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MG Midget and Sprite Technical - Boot spoiler in aluminium
|Having partially hi-jacked Guy's bodywork thread and now found someone who is potentially a better bet to re-skin a standard Sprite/midget boot lid and incorporate or add an aluminium boot spoiler into the design, I've started a dedicated thread for this subject.|
I have reliable test data, at least for my car, on the effectiveness of a boot spoiler. Consequently if your car has a front spoiler or air-dam it will almost certainly benefit from the fitting of a boot spoiler (in one if the sizes and positions I tested) even at speeds starting as low as 60mph. Obviously every car is different so the benefits will vary from car to car.
So drop me an e-mail if you are interested in buying an aluminium boot spoiler or having a boot lid re-skinned in aluminium and a boot spoiler added to it.
|Did you follow up on that link I posted to the Nuneaton company?|
|Aah Prop... |
This is right up your street. Let's see your low-cost version!
Daniel - joking aside do you have any figures to share about the effects? Very intriguing.
|Guy - Yes - though it was someone else who provided the detals.|
Prop - you need to try to keep up! I didn't spend a lot of money in a full scale wind tunnel with my Sprite just to take photos! I realise I haven't posted a Youtube clip of the rear spoiler, but I do have footage! So, yes, I have precise data on CDa and lift without the spoiler and with one in 4 different configuratons (2 positions, 2 sizes).
|Daniel, my link did provide the details!|
I presume what you mean is that someone else also suggested them. ;-)
Are you having a premonition about Prop's response? He hasn't posted yet!
I wouldnt do anything less thwn. 1983 Porsche whale tail spoiler on thw back of the midget...haha
I seem to remember Simon Wood fitted one of those on the back of a frogeye racecar some years ago and found there was too much down force.
For the avoidance of any doubt, that's not me!!
|Good luck with the project Daniel, be interested to see how it goes|
My apologies I was thinking of another Simon that posts here from time to time.
|Simon Page - A cut down whale tail and possibly it's his car on page 40 of Simon McBeath's book.|
|Wouldn't an aluminium snow shovel do!!!!!|
|Having a whale tail spoiler is not about actual performance as Porsche found out... its more about making panties hit the floor... weather thats a 20 year old sweedish bikini swim suit modle or a steven devines ...well lets just say the jury is still deliberating that one|
There was a company state side maybe 15 years ago that did offer for a short time some kind of whale tail for the midget ... but it was a flash in the pan.. they did flared fenders amd other fiberglass body parts as well... but there name completely escapeess me at the monent
Danial... what application would this spoiler be used for... drag racing?
Im just not aware of the back end getting light or needing extra teaction.... but i can see the advantages of a spoiler and living proof of the need for a front spoiler
I cant imagine you would need much spoiler on the back
Jist a thought but what about modifing the nice looking luggage racks with the 4 flat slats.. it has a little legg at the back used for tying down the picnik basket that wohld be ideal as a spoiler ... and no mods to the car
|This luggage rack...mine
|In fact you could even make an altered angle insert that would just sit on top of the luggage with a little tail flip to rest agianst the back of the rack and zip tie onto the 4 slatesinto place for easy removal for street use ...plus make the insert louvered or even adjustable louvered like a heat vent to control the amount of down force you want you want applied|
By altered angle i mean ... so that the front of the spoiler is lower then the rear of the spoiler as it is now based on the shape of the car
Intead of aluminume maybe stianless steel to avoid any flapping distrortion
|On 2nd thought....bad idea ... that is a whale tail and and create way to much down force even ...that would be about guessing 5 sq ft of surface area|
Maybe make something in stainless steel sheet that can be zip tied and just that back high part and has some kind of angle adjustablity designed into it for fine tunning
The best part ... no body modification and its a duel purpose... piknick basket holder by day and race spoirer by night
|I don't think that Daniel's aim is to do with down force. Its about reducing the drag on the back of the car by smoothing the air flow and reducing turbulence off the back of the boot. |
Most aerodynamic performance road cars these days gain any necessary downforce by ducting and shape of the underside of the car, not by use of an oversized spoiler. They then reduce drag by shaping of the rear of the car with quite subtle boot spoilers. Anything more than that is just for looks and isn't used these days on any decent designs.
|So he is just looking to increase the efficiency of the air flow across the back of the car ???|
Initial thoughts are just a slip on box ... but if you thought pre mid 80s shoe box volve station wagons where rat butt ugly... this could be that but ugly on stroids.
Winnings not everything....haha
It also may be down to reducing rear lift at speed, just ask VAG regarding the Audi TT and IIRC the modern Beetle.
|A rear wing creates downforce but also creates drag and so a wing indirectly uses power to deliver downforce and so your car ultimately has a reduced top speed but will corner faster (unless the wing is stalled...).|
A rear spoiler reduces lift and (at least in my testing on my Sprite) reduces drag as well.
A reasonably subtle boot spoiler on the Sprite/Midget will therefore either increase mpg or top speed but always reduce lift and thereby increase stability. It could be made in steel or GRP but that would increase weight unnecessarily. Testing proved effective from a speed as low as 60mph and obviously worked at higher speeds - simply providing greater benefits.
