Custom aero carbon DIY
Moderators: MrCurrieinahurry, maxim809, Moderator Team
-
climbandpunishment
- Posts: 62
- Joined: Fri Mar 20, 2015 4:40 am
Sure! Stefano's been working on getting set up to do some better manufacturing (pre-impregnated carbon fiber vs. wet layup) which will give a more finished frame result.
I've been working on some improved shaping and CFD for the next iteration of the frame. While the 41-odd different tube shapes were a good first step, I want to add even more variation along each tube so that they match the local airflow better. We're also looking at some better bottle aerodynamics. My best guess is that the Cervelo S5-esque downtube shape is probably the right strategy for bottles, but I want to run simulations on some alternatives. There's some small improvements to be made there even if the alternatives don't work out.
I've also been looking at other component aerodynamic integration. A lot of this year's aerodynamic frames have begun pushing integration farther, but personally I want to quantify the benefits before we make that kind of decision. I don't think the maintenance hassle of integrating a lot of drivetrain components is going to be worth the relatively small drag benefit, but I want to quantify that.
What do you guys think on the integration front? How many watts would, say, a more integrated headtube/front brake need to drop the drag before you were willing to put up with the extra maintenance hassle?
I've been working on some improved shaping and CFD for the next iteration of the frame. While the 41-odd different tube shapes were a good first step, I want to add even more variation along each tube so that they match the local airflow better. We're also looking at some better bottle aerodynamics. My best guess is that the Cervelo S5-esque downtube shape is probably the right strategy for bottles, but I want to run simulations on some alternatives. There's some small improvements to be made there even if the alternatives don't work out.
I've also been looking at other component aerodynamic integration. A lot of this year's aerodynamic frames have begun pushing integration farther, but personally I want to quantify the benefits before we make that kind of decision. I don't think the maintenance hassle of integrating a lot of drivetrain components is going to be worth the relatively small drag benefit, but I want to quantify that.
What do you guys think on the integration front? How many watts would, say, a more integrated headtube/front brake need to drop the drag before you were willing to put up with the extra maintenance hassle?
Visit starbike.com Online Retailer for HighEnd cycling components
Great Prices ✓ Broad Selection ✓ Worldwide Delivery ✓
www.starbike.com
Integrated head tube/front brake vs. something aero like a TriRig Omega front brake. If the fork is wide enough for the front brake, like a Cervelo fork, then gaining on top of the Omega will be hard. 2-3 watts wouldn't be worth it imo. Find 8-10 watts and it probably would be.
The other interesting thing is what Specialized is doing with the new Venge and putting the brakes behind the fork and then having them shielded with a fairing of sorts. Helps fill in that area between the back of the fork and the downtime. That would be worthwhile. Just don't see the route Giant went with the Propel as being that great, especially with the cable hanging out in the wind. Might as well go with a nice aero TriRig brake that is center pull.
The other interesting thing is what Specialized is doing with the new Venge and putting the brakes behind the fork and then having them shielded with a fairing of sorts. Helps fill in that area between the back of the fork and the downtime. That would be worthwhile. Just don't see the route Giant went with the Propel as being that great, especially with the cable hanging out in the wind. Might as well go with a nice aero TriRig brake that is center pull.
"Marginal gains are the only gains when all that's left to gain is in the margins."
I'm getting either a Cervelo s3/s5 or an Canyon aeroad. I want as aero as possible with stadard components and traditional rear brake placement.
I want the standard components because it will be cheaper and easier to maintain in the long run and because I want to choose the bits on my bike.
I want the rear brake in the traditional place because I live in Denmark. My bike will se a lot of foul weather and i dont want to place my rear brake directly in the waterspray from the front wheel.
These points are more important to me personally than chasing the last few watts using proprietary components. When that's said I really like the look of the new Trek Madone though. The new Venge looks like a science project. It's not for me.
/Martin
I want the standard components because it will be cheaper and easier to maintain in the long run and because I want to choose the bits on my bike.
I want the rear brake in the traditional place because I live in Denmark. My bike will se a lot of foul weather and i dont want to place my rear brake directly in the waterspray from the front wheel.
These points are more important to me personally than chasing the last few watts using proprietary components. When that's said I really like the look of the new Trek Madone though. The new Venge looks like a science project. It's not for me.
/Martin
Last edited by Martin.dk on Tue Jun 16, 2015 8:42 pm, edited 3 times in total.
Samuel Sanchez Gonzalez wrote:Ohh okay! I just knew "plug" was something to put inside a hole... yikes
An S3 or S5 with some aero components that actually work would be key to me. Something like the new Cervelo Drop bar, TriRig brakes and TriRig stem if it works with the cervelo bars would make the front end very aero without any sacrifice. I do not like all of the integration that is going on these days as I believe that you can be just as aero or more aero if you pick the right components.
