JPN Fairing aero discussion

dennisgb said:

Dances with Shrapnel said:

I lost a race weekend chasing electrical problems which included an inadequate needle jet...

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I'm very confused. Is this some sort of racing trick? Electric needle jets

Sorry I couldn't help myself...It all ran together.

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They often give the same symptoms, particularly on two strokes. You can get a miss by having mixture too lean on the needle, or due to the ignition system. Typically if you get a miss on the tight twisty stuff where you have larger variations in throttle openings, you will pick up the source that way. On a two stroke you can 'cough a crank' or get a seizure as you back off - four stroke motors are safer.

Dances with Shrapnel said:

pommie john said:

I'm happy to say that my top speed is well off that chart

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Go to the formula of drag force or drag power and you can calculate and plot the same; create your own graphs in a spread sheet if you are inclined to do so. Phil Irving's Tuning for Speed
has a simple calculation for the same but it is in scary Imperial Units which at least one individual on the forum chokes on. Plenty of SI references for the same.

In the end it is all academic as frontal area and Drag Coefficients are to calculate/predict power/speed relationships; you already have that if you know you rear wheel HP characteristics. Bottom line is trial and error regardless of whether you know your Drag Coefficient or frontal area.

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Perhaps the differences you are experiencing are similar in magnitude to those created by differences in tyre pressures ? The difference between faired and unfaired is usually substantial, I don't know about the rest. I think the law of diminishing returns might apply. I suggest that if the carburation is slightly rich the bike will probably slow as much as the improvement you are seeking, so when you measure the speeds of various bikes through a speed trap what you see might not be what you get - especially if some bikes are getting on the gas earlier in the previous corner, or if it is a high speed bend staying on the power better like a Ducati 900 . What you probably need to do is set your bike up with the various fairing configurations without changing anything else then do the speed trap thing several times with each fairing configuration. You might need two speed traps - one at the start of the straight, and one at the fastest point on the straight, just before the braking point.

The 170 mph 750 was ridden by Normal White IIRC but its was a magazine sponsored timed run in France and even Normal does not believe it either. I only know what I read in magazines, which have discussed issue of in line 4 width and the drag their radiators cause so BWM and Guzzi have similar drag issues. The Texas Mile was very educational on all issues of wind drag, time of day heat/humidity to strapping down low, covering by fairing changes and tape over vents and seams and radiator openings. The few cycles that did top 200 mph had rather more than 200 hp on tap - by boost and by NOX spraying. I'd toss out the two outliers.

by pleading with vacationing racers here on paired down Yama's an Suzik's in matching factory colored leathers and no chicken stripes, to please see what their speedo's read following me in one of the few straights here ~1/2 mile long with no driveways or intersections - told me they saw 130 before they chickened out but would not stay with Peel which ended up 100 yrd ahead before pulled over. Smith guage was very stable reading 135 which don't agree with the gearing ratios but somewhere above 125 I think the rear 129 mph rated dual purpose cleated tire expanded a good bit to raise ratio. Going by the color graph this implies Peel had ~75 rwhp if cd under 5. This was my guessimate too going by past P!! and Peel's distinctly better pull than my 70 hp 6 spd modern with Givi Bikini fairing, which felt like a dog after 80's compared to Peel. Oh yeah these moderns had streamlining sports fairings and humps in their jackets but Peel sure didn't. Tucking my head-helmet down on clock faces the only time I held on to Peel's top out showed about 3 more mph rise of spdo needle to stifle vision blurring wind buffeting.

In late fall i saw a red Duci 1198 followed by SR1000 BMW, Aprilla V4 and GXSR's stop at my office drive way so went out to oggle them to find they were looking for me too see it was some the guys I run with in '03 and were hot to trot but alas nothing to ride then. Peel may be unbelievable here but left lasting impression on dozen of other disappointed hot shots.

Here's '03 winter outfit I'd cruise showing 120 where I could see ahead in such still air I'd flick my bic to light my cig over the ton and didn't need but sweat shirt under jacket to be fine in 20'F commutes which I enjoyed the wide eye looks of those I passed in enclosed cages. Cd about chart topping cuting 15 mph off top speed. After over rev' event took out cam chain ignition timing and removed top of RH exhaust lobe, would only push the barn door fairing too 110.


After hwy games so easy and sure on Peel I'd arrive home w/o the adrenalin knee tremble hit I craved so would shoot off drive way off culvert to land on gravel bar then power into the water with foot tall rock and root lips and foot ball size rocks trying not to fall down then the extra strain trying to climb back out with some momentum on careful controlled spun rear and leaning with straight steering crossed up drift to get back to level-ish pasture into shed. I always made it on Peel and it was right after a frosty glide down from home into creek to warm me up for a hwy ride - I'd puttered into shed to suit up when the throttle stuck and broken heart.

