Foil shaped spokes

Bar Shaker

Does anyone make these?

It seems a no brainer. I used to fly microlights and you could dramatically reduce drag by putting foil shaped covers on the wires and tubes that were exposed to the airflow. A round tube had 5 times the drag of a foil shaped one.

Deep section wheels cut drag by reducing the amount of spoke cutting through the air at the fastest point of the spokes' travel - the top of the wheel, but foil shaped spokes may do a better job and give a much lighter wheel.

Does anyone know if there has been any work done on this or if anyone makes them?

smidsy

Foil is a sheet material normally sold in rolls.

Or am I missing something?

Ouija

Probably means Aerofoil spokes. Never seen any though you can get bladed spokes.

smidsy

Ouija wrote:

Probably means Aerofoil spokes.

Aahh. In which case they would be terrible, imagine all that lift

imposter2.0

How fast is your microlight going? Bit faster than a bike, I suspect. The biggest aerodynamic block on a bike is the human body's frontal area. No amount of 'foil spokes' will do a lot to mitigate that.

Bar Shaker

Sorry if I was being too technical. In aviation, the shape of a wing is called a foil. The proletariat would probably know it as an aerofoil, but I didn't think the link shouldn't be too hard to establish.

A typical microlight cruises at around 60-70mph. A bike being ridden at 30mph has spokes travelling forward at 60mph, at the top of the wheel.

Tubes that are foil shaped on both sides create no lift.

smidsy wrote:

Foil is a sheet material normally sold in rolls.

Or am I missing something?

Possibly a cortex.

danowat

Some wheels used to have carbon aerofoils on them, but I'd imagine the cost vs the actual difference between bladed spokes wasn't enough to make them viable.

Monty Dog

Bladed spokes can held on a front wheel where the leading edge is curring into relatively 'clean' air whereas the advantage on the back is considerably less. The problem is there's so much marketing BS about wheels, it's hard to seperate genuine fact from hokum. The shape and depth of the rim + tyre is more important than the spokes.

ugo.santalucia

Monty Dog wrote:

The shape and depth of the rim + tyre is more important than the spokes.

And none of them make the slightest difference in the real world...

imposter2.0

Bar Shaker wrote:

A typical microlight cruises at around 60-70mph. A bike being ridden at 30mph has spokes travelling forward at 60mph, at the top of the wheel.

still a relatively minor consideration from an aero point of view...

lawrences

ugo.santalucia wrote:

Monty Dog wrote:

The shape and depth of the rim + tyre is more important than the spokes.

And none of them make the slightest difference in the real world...

lets not go and get the world of cycling confused with the real world now. :P

smidsy

Bar Shaker wrote:

Tubes that are foil shaped on both sides create no lift.

smidsy wrote:

Foil is a sheet material normally sold in rolls.

Or am I missing something?

Possibly a cortex.

Blimey someone needs to develop a sense of humour

Crozza

Bar Shaker wrote:

smidsy wrote:

Or am I missing something?

Possibly a cortex.

Tea.on.screen

Bar Shaker

Most people miss the point of deep section carbon wheels. They don't work because a foil shape is going forward at, say, 28mph, they work because the fastest part of the spokes is replaced by a smooth surface over which the air takes laminar flow... most noticeably at the top of the wheel.

The extreme example is disc wheels, where all spokes are hidden away and the wheel creates almost no drag at all. If it wasn't for the UCI limit on section sizes for racer safety, some would try to use discs on the road, such is their aero advantage. Some TT boys due use discs on the back.

Aerodynamic drag works as a square as speed doubles. If spoke drag uses 10watts at 15mph, it uses 100watts at 30mph.

Cost issues aside (what is the cost of 34 spokes when you are paying a rider £2m a year), I am surprised no one has tried it.

Shame it's not really the sort of thing you could experiment with from a few hours in the shed.

smidsy wrote:

Bar Shaker wrote:

Tubes that are foil shaped on both sides create no lift.

smidsy wrote:

Foil is a sheet material normally sold in rolls.
Or am I missing something?

Possibly a cortex.

