Long Distance Competition/Ultracycling, Randonneuring and Endurance Cycling - How much aero penalty is caused by handlebar bags?

Many non Tri riders scoff at concerns about aero penalty. However, I have played, experimented, and used aerobars on road and tri bikes since the mid-80's and know that I can drop to the aerobars and pickup 10% more speed. And, although aero penalty increases dramatically (exponentially?) with increase in speed, it is still very real, though not quite as intense, in the 15 mph range.

So, does a handlebar bag create an aero penalty? I've got to think it has to unless it is in the same vector as the riders legs and butt, thus creating no additional penalty.

Has this effect been tested and documented? Any unsubtantiated opinions?

Thanks

RFC

Bicycle Quarterly did some wind tunnel testing a while back. IIRC they found little penalty for a front bag because a front bag typically adds little if any frontal area. Large saddlebags added more drag because they tend to stick out to the sides, which does add to frontal area. All bags add drag in quartering headwinds, because they significantly add to the area the wind "sees".

I would very much like to see pictures once you have attached your bag to your aero bars. :p

So, does a handlebar bag create an aero penalty? I've got to think it has to unless it is in the same vector as the riders legs and butt, thus creating no additional penalty.
That's a goof thought. However, if you strap your handlebar bag -firmly to your chest - you may have a point. Better yet - put the handlebar underneath the front of your jersey and you may be right!

The logic about frontal area is partially correct.

Drag is a function of frontal area and turbulence. Does a handlebar bag increase turbulence? It could.

Imagine putting a compact snow plow on a modern pick-up truck. It may not increase the frontal area, but it will create turbulence and reduce mpg's.

However, a good handlebar bag can help a rider maintain pace by putting directions and food in a convenient place.

A rider should not need to slow while eating or checking directions.

Michael

Bicycle Quarterly did some wind tunnel testing a while back. IIRC they found little penalty for a front bag because a front bag typically adds little if any frontal area. Large saddlebags added more drag because they tend to stick out to the sides, which does add to frontal area. All bags add drag in quartering headwinds, because they significantly add to the area the wind "sees".

I would very much like to see pictures once you have attached your bag to your aero bars. :p

You are absolutely right about crosswinds.