Comments on the Last Vetter Fairing April 9 - May 10 Page 2
This is where I post the more interesting comments and questions. My comments in blue.
April 8, 2008, Claude wrote: I just found your streamlined Helix site. I used a Helix as my daily transport for the last few years, trading it in on a Burgman 400 because of the hill climbing ability and the undersized rear tire, which wore quickly and was a beast to replace. My normal milage was about 65mpg on surface streets, 70-75 if I ran the open roads with fewer stops, and about 60mpg on the interstate. Running wide open kills the milage.
If you have a good backrest, I would encourage you to lower the seat as much as possible. Maybe even replace it with something thin, like the seat from a farm tractor. (surprisingly comfy.) That will let you lower the rider and use a smaller fairing.
I'm curious to know how it does on hills. My area is rich with 6% grades, and the Helix was definitely overmatched. Reducing the air resistance would help, but is it enough to overcome the extra weight? The tendency of engine makers to sacrifice usable torque on the alter of high horsepower just makes it worse. The bikes are faster, but they won't climb or carry a real load.
I agree on the advantage of venting air behind the windshield. I added a small extension made from a helmet visor, and adding even a tiny gap between the windshield and extension for a sheet of air made it much more comfortable. It stopped trying to suck me into the dash board.
I'm putting this project in my Favorites so I can follow it.
April 8, 2008 Craig answered: Thank you Claude. I think things may get a little boring as I go to work on the other side. It bores me too as all I am doing is copying something I have already done once.
Then as I reveal my solution for a fairing, the likes of which the world has never seen, it will get interesting again.
My Helix, too gets 65 mpg. It will climb most Monterey-Santa Cruz Hills at 65. I really don't expect much from the streamlining on hills. I do expect a lot out of it in mileage and rider comfort. I got 107 mpg from my 250cc Streamliner of 1981 and it was not as well streamlined as my, to use your words "Helix-Liner" will be.
All ready, because of "0" wind on me, it is my bike of choice.
Thanks for the tip on the seat.
From Andrew Apl. 9: Craig, A couple of thoughts from a Feet Forward nutter:
My experience owning a Quasar taught me that it's quite possible to have a bike that's auto-stable in crosswinds, but all that side area will generate side force and the bike has to bank into the wind to balance out that side force. So the Quasar would run straight in quite violent crosswinds, but to do so it would roll itself *really* quickly - like quick enough to make me feel that I might get left behind. Your side walls alongside your shoulders should prevent you getting this effect, but the really fast rolling still may get you clenching your buttocks, unless you are one of the rare guys who can actually carry out that 'relax in cross winds' guidance!
After the airflow has left the front fairing, you want to get it to re-attach to the rear fairing. Doing this with a sharp leading edge is going to be difficult - which is why I radiused the front corners of the 'tailbox' on the ComforTmax (my FF scooter). I can't prove this works as I never got round to putting tufts on it, so it's just a suggestion.
Incidentally, the ComforTmax has superb cross-wind performance - I've ridden it in weather that had trucks coming close to tipping over and it remained stable. However, it wasn't pleasant as it suffered from a less serious problem - as the wind direction went off centre, it reached a point where suddenly my face and helmet came out of the wind shadow of the windscreen and the force on my helmet was severe - I never overcame the feeling that my helmet might get pulled off my head (and I wear it with a tight strap). I suspect that, as well as the shock of suddenly getting wind blast when normally there was none, having the helmet as the front of an aerofoil also increased the side force on it.
Keep up the good work - I'll keep watching. Best regards Andrew in Newcastle, England
From Craig April 9: Andrew: I was not ready for the "hiking over" like a sailboat on that cold Illinois day in 1966 when I took my first ride on my first fairing.
I soon learned to just let it happen and - as most seasoned riders do - and became adept at anticipating trucks. wind shadows from trees, etc. Once on the way from Daytona in 1967, the wind was so severe from the left (west) that when I stopped for gas and looked at my rear tire, I saw little that rubber balls were rubbing off, sideways!
My experience with my foamboard Helix fairing is that sidewinds are much much less severe than any previous bikes I have ever ridden. Less noticeable than with no foamboard fairing at all, in fact, Denis Manning confirmed, this morning that he found that the tail on his BUB 350 mph streamliner does the same thing. And all this with "Slab sides!" Handling can only improve with the fishy shape I am sanding on this very day.