Blimey someone needs to develop a sense of humour

Chill Smidsy, humour flows both ways :P

sungod

there're figures here based on wind tunnel testing of cx-ray bladed spokes vs. round...

http://www.novemberbicycles.com/blog/20 ... -rays.html

assuming the results are comparable when used in other rims, for someone doing a tt then they could get a few seconds advantage, but general use seems it's going to make no difference

spokes with a more extreme aspect ratio should do a bit better, but are less common, still can't see it being a major factor in overall drag

Bar Shaker

Sungod, it would be nice to have seen how the tests were done. Just putting the wheels in a wind tunnel does not reflect how the airflow and drag work. Without explanation the results are meaningless marketing BS. Eg most people cannot get their head around the fact that the bottom of the wheel, where it contacts the road, offers no aero drag whatsoever.

That said, my previous experience would lead to the conclusion that bladed spokes would only offer a small reduction in drag.

rolf_f

Bar Shaker wrote:

Most people miss the point of deep section carbon wheels. They don't work because a foil shape is going forward at, say, 28mph, they work because the fastest part of the spokes is replaced by a smooth surface over which the air takes laminar flow... most noticeably at the top of the wheel.

Yes, lets get it right. The lack of any real world benefit you get from deep rim wheels is not caused by the aerodynamics of the rim but rather you are going no more quickly than you would on shallow rims because of the shorter spokes

desweller

The spokes are always running in the wake of the rim, so the airflow is already disturbed. Plus they are changing orientation continuously w.r.t. direction of airflow. So it's by no means a given that the air will always flow in one direction over the spoke.

Struts and wires on aircraft are generally travelling in one direction w.r.t. airflow so it is much easier to make savings.

Bar Shaker

I told you people don't get it

Bar Shaker

DesWeller wrote:

The spokes are always running in the wake of the rim, so the airflow is already disturbed. Plus they are changing orientation continuously w.r.t. direction of airflow. So it's by no means a given that the air will always flow in one direction over the spoke.

Struts and wires on aircraft are generally travelling in one direction w.r.t. airflow so it is much easier to make savings.

We can take almost all of the drag of the wheel as occurring in the top half of it and most of that in the top 25% of the wheel. The very end of the spokes is in the lee of the rim so is shielded.

If we can take 80mm of fast travelling spokes out of the air by wrapping it in, or replacing it with, a carbon shell, we will see reduction in drag.

If you want to see how much drag there is at the front of the wheel, caused by your 23 tyres, hold your index finger up and feel the air pressing against it. It's barely measurable.

desweller

Bar Shaker wrote:

DesWeller wrote:

The spokes are always running in the wake of the rim, so the airflow is already disturbed. Plus they are changing orientation continuously w.r.t. direction of airflow. So it's by no means a given that the air will always flow in one direction over the spoke.

Struts and wires on aircraft are generally travelling in one direction w.r.t. airflow so it is much easier to make savings.

We can take almost all of the drag of the wheel as occurring in the top half of it and most of that in the top 25% of the wheel. The very end of the spokes is in the lee of the rim so is shielded.

If we can take 80mm of fast travelling spokes out of the air by wrapping it in, or replacing it with, a carbon shell, we will see reduction in drag.

If you want to see how much drag there is at the front of the wheel, caused by your 23 tyres, hold your index finger up and feel the air pressing against it. It's barely measurable.

I don't understand. The OP is not about deep section rims, is it?

bernithebiker

Barshaker talking a lot of sense here - coming from aeronautics means a good understanding of aerodynamics is almost a given.

A round spoke is harder to push through the air than a bladed or foil shaped one. Fact.

It also leaves more turbulence behind it for the next spoke. Fact.

The tips of the spokes are traveling considerably faster than you are, thus increasing drag forces by the square of their velocity. Fact.

Bladed spokes are therefore clearly more aero than round ones, but the question is, are foil shaped ones even more aero? I suspect the difference is very, very slight.

smidsy

I would have thought AEROfoil spokes could actually be less efficient than bladed ones, given their increased frontal area?

But I confess to knowing little to nothing about the subject. :oops:

imposter2.0

How are you planning on getting these 'foil shaped' spokes through the hub ??

smidsy

Plus if they are aero on both sides (referring to the earlier comment about no lift) are they not essentially a round spoke at the front and a bladed one at the rear? Thus merley providing a hybrid solution that is neither one thing or the other!

Bar Shaker

Imagine a shape, in section, not dissimilar to a suspension strut on an F1 car, round at the front and tapering to a point at the back. The wheels would only rotate well in one direction. The fattest part of it would be less fat than a round spoke as the tail would add some strength.

Modern spokes hook into hubs rather than go through them (see Mavic R2R spokes) so I don't see this as a problem.