Tony C

Yup. I'll leave it a few days to give all a chance to indicate what they require. Also I'll check the delcity site for alternative wire attachments to the switch as I don't know whether everyone who wants a switch and a cover would prefer screw attachment or spade. I think our cousins across the water may use different terminology. The site includes pictures, so I'll report back later for preferences. No doubt as soon as I place the order, more people will indicate a requirement, so I'll order a few spares. Later with info, TFC

Julian, Thanks for the info. I remember seeing the wind tunnel thread, but couldn't see any data. Basically, that was what I was after. As far as your not being "university schooled in aerodynamics (by your own comments) so my results will be very common sense, I'm afraid, but nonetheless I will post them down when we get some nice weather". Me either; I just teach pilots and try to stick to the "hand out the window of your car" variety of instruction. I've managed to work backwards through Peter's data and can now see what is what. I appologise to everyone if I gave the inpression of being a "smart Arsenel" newcomer. I too will be interested in your findings - more power to you! It turns out that the student with a contact with a Formula 1 team was exaggerating, just a little. Regards TFC

One of my students has a contact in one of the F1 teams. I'll try to arrange for a seven to be wind tunnel tested in various configurations, in order to come-up with some definite figures for both Lift and Drag. From the point of view of a basic understanding of an extremely complex subject, I think it is fair to say that an improvement in one area of aerodynamic efficiency frequently leads to a reduction in efficiency somewhere else - look at the trouble the Jaguar team are having with their F1 aerodynamics. The Se7en's inherent efficiency is due to its excellent power/weight ratio, weight distribution and suspension geometry. It is worth considering that any attempt to significantly alter its aerodynamic performance would require modifying it so extensively that it would no longer be a Se7en - QED. Cooling drag, I would imagine, is a significan contributor to its Total Drag. I've seen some discussion concerning partially fairing-in the bottom of the engine compartment, leaving a small opening to allow efficient cooling airflow. The cooling exhaust grille's on the top of the bonnet would be another source of Drag. Sorry to talk aircraft again, but the P51 "Mustang" of WW2 vintage was significantly faster than its peer fighter, later Marks of Spitfire. This was due to two things. Firstly its laminar flow wing, which is of no significance here, but also to its reduction in cooling drag, entirely from the clever design of its radiator inlet and exhaust ducting. This was designed in such a way to generate "negative drag". It consists of various cross sectional areas of inlet duct and a variable area exhaust (to cater for different 'speeds'). I'm not suggesting for a moment that such a complicated system be considered for a Se7en, the weight increase alone would negate any saving in drag, but an accurately calculated exhaust for the cooling air from the engine compartment might give a worthwhile reduction in cooling drag. Something like this would need extensive trial and error and use of a wind tunnel - so I guess it's not really practical. I think we all have to accept that using empirical values for Drag is possibly going to lead to false assumptions - has the quoted advantage from removing the standard windscreen been verified, or is it an empirical value. Bear in mind that just calculating the result of the reduction in cross sectional area is possibly going to result in an optimistic (that's not spelt right!) assumption. The car has the aerodynamics of a brick, but if removing the standard windscreen and fitting an aero screen gives a perceived advantage - as I'm sure it does - wack-oh!!! At least this discussion gives me something worthwhile to do while waiting for my SV to be delivered. If you want me to shut-up about it - all you have to do is ask - I'm not too sensitive. Best Regards TFC

Thanks for the detailed info' Joe and all your help. TFC

Peter, Sorry to keep going on about this, but there are a couple of things I do not understand, which maybe you would be willing to explain. I instruct Principles of Flight to Airline Transport standard and the Parasite drag formula we use is: Parasite Drag equals half the air density, multiplied by Velocity squared, multiplied the Drag Coefficient (Cd), multiplied by frontal area. I am not aware of any other formula for Parasite Drag. Parasite Drag is made up of: Skin Friction - hardly of significance in this case, Form (pressure) Drag - which is the difference in pressure between the leading edge (front) [higher than atmospheric] and the trailing edge [pretty much atmospheric], and Interference Drag - made up of the interference between the boundary layers of the components where they attach to one another. Drag coefficient is the ratio of Dynamic Pressure (half the air density multiplied by the velocity squared) to "Drag Pressure" (Pressure differential between front and back. For example: a sphere of any cross sectional area will have a Drag coefficient (Cd) of 0.6 Can you tell me what CdA is? How can the aerodynamics of a car differ from those of an aeroplane? Scale effect? In this case it has no significance - in my opinion. Very confused of Aylesbury, Respect, TFC