I suppose it is important to match your bike against others on a straight. However I know how I've been beaten in many races and what the other guys are riding. With a relatively low powered bike it is essential that you get into the straights going faster earlier. If the higher powered bikes catch and pass you before the end of the straight they will often get in your road on the tight corners and slow you and it all becomes that much more difficult. If you can turn under them while they are out on the ripple strip and get the run on them, it is very difficult to catch you before the end of the straight, and after that you have advantage. With my old 500cc Triton, with it's low spread of torque, you could choose where you wanted to lose the race - in the twisty bits if the gearing was high, or at the ends of the straights when you ran out of puff, if the gearing was low. If you get into the straight 5 to 10 MPH faster, and you are accelerating earlier, it takes a lot of horsepower to beat that as long as you don't run out of puff. It depends on the handling and a top end motor usually dictates a wide line in corners, only very brave people would have that sort of bike do otherwise. A lot depends on the circuit shape and whether it is bumpy. Sometimes Ducati 900 handling is better. 'Horses for courses '.

Al tri-linked Peel was under powered compared to the 600's to 1200's i contested with and definitely had to go into turns hotter than they or they could pull out of them harder than Peel - up to their wheelie tolerance, but Peel was so amazing secure in any leaned state she could change line mid turns to avoid slow pokes or hazards so really didn't have a best line around but multitude of lines and ways to take em, both tires working or just rear in contact. I mostly felt like a 125 cc that could not let off on leans to get ahead enough the straights weren't long enough to be caught before more leans left them further behind. When I let Peels hair out all contests became solo rides. I only ever got passed when I like off 40 mph to 90's d/t fear of what I'd encounter prior over crests and on initial starts of heats into hwy straights about 90 mph 900-1200 could get by me, ugh. Mostly what I liked to do with such advantage in handling was to let them get close as turns apporached then next time they saw me was 100+ yd ahead, then i'd slow again to let them get close to repeat the sensation of about to nab me then magically reappear way ahead again. The bike capacity matters more than the pilot for sure.

Steve, I don't know how you can do that stuff on public roads. With my bike you are likely to end up anywhere coming out of corners fast. It steers spot on however you would not want to lose concentration. It all happens extremely quickly, - you put your mind where you want it to go, and it is there. On a race circuit, all you have to do is miss other riders, and they are all going the same direction. In fact I always know where I can crash the bike safely when I'm getting stupid. I don't do anything smart where there are walls around.

acotrel said:

They often give the same symptoms, particularly on two strokes. You can get a miss by having mixture too lean on the needle, or due to the ignition system. Typically if you get a miss on the tight twisty stuff where you have larger variations in throttle openings, you will pick up the source that way. On a two stroke you can 'cough a crank' or get a seizure as you back off - four stroke motors are safer.

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It was truley a combination of electrical (loose coil terminals and needle jet). Once wiring was sorted out and about 1/4 lap of Road America it would run WOT but mid range and transition was trash. It was a hot low air density weekend.

acotrel said:

Perhaps the differences you are experiencing are similar in magnitude to those created by differences in tyre pressures ?

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In some instance they could be but if you have a 15 mph tail wind in the morning and a 15mph head wind in the afternoon and you are geared for the morning at someplace like Daytona or Road America in Elkhart Lake, WI, you know what, it makes a huge difference (up to 30mph). Now if everyone else is in the same boat then fine but gearing change for changed conditions is an edge you can use to make a substantial difference.

I've never experienced those conditions when racing however I would think the 6 speed CR box would be an advantage whatever streamlining you used ? Our biggest circuit is Phillip Island and the wind usually blows in from Bass Straight . The wind change you've mentioned is what most of us are afraid of in bushfire season.

Peel definitely had to most stay in upper 6000's most the time and not drop rpm below 6000 to play with the squids and racers in Ozarks, so ate up her drive train in a number of ways, so sure could of used a 6 spd. Alas my Sv650 spd speed 10.5K redline was not worth running over 9000 in upper gears as torque fell off. Peel's torque pull allowed me touring-commuting upright ease in the opens till 120 indicated before it helped much to tuck. In turns upper 80's in 2nd I had to get back and low or get throw off or rise CoG too hi or too forward for the fling rates needed. Never stuck a knee out for drag on her like the SV nor hung off either as no room for one thing. Her Vesco Rapid Transit fairing has similar shape as the BMW but likely not as low or sleek over all so may be apples and shovel comparison, unless when she's sucked down over an inch below factory height. I did replace signal with pencil beam lights and lexan covers over the cut outs. Mostly just expect wind, bug and hail protection and stereo mount + store space.
Oh yeah Peels mirrors are the classic vintage sharp cone kind but in light weight plastic mostly for looks and low mass vibration off road.

Dances with Shrapnel said:

Besides the fact that the JPN's and Motoguzzi appear to be outlier data points, my opinion is that the data points for the two JPN's and the Motoguzzi have what appear to be identical indicated horse power at their respective terminal speeds. JPN to JPN, identical - fair enough but a completely different bike with what I would consider a completely different frontal profile (JPN vs MotoGuzzi) and I have questions. Could be data entry error(s) or some pure marketing BS.

