The effects of airflow on the weights and balance of a Caravan.
iana said
11:25 AM Nov 21, 2020
The one thing I notice when the discussion of weights and balance take place, is that the vehicle and van are stationary. However once the unit is in motion, we have the effects of air flow over the van. There would be a high pressure area at the front of the van, and a low pressure area (drag) at the rear, also the effect of parasite drag over the surface (Air con, vents etc).
This would exert a turning force about the axle pivot point, tending to rotate the van backwards, this in turn would have the effect of reducing the ball weight, and moving the center of gravity back. Even the weight of the van could be reduced depending on the amount of lift created over the van.
The interesting thing is, the effect of this would also increase, the faster a van was towed (don't be funny and say it will leave the ground above 130 Kpa). But I have never read anything about this effect, and wonder if this has attributed to some of the van accidents.
Whenarewethere said
11:55 AM Nov 21, 2020
One could build a 3d model of their setup up & do a wind tunnel simulation, or drive slower & do not put weight at the extremities.
Rob Driver said
12:10 PM Nov 21, 2020
Iana you are correct.
It is most obvious when encountering certain road conditions such as high bridges across river gorges like some on the Hume Highway.
These situations are generally marked with wind socks and signage.
Having said that, there are many other situations which may cause instability.
The main one encountered by caravanners is when passing a large truck in either direction.
The air pressure differential created by the moving truck and to a lesser extent by the moving van will cause the lighter weight vehicle to become unstable.
This situation is not new to any experienced caravanner and most good truck drivers are aware of the effect of their vehicle on lighter vehicles and in particular, caravans.
As you point out above, the caravan and car combination creates instability just purely by design.
The speed of the vehicle also may magnify an already dangerous situation.
As we drive down the road there are many Vanners who may not notice this, but if approaching a good truck driver that truck driver will move his vehicle to travel along the fog line so as to create a larger gap between the two vehicles and this reducing the effect caused by the low air pressure area between the two vehicles.
A word of note is dont expect this courtesy from all truck drivers as many of them are either cowboys or just really dont know or care.
A car and van combination can become the most unstable unit we may have on our roads and my view is that the drivers of these combinations need specialist training BEFORE being permitted to operate thei vehicle on a public road.
Regards
Rob
iana said
01:28 PM Nov 21, 2020
Rob, you also raise an interesting point, in as much I hear of vanners feeling the efects of trucks passing, and wondered if that was due to the air (pressure) being trapped between the two vehicles, either pressure or vacuum. With our van which is very high off the road, with plenty of clearance underneath, can allow these pressures to escape. The most we have felt with a road train, or a large semi passing is a little nudge, quite often we don't know its there until its beside us, but we have little or no effect. However I wonder how the English designed vans get on, with less escape for the air pressure.
Just furthering on my original post, it also makes one think about the advantage of having a pow profile van (pop top), reducing the turning effect, and then the opposite and that is these small full height vans that just look like a lever on wheels.
Whenarewethere said
02:52 PM Nov 21, 2020
You can see why one gets a lot of dust on the back of the car.
Test aerodynamic of caravan
https://m.youtube.com/watch?v=karGqjCZOV8
Also with roof box on car roof
https://m.youtube.com/watch?v=sweZltfD-no
Every setup will be different, but it gives some indication of what is happening.
Whenarewethere said
02:56 PM Nov 21, 2020
iana wrote:
Just furthering on my original post, it also makes one think about the advantage of having a pow profile van (pop top), reducing the turning effect, and then the opposite and that is these small full height vans that just look like a lever on wheels.
Isn't a problem with pop tops is the extra weight up high to strengthen the pop top structure.
Swings & roundabouts!
Whenarewethere said
03:08 PM Nov 21, 2020
I have a crap on my roof but have done my best to tuck it all in as tight as possible. Also thinking of getting a wheel cover to have a smooth front surface.
You could put a aero foil on the tug, air goes right over van, less drag, no bugs on van, do not even feel a road train go by and better fuel economy
Or you could join the tug to the caravan and call it a motorhome....
Cheers,
Peter
Bobdown said
07:37 PM Nov 21, 2020
Peter_n_Margaret wrote:
Bobdown wrote:
You could put a aero foil on the tug, air goes right over van, less drag, no bugs on van, do not even feel a road train go by and better fuel economy
Or you could join the tug to the caravan and call it a motorhome....
Cheers,
Peter
Yes Peter, been there and done that, Jayco Conquest years ago.
