Sagaris Bonnet stuff
Discussion
OK just spoke to Lisa at DM...ok so she rang to ask for £4k off me, but I thought Id take the chance to chat about bonnets anyway :)
Told her had 4 confirmed reports of this now and what did they know of it. She will ask James and a new techy guy there Gary and they will get back to me.
As to design...Ive been using the old grey matter again. These are my thoughts only dont forget and in no way conclusive. In my humble there are 2 aspects to consider. One is a quality issue on the retaining nuts and seals. Has there been a bad batch of a perfectly adequate design produced and that is the problem? Or, is there a design issue? Design issue with the retaining nuts/locking mechanism? Design issue with the bonnet. The airflow over the bonnet is fast flowing, fast flowing air as we know creates a low pressure area....lift. With the open trailing edges of the bonnet, you do allow backraft air to get under those edges. The air "bleeds" over the very top of the edge and gets sucked under it. Now, immediately after that trailing edge, in the space created is a partial vacuum, created by the fast flowing air above. What this means is there is an area of drag there. It is a very confused area of air, because air *is* being sucked out...hence one of the ways it expels heat, but air is also being sucked into that area. It is very turbulent air, a lot of buffeting, a lot of energy. If there is a weakness in fastening, it will expose this. Once you have started to buffet this enough and allow more air to get under there it doesnt take much to work out what will happen! So the question is, is there a flaw in the bonnet design?
Now, Ill throw another cpl of spanners into this.
1. The front splitters are ensuring less air goes under the car, this air has to go somewhere, either around the car or over. A lot of this extra air will be re-directed over the car. Now, I have no idea if TVR designed for this or not over the T350, but it does mean there is more air flowing over the bonnet and therefore for any given speed faster air and therefore areas of lower pressure over the bonnet. Lower pressure = more lift on the bonnet = more turbulence around the area of the trailing edges of bonnet louvres.
2.The initial design was for moving flaps in the bonnet. Now they are fixed. I dont know how much the shape and design of the flaps has changed from the moving idea to fixed, but I would be *very* suprised if the change in applications didnt have consequences when it came to airflow and pressure figures being produced over the bonnet.
These are just my initial thoughts ppl and Im working from no raw data here. I do have a cpl of suggestions for you though. Increase the robustness of your fastening mechanism. Whether there is a design flaw or not, talk to your dealers, look at the nuts and mechanism used and between you agree an upgrade. Choose to involve the factory or not, but I would recommend getting this upgrading done. I certainly will be with DM. Now I know there will be some amongst you who will try and argue you shouldn *need* to have to do anything and the factory/dealer/Santa Claus or whoever should be doing something. Tough. That isnt how engineering works, like it or lump it. Im shelling out the same £55k as you, Im in the same boat and Im telling you exactly the same path I will be taking. I strongly suggest you go down it. Ive just spoken to Ben at DM over the phone and I have said split pin, race fastenings on the bonnet. He has said yes that is a possibility, but we are waiting to see what the factory say and they *will* be getting back to him next week after investigation. So YES the factory are investigating this.
Everyone who cares to comment on this thread, please note: keep it civil and dont post without a little thought applied. This isnt a slanging thread and I dont want wild rampant speculation. We leave that to certain scriptwriters on PH with less knowledge of engineering.
Told her had 4 confirmed reports of this now and what did they know of it. She will ask James and a new techy guy there Gary and they will get back to me.
As to design...Ive been using the old grey matter again. These are my thoughts only dont forget and in no way conclusive. In my humble there are 2 aspects to consider. One is a quality issue on the retaining nuts and seals. Has there been a bad batch of a perfectly adequate design produced and that is the problem? Or, is there a design issue? Design issue with the retaining nuts/locking mechanism? Design issue with the bonnet. The airflow over the bonnet is fast flowing, fast flowing air as we know creates a low pressure area....lift. With the open trailing edges of the bonnet, you do allow backraft air to get under those edges. The air "bleeds" over the very top of the edge and gets sucked under it. Now, immediately after that trailing edge, in the space created is a partial vacuum, created by the fast flowing air above. What this means is there is an area of drag there. It is a very confused area of air, because air *is* being sucked out...hence one of the ways it expels heat, but air is also being sucked into that area. It is very turbulent air, a lot of buffeting, a lot of energy. If there is a weakness in fastening, it will expose this. Once you have started to buffet this enough and allow more air to get under there it doesnt take much to work out what will happen! So the question is, is there a flaw in the bonnet design?
Now, Ill throw another cpl of spanners into this.