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Fairing efficiency could also account for it ? Certainly the guzzi = wind tunnel developed, at full size.
I've been for a spin on a Rickman that certainly had less than 100 bhp, and was good for 150,
blew my 1000cc BM into the weeds. That fairing sure makes a difference.
But, obviously, didn't cover the front wheel, like the Guzzi's did.....

Dances with Shrapnel said:

but it is in scary Imperial Units which at least one individual on the forum chokes on. Plenty of SI references for the same.
.

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It was you denying the SI references validity that was the point of disagreement in that discussion, lets not mince words...

Rohan said:

It was you denying the SI references validity that was the point of disagreement in that discussion, lets not mince words...

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I even went back and reread my posts to see if something could have even been construed as "denying the SI references validity". No, nothing. I embrace SI as well as Imperial.

I have concluded that I am not the source of all this confusion.

Rohan said:

Fairing efficiency could also account for it ?

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By fairing efficiency, are you referring to Coefficient of Drag?

Rohan said:

I've been for a spin on a Rickman that certainly had less than 100 bhp, and was good for 150,

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Which is on the high side of the cluster of data trend of the subject graph, not an outlier unless it was substantially less than 100 bhp.

Perhaps the Guzzi had improved their CoD by that 12500 % mentioned.
Since they wouldn't be using pounds shillings and pence.
Oops, wrong system, again...

A well designed fairing may possibly get down into the 0.30 range, from other fairings mentioned.
Some of these LSR cigars (Land Speed record missiles) must be down under that even ?

Rohan said:

Fairing efficiency could also account for it ?

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Dances with Shrapnel said:

By fairing efficiency, are you referring to Coefficient of Drag?

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That is what the drag coefficient is indirectly measuring, is it not ?

Or are we referring to it solely as a number to plug into an equation to make the answer 'come out right'...

Dances with Shrapnel said:

Besides the fact that the JPN's and Motoguzzi appear to be outlier data points, my opinion is that the data points for the two JPN's and the Motoguzzi have what appear to be identical indicated horse power at their respective terminal speeds. JPN to JPN, identical - fair enough but a completely different bike with what I would consider a completely different frontal profile (JPN vs MotoGuzzi) and I have questions. Could be data entry error(s) or some pure marketing BS.

.

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I took the data points from various sources and put them into a spreadsheet that drew the chart. The reason both the JPNs have the same HP is that there are no reliable sources so I guessed at 72 HP which is what the works motors were claimed to be making. The Guzzi made about the same power as the JPNs 72-78 depending where you look and went to 171MPH to 187 MPH depending where you look.
Those data points may not be totally accurate, but they are so far from the trend they have to be questioned.

Rohan said:

Perhaps the Guzzi had improved their CoD by that 12500 % mentioned.
Since they wouldn't be using pounds shillings and pence.
Oops, wrong system, again...

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Now you are trying to save face with lame humor.

Thank you sir, may I have another. Did you forget that the 12500% is something you came up with in a state of utter confusion, not me. Of course we want to conveniently overlook those important facts. keep digging your beyond rock bottom

Rohan said:

A well designed fairing may possibly get down into the 0.30 range, from other fairings mentioned.
Some of these LSR cigars (Land Speed record missiles) must be down under that even ?

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Yes, the Guzzi or other bikes might have a chance with streamlining and a low achievable CoD but the three subject data points seem to be outliers when considering the other two are JPN's. In a dull moment I might have a go at a 0.30 and see what the calcs show.

Rohan said:

Rohan said:

Fairing efficiency could also account for it ?

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Dances with Shrapnel said:

By fairing efficiency, are you referring to Coefficient of Drag?

Click to expand...

That is what the drag coefficient is indirectly measuring, is it not ?

Or are we referring to it solely as a number to plug into an equation to make the answer 'come out right'...

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Drag coefficient does not do "measuring", it is a measure. By the way - love your non committal style of putting a question mark after just about everything - can't be cornered, eh?


Let's do this right out of the Rohan play book. :lol:

Rohan said:

When someone throws jargon into the conversation, THEY need to define it.

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Define "fairing efficiency". :lol:

pommie john said:

Dances with Shrapnel said:

Besides the fact that the JPN's and Motoguzzi appear to be outlier data points, my opinion is that the data points for the two JPN's and the Motoguzzi have what appear to be identical indicated horse power at their respective terminal speeds. JPN to JPN, identical - fair enough but a completely different bike with what I would consider a completely different frontal profile (JPN vs MotoGuzzi) and I have questions. Could be data entry error(s) or some pure marketing BS.

.

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I took the data points from various sources and put them into a spreadsheet that drew the chart. The reason both the JPNs have the same HP is that there are no reliable sources so I guessed at 72 HP which is what the works motors were claimed to be making. The Guzzi made about the same power as the JPNs 72-78 depending where you look and went to 171MPH to 187 MPH depending where you look.
Those data points may not be totally accurate, but they are so far from the trend they have to be questioned.

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Agreed and reasonable assumptions, especially for the JPN's as I am familiar enough with them. I was thinking that maybe the Guzzi on the other hand could have been a larger displacement and/or streamlined but that is really giving a big benefit of the doubt. Good stuff.