BIG DADDY B FLOW
AERO & LIGHT is RIGHT for 2 decades
AERO & LIGHT is RIGHT for 2 decades
The new madone is worth investigating seeing that there's zero cables out at the front and the brakes just nests itself directly under the head tube with no break in between at all.
Sent from my SM-G900F using Tapatalk
Sent from my SM-G900F using Tapatalk
-
climbandpunishment
- Posts: 62
- Joined: Fri Mar 20, 2015 4:40 am
Yeah, I hear you. Not a huge fan of the integration approach myself either, so good to hear I'm not alone there. I think there's potential there, but most of what they're doing so far looks like it may be as much about marketing as it is about performance.
Kayrehn, I like that suggestion, thank you. I've looked into that approach and I really, really like the idea, but have had real trouble implementing it effectively. For the head tube, it's extremely difficult (maybe impossible) to make an airfoil with the necessary geometry to house all the components that way. By extending the front of the tube forward to house the brakes, you push your point of maximum tube thickness farther back relatively, which makes it very difficult to avoid separation (and drag). Trek probably mitigated that by using their Kammtail shaping, but I'm not a fan of using Kammtails unless it's to shield other components. Once I'm finished with the current round of CFD I'll have to test that out more.
53x12, good to hear numbers put to it. That Propel brake definitely drives me nuts too; it's like they came so close and then just gave up on the cable routing. I'll have to think about routing with the new Venge approach. It doesn't leave any (obvious to me) easy options for brake controls besides the possible hydraulic route with its own challenges, but maybe there's a way.
Anyways, thanks guys, that's great food for thought! Hopefully we'll have some simulations or CAD in the not-too-distant future for the next iteration.
Kayrehn, I like that suggestion, thank you. I've looked into that approach and I really, really like the idea, but have had real trouble implementing it effectively. For the head tube, it's extremely difficult (maybe impossible) to make an airfoil with the necessary geometry to house all the components that way. By extending the front of the tube forward to house the brakes, you push your point of maximum tube thickness farther back relatively, which makes it very difficult to avoid separation (and drag). Trek probably mitigated that by using their Kammtail shaping, but I'm not a fan of using Kammtails unless it's to shield other components. Once I'm finished with the current round of CFD I'll have to test that out more.
53x12, good to hear numbers put to it. That Propel brake definitely drives me nuts too; it's like they came so close and then just gave up on the cable routing. I'll have to think about routing with the new Venge approach. It doesn't leave any (obvious to me) easy options for brake controls besides the possible hydraulic route with its own challenges, but maybe there's a way.
Anyways, thanks guys, that's great food for thought! Hopefully we'll have some simulations or CAD in the not-too-distant future for the next iteration.
climbandpunishment wrote:Not a huge fan of the integration approach myself either, so good to hear I'm not alone there. I think there's potential there, but most of what they're doing so far looks like it may be as much about marketing as it is about performance.
That's a very bold claim from someone who has such a serious knowledge-work on aerodynamics. Could you explain that a bit further? It would be really eye-opening. (I agree BTW...)
-
climbandpunishment
- Posts: 62
- Joined: Fri Mar 20, 2015 4:40 am
I should preface this by saying I'm a bit biased against the integration approach. It's a perfectly valid approach that I disagree with philosophically because I don't think the industry is at the point where integration is the lowest-hanging aerodynamic fruit.
Pointing out what I mean is going to require talking about specific bikes; although I'm being critical of some of the latest aero bikes (Madone and Venge especially), they are also a big step forward for the industry. I want to make it very clear that I can't say conclusively that the integration could be done better on either bike without testing them, but there's some features that look suspect to me.
From the armchair, the Venge's front brake looks like a good overall approach but maybe not the best execution. Filling in the area behind the fork/frame interface is a step in the right direction, but the sharp line of the down tube behind the fork and brake is very to cause separation and extra drag. Then again, I could also be completely wrong and that sharp line may intentionally disrupt the airflow to keep flow attached, but I'm doubtful.
I'm not really sure about some of the shapes around the Venge's stem either, but that may be more an indicator of my own ignorance about what their specific purpose is rather than a marketing-aero design. I will say that the new Venge looks to have done a really good job of the seat stay-front triangle attachment, which is pretty rare and deserves kudos.
The new Madone's front end is beautifully clean, but I'm suspicious of how sharp the front edge of the headtube is. Again, I could be wrong, but in my experience a leading edge that sharp is very likely to cause separation in crosswinds. And leading edge separation is bad news from both a drag and stability standpoint. I'll have to do some better testing for this next iteration to see if a sharp head tube like that is possible without separation or taking the easy route and using a Kamm shape.
