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Author Topic: APS/Ω Gas turbine bike build  (Read 553822 times)
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wobblywalrus
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« Reply #1095 on: October 12, 2015, 11:01:57 PM »

Anders, a couple of "lessons learned" are posted in my build diary.  They might help you.
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Mobacken Racing
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« Reply #1096 on: October 13, 2015, 04:29:51 AM »

Anders sorry it took me so long to get back to you. I am not sure about some of the termonology. My understanding of ATTACHED is that it is a good thing. in the case of your upper fairing and helmet I think the air would continue a smooth flow. If you were farther back or in such a position that the air would not have a continous flow it would seperate, not a good thing.

No rush whatoever, I have all winter to clear this out. Smiley

That sounds reassuring, I have basic knowledge about aerodynamics but I haven´t yet caught up on all the english names involved. I would simplify things a lot if you guys start writing in Swedish instead.  grin

Yes. Keeping the air attached and as free from turbulence as possible = reduced aero drag. Obviously less drag means more power being applied to increase velocity and not wasting it just to overcome the drag you are creating.

The less you disturb the air the better. If you have to disturb it, try to control it so that it limits the amount of drag it generates. Keeping it "attached" means you are providing a path of least resistance for the air to move around/over/through a shape.

For visual purposes use the picture below. Laminar flow is what you want. You will never get it to look like that, but you want to strive to be as close as possible to it as you can. Let's assume that the flow over the front fairing is laminar. When it leaves that area what will happen to it? It looks like it should flow nicely right onto the helmet by jumping off the windscreen and "attaching" back onto your helmet staying relatively laminar.

If you look at the picture below, the further the "jump" the air has to make or the less controlled it is when leaving the surface it becomes more like the flow on the right side of the illustration. Your job as the chief aerodynamicist is to try and get as much of the air to move like the left side of the picture!

If you start thinking in terms of how to achieve the maximum laminar flow (keeping the air "attached") you will have one portion of your aerodynamic drag reduction completed.



Separation drag is another area to consider. In my comment a while ago about not having a blunt fender I was referring to separation drag. This happens when you lose control of the air and it goes turbulent creating a vacuum. This effect can be used to advantage to make down force but that typically happens in a horizontal plane.

Making it in the vertical plane (Stubby/blunt endings) generate a vacuum that causes noting but pure drag. You want to avoid this too.



All of this information is rudimentary and not given to you to change your mind or say I am an expert. Every aero problem is unique and solving one leads to another. I am NOT a bike guy. Driven them, raced them on dirt...not a high speed racer. There are things you can do on a bike that will help the aero but MAY make the bike unstable and unable to be ridden. Listen to the advice of the bike guys here.

More free info - Do with it what you like...no charge!


Then I get it, as I wrote to fredvance I am slowly learning the English terms and now I know what attached flow means. Thanks a lot for the lengthy reply, I owe a lot to you guys here trying to get me on the right track with the aerodynamics!

One thing that I got aware of from looking at the pictures is that the helmet and leathers aren´t optimal with regard to air flow over the rider, the sharp edge at the back of the helmet might upset the flow and the lack of a motoGP "hump" at the back of the leathers most certainly cause flow separation.

I see that some tails are kept at more or less the same height all the way back to form sort of a wedge shape, what is the reason for this shape compared to the one I have where the height decreases in an imaginary curve pointing at the ground behind the bike?

Cheers!
/Anders
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Mobacken Racing
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« Reply #1097 on: October 13, 2015, 04:50:00 AM »

If I were in the position you're in, Anders, I'd get in touch with Pork Pie.  He's an aero specialist (as well as a damned good photographer) and might be able to give you some tips and help.  He lives in Heilbron, Germany, by the way, so I have no clue what language you'll share huh

Best wishes and have fun with the bike.

That is a good advice, for now I think that sorting out the most fundamental errors here in the build thread will do wonders. When the time comes to rebuild the bike fairings completely I´ll send him a PM, but not until I have done some more high speed runs with the larger engine so I know how much extra space I´ll need for everything.

At the moment I am gathering parts and making the sand casting patterns for the compressor section so hopefully I will have the front end made by the end of this winter.



It will have twice the power of the engine I use now so 300hp or slightly more is the goal.



Here is the new engine case next to the bike, it is 30cm in diameter so I might need to modify both the chassis and fairings in order to fit everything.



It will take a couple of years to finish so the plan is to race the bike with the old engine in the meantime and try to figure out how to make the fairings as slippery as possible, if this engine is capable of 300km/h on the mile the bike will be a serious contender with twice the power! cheesy

Another method for finding Frontal Area. Complete with battle dress (leathers and helmet) sit in the tuck position on your bike,, have a friend using a dress makers tape measure around the extremities as viewed from the front,, this will give a "circumferance", do the maths,,,  smiley

 Anders, Enjoying your journey mate,  cheers

Another good idea for measuring the frontal area, it seems I have to bake a cake to trick a friend to drop by some day. smiley

Anders, a couple of "lessons learned" are posted in my build diary.  They might help you.