There isn't a truck on the road without some sort of aerodynamics, like your in-built air foil at the front of your rig.
Cheers Bob
yobarr said
07:59 PM Nov 21, 2020
Peter_n_Margaret wrote:
iana wrote:
With our van which is very high off the road, with plenty of clearance underneath, can allow these pressures to escape.
I suggest that the greater the ground clearance, the worse the aerodynamic drag will be, and by a significant margin.
Cheers,Peter
I would be very interested to receive input from someone who knows the answer to Peter's 'question',as my van has underfloor clearance of over 700mm.I had an aerofoil fitted to the roof of the car,but got rid of it because I was advised that,being over 2 metres from front of the van's sloping front roof area,it would have very little effect,as a result of turbulence between the vehicles.Cheers
-- Edited by yobarr on Sunday 22nd of November 2020 06:45:48 AM
Bas + Eve said
09:27 PM Nov 21, 2020
V1....Rotate
Tony Bev said
09:33 PM Nov 21, 2020
Hi Ian
In my opinion, there is a good chance, that wind may be a contributing cause of RV accidents, and/or alter the weight distribution
I have no idea how the RV manufactures could plan for it, except to put a sticker on, saying slow down in high wind, etc
I certainly feel the wind in my RV, as it has a high roof
I can tell if it is a headwind, tailwind, or which side it is coming from
I also know that going slower, with noticeable wind around, is the safer option
iana said
09:41 PM Nov 21, 2020
I think yo-all need to re read my original post, we've gone off track, funny that never happens on here.
Tony you stand on the roof of my van when we are moving you will find there is wind up there.
p.s. could be down your way next year with a house sit.
Ian
Tony Bev said
10:11 PM Nov 21, 2020
Hi Ian
To get back on track, it will be a pleasure to catch up with you again, when you are down this way
Rob Driver said
10:16 AM Nov 22, 2020
iana wrote:
Rob, you also raise an interesting point, in as much I hear of vanners feeling the efects of trucks passing, and wondered if that was due to the air (pressure) being trapped between the two vehicles, either pressure or vacuum. With our van which is very high off the road, with plenty of clearance underneath, can allow these pressures to escape. The most we have felt with a road train, or a large semi passing is a little nudge, quite often we don't know its there until its beside us, but we have little or no effect. However I wonder how the English designed vans get on, with less escape for the air pressure.
Just furthering on my original post, it also makes one think about the advantage of having a pow profile van (pop top), reducing the turning effect, and then the opposite and that is these small full height vans that just look like a lever on wheels.
Hi iana
The varying size and shape of trucks, semi trailers and their respective loads will cause varying effects on the lighter vehicle while travelling in proximity.
It is my experience that when both vehicles are travelling in the same direction there is created a low are pressure area between the two vehicles. The effect of this may be magnified with road train configurations and may also result in an extra buffeting from wind or varying air pressure due to the gap above the dolly between the two (or more) trailers.
When the two vehicles are travelling in the opposite directions the shear volume of air created by the moving truck manages to buffet the lighter caravan at the moment the two vehicles meet and then as they pass each other the movement creates a lower air pressure area between the two vehicles which will cause the lighter vehicle to be drawn toward the heavier one.
These situations may also vary with speed which is obvious but also with wind direction and speed.
All these situations need to be taken into account when towing a caravan at speed when operating with trucks and in particular, large volume semi trailers and combinations.
Apart from being a professional driver for my working life I have also owned various caravans, campers and tow vehicles.
My current van is classed as off road and is higher off the ground than any other van I have ever owned. My observation when towing this new van is that it is a lot more stable in the passing truck situation than was any other van that I had owned.
Now without more research I can not comment on wether the height is actually creating the situation of a lesser effect from passing trucks but I strongly suspect that this is so. This not only comes from my personal experience with my current van but from my observations when actually driving large truck trailer combinations.
From these observations my thoughts are that the vacuum is broken to an extent from the air flowing more freely under the van and helping to balance the varying pressures from each side of the van.
The same applies from the truck combination as well with for example a two trailer road train or B Double with irregular shaped tarped loads and on standard semi trailers will have a lesser effect than one of these newer aerodynamically designed and built combinations with large pan tec bodies with wings and wind deflectors between each unit of truck and trailers. As a driver this is a very noticeable difference between these various truck combinations. Many of these trailers are also built closer to the ground to assist with wind deflection and fuel economy.