1. The front splitters are ensuring less air goes under the car, this air has to go somewhere, either around the car or over. A lot of this extra air will be re-directed over the car. Now, I have no idea if TVR designed for this or not over the T350, but it does mean there is more air flowing over the bonnet and therefore for any given speed faster air and therefore areas of lower pressure over the bonnet. Lower pressure = more lift on the bonnet = more turbulence around the area of the trailing edges of bonnet louvres.
2.The initial design was for moving flaps in the bonnet. Now they are fixed. I dont know how much the shape and design of the flaps has changed from the moving idea to fixed, but I would be *very* suprised if the change in applications didnt have consequences when it came to airflow and pressure figures being produced over the bonnet.
These are just my initial thoughts ppl and Im working from no raw data here. I do have a cpl of suggestions for you though. Increase the robustness of your fastening mechanism. Whether there is a design flaw or not, talk to your dealers, look at the nuts and mechanism used and between you agree an upgrade. Choose to involve the factory or not, but I would recommend getting this upgrading done. I certainly will be with DM. Now I know there will be some amongst you who will try and argue you shouldn *need* to have to do anything and the factory/dealer/Santa Claus or whoever should be doing something. Tough. That isnt how engineering works, like it or lump it. Im shelling out the same £55k as you, Im in the same boat and Im telling you exactly the same path I will be taking. I strongly suggest you go down it. Ive just spoken to Ben at DM over the phone and I have said split pin, race fastenings on the bonnet. He has said yes that is a possibility, but we are waiting to see what the factory say and they *will* be getting back to him next week after investigation. So YES the factory are investigating this.
Everyone who cares to comment on this thread, please note: keep it civil and dont post without a little thought applied. This isnt a slanging thread and I dont want wild rampant speculation. We leave that to certain scriptwriters on PH with less knowledge of engineering.
PetrolTed said:
No problem, my comment wasn't aimed at you, just a bit of info I gathered this morning.
Snap Ted. Ill be informed of what the factory does/says next week also and Ill pass on what the factory comes up with. There are some things I cant say, but I thought it was only fair that those on here with concerns were given some idea of what might be going on and a reassurance path if they want.
hemo said:
another thread on the Sagaris forum about this folks
This is the Sagaris forum. I think you will find there is another thread on this in the general forum. That makes it a very good reason why this thread is here, it is for the grown ups to talk in and where the use of braincells is encouraged. I have no interesting in contributing to the ignorant slanging match in the general forum and so keep my analysis in here for those that want to read.
DJC said:
another thread on the Sagaris forum about this folks
This is the Sagaris forum. I think you will find there is another thread on this in the general forum. That makes it a very good reason why this thread is here, it is for the grown ups to talk in and where the use of braincells is encouraged. I have no interesting in contributing to the ignorant slanging match in the general forum and so keep my analysis in here for those that want to read.
sorry DJC...got my forums the wrong way round...
DJC said:
another thread on the Sagaris forum about this folks
This is the Sagaris forum. I think you will find there is another thread on this in the general forum. That makes it a very good reason why this thread is here, it is for the grown ups to talk in and where the use of braincells is encouraged. I have no interesting in contributing to the ignorant slanging match in the general forum and so keep my analysis in here for those that want to read.
i am,however ,very interested in your analysis,as i am one of the unlucky Sagaris owners that nearly lost a bonnet on the way down to Le Mans !!
OK, OK, back to topic please esp. as I believe it's a really important one.
Has any of the more observant ones among you noticed that the orange sagaris tested on autocar recently had a different design of service bonnet to the others?
I would describe it as just having outlet holes and lies flush with the rest of the bonnet. It's different to the angled plates of the original design which I prefer to look at but hey if it keeps things stable and fastened down, I'll take that.
The guy with the starmist grey one - andy95 - which you can hire also has this bonnet. You can see on his video of it going round brands hatch and it's rock solid - no wobble at all. And that's at what must be over 120 down the pit straight at Brands. Check out the video on his website as featured on his profile. So maybe tvr are already ahead of us this time....
>> Edited by the pits on Tuesday 21st June 20:32
Has any of the more observant ones among you noticed that the orange sagaris tested on autocar recently had a different design of service bonnet to the others?
I would describe it as just having outlet holes and lies flush with the rest of the bonnet. It's different to the angled plates of the original design which I prefer to look at but hey if it keeps things stable and fastened down, I'll take that.
The guy with the starmist grey one - andy95 - which you can hire also has this bonnet. You can see on his video of it going round brands hatch and it's rock solid - no wobble at all. And that's at what must be over 120 down the pit straight at Brands. Check out the video on his website as featured on his profile. So maybe tvr are already ahead of us this time....