My windshield is so close to my face that I simply never felt any winds whatsoever. Only by sticking my hand out could I tell that the winds were fierce. This is all very exciting stuff.
By the way, I am hoping to have a continuous surface so the air should never detach nor should it ever have to re attach. For the most part, anyway. We'll see.
Apl 9, 2008, Jerry wrote: Craig- You mentioned in the last update that the new fairing was very pleasant to ride with, stable in the wind and smooth air in the cockpit. You also mention that the mileage has stayed at around 64 mpg. Your '81 touring bike managed about twice that. The two bikes have similar hp and there is some similarity in the fairings. If I were guessing I'd look at the cardboard fairing flexing and not being aerodynamically dirty and losses in the cvt versus the manual transmission of the older bike. What do you think causes the big difference? Jerry in Colorado
April 9, Craig answered: All good questions, Jerry. I think the streamlining on my Helix stinks as it is now. Look at it! It is all angular and ragged... where I sit is a big air scoop. The bottom is open... It is not streamlined. This is only a quick study to verify that the tail - which is needed for real streamlining - does not cause problems in side winds. Real streamlining is totally smooth, a continuous surface, round at the front, pointed at the rear. My foamboard Helix does not have those qualities, thus it is not streamlined yet.
RE my 1981 machine, my real 107 mpg was in a contest, where I accelerated slowly, went just fast enough to stay in the contest and not be disqualified and really tried to conserve fuel. It, too was not correctly streamlined. Look at how the sides are cut away. Air hates that stuff. I wanted to see "streamlined" but it was not true. It is hard to see the truth when we see "what we want to see". I am smarter now. My finished Helix really will be streamlined.
By the way... I continue to ride my Helix in my normal, aggressive manner, trying to keep that part constant. That is why the 64 is unchanged. At least the foamboard is not hurting mileage. I am a little concerned about the CVT. Will it self adjust, meaning, if it requires less horsepower to go 65, will the pulleys "gear themselves up" doing what a bigger c'shaft sprocket does on chain bikes? What do you think?
April 10, Jerry answered: I'm concerned about the CVT also. I have very little hands-on experience at this point so this is all research based conjecture. One thing that can be done is to make the clutch weights heavier to engage at a lower rpm. This will give mileage at the cost of acceleration. It won't change the final drive ratio though. The springs in the driven pulley can also be changed to modify the rpm. In general I'd look at what people are doing to increase power and do the opposite. I had a short chat with a scooter mechanic and found out the larger scooters have different pulley diameters than smaller ones. I don't see kits for modifying or adapting pulley sets from one bike to another. It may be possible to attach a smaller engine to a larger cvt.
On the other hand a manual transmission is guided by a highly programmable computer (brain) making it easy to switch from mileage performance to power performance on the fly. It's also easy to adjust the final drive ratio by changing out the sprockets. Perhaps the optimum is a manual transmission with an automatic clutch. I found kits for this change on the web. This would let the rider choose the appropriate gear and still have the convenience of the automatic clutch.
BTW I test rode a Helix last night. It was a bit squirrelly because both tires were essentially bald but otherwise fun. Jerry in Colorado
Apl 10, Andrew wrote: Craig, Actually a fishy shape, at least in plan form, will usually be worse - in cross winds the flow will detach from the front corner of a slab-sided body and so 'stall' the body, minimizing its side force. But round the body thoroughly in plan and you create a perfect aerofoil to generate really big side forces. There is also the disadvantage that most aerofoil shapes have a centre of pressure well forward of the middle. However rounding the top and bottom will help reduce the extra side force the body develops so with luck it won't create much more than the slab-sided version.
The ideal shape is probably slab-sided with very carefully rounded front corners. The rounding has to be just smooth enough that the air flow sticks to it in straight-ahead flow, but also just sharp enough that the flow detaches from the corner when the air flow is at an angle. The drag penalty of this sort of body, compared to an aerofoil shape, is very little - but the downside is that it really needs time in a wind tunnel to get the corner sharpness right. But if you have the skill to relax in cross winds, you have the biggest single advantage - unlike the guy I was emailing recently who had ridden a long way in the mid-west in gusting cross-winds, who said at the end of it his saddle had a permanent crease down the middle....Andrew in England
Apl. 10, Craig wrote: Hmmm... I am committed to the big fish since I am down to the last 1/4" of shaping. You will notice that the tail is lower on the final shape than on the Foamboard runner. Denis Manning confirms that lower is better. I will do a side CP study and post it for your consideration. In the end, I hope to reduce what we do to very simple truths. Looks like you can be a big help.