I am probably guilty of going away from your original topic contents and enquiry but with your original observatIons of the instability varying with speed and movement is a fact and with a caravan and tow vehicle combination this situation is probably for the worse due to the simple fact that most of these combinations are a balancing act using near maximum allowances on both vehicle and caravan suspensions.
It is such a shame in this country that we as a consumer have to the most extent Boo Hooed 5th Wheeler caravans when in all honesty these combinations are just so much safer than our pig trailer caravans.
I am as guilty as anyone else as I chose to buy a conventional caravan mainly due to the cost and the general unavailability of Aussie built 5th Wheeler vans. Having bought this new van I am aware of the limitations being put on me by towing a pig trailer as opposed to a semi trailer but in the same breath I am not in a hurry and fully aware of the instability when operating a caravan in windy conditions, uneven road surfaces and in the proximity of large trucks and combinations.
Regards
Rob
-- Edited by bentaxlebabe on Sunday 22nd of November 2020 10:21:37 AM
Rob Driver said
10:26 AM Nov 22, 2020
If I may I should make mention that behind each travelling truck there is also a large vacuum area that need to be seriously considered by the driver of a car and caravan combination. I should not have neglected this in my above posts as this is a major cause of creating instability with a caravan.
Regards
Rob
iana said
10:44 AM Nov 22, 2020
Hi Rob, My original post probably not clear, was that all the careful weight calculations basically go go out the window once a tug-van combination starts moving, i.e. the rotational forces created rearwards, increasing with speed. Different designs, combinations, head winds, following winds what ever. So ball weights and all change.
You bring up some interesting points paralleling with my thoughts on the effects of the passing rigs, our van is quite high off the ground. We get more buffeting effect when there is a cross wind and have rows of trees along the road, but nothing that worries us.
It would be interesting to see wind tunnel tests on some of our rigs.
PS if you travel close enough behind a truck, one can save on fuel , don't try it, just joking.
Whenarewethere said
12:43 PM Nov 22, 2020
Open source fluid dynamics software
https://openfoam.org
A video for getting started
https://m.youtube.com/watch?v=KznljrgWSvo
Rob Driver said
01:53 PM Nov 22, 2020
Hi iana,
An apology to be still talking trucks but searching hasnt found much info on caravan aerodynamics.
I did come across this truck which has a aero wing fitted under the trailer. It appears to create a low pressure area directly under the trailer. This would be for improved fuel economy.
My thoughts with a caravan would be a system of creating downforce might be better for stability.
When thinking about the low pressure area created at the rear of a van may actually help to keep the unit straight by providing a drag at the rear.
Iana, your theory in your first post mentions both the high pressure at the front opposing the low pressure at the rear so my thoughts are by eliminating the high pressure at the front with maybe the use of a designed wing or foil, then this may help to keep the unit straight. The explanation in the video covers sway but not aerodynamics in design.
Here is the link to a video which explains a little about caravan sway or instability.
I am not a fan of linking to advertising but it does cover some interesting points.
It would be interesting if the rear of a caravan is too symmetrical left to right which causes an oscillation. Together with an added issue maybe just enough to cause the caravan to be unstable.
Tall towers or chimneys have a spiral so the air always goes one way & up.
If you have a look at Burj Khalifa tower the sub towers step up clockwise around the building to dissipate wind energy clockwise & up.
If buildings are not designed this way, wind will destroy them.
Mobi Condo said
07:13 AM Nov 23, 2020
A really interesting discussion here.
1st - BobDown, quote - "You could put a aero foil on the tug, air goes right over van, less drag, no bugs on van, do not even feel a road train go by and better fuel economy", do you have figures of fuel economy betterment before /after foil use? I am seriously keen to see the improvement - could be I go that way.
2nd - iana I have enjoyed all the contributions as they have been very informative.
iana said
09:26 AM Nov 23, 2020
Interesting, that rig i.e. the Silverline and ranger in the video clip, is similar to ours, I have to set some hearing apparatus up to listen to them, I'm a bit deaf, so have the sound turned off. Retired life is all a bit busy, and there are time I wish I had some time of my own.
I did a fair bit of "Aero dynamics" theory during my apprenticeship, we were taught clean was good. Have a look at the birds and fish, they can be blunt at the front, but they all taper cleanly to the rear. We tend to think in terms of say an arrow head being pushed through margarine, but the trouble is air, being a gas does not behave like that. The air swirls and eddy's and seeks out the low pressure areas. As for fitting aero foils, we really don't know what the effect is, unless it was tested in a wind tunnel in controlled conditions.