Very good lessons, I´ve learned them the hard way with a couple of earlier engine builds so I try to make everything as easy to work with as possible. I can remove the engine from the frame and take it apart completely in less than two hours if I need to, one of the earlier kick sled engines gave me a head ache just from thinking about taking it apart... smiley

Cheers!
/Anders
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MattGuzzetta
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« Reply #1098 on: October 13, 2015, 12:28:06 PM »

Anders, one way to think about aerodynamics on a motorcycle is to forget about the motorcycle and realize that you are actually trying to streamline the rider, not the bike. The rider is usually the biggest part of the vehicle.  The reason (theoretically) that the tails of many bikes are almost level is that you need to clean up the turbulence coming off the back of the rider. By having the tail taper down you end up with nothing to clean up the air coming off the back of the rider.  You can see that by taking a photo of the bike from the side with the rider and see that the back of the rider is actually the end of the bike, aerodynamic wise. If you take a photo with a 200mm or longer lens, you can almost take dimensions off the photo.
Cheers to you,
Matt Guzzetta
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« Reply #1099 on: October 13, 2015, 02:43:03 PM »

Anders, one way to think about aerodynamics on a motorcycle is to forget about the motorcycle and realize that you are actually trying to streamline the rider, not the bike. The rider is usually the biggest part of the vehicle.  The reason (theoretically) that the tails of many bikes are almost level is that you need to clean up the turbulence coming off the back of the rider. By having the tail taper down you end up with nothing to clean up the air coming off the back of the rider.  You can see that by taking a photo of the bike from the side with the rider and see that the back of the rider is actually the end of the bike, aerodynamic wise. If you take a photo with a 200mm or longer lens, you can almost take dimensions off the photo.
Cheers to you,
Matt Guzzetta

That is a very good explanation Matt, now I get it.
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wobblywalrus
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« Reply #1100 on: October 13, 2015, 10:42:38 PM »

Back when I was a teenager I had a Honda 305 Superhawk.  It is Honda's best bike.  The footpegs could be moved to the rear with simple adjustments.  I did this and then it was easy to get down low on the tank at high (for a Superhawk) speeds.  I was limber then and my chin almost rested on the speedo lens.  Unfashionable at the time, I had the standard seat.  It kept my butt high and my back level when I was tucked down.

The bike suffered from one of my early attempts at performance tuning and it was not as powerful as my friend's 305's.  It had equal top speed when I got tucked down.  My best guess is it was me having a level backside that made the difference.  It created a lot less turbulence and aero drag.   
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Mobacken Racing
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« Reply #1101 on: October 16, 2015, 04:49:09 AM »

A friend of mine at a jet forum managed to measure the frontal area from the picture I posted, he found it to be 0.42m2 which isn´t bad at all.



To decrease the frontal area noticably I would have to make drastic changes to the riding position, and that is impossible since the jet exhausts keep me from moving the pegs further to the rear.
« Last Edit: October 16, 2015, 04:52:21 AM by Mobacken Racing » Logged
fredvance
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« Reply #1102 on: October 16, 2015, 09:23:00 AM »

I wouldn't worry about the front. Look at Joe Amo's, looks like a hammerhead shark and it works!
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« Reply #1103 on: October 16, 2015, 02:25:11 PM »

Joe can really mow down the numbers!

(Especially the 4.)
« Last Edit: October 16, 2015, 02:32:34 PM by Stan Back » Logged

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« Reply #1104 on: October 16, 2015, 02:42:54 PM »

To do things in your sleep is a measure of high skill, up until now all I could produce was snoring but with the addition of the 3D printer I suddenly have a much wider repertoire. smiley



Something that has bothered me from the beginning has been the sloppy placement of the quick fittings for propane and starting air, so last night I made a drawing of a fitting, loaded some Bridge Nylon in the printer and put it to work while I went to bed for a couple of pages of Joe Abercrombie´s The First Law fantasy triology before falling asleep.



This morning I woke up with the finished nylon fitting waiting for me on the printer table, and after dinner I went out to mount it on the bike. This 3D-printing business is so darn useful! smiley



Cheers!
/Anders
« Last Edit: October 16, 2015, 03:15:41 PM by Mobacken Racing » Logged
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« Reply #1105 on: October 16, 2015, 03:57:59 PM »

That's a great idea. When I first saw it I thought it was the updated hot dog holder!. grin

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wobblywalrus
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« Reply #1106 on: October 16, 2015, 09:47:04 PM »

Anders, doubling the power is a big step.  Maybe enough to justify a perimeter or trellis frame and some way to direct the exhaust out the back. 
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Mobacken Racing
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« Reply #1107 on: October 17, 2015, 11:36:31 AM »

That's a great idea. When I first saw it I thought it was the updated hot dog holder!. grin

Not a bad guess. smiley

Anders, doubling the power is a big step.  Maybe enough to justify a perimeter or trellis frame and some way to direct the exhaust out the back. 

I have thought about making a completely new bike around the new engine, but I came to the conclusion that I want to see how fast this one can go first. I´ve spent way too much time and money on it just to scrap it after a couple of seasons of landracing.

Routing the exhaust up through the tail is difficult to say the least since the gearbox is in the way and the seat will become unbearably hot with the jet exhaust just beneath it.
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« Reply #1108 on: October 18, 2015, 03:43:42 PM »

I found a use for the Neutrik bayonet plug that was used for the external ignition before I decided to fit it to the bike, I figure out I can use it for the battery charger so I won´t have to remove the rear fairing every time I charge the battery.



Most of the stuff I ordered for the water injection has arrived so I made a spray nozzle holder to find out the flow rate and discharge angle, I need to know this before I decide where to fit the nozzle in the air box.



Cheers!
/Anders
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« Reply #1109 on: October 18, 2015, 09:14:54 PM »

The G model B52 used water injection and it was impressive cheers
 
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