Pointing out what I mean is going to require talking about specific bikes; although I'm being critical of some of the latest aero bikes (Madone and Venge especially), they are also a big step forward for the industry. I want to make it very clear that I can't say conclusively that the integration could be done better on either bike without testing them, but there's some features that look suspect to me.
From the armchair, the Venge's front brake looks like a good overall approach but maybe not the best execution. Filling in the area behind the fork/frame interface is a step in the right direction, but the sharp line of the down tube behind the fork and brake is very to cause separation and extra drag. Then again, I could also be completely wrong and that sharp line may intentionally disrupt the airflow to keep flow attached, but I'm doubtful.
I'm not really sure about some of the shapes around the Venge's stem either, but that may be more an indicator of my own ignorance about what their specific purpose is rather than a marketing-aero design. I will say that the new Venge looks to have done a really good job of the seat stay-front triangle attachment, which is pretty rare and deserves kudos.
The new Madone's front end is beautifully clean, but I'm suspicious of how sharp the front edge of the headtube is. Again, I could be wrong, but in my experience a leading edge that sharp is very likely to cause separation in crosswinds. And leading edge separation is bad news from both a drag and stability standpoint. I'll have to do some better testing for this next iteration to see if a sharp head tube like that is possible without separation or taking the easy route and using a Kamm shape.
-
pitbull
I unterstand your point but in my opinion every Watt counts if you want to make a truly fast bike. In my opinion even if that leads to a little more complicated integration. Isnt the Front brake very bad for the overall airflow because it creates some turbulences at the front of the bike influencing the overall airflow ? I would also like to see the stem being integrated improving the airflow at the front of the bike. And i am curious why you dont go with some aero bottles which i think you could also integrated better?
Finally it's awesome how you share your knowledge. Thank you very much for that! It helps me with some of my carbon projects
Finally it's awesome how you share your knowledge. Thank you very much for that! It helps me with some of my carbon projects
Aero bottles on a road bike don't make sense for two reasons. The first is that they wouldn't be UCI legal and the second is that handing up bottles would be a pain if they're proprietary.
A standard front brake isn't the most aero solution, but it's all about a compromise between lower drag, stopping power and cost. Direct mount goes a long way to tackle these issue and brakes like the TriRig are pretty much drag neutral when compared to integrated solutions (although they still don't stop as well as DA).
A standard front brake isn't the most aero solution, but it's all about a compromise between lower drag, stopping power and cost. Direct mount goes a long way to tackle these issue and brakes like the TriRig are pretty much drag neutral when compared to integrated solutions (although they still don't stop as well as DA).
Re bottles and brakes, agreed with Grill completely. For a tri-specific bike, those could be areas to work on, but for the moment not in the plans.
Eventually, we would like to work on our own fork-- it would give us a lot of freedom to experiment and could help shave serious drag. Need to do quite a bit of design/testing though, and we are a bit leery in designing such a safety critical part. Too bad there are no aftermarket dual mount forks with decent aero.
Eventually, we would like to work on our own fork-- it would give us a lot of freedom to experiment and could help shave serious drag. Need to do quite a bit of design/testing though, and we are a bit leery in designing such a safety critical part. Too bad there are no aftermarket dual mount forks with decent aero.
-
climbandpunishment
- Posts: 62
- Joined: Fri Mar 20, 2015 4:40 am
Hi guys, quick update. I've been working on airfoils for the new iteration, and I did that testing of new-Trek-Madone-like headtube shapes that I promised.
First off, I'll eat my words a bit, since the stall on the Trek-Madone-esque sharper front headtube edge sort of shape is not quite as bad as I had thought. It's inevitably never going to get you as gentle and predictable a crosswind behavior, since moving the thickness farther back necessarily limits the amount of curvature you can play with on the rear half of the airfoil. BUT the difference in stall angle where you'd start to notice some handling issues is less than 5 degrees from a more crosswind-friendly rounder front edge airfoil shape, so it's probably tolerable for the majority of crosswinds, especially if the geometry takes that into account and you don't live in a particularly windy area. Their head tube also is small in area, which may reduce the impact of the crosswind issue, since there's less area for the wind to act on and therefore the difference in force when that area suddenly stalls is smaller for the rider to deal with.
We're still going to go with a less aggressive, more crosswind-friendly airfoil shape I think. You have to have a higher-aspect ratio headtube to make that method work, but you get more predictable crosswind performance with drag that's usually a bit better. It'll be a bit heavier, but the headtube's not the right area to make weight gains at the expense of aero performance in my opinion.
Anyways, airfoils for the new version are almost done. I went back to clean slate airfoils to try a few new strategies for most tubes, as well as refining the previous iteration's airfoils to ensure we're choosing the right shape. The old bike had around 15-30 iterations for each of the 40-odd tube sections - this one will have well over 200 each, which is pushing the limits of sanity for engineering effort even by aerospace standards. With a real bike I could test, I was able to get more aggressive with most of the tube shapes, making it more worthwhile to spend that amount of time on every part of every tube.
