-ish mpg to just over 70. I'm particularly fond of gentlemen's wagers that involves eating crow. (coughs out old feathers).

1) 'Aircraft-type bodies do have optimum fineness ratio values ( for which drag is a minimum ), and our data suggest that road vehicles do also.'
William H. Bettes, Graduate Aeronautical Laboratory California Institute of Technology ( GALCIT ), ' The Aerodynamic Drag of Road Vehicles Past, Present, and Future, Engineering & Science, January 1982, page-8.
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' low drag can only be achieved when the separation at the rear is eliminated.' Hucho, 2nd Ed. page- 16.
' (T)he optimum shape in terms of drag is a ( streamline ) half-body, which forms a complete ( streamline ) body of revolution together with its mirror-image produced through reflection from the roadway.' Hucho, 2nd-Edition, page 15.
' The fineness ratio of...5.53...corresponds to an effective ratio in free air of 2.27. This approaches the drag minimum recognizable... With a greater fineness ratio, the drag would increase again as a result of the increasing friction drag.' Hucho, 2nd-Ed. page 210.
' With a lesser fineness ratio, the drag would increase again as a result of increasing pressure drag.' Aerohead, corollary to the above.
' If we conservatively limit aft-body downward/ inwardly sloping surfaces to respect W. A. Mair's 22-degree limit, then we're limited to streamline bodies of revolution no 'shorter' than 2.5:1 fineness ratio. Cd 0.04.
Hucho, 2nd Ed. Page-61, Table 2.1, 3rd from bottom, ( from S. Hoerner's Fluid-Dynamic Drag, 1965 ).
The more you study, it will become obvious that, it'd a major mistake introducing aeronautical engineering into road vehicle aerodynamics.
Airfoils have no place.
2) Aerodynamic detail optimization is much more granular than with lumping the nose, cooling system, and air curtains, etc. together in a broad sweep. It's not done.
3) If the pump volume is to remain constant, and the object is to increase residence time within the heat exchanger, then we're talking about adding more core, or enlarging passages. Just engineer for the worse-case scenario.
If you add core, your now increasing the porosity of the car, kind of a backwards move, aerodynamically speaking.
4) We weren't talking about 'prediction.' You spoke as if referring to a bird-in-hand, prima facie evidence.
* there's little probability that reshaping the nose will net 3%. 14% was the limit, and you were already there.
* The BMW air-curtain is attributed with a 0.01% drag reduction if my notes are correct.
* If you removed the cooling drag completely, you're only looking at delta- Cd -.025. That would put you at Cd 0.235. Only a 9.6% drag reduction, and maybe a 3% mpg improvement.
5) A wager is problematic, as your testing protocol is also problematic. The hybrid system makes nonsense of conventional methodologies. Regen compounds it further. Any 'hypermiling' throws it completely into outer space.
I don't know how we'd ever sort it out into anything definitive.
This is why we have wind tunnels. And my science background dictates that this is the only appropriate venue in which to adjudicate the exercise.$$$$$$
A little salsa makes crow a fine meal! I have no reservation about the contest. We'd all learn something. It's the 'measuring' and 'quantifying' that would be the challenge.
The fellas did a crowd-funding for me back in 2014, to help defray some of the wind tunnel costs. I'm indebted to them all. In 2017 I paid for another member's wind tunnel time. I'm no longer in a position to do that.
Maybe we could pass the hat another time, and help get Champrius into the A2 Wind Tunnel. They tested the 2013 Prius and we know something about intra-tunnel blockage-ratio data variability compared to Toyota's wind tunnel. Something to think about.