Cd deletion
 

I think we'ce all seen the aero civic but I think the aircraft the AR-5 and it's follow on the AR-6 racer may have taken things a little further... and all starting about 16 years ago!

Now sadly I can't post a link officially until I've posted 5 posts here.. this is my fifth, so I hope the moderators will tolerate a little bending of the rules

the URL is

dubdubdub dot AR-5 dot com

Just to summarise why I've posted this.

This aircraft achieves 207mph on just 65hp!... by my calculations that's 32mpg @ 207mph (assuming 20% thermodynamic efficiency)... hence the title of this post. More importantly he seems to have gone further than just making it slippery, he did some very careful design around joins between sections etc.

It made me wonder if the same technique could be used on belly pans (keep the area of the gap beneath the car the same at every point along the length, so raise the pan a little at the axles.. if there's room of course).

Derek

Some very interesting reading there Derek. Thank you.

What a cool plane in more respects than one!!! Not only is it beautiful aesthetically, but it weighs less than 500lbs and has a almost a 600 mile range on 12 gallons of fuel. I WANT ONE!!!

4gph @ 175mph (air speed) = 43.75mpg
3gph @ 165mph (air speed) = 55mpg

And he calls this "thirsty" !!

He says the plane has a Cd of 0.016 and a frontal area of 0.88 ft^2, giving a CdA of only 0.01408!!! Imagine what the numbers are without the wings and aileron winglets!

He attributes most of his low drag design to meticulous reduction in interference drag. He worked very hard to make sure the drag of each component of the exterior did not effect other parts.

There is some very interesting reading there for sure.

Very light with hardly a flat slab to it (less than a square foot !) and excellent workmanship in building and finishing it.

Now compare that to your car.
Lots of flat slabs - often of the see-thru kind ;)
Rubbers sticking out into the breeze to hold those windows.
Panel and door gaps.
Windshield wipers that for the most part aren't aerodynamically covered (despite that it has been known for years that they also cause additional injury to pedestrians when exposed).
Sharkfins that are mounted as standard even if none of the equipment that requires them is installed in the car.
Roofrails standard with free option to delete them - rather than the other way around.
Dirty underside, though all manufacturers know it'd improve the mileage to clean up that mess.

The list is nearly endless.
They all like to keep something behind the cupboard to make future improvements, rather than apply known mods NOW and research others for future use.

Maybe governments should force the simple measures that are known to improve mileage upon the manufacturers as must-do measures, rather than do-as-you-please.

1. Note the engine cooling exit vent on the AR-5. At the very least, this is a good example of how engine air could/should be vented from a car engine bay back into the slipstream and past the belly pan.

2. Remarkable as it is, the AR-6 is still probably not as efficient as the Strojnik Laminar Magic.

3. Google for "Davis DA-11" and note that even without much aerodynamic refinement, Davis' little ~165 lb. plane got over 100 mpg cruising at ~130 mph on a 20 hp lawn mower engine. What would the DA-11 do with aero cleanup of landing gear, wing roots and tips, etc.?

I have a vhs tape set on this airplane. Very useful for construction techniques and aerodynamics. He shows how they repaired the airplane after a crash.

The big problem is that the work is done in composite and is not very healthy to work with and work proceeds very slowly while the epoxy is curing.

I certainly don't think the government should be the nanny behind society.

The 0.88 is equivalent flat plate area, which has a Cd of 1.0 or 1.1 depending on who you ask. So the CdA is 0.88 or 0.968. The convention with aircraft is to compute the Cd based on planform area, so 0.88/.016 = 55 sq ft of planform area (silhouette viewed from the top).

motorcycle
 

Kenny Lyon's Cd 0.11, Becker-Lyon motorcycle streamliner does 207-mph with 150 Bhp,in ground-effect with tires on the ground,so 207mph with 65 Bhp sounds very reasonable for an aircraft.
The mpg would vary as a function of load and BSFC map of course.
I don't know about the Cd figure.Abbott and Von Doenhoff ( sp?) warn about using any aeronautical values outside of 'flight conditions.'
My opinion is that Cd 0.016 should be 0.16.The fuselage cannot be lower than Cd 0.04 in free flow and that would put it at Cd 0.08 in ground proximity.Adding 'skinny' tires would push it to Cd 0.12,same as 1953 MG EX 181,or GM Sunraycer ( 1987 ).
If it's a 'laminar' aircraft you can increase the Cd significantly,as it is not possible to have laminar flow above critical Reynolds number in ground-effect.( 20-mph up ).

"If it's a 'laminar' aircraft you can increase the Cd significantly,as it is not possible to have laminar flow above critical Reynolds number in ground-effect.( 20-mph up )."

Do you have a reference, or a rationale for that? Thanks.

Bob,

I was thinking of you when I went to the AR-5 website and was reading about just how *smooth* the aircraft was shaped.

Flashed back to our earlier discussion of how laminar flow can be easily *tripped* into turbulence by any roughness in the surface finish.

Jim.