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 Why Are Tandems Slower
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bajajoaquin

USA
1 Posts

Posted - 09/16/2013 :  09:19:43  Show Profile  Reply with Quote
I'm new here, and have only sniffed around the periphery of HPV records before. I became interested enough this year to follow the posted results when I saw that Graeme Obree was competing.

I came across Larry Lem's description of building Glowworm, and was fascinated by the fact that the tandem record is 10 mph slower than the single rider. I came up with a couple reasons it might be, but was hoping someone had a more definitive answer. My guesses:

1) The "best" riders are driven to do the solo record, and don't compete in the multi-rider category.
2) There is enough additional instability with two people that aerodynamics are compromised
3) The body form is longer than it needs to be for flow to reattach itself before the tail, so any additional length is just additional skin-friction drag
4) Extra weight can't be accommodated on available tires, so there is a surprisingly large amount of rolling drag
5) A sufficiently aerodynamic body doesn't provide enough airflow inside to maintain adequate power output

I saw that Glowworm came within 0.05 mph of their previous record before crashing last week. Heart-breaking. I was rooting for you.

Don S

USA
83 Posts

Posted - 09/17/2013 :  16:52:45  Show Profile  Reply with Quote
My opinion is that a combination of 1,2, & 3 may be contributing factors but are also variables that could be overcome by the additional power of the second rider. 4 & 5 are variables that could apply equally to single rider vehicles so while they present challenges that must be overcome, they don't factor into a greater challenge for multi-rider vehicles.

It seems logical that, when power and drag are maximally balanced, a multi-rider vehicle would be capable of exceeding the current land speed record.

"it's important to understand what makes them fast. It's more important to understand what keeps them from going faster." DS
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Larry Lem

USA
40 Posts

Posted - 04/17/2014 :  14:46:38  Show Profile  Reply with Quote
I'll say that #1 and a reason not listed are the primary reasons.

Reason #6 is that multirider vehicles are more difficult to design, build, develop, transport, coordinate and store. Folks have limited time and money so they pursue the single rider vehicle record. With so few multirider vehicle efforts, unless a top team takes on the challenge, speeds for multirider vehicles will continue to lag behind single rider vehicles.

Larry Lem
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Don S

USA
83 Posts

Posted - 04/21/2014 :  18:55:46  Show Profile  Reply with Quote
Larry,
Kara's senior project may tackle this problem. If so, she will have the full resources of our team available for the project. We do not consider ourselves a "top team" but we are a committed team.
Would you be willing to add your knowledge and experience to Kara's project even if it unseated your own efforts?

Don

"it's important to understand what makes them fast. It's more important to understand what keeps them from going faster." DS
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Larry Lem

USA
40 Posts

Posted - 06/27/2014 :  10:12:18  Show Profile  Reply with Quote
Of course!

Larry Lem
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Don S

USA
83 Posts

Posted - 06/27/2014 :  12:21:15  Show Profile  Reply with Quote
Thanks Larry! Your knowledge and experience in the tandem realm will be a valuable asset.

"it's important to understand what makes them fast. It's more important to understand what keeps them from going faster." DS
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shooky56

USA
1 Posts

Posted - 09/30/2014 :  17:39:01  Show Profile  Reply with Quote
Several decades ago (early 80s?), there was a Vector(sp) project. Both a single rider and a tandem version were made. The tandem set records faster than the solo rider IIRC. The one hour record went to the tandem guys, pretty sure about that part anyway.

But the project featured committed elite athlete efforts for both solo and tandem and I'm pretty sure the tandem was faster.
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Don S

USA
83 Posts

Posted - 09/30/2014 :  20:01:13  Show Profile  Reply with Quote
Shooky,

You are correct for the time period referenced. For a while it was assumed that CdA was the more important drag coefficient and that multiple rider efforts not only held but would continue to secure the world records. At present most drag coefficients of human powered efforts are still determined by CdA.

When the first single rider vehicles went faster than the tandem record holders, the reasons Larry mentioned logically led to most of the team efforts being directed to the design and construction of single rider vehicles without a thorough understanding of the intricate relationship between CdA and CdS, which is possibly one of the more critical design elements, especially as applied to multiple rider vehicles using aerodynamic hulls.



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