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Author Topic: Will 300 mph ever be achieved on a open streetbike?  (Read 41342 times)

Offline RansomT

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Re: Will 300 mph ever be achieved on a open streetbike?
« Reply #75 on: November 29, 2021, 08:44:57 AM »
Agree ... With "suitable" modifications on the Hayabusa (don't know about anything else), 250 - 270 mph is marginally safe.  The aero fairings that allow current "stock" framed bikes to eclipse 270 have major issues with cross winds at any speed. 
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Offline Frank06

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Re: Will 300 mph ever be achieved on a open streetbike?
« Reply #76 on: November 29, 2021, 11:33:19 AM »
I sometimes think that the fairings are *too* good i.e. they reduce drag by a fair amount but at the price of acting like big wings.  The slightest crosswind component and you get lift: sideways.
206 mph on street legal electric ' Busa

Offline fj1289

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Re: Will 300 mph ever be achieved on a open streetbike?
« Reply #77 on: November 29, 2021, 08:28:30 PM »
So many aspects to it…

How pronounced is the “side lift” from a crosswind component?

What are the effects of increased cross sectional area - both fairing and tail sections?

Sustained acceleration rate and reduced contact patch on the front wheel - and the resulting change in steering?  How dynamic is the change in handling if you ease up on the throttle and increase weight on the front in reaction to some handling issue?  What if you chop the throttle quickly if something bad is happening “right now”?!

If you do start generating a lot of “side lift” and something causes that crosswind component to exceed the “critical angle of lift” and it “stalls” - what happens to the handling of the bike?!  What happens if this flow manages to stay attached (or re-attaches) to the tail section while the “side lift” is lost on the fairing with the “side stall”? 

How does all this change if you try adding a “flat bottom” to the fairing?

I bet that is just the tip of the iceberg …

Offline scott g

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Re: Will 300 mph ever be achieved on a open streetbike?
« Reply #78 on: November 29, 2021, 09:08:11 PM »
Agree ... With "suitable" modifications on the Hayabusa (don't know about anything else), 250 - 270 mph is marginally safe.  The aero fairings that allow current "stock" framed bikes to eclipse 270 have major issues with cross winds at any speed.
Yes, Ransom, I think we are pretty close on understanding all this.

250mph - 275mph seems about the safe upper limit with the stock
Hayabusa package - and the use of a raked frame and extended
swingarm from the 260-75 range seems very helpful.

I suspect that if our bikes were running in perfectly
still and motionless air, the safe limit would go higher -
 especially with SUITABLE LSR bodywork. 

That could take us to the 296-310mph area. 

Conditions "downtrack" - especially at Bonneville - are
 hard to predict, so things get very chancy in a real hurry.

Bike-specific inputs. like putting 700hp through a swingarm
built for 300hp, or side forces put into the steering at 325mph
on  a bike built for 225mph also bring surprises.

I have a 45psi turbo alcohol bike that has shown about 700hp,
and I am afraid both to put a fast body on it, OR a fast rider on it...............

Right now, we are putting our "fast bike" efforts
 into our side-car bike based on a Hayabusa.

320mph (and still pulling on the way out) with only 550hp ..............

Offline Frank06

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Re: Will 300 mph ever be achieved on a open streetbike?
« Reply #79 on: November 30, 2021, 06:50:32 AM »
So many aspects to it…

How pronounced is the “side lift” from a crosswind component?

What are the effects of increased cross sectional area - both fairing and tail sections?

Sustained acceleration rate and reduced contact patch on the front wheel - and the resulting change in steering?  How dynamic is the change in handling if you ease up on the throttle and increase weight on the front in reaction to some handling issue?  What if you chop the throttle quickly if something bad is happening “right now”?!

If you do start generating a lot of “side lift” and something causes that crosswind component to exceed the “critical angle of lift” and it “stalls” - what happens to the handling of the bike?!  What happens if this flow manages to stay attached (or re-attaches) to the tail section while the “side lift” is lost on the fairing with the “side stall”? 

How does all this change if you try adding a “flat bottom” to the fairing?

I bet that is just the tip of the iceberg …

Tip of the iceberg indeed!  All great questions!