With regards the high pressure areas at the font of the van, we were taught that streamlining at the front (of an aircraft) was not that important, that there would be a pocket of Hi pressure air at the front, the on coming air would sense this, split into laminar flow streams and go around, but the rear was important. A bit of trivia, all goes well until we reach a speed of 550mph or so depending on altitude, the plane starts to go through the sound barrier, and **** hits the fan.
Whenarewethere said
12:53 PM Nov 23, 2020
Ideally one would want to use a wind tunnel with a moving road & rotating wheels.
The various TV programs I have seen over the years. Often very minor changes to an aircraft can make a lot of different.
A small amount of plutonium was put in the ends of the 747 wings to add some weight to stop the wings vibrating.
Wing tips to increase fuel efficiency on various aircraft.
High speed reconnaissance Spitfire had all the rivets made flush so they could get an extra 100mph out of it.
An old 747 weighs about an extra tonne with all the ground in dirt, so more fuel used.
Magnarc said
02:13 PM Nov 23, 2020
Ian, apologies for going off topic but your post reminded me of something that has puzzled me for a while. What is the origins of V1 and rotate when taking off. I would have thought that lift was a better description?????
iana said
11:23 PM Nov 23, 2020
I could Google the subject, however I have passed the question onto "The Big Gorilla" who will be far more versed and is a professional on that subject (ex 747 pilot).
Re the small things that effect airflow, back at one of the places I worked at, the chief pilot there asked me to install a big electric fan in the ****pit of his Piper Pawnee Ag plane. I refused, but we did make up an air duct on the roof of his canopy to give him fresh air. The first flight and he said it was unusable, the buffeting on the rudder made it completely unsafe.
I think you meant winglets on the end of the wings, they reduced, or effected the wing tip vortices' that also caused drag.
Re the flush riveting on the wing leading edge, and other areas, reducing parasite drag, common practice towards the end of WW2 on the very high performance aircraft that were being built.
The one thing I notice when the discussion of weights and balance take place, is that the vehicle and van are stationary. However once the unit is in motion, we have the effects of air flow over the van. There would be a high pressure area at the front of the van, and a low pressure area (drag) at the rear, also the effect of parasite drag over the surface (Air con, vents etc).
This would exert a turning force about the axle pivot point, tending to rotate the van backwards, this in turn would have the effect of reducing the ball weight, and moving the center of gravity back. Even the weight of the van could be reduced depending on the amount of lift created over the van.
The interesting thing is, the effect of this would also increase, the faster a van was towed (don't be funny and say it will leave the ground above 130 Kpa). But I have never read anything about this effect, and wonder if this has attributed to some of the van accidents.
One could build a 3d model of their setup up & do a wind tunnel simulation, or drive slower & do not put weight at the extremities.
It is most obvious when encountering certain road conditions such as high bridges across river gorges like some on the Hume Highway.
These situations are generally marked with wind socks and signage.
Having said that, there are many other situations which may cause instability.
The main one encountered by caravanners is when passing a large truck in either direction.
The air pressure differential created by the moving truck and to a lesser extent by the moving van will cause the lighter weight vehicle to become unstable.
This situation is not new to any experienced caravanner and most good truck drivers are aware of the effect of their vehicle on lighter vehicles and in particular, caravans.
As you point out above, the caravan and car combination creates instability just purely by design.
The speed of the vehicle also may magnify an already dangerous situation.
As we drive down the road there are many Vanners who may not notice this, but if approaching a good truck driver that truck driver will move his vehicle to travel along the fog line so as to create a larger gap between the two vehicles and this reducing the effect caused by the low air pressure area between the two vehicles.
A word of note is dont expect this courtesy from all truck drivers as many of them are either cowboys or just really dont know or care.
A car and van combination can become the most unstable unit we may have on our roads and my view is that the drivers of these combinations need specialist training BEFORE being permitted to operate thei vehicle on a public road.
Regards
Rob
Just furthering on my original post, it also makes one think about the advantage of having a pow profile van (pop top), reducing the turning effect, and then the opposite and that is these small full height vans that just look like a lever on wheels.
You can see why one gets a lot of dust on the back of the car.
Test aerodynamic of caravan
https://m.youtube.com/watch?v=karGqjCZOV8