>> Edited by the pits on Tuesday 21st June 20:32
DJC - you mention the bonnet vent being fixed now, & my initial thought was that this might be part of the problem - but I would be suprised to see the factory fitting adjustable vents as origonally designed.
Would that make a whole lot of difference at speed to the fixed vents we see on the current cars?
As Im sure you know, most Tivs suffer from the bonnet lifting at speed but they (generally) manage to stay put - surely its just a case of the fixings not being very good, & hopefully easily rectified. The split pin suggestion sounds like a winner - how is it fixed at the moment?
Nick
Would that make a whole lot of difference at speed to the fixed vents we see on the current cars?
As Im sure you know, most Tivs suffer from the bonnet lifting at speed but they (generally) manage to stay put - surely its just a case of the fixings not being very good, & hopefully easily rectified. The split pin suggestion sounds like a winner - how is it fixed at the moment?
Nick
the pits said:
OK, OK, back to topic please esp. as I believe it's a really important one.
Has any of the more observant ones among you noticed that the orange sagaris tested on autocar recently had a different design of service bonnet to the others?
I would describe it as just having outlet holes and lies flush with the rest of the bonnet. It's different to the angled plates of the original design which I prefer to look at but hey if it keeps things stable and fastened down, I'll take that.
The guy with the starmist grey one - andy95 - which you can hire also has this bonnet. You can see on his video of it going round brands hatch and it's rock solid - no wobble at all. And that's at what must be over 120 down the pit straight at Brands. Check out the video on his website as featured on his profile. So maybe tvr are already ahead of us this time....
>> Edited by the pits on Tuesday 21st June 20:32
The Pits...mine should arrive within the next couple of weeks.. will let everyone know the design..
PS
- still really looking forward to it Nick...ive never noticed my Griff bonnet flexing at speed. No lift, nothing, solid as a rock. There is also another aspect of this bonnet situation that is certainly exacerbating the situation but I dont want to mention it at the moment. A little brainpower should possibly be able to work it out from what I said in the first post however.
I am sure the factory will not go back to movable vents. I would imagine what Pits is saying about already seeing a different vent design is accurate. Having them flush creates much less of an aerodynamic effect than having them raised into the airstream. You are "exciting" the air much less and so it has much less energy as it passes over the surface. You are also creating a much smaller hole under the trailing edge of the vent for a semi vacuum to form and the air to be turblent in and work underneath the flaps.
Cleaner designs are almost *always* a better design. There is an argument that road cars work best without aerodynamic aids and that design effort should be concentrated upon making the car as "clean" as possible. I kinda agree with it. The raised flaps as they currently are are effectively acting like an aero device.
I am sure the factory will not go back to movable vents. I would imagine what Pits is saying about already seeing a different vent design is accurate. Having them flush creates much less of an aerodynamic effect than having them raised into the airstream. You are "exciting" the air much less and so it has much less energy as it passes over the surface. You are also creating a much smaller hole under the trailing edge of the vent for a semi vacuum to form and the air to be turblent in and work underneath the flaps.
Cleaner designs are almost *always* a better design. There is an argument that road cars work best without aerodynamic aids and that design effort should be concentrated upon making the car as "clean" as possible. I kinda agree with it. The raised flaps as they currently are are effectively acting like an aero device.
where's andy95 when you need him. Andy, if you can post some pics here of the new bonnet that would be most interesting. Plus what's you're view, it certainly looks more stable than mine on your video.
Djc, aren't the bonnet flaps making more downforce at the front as well as the inevitable drag?
Djc, aren't the bonnet flaps making more downforce at the front as well as the inevitable drag?
Apache said:
DJC, my Griff bonnet used to bang up and down quite severely and I tried all manner of things to stop it, I'd be interested in your view on this (offline if you wish)
I'm pretty clued up on aerodynamics myself and did wonder how the production Sagaris would fare
Nope, never seen it on my Griff bonnet neither, steady as a hard thing.
PetrolTed said:
No problem, my comment wasn't aimed at you, just a bit of info I gathered this morning.
Ted,
when you speak to the factory again can you ask them the cure to stop the Chim 500 bonnet popping right out the mountings at 1.5 leptons as well please...
Hughesie2
P.S My passenger who has never been in a Chimaera before shat himself...
the pits said:
Djc, aren't the bonnet flaps making more downforce at the front as well as the inevitable drag?
Increasing the downforce comes at a price unfortunately which is that the parasitic drag also increases, and because the effect of parasitic drag rises rapidly with speed this additional downforce is really only of value at low speeds, so ideal for holding the nose down into corners but not so good at high speed. The ideal would be to move them, much like the trim on an offshore power boat.
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