A couple of years ago I ran some simulations to calculate side lift using a simulator I found on a NASA site.  Somewhere I have the notes but IIRC it wasn't very hard to generate a couple hundreds pounds side force using typical fairing size and a small cross-wind component.  I'll look for those numbers and/or try to regenerate them.  We typically think of wings as being asymmetrical but symmetrical wings will generate lift if the angle-of-attack isn't zero degrees.
206 mph on street legal electric ' Busa

Offline scott g

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Re: Will 300 mph ever be achieved on a open streetbike?
« Reply #80 on: November 30, 2021, 08:21:29 AM »
So many aspects to it…

How pronounced is the “side lift” from a crosswind component?

What are the effects of increased cross sectional area - both fairing and tail sections?

Sustained acceleration rate and reduced contact patch on the front wheel - and the resulting change in steering?  How dynamic is the change in handling if you ease up on the throttle and increase weight on the front in reaction to some handling issue?  What if you chop the throttle quickly if something bad is happening “right now”?!

If you do start generating a lot of “side lift” and something causes that crosswind component to exceed the “critical angle of lift” and it “stalls” - what happens to the handling of the bike?!  What happens if this flow manages to stay attached (or re-attaches) to the tail section while the “side lift” is lost on the fairing with the “side stall”? 

How does all this change if you try adding a “flat bottom” to the fairing?

I bet that is just the tip of the iceberg …

Tip of the iceberg indeed!  All great questions!

A couple of years ago I ran some simulations to calculate side lift using a simulator I found on a NASA site.  Somewhere I have the notes but IIRC it wasn't very hard to generate a couple hundreds pounds side force using typical fairing size and a small cross-wind component.  I'll look for those numbers and/or try to regenerate them.  We typically think of wings as being asymmetrical but symmetrical wings will generate lift if the angle-of-attack isn't zero degrees.

This is some pretty good thinking !

If one unexpectedly encountered a side wind of 10 mph - which is not so unusual at Bonneville, or even airport tracks, that is a side-force showing 15 feet per second of direction change.

With NO input from the rider (who may even be unaware of the wind) the bike will move toward the side of the track 15 feet in the 1st second, a total of 30 feet at the end of the 2nd second........etc.

Most of us who go over 250mph while fully tucked in prefer to not make sudden moves at those speeds.

HOWEVER, if we wait long enough - we are off the track........

Offline FlaminRoo

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Re: Will 300 mph ever be achieved on a open streetbike?
« Reply #81 on: November 30, 2021, 04:39:51 PM »
Hayabusa, ZX14, etc, chassis with rider, see center of gravity average at, and just below steering head heights, this combined with 23* 24* rakes, serve to exacerbate high speed handleing
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Offline scott g

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Re: Will 300 mph ever be achieved on a open streetbike?
« Reply #82 on: March 15, 2022, 08:26:29 PM »
Hayabusa, ZX14, etc, chassis with rider, see center of gravity average at, and just below steering head heights, this combined with 23* 24* rakes, serve to exacerbate high speed handleing

I think that's several very good points.

The Honda MotoGP bikes showed that the center of Gravity (CG) can be TOO low, but now EVERYBODY is using "shape shifting" to lower BOTH the front and rear of the bike - by possible 4-6 inches !

Makes me wonder about the electronics .................

The leader of that stuff is DUCATI.  At the last MotoGP, a FACTORY MotoGP bike - think $3,000,000 and a possible world championship went AWOL on track.  The rider pulled in, saying the bike seemed to not know where it was on the track, and was messing with the tuning (Including the "ride height"), and it became unridable.

Would YOU be apprehensive if your bike "Dived" the front end six inches at 230 mph without your input ?

If the Center of Pressure CP - think the CG, but for the wind - is too HIGH, it will tilt the bike AWAY from the wind.  Will it cause the bike to counter-steer INTO the wind?

If the CP is low, will it push the bike the other way, and what effect does THAT have?

Likewise, if the CP is FORWARD of the CG, will it tend to blow the bike off the track ?

Is it better to have the CP BEHIND the CG ?

At 50mph, who cares.
 
At 300 mph, it might be more attention getting .............