April 10, Julian wrote: Did you find this page?
I'd guess that my experiments in modding a Helix might be of interest. Especially:- You can cut the seat foam down by nearly 2" and end up with a *more* comfortable seat.
- Add C-Piece handlebar risers, cut the plastic a bit on the handlebar cover and you can tilt the handlebars back quite a bit. This makes the bars less of a stretch. They can usefully be narrowed a bit as well by 1/2" each side. If you just remove the handlebar cover completely, you might not need the C-piece risers. Combined with a backrest, which you're building, it makes the bike a lot more comfortable and laid back. If you're prepared to remake the seat there's another 2" or so in seat height to be lost before you hit the frame rails. I would have thought getting the rider lower and leaned back a bit and pulling narrower bars back a bit would all help your streamliner project.
April 10, Craig responded: Morning Julian: Yep.. I took a look. RE handlebars... for me the original Helix bars wanted to hold my arms in a squished position which I don't like. Now that I think about it, the stock Helix bars felt sissy-like to me. I went the other way, rebending my bars to be more motorcyclish. I know that streamlining will be more difficult, but I have a plan to deal with that. Now it feels good to me. I know very well that handlebar location and grips are subjective decisions. I am American, too, which might explain my desire for high, wide bars.
The result is I sit more vertical and don't slouch back as far as before. This is bad because it increases my frontal area a bit... good because my CG is more forward.
RE backrest: I had a backrest on my original 1981 Streamliner and did not like it. I like the space. Probably this is because of my American style sitting position.
RE lower: I have a short mid section with long arms and legs My mom was 4'11. My dad 6'2"
This has caused problems for me all my design career. Until I realized this, in about 1970, my windshields tended to be too low. anyway, I am saving your lower seat for "normal" torso riders so they can fit into this thing.
Don't you like design? "You want this... you gotta give up that"
Lets link our pages. Give me the your most appropriate page and I'll put in on my site in my appropriate spot.
Start with the following as my link to Helix stuff:
Keep your comments coming. I'll post them when appropriate.
April 10 “Cam” wrote: Hi Craig - very exciting to see you working on a new fairing, thanks for sharing your process, too, that's priceless information. I'm curious about the long tail - you mention a few times that it's essential to good aero, but you also seem concerned w/ the overall length of the Helix when you're done, and about the amount of side area. What about the Kamm studies? They certainly sold me on the idea that you can cut off the long tail abruptly and not lose much aero, and lose unwanted weight, length, and side area. But I'm still working on my first vehicle - what does your experience tell you that leads you to favor the full tail? thanks, -=cam
April 10, Craig replied: Kamm says you can cut it off and not loose too much. The reality is, I think point is very pretty. If I can figure out how to keep it, I will. That means that I will have to come up with some clever way to display the taillight and license plate.
The point is just too pretty and pure to eliminate. Good question.
|A couple of additional comments you might find interesting: Today, my friend, Ed assumed that the Helix must be very slippery and shaped in a wind tunnel because it gets 64 mpg. I explained that the good mileage comes because it has the right horsepower, not the right shape. I'd bet that all 18 hp cycles get around 64 mpg. I am hoping, of course that real streamlining will make a dramatic difference. You will see it here. |
Ed also wondered how the Harleys in my first Fuel Economy Contest of 1980 got close to 100 mpg. I wondered at the time, too. A clue to the answer came a couple of years ago when I tried to get straight answers from the (living) winners about how they did it. Instead of the intelligent responses like the other competitors, Charly, Dan, Matt and Matsu, I got this:
"I think the main modification was a hidden gas tank. Lammy - was there a guy named Smokey Yunick hanging around? One the most effective mileage aids I know of was one I saw in one of the bike mags many years ago. The editors wanted to do a mileage run of their own, and one of the guys fashioned a hook that he used to sneak up on his competitors, hook up to some bike part, and shut off his engine to take advantage of the tow. "
The note went on and on with nonsense. In hindsight, I disregard the Harley's numbers. Such mileage figures have never been repeated.
This page updated April 18, 2008