HPV Wheel Configuration Aerodynamics

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   Hi there,
Currently designing an HPV for a university project and need some help from some experienced HPV members.
My group is tossing up whether to use a two wheeled design (front and back) or a tadpole design (one at the back, two at the front). From your experience what performs best in terms of aerodynamics and why?

Thanks,

Ben

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benwhiting Members Profile Send Private Message Find Members Posts Add to Buddy List Visitor (new) Joined: 09 March 2023 Location: New Zealand Status: Offline Points: 7	Post Options Post Reply Quote benwhiting Report Post Thanks(0) Quote Reply Topic: HPV Wheel Configuration Aerodynamics Posted: 09 March 2023 at 8:09am
	Hi there, Currently designing an HPV for a university project and need some help from some experienced HPV members. My group is tossing up whether to use a two wheeled design (front and back) or a tadpole design (one at the back, two at the front). From your experience what performs best in terms of aerodynamics and why? Thanks, Ben

AlanGoodman Members Profile Send Private Message Find Members Posts Add to Buddy List Admin Group Club Chairman Joined: 04 March 2005 Location: United Kingdom Status: Offline Points: 8036	Post Options Post Reply Quote AlanGoodman Report Post Thanks(1) Quote Reply Posted: 09 March 2023 at 8:17am
	Hi Ben, If everything else is equal the two wheeler should be faster. It should be narrower and there is of course one less wheel giving rolling resistance. I’d suggest joining our Facebook Group which sees more activity than this forum. :)


russellbridge Members Profile Send Private Message Find Members Posts Add to Buddy List BHPC Member Joined: 21 October 2013 Location: Manchester Status: Offline Points: 843	Post Options Post Reply Quote russellbridge Report Post Thanks(2) Quote Reply Posted: 09 March 2023 at 3:06pm
	Hi Ben There's a good forum post here which contains lots on info on relative cda figures of the best HPV's: http://recumbents.com/forums/topic.asp?TOPIC_ID=6913 or have a rummage through Matt Weaver's Speed101 website - from early 2000's era and only available now via the WayBackMachine, but none of the aero-concepts have been surpassed, or explained more thoroughly to my knowledge: https://web.archive.org/web/20060705045401/http://www.speed101.com/ Good luck. Start building, get it wrong-ish, do it again a bit better...repeat ad infinitum, have fun! :) Russ

atlas_shrugged Members Profile Send Private Message Find Members Posts Add to Buddy List BHPC Member Joined: 03 November 2014 Location: Cambs Status: Offline Points: 1025	Post Options Post Reply Quote atlas_shrugged Report Post Thanks(0) Quote Reply Posted: 11 March 2023 at 6:25pm
	Ben The fastest cycles (HPVs) are the two wheelers which we call streamliners. In the UK have a look at bikes called 'Beano' and in Switzerland The Birk Comet Three wheelers are generally in tadpole format and they can be used on the road because they are more stable - a popular format is the 'velomobile' and there are many: DF, After 7, Quest, Mango, Evo K. There are also 4 wheelers which are even more stable and less prone to issues after a puncture: e.g. the Quatro velo. These are possibly a little slower that the 3-wheelers but they are more stable. If you are designing anything for the road then go for 3 or 4 wheels. If it is speed you are after on a closed quality racetrack then 2 wheels. Also have a look at all the videos featuring Russell and Barney about making their Battle mountain bike (Laidback bike report). Finally subscribe to eMembership of the BHPC or pay to download all the PDFs. There is also the online EuSupino magazine for free. Edited by atlas_shrugged - 11 March 2023 at 6:41pm

Yanto Members Profile Send Private Message Find Members Posts Add to Buddy List Moderator Group Joined: 11 July 2005 Status: Offline Points: 1521	Post Options Post Reply Quote Yanto Report Post Thanks(1) Quote Reply Posted: 12 March 2023 at 6:26am
	Hopefully I can add to the above: You ask a simple question which is faster as answered above 2 wheeled is; As for the supplementary question "why" that is much harder as I'm sure you'll appreciate, but to list: 1. Two wheeled has smaller cross sectional area so even if the Cd is the same the CdA is smaller. 2. Three plus wheels has more bearings, tyres etc so higher losses. 3. Two wheeled generally lighter You don't state usage, so if pure race machine all things being equal (ha but they're not) a 2 wheeler will beat a 3 or more. For road use however things become more complicated with 2 wheelers having to have the rider put feet down or have landing gear, usage of both these methods can cause problems with hilarious results for bystanders, but not the rider. Three plus wheels obviously more stable at low speeds and easy to hold still at lights/junctions, no problems with hill starts, and in fact can be extremely quick off the line with correct gearing as feet are always clipped into the pedals, I often beat racing snake cyclists on featherweight tracing bikes from junctions in my heavy velomobile purely because I'm clipped in and ready to go. Hope all the answers from the much more knowledgeable folk than me above help. As an aside there is a chap who did post videos of riding what is a fast 2 wheeled faired bike in Australia. https://www.youtube.com/watch?v=gjEkQZNOqb4&ab_channel=rhubarb2407 there are also videos by Shaun Moran (same person I believe as rhubarb2407) and AirpollAerialSystems. Ian