OK guys. I'll wait for a while to see how many people want stuff from delcity before making the order. I want to make sure that the switches I purchase on your behalf are of sufficient amperage, can somebody please advise what current the ignition circuit draws? TFC

Nice One Joe, thanks. I wouldn't mind organising a bulk purchase - who would like one. Either buy the covers and switches or just the covers and source the required switches from Farnell - they seem cheap enough. I checked at work today and still await details, but as they are MIL Spec'. aircraft parts they're likely to cost a WHOLE heap more than US 2.50. Regards Tony

Peter, Bli'me! Please understand, I'm not disputing anything you say; you seem to have fact and figures to back-up you calculations. Bearing in mind that the rolling resistance on the rolling road might be slightly different to the rolling resistance obtained on the road - my estimation is that it can't be significantly different. What other value can be used to give a reasonable estimate of Thrust Available? Maybe you can e-mail me the data you have on Drag and Cd of a car. I've been using the basic information relating to aircraft - as I consider it to apply to a car. Where do you get the 34kg force reduction from changing the standard screen for aeroscreens? My understanding is that if you consider the Se7en car, it will have a Cd of, I am now aware, of 0.7. and an estimated frontal area of 1.6 square metres. If the standard screen is exchanged for an aeroscreen, the frontal area is reduced, but the Cd will probably increase because of increased Pressure Drag due to the more open cockpit. I guess the only way is to put a Se7en in a wind tunnel on balances so that Drag (Thrust Required) can be measured with various configurations. BUT, I "think" that using my "back of the envelope" figures could be used for comparison purposes, rather than empirical values. Good stuff, eh? Best Regards Tony

No worries Hoopy, I need all the eggs I can get. TFC

What a 'Numpty' I am, sorry - not up to speed yet on the shorthand. I saw the guarded switches on DT and thought they were a bit expensive. Didn't see the covers alone, I'll look again - thanks. I work at Oxford Airport so will try to get hold of an actual aircraft cover to see if I can discover the manufacturer - maybe the cost price will be more reasonable. They are probably of American manufacture though. TFC

Thanks for the info' Mark. Can you be a little more specific about DT please. I visited a DT Electronics website, but it seemed to be all about computer stuff. I'm after a red plastic guard for a toggle switch. Hoopy, A 25A switch from Farnell is only 3 quid something. I'm assuming 25A will be enough for most things - what is your view? TFC

Does anyone know where those red 'plastic' switch guards can be purchased. I've seen the ones advertised on Demon Tweeks, but I'm certain they can be obtained much cheaper without the switch. I've found a couple of US websites which sell just the guard for between 13 and 17 US Dollars. The switch can be obtained for a couple of quid from Farnell's; I've just ordered my Big Red Start Button from them for about 8 quid + VAT. I don't have my car yet, but I'll soon have a start button!!! My SV doesn't arrive until next April and I'm going nuts trying to occupy the interminable waiting time, visting all your web sites and reading BlatChat for advice and tips. Regards TFC

Not really! What on earth are wobbly wheels? TFC

Or a loose plug.

I suspected there would be solid technical reasons for them not being a good idea - pity though, they do add a nice 'look' to certain cars. One of the guys where I work has a Morgan with wire wheels - sigh! I had them on my MGC - now there was a poor excuse for a car TFC

I guess that about sums it up then. It's just that I came across a website which advertised wire wheels for a se7en and wondered if they looked good or naff. TFC

Pardon the silly question, but has anyone ever seen a Se7en fitted with wire wheels? TFC

The Thrust figures I quoted are very accurate. When I mentioned 'roughly' I was refering to the approximate, but not too bad Drag figures. As we all know, acceleration is proportional to Thrust (Force) and inversely proportional to mass. I worked out the thrust figures using a rolling road trace; what is required is the hp at the wheels. I understand the rolling road supplies wheel torque and all other values are calculated from that - can anyone confirm my assumption. The formula for Thrust is Wheel hp x 550 ft/sec divided by vlocity (ft/sec). Regards TFC