I already have a boot lid with a spoiler that works - in 4 different configurations - some configurations reduced more lift than others and some reduced more drag than others, while some reduce more lift and more drag than others, but they all worked. All I need now is a neater and lighter copy of that spoiler which I'll be having made in my preferred configuration. It's possible that being a tidier design it will be slightly more efficient than my test model.
The test data on the rear spoiler will be on page 167 in about 8 weeks time.
Im a bit confueswd...
what is the application for this modification (everyday use or 1/8 mile dirt track racing) and what are you wanting the end results to be and what is the purpose of this thread..aka how to make it or best design ideas
|Prop - you're still not keeping up!|
Fitting a rear spoiler provides a benefit in everyday driving from speeds of 60mph upwards (lower speeds as well I guess).
The end result for me will be a neater and lighter spoiler than the 'test mule'.
The purpose of the thread is to see if anyone else is interested in having a boot spoiler or re-skinned boot lid or spoiler so the person who will make one for me can potentially make a few more and everyone gets one a bit cheaper. Also the person making them has the advantage of working from the 'test mule' for all the spoilers, not just mine, which again should reduce the time they spend making one.
Based on that small amount of video just reducing the pitch of the hood at the back would do alot to help airflow effecancy
Im aware of what guy mentioned about controlling aerodynamics from under the car grsnted the knowesge is above my pay grade...
have you looked into that considering the amount of wind distrortion id think is present with the rear axle fuel tank and muffler ...esp if the muffler is the 1500 design
i could see how a fflat sheet under that whole back end could have a big impact on handling and down force if all those obstructions were taken out of play.
(Remember to remove the S from the end of https to make it cljckable)
Thank you... now i think im on the same page as everyone else or at least with down syndrom timmy
that little spoiler sure does the job you wanted it to do.... do you have a wind tunnel vid of what the smoke looks like withOUT the spoiler
Thanks for sharing that....
|Hey Prop, be careful what you say about boxy volvo's...
|Alex G Matla|
|At the time i wasnt a fan... but the old shoe box volvos do have some sex appeal now|
|Off topic but Alex,that fire extinguisher does look to be awefully close to the Volvo?|
Daniel: A new powertune book!!!
|There isn't a picture of what the smoke visualisation looks like without the boot spoiler because most of the testing is done without smoke. |
The test vehicle (in this case my Sprite) sits on 4 sensitive pressure pads in the wind tunnel - one for each wheel. As the wind passes over the car (at higher speeds than used for smoke visualisation) the pressure pads measure the difference in load on them. In my case the pressure was reduced due to lift. The data is calculated and presented on a computer print out of front and rear lift and CDa - for each test undertaken (I did a test for each of the 4 configuration changes of the rear spoiler)
So, the smoke isn't part of the measurement of the efficiency of the aerodynamic changes made in testing. Rather it exists to show what the air is doing (visualisation) so the aerodynamic experts can see what they might want to change to improve the efficiency.
Prop - you are 'on the money' for considering aero improvements under the car (if you get chance to see what the 1960s Le Mans Spitfires looked like underneath you'll see what might be achieveable as well as the problems. It's also possible to create a venturi section at the rear of the car with the aim of creating suction. However, all of those things take time and money which I never have much spare of. It's also possible for simpler and equally effective gains to be made elsewhere on the car.
Fitting a fast back design - 'reducing the pitch of the hood at the back' might create a more aerodnamic shape but also create more lift which would need to be addressed with a fastback/boot lip spoiler which might increase drag on a fastback design - I'm not certain.
The next priority, after a nicer spoiler than my test mule used, is wing vents which I'm confident will reduce drag and lift at the front of the car and possibly at the rear.
|Id seen a phofo of a spridget that some had add vents on top of the wings like the 1970ish mclearn Fi that was supposed toadd more down force...interesting but ugly|
|Daniel, I have the first two editions. I'll be keeping an eye out for the next. 😉|
|Daniel, I may have missed it in the discussion, but did you test it with the hood up and down? I don't usually drive with mine up. Of course, I don't drive a lot over 65 either! :)|
|With the hood down the drag was significantly increased while the lift was significantly decreased.|
|Is that because of the turbulance from the cockpit...i have not driven mine hood down in years...odd I know...i guess i just love the hard top to much...it really cuts thur the wind with such ease|
Or im just really that lazy that i cant be bothered by the 5 min needed to remove it....haha
|More drag because the shape of the car with the hood down and less lift because of the shape of the car with the hood down. It needs a lot more words and a more knowledgeable person than myself to explain properly, Prop.|
|Many years ago the plastic boot badge detached itself while I was doing about 60mph (roof down). The turbulence threw the badge forwards, where it hit the centre of the windscreen, bounced off and landed in my lap.|
This thread was discussed between 16/01/2017 and 25/01/2017
This thread is from the archive. The Live MG Midget and Sprite Technical BBS is active now.