The relative benefits of a pull rod suspension

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segedunum
segedunum
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Joined: 03 Apr 2007, 13:49

Re: The relative benefits of a pull rod suspension in 2011

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Goodness me.

Take a long look at that diagram above and have a look at how much space there is underneath the pull-rod compared with the push-rod that obstructs that space. Given the single diffusers we have now that fit completely into that space then there really is no disadvantage to using a pull-rod this year. Pushing will tend to give you more control and adjustment than pulling but any performance you can gain from that will be small in comparison to the aerodynamic effect of the air you free up.

Ferrari can change the geometry of their rods and wishbones all they like but their push-rod will still be obscuring that space.

shelly
shelly
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Joined: 05 May 2009, 12:18

Re: The relative benefits of a pull rod suspension in 2011

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@myurr: when I write about aerodynamic freedom of a pull rod, I am not talking about packaging of the elastic elements of the suspension inside/over the gearbox, but instead I am referring to the advantage of a thinner pull element compared to a fatter push element in terms of aerodynamic blockage and perturbation of the flow towards the beam wing and on the upper part of the floor.

This freedom becomes still more important if you consider 2011 strict regualtions on diffusers and teams' efforts to gain downforce working on the upper part of the floor, with exhaust blowing or double floors.

I think that we both agree on the fact that ferrari's 2011 push is an attempt to gain part of the advantage of a pull, while keeping a push.
There could be a lot of reasons we can not know behind that choice; and even if it could seem odd, I would not dismiss the fact that ferrari would not have liked to have been considered a follower of others' technical choices as an element in the trade off
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myurr
myurr
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Joined: 20 Mar 2008, 21:58

Re: The relative benefits of a pull rod suspension in 2011

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segedunum wrote:Goodness me.

Take a long look at that diagram above and have a look at how much space there is underneath the pull-rod compared with the push-rod that obstructs that space. Given the single diffusers we have now that fit completely into that space then there really is no disadvantage to using a pull-rod this year. Pushing will tend to give you more control and adjustment than pulling but any performance you can gain from that will be small in comparison to the aerodynamic effect of the air you free up.

Ferrari can change the geometry of their rods and wishbones all they like but their push-rod will still be obscuring that space.
Care to highlight on that diagram exactly which space you're referring to?

myurr
myurr
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Joined: 20 Mar 2008, 21:58

Re: The relative benefits of a pull rod suspension in 2011

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shelly wrote:@myurr: when I write about aerodynamic freedom of a pull rod, I am not talking about packaging of the elastic elements of the suspension inside/over the gearbox, but instead I am referring to the advantage of a thinner pull element compared to a fatter push element in terms of aerodynamic blockage and perturbation of the flow towards the beam wing and on the upper part of the floor.

This freedom becomes still more important if you consider 2011 strict regualtions on diffusers and teams' efforts to gain downforce working on the upper part of the floor, with exhaust blowing or double floors.

I think that we both agree on the fact that ferrari's 2011 push is an attempt to gain part of the advantage of a pull, while keeping a push.
There could be a lot of reasons we can not know behind that choice; and even if it could seem odd, I would not dismiss the fact that ferrari would not have liked to have been considered a follower of others' technical choices as an element in the trade off
The narrowness of the pull rod is probably negated by the additional length, as shown in scarbs's diagram. And what you gain in airflow to the beam wing you lose in freedom to position the exhausts and losses over the diffuser.

As with everything in F1 it's a compromise and whichever is the best compromise that works with the rest of your car is the solution you should choose. If it's just about lack of obstruction in front of the beam wing then Williams should be the dominant car this year but that is unlikely to be the case.

myurr
myurr
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Joined: 20 Mar 2008, 21:58

Re: The relative benefits of a pull rod suspension in 2011

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myurr wrote:
segedunum wrote:Goodness me.

Take a long look at that diagram above and have a look at how much space there is underneath the pull-rod compared with the push-rod that obstructs that space. Given the single diffusers we have now that fit completely into that space then there really is no disadvantage to using a pull-rod this year. Pushing will tend to give you more control and adjustment than pulling but any performance you can gain from that will be small in comparison to the aerodynamic effect of the air you free up.

Ferrari can change the geometry of their rods and wishbones all they like but their push-rod will still be obscuring that space.
Care to highlight on that diagram exactly which space you're referring to?
Further to my request, here is my crude diagram. Green indicates advantage push rod, blue advantage pull rod. Maybe you can show me where I'm going wrong and where this massive aero advantage is underneath the pull rod.

To me it just looks like two different aero compromises and you choose the best for the rest of your car.

Image

shelly
shelly
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Joined: 05 May 2009, 12:18

Re: The relative benefits of a pull rod suspension in 2011

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@myurr: narrowness of the pull rod is anadvantage, even if it is longer than a push rod: long and thin is better of short and fat when yuor concern is blockage.

Moreover, it is not necessairily true that a pull rod would give harder constraints on exhaust positioning, nor that it would affect negatively diffuser flow.