There'll be some overall shape and design changes that should help even more than the tube shapes too, so I'm really excited about the performance of the new iteration.
First off, I'll eat my words a bit, since the stall on the Trek-Madone-esque sharper front headtube edge sort of shape is not quite as bad as I had thought. It's inevitably never going to get you as gentle and predictable a crosswind behavior, since moving the thickness farther back necessarily limits the amount of curvature you can play with on the rear half of the airfoil. BUT the difference in stall angle where you'd start to notice some handling issues is less than 5 degrees from a more crosswind-friendly rounder front edge airfoil shape, so it's probably tolerable for the majority of crosswinds, especially if the geometry takes that into account and you don't live in a particularly windy area. Their head tube also is small in area, which may reduce the impact of the crosswind issue, since there's less area for the wind to act on and therefore the difference in force when that area suddenly stalls is smaller for the rider to deal with.
We're still going to go with a less aggressive, more crosswind-friendly airfoil shape I think. You have to have a higher-aspect ratio headtube to make that method work, but you get more predictable crosswind performance with drag that's usually a bit better. It'll be a bit heavier, but the headtube's not the right area to make weight gains at the expense of aero performance in my opinion.
Anyways, airfoils for the new version are almost done. I went back to clean slate airfoils to try a few new strategies for most tubes, as well as refining the previous iteration's airfoils to ensure we're choosing the right shape. The old bike had around 15-30 iterations for each of the 40-odd tube sections - this one will have well over 200 each, which is pushing the limits of sanity for engineering effort even by aerospace standards. With a real bike I could test, I was able to get more aggressive with most of the tube shapes, making it more worthwhile to spend that amount of time on every part of every tube.
There'll be some overall shape and design changes that should help even more than the tube shapes too, so I'm really excited about the performance of the new iteration.
Visit starbike.com Online Retailer for HighEnd cycling components
Great Prices ✓ Broad Selection ✓ Worldwide Delivery ✓
www.starbike.com
Hi climbandpunishment and Stefano,
First of all, congratulations on the project. Mechanical engineer with some background in aerodynamics and CFD here.
Some questions/remarks:
1- I do not see how this frame could be legal for UCI road races. You are clearly making use of the 8x8cm compensation triangles (article 1.3.021 of the UCI rules on equipment) between tubes so this frame could only be legal for UCI time trials or track events.
2- Have you experimented with alternative molding methods? It seems that you have almost free access to a CNC machine so you could try to do some EPS molding.
3- Can you comment on where does the "within 2W of the S5" come from? Ivan Sidorovich (Cervélo's aerodynamicist) claimed that 16% of the total drag of a S5 complete bike is due to the frame (about 120gF). Are you using that value as a comparison?
4- Can you give some technical notes about the CFD simulations? Name of the code? Scheme order? Number of volumes for the full simulation (10-50·10^6 seems typical in the industry) Turbulence model? Does it allow to predict transition or you are running full turbulent simulations?
5- Are you employing panel method software (XFOIL/MSES) or 2D CFD for airfoil development? What kind of optimisation algorithms or inverse methods are you employing to improve the performance of the airfoil? Do you optimise the airfoils in a standalone configuration or you take into account the airfoil "cascade" formed by the front wheel-DT-ST-rear wheel?
First of all, congratulations on the project. Mechanical engineer with some background in aerodynamics and CFD here.
Some questions/remarks:
1- I do not see how this frame could be legal for UCI road races. You are clearly making use of the 8x8cm compensation triangles (article 1.3.021 of the UCI rules on equipment) between tubes so this frame could only be legal for UCI time trials or track events.
2- Have you experimented with alternative molding methods? It seems that you have almost free access to a CNC machine so you could try to do some EPS molding.
3- Can you comment on where does the "within 2W of the S5" come from? Ivan Sidorovich (Cervélo's aerodynamicist) claimed that 16% of the total drag of a S5 complete bike is due to the frame (about 120gF). Are you using that value as a comparison?
4- Can you give some technical notes about the CFD simulations? Name of the code? Scheme order? Number of volumes for the full simulation (10-50·10^6 seems typical in the industry) Turbulence model? Does it allow to predict transition or you are running full turbulent simulations?
5- Are you employing panel method software (XFOIL/MSES) or 2D CFD for airfoil development? What kind of optimisation algorithms or inverse methods are you employing to improve the performance of the airfoil? Do you optimise the airfoils in a standalone configuration or you take into account the airfoil "cascade" formed by the front wheel-DT-ST-rear wheel?