About 10 percent of very little. Cover-in the cockpit - now you're talking. TFC

I saw an old thread which referred to the possibilities of making the Se7en more aerodynamically efficient and though this might help pass some time during these long cold winter evenings. The formula for Parasite drag (Form [ pressure] Drag plus Skin Friction Drag plus Interference Drag) is:- Half the air density multiplied by Velocity squared multiplied the Drag coefficient multiplied by the frontal area. You must use SI units (kg/cubic metre for density, metres per second for Velocity and square metres for frontal area). The resulting Parasite Drag will be in Newtons. Don't despair, it is quite straightforward really!! If we consider Sea Level, the air density is 1.225 kg/cubic metre on a "Standard" Day, so half of that makes it 0.6125. 50 mph is 22 m/s - near enough 100 mph is 44 m/s - near enough But don't forget the velocity has to be squared. The Drag Coefficient (Cd) of a flat plate is 1.2, a sphere of the same area is 0.6 and a streamlined shape of the same area is 0.06. The Se7en body alone is quite streamlined, but I think that because of the openings - cooling air intake, cockpit, gaps in the front suspension and all the openings underneath it might be better to use 0.6 for the Cd as a rough guess (WAG). Frontal area is roughly the area of a frame through which the car could roll - I need an estimate here because I haven't got my car yet!!! From the dimensions in the catalogue, I estimate 1.6 square metres. All that gives: 0.6125 x 22 x 22 x 0.6 x 1.6 = 285 Newtons Divide that by 9.81 gives kg (not really the 'correct' thing, but who cares!): 29 kg at 50 mph However, because of the speed squared function, that will be 116 kg at 100 mph. Frontal area can be reduced by, for example, replacing the standard windscreen with a wind deflector, but what you have gained on this particular 'swing' will probably be lost in the increase on the 'roundabout' of increased Form [pressure] Drag and Interference Drag from the big hole filled by a big body, of the cockpit. With a 140 bhp K Series engine, six speed gearbox, 205/50 15 tyres and 3.62 Diff', changing up at 7000 rpm in each gear gives approximately: 291 kg Thrust at 50 mph and 188 kg Thrust at 100 mph. At 50 mph only roughly (291 - 29) 262 kg is left to accelerate the car, but at 100 mph only (188 - 116) 72 kg Thrust remains to accelerate the car. Obviously, any reduction in Parasite drag will significantly improve performance. Regards Tony

All you wanted to know about engines, but were afraid to ask! I came across this website: http://www.howstuffworks.com/category.htm?cat=Eng today and thought it might interest those with less than a full understanding of engine basics. It's American and the animated piston engine doesn't seem to use the modified Otto cycle, but it gives the basic idea. Cam's, gear ratio's, dynamometers - it's all there. Enjoy, Tony

I know what you mean Scott. The se7en I test drove had a six speed box. Everything about the se7en is OUTSTANDING, that's why I ordered one. I drive 70 miles to and from work every day (currently in a Polo GTI) and lately I've been analysing both my driving and speeds into and out of corners, roundabouts and bends - sad isn't it? It's all very well using the se7en to its limits on an empty road or the racetrack, but the roads I drive on have other cars and I've found it's not safely possible to 'wang' the car around too much. (I'm one of those weirdo's who prefers to keep all four wheels on the ground and the rubber on the tyres). For example, if traffic allows, I drive onto roundabouts at about 20 -25 mph in second gear. The se7en engine rpm is within 50 rpm whether it's a five speed or a six speed box. "Distant sound of cat landing among pigeons!" By the way, if anyone's interested, I have a couple of formulae to calculate (roughly) the lift from flares and/or the drag from a standard windscreen - or indeed any other protuberances you fancy. Regards Tony

Thanks guys, I can work out my ratio's now. Stll not convinced about the advantages of a 6 speed when I'm only going to drive on the road. I know this subject has been done to death, but despite all the calculation in the world it must end up being what 'feels' better - and I guess to those that have tried both, the 6 speed feels better. Regards Tony

Thanks guys, I can work out my ratio's now. Stll not convinced about the advantages of a 6 speed when I'm only going to drive on the road. I know this subject has been done to death, but despite all the calculation in the world it must end up being what 'feels' better - and I guess those that have tried both, the 6 speed fools better. Regards Tony

Need the size of the Avon Road tyres fitted as standard to SV rear wheels. I'm trying to calculate gear ratios. Has anyone got anything nice to say about the 5 speed box / 140 bhp 1800 cc engine, for purely road use? "Boat Anchor" is not an answer I'm looking for. Thanks