In Scarbs diagam areas occupied by elastic elements of pull or push ar more or less the same, but maybe with 2011 regs is less harmful to put obstruction in the lower center area than in the upper.

In the end, the well known fact that everything on an F1 car comes from a compromise must not be used as a stopping point to a technical discussion. I agree that it is unlikely that willams will be the fastest car, but their technical treatment of the rear end compormise could still be the best in the field, giving them some advantage that probably in the overall sum will be made ineffective by lackness of performance in other ares of the car.
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myurr
myurr
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Re: The relative benefits of a pull rod suspension in 2011

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@shelly: the narrowness is not a pull rod specific advantage, as shown in the diagram where it is actually wider at the base. Red Bull elongated their gearbox allowing them to create space to mount more of the components inside the casing, but that is a specific packaging solution rather than an inherent pull rod advantage, and is something that Ferrari looks like they've replicated for the pull rod.

The reason for the pull rod interfering with the exhaust is if you wanted to mount it inboard. You can clearly see on many of the cars this season how close the exhausts come to both the pull rod and the lower suspension arm, so it would not be surprising if there had been a bit of a compromise there on some of the cars. This is one of the reasons, I believe, that Red Bull are so focussed on working the outer sections of the diffuser rather than the centre - I have no idea if that in and of itself has relative advantages or disadvantages compared to working the centre of the diffuser, or what they may be.

Your third paragraph about the areas being more or less the same was exactly my point. You choose where you want those components and that is why you choose one design over the other. Both suspension setups have more or less the same number and volume of components that need to be housed, so there is nothing magical about the pull rod in that regard.

I completely agree that this is a topic worth discussing, and I have no wish to stop that discussion or prove one side is better than the other. Where I feel the need to speak out is where some board members, not yourself, consider the pull rod to be a magical solution that doesn't involve any compromise and is the only valid solution for the 2011 cars. It isn't, and there are valid reasons for teams like Ferrari going a different route.

segedunum
segedunum
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Re: The relative benefits of a pull rod suspension in 2011

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myurr wrote:Care to highlight on that diagram exactly which space you're referring to?
The area you've highlighted in green, where the push-rod isn't on a pull-rod layout and exactly where the single diffuser fits into.

Ferrari have tried to get around that with an intricate push-rod layout where they restrict less of that space by sweeping it forwards, but nevertheless, they still have an obstruction there that a pull-rod won't give you. On top of that, because they're sweeping it forwards with more force involved the push-rod is longer and thicker than it would otherwise be and certainly longer and thicker than a pull-rod. They might be obstructing less of the space immediately in front of the diffuser but they've created more obstruction further forward where there wouldn't have been before and still isn't with a pull-rod.

Fair play to Ferrari, it's a lovely bit of mechanical juggling, but I'm not sure they're going to have enough space to play with when they need more airflow and downforce later on in the season. Certainly, with the exhaust layout McLaren are going for freeing up space in front of the diffuser will be vitally important for them as they develop that system. That's why, although McLaren are looking in poor shape right now, there is a lot of scope there for them.

shelly
shelly
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Joined: 05 May 2009, 12:18

Re: The relative benefits of a pull rod suspension in 2011

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@myurr: maybe there has been some incomprehension on "narrowness". I was referring, with narrowness, to the slenderness of the rod, which is higher for a pull thus producing less blockage.
As for the narrowness of the casing and packaging considerations, it is dow to choices. I think that pullrod gives more options, frees useful room in the upper part while occupying the same room in a zone whose exploitation maybe is useful.

Is str06 with rear pullrods or with pushrods?
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ringo
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Joined: 29 Mar 2009, 10:57

Re: The relative benefits of a pull rod suspension in 2011

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myurr wrote:
myurr wrote:
segedunum wrote:Goodness me.

Take a long look at that diagram above and have a look at how much space there is underneath the pull-rod compared with the push-rod that obstructs that space. Given the single diffusers we have now that fit completely into that space then there really is no disadvantage to using a pull-rod this year. Pushing will tend to give you more control and adjustment than pulling but any performance you can gain from that will be small in comparison to the aerodynamic effect of the air you free up.

Ferrari can change the geometry of their rods and wishbones all they like but their push-rod will still be obscuring that space.
Care to highlight on that diagram exactly which space you're referring to?
Further to my request, here is my crude diagram. Green indicates advantage push rod, blue advantage pull rod. Maybe you can show me where I'm going wrong and where this massive aero advantage is underneath the pull rod.

To me it just looks like two different aero compromises and you choose the best for the rest of your car.

Image

You should take into account the size of the gearbox and also what's behind it. and in front of it. Scarbs diagram was just a demonstation, so he used the same size on both sides. That is not the case in reality.
It's more like this:
Image

Red strokes are bad flow, green is good. Notice how much bigger the cooling exit is for the push rod. Also take note of what proportion of beam wing is exposed to bad flow from the push rod itself and also the suspension parts.

Notice also how much narrower the gearbox is at the top. Williams are extreme example.
The push rod can't do this, it needs structure to take all the forces and also to fit the parts imbetween.
Notice as well the cooling flow area. You can't leave the push rod lump exposed to the free stream, it has to be covered. Secondly, all those dampers and other parts are messing up the flow, so this is also a reason to have a bigger hole in back.

I should have made the pushrod 3 times fatter as well. :lol: Buckling load is related to the length, and Ferrari's push rod is extra fat because of the extra length to place it so far upstream.
What your diagram also fails to demonstrate is the distance to the diffuser of the area you think the pull rod is compromising. The pull rod rocker is pretty far upstream and on the floor. There is no aero disadvantage in that area.

Ask Torro Rosso, who are championing diffuser flow right now. They don't have the compromise on the floor that you are proposing.
Image
No exhaust compromise on the ground as you can see. And this uses a Ferrari engine and KERS to boot.
Last edited by ringo on 06 Mar 2011, 18:44, edited 1 time in total.
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ringo
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Re: The relative benefits of a pull rod suspension in 2011

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myurr wrote:@shelly: the narrowness is not a pull rod specific advantage, as shown in the diagram where it is actually wider at the base. Red Bull elongated their gearbox allowing them to create space to mount more of the components inside the casing, but that is a specific packaging solution rather than an inherent pull rod advantage, and is something that Ferrari looks like they've replicated for the pull rod.
No. Buckling load is related to length. Tension has no relation to length.
Longer the push rod the fatter it needs to be. So ferrari are actually limited in tat regard.
For a pull rod length doesn't matter much.
Ferrari couldn't do what redbull are doing with a pushrod. Oh yeah, they have to pass the push rod through the A arm. So that is another restriction to gearbox length.
I completely agree that this is a topic worth discussing, and I have no wish to stop that discussion or prove one side is better than the other. Where I feel the need to speak out is where some board members, not yourself, consider the pull rod to be a magical solution that doesn't involve any compromise and is the only valid solution for the 2011 cars. It isn't, and there are valid reasons for teams like Ferrari going a different route.
Oh Oh it's magic, you know !! never believe it's not so!!! Image

You see, i don't have to proclaim it's magic. All i have to do is release little facts here and there as the discussion goes on to prove that some things can simply be better.
I'm backing up the warlock rods with sound reasoning. I am yet to see a performance compromise so keep hoping and praying that there is!! :lol:
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imightbewrong
imightbewrong
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Joined: 07 Aug 2008, 16:18

Re: The relative benefits of a pull rod suspension in 2011

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A comparison I made a few weeks ago, make sure your browsers can show animated pngs
Image
http://i.imgur.com/6SIHi.png

The originals:
http://farm6.static.flickr.com/5213/540 ... 8d3e_o.jpg
http://farm6.static.flickr.com/5014/540 ... 47a0_o.jpg

The push-rod is definitely thicker.
Last edited by imightbewrong on 06 Mar 2011, 21:56, edited 2 times in total.

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raymondu999
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Joined: 04 Feb 2010, 07:31

Re: The relative benefits of a pull rod suspension in 2011

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Just a suggestion - could someone make an animated GIF out of these? Animated GIFs are universally browser-compatible, AFAIK
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Sayshina
Sayshina
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Joined: 04 Mar 2011, 21:58

Re: The relative benefits of a pull rod suspension in 2011

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ringo wrote: You should take into account the size of the gearbox and also what's behind it. and in front of it. Scarbs diagram was just a demonstation, so he used the same size on both sides. That is not the case in reality.
It's more like this:
Image

Red strokes are bad flow, green is good. Notice how much bigger the cooling exit is for the push rod. Also take note of what proportion of beam wing is exposed to bad flow from the push rod itself and also the suspension parts.

Notice also how much narrower the gearbox is at the top. Williams are extreme example.
The push rod can't do this, it needs structure to take all the forces and also to fit the parts imbetween.
Notice as well the cooling flow area. You can't leave the push rod lump exposed to the free stream, it has to be covered. Secondly, all those dampers and other parts are messing up the flow, so this is also a reason to have a bigger hole in back.

I should have made the pushrod 3 times fatter as well. :lol: Buckling load is related to the length, and Ferrari's push rod is extra fat because of the extra length to place it so far upstream.
What your diagram also fails to demonstrate is the distance to the diffuser of the area you think the pull rod is compromising. The pull rod rocker is pretty far upstream and on the floor. There is no aero disadvantage in that area.
Erm, you've arbitrarily added a massive total volume to the pushrod side with no justification other than it needs it to take the pushrod loads. The pullrod side also needs to accept loads, and unlike tubes, a structure like a gearbox housing is much more likely to be stronger in compression.

Both suspension concepts are ultimately feeding all of their loads into the gearbox, how does 1 setup manage to make due with 70% or so of the volume needed for the other?

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ringo
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Re: The relative benefits of a pull rod suspension in 2011

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I didn't add or remove any volume, that is how it is. Especially if you are taking a crossection nearer the wing.

rb5 box:
Image
Image
click to zoom.

I never said the structure is weaker for the pullrod either. It's simply at the bottom of the gearbox, in a better location. The best place to keep all the weight and structure is at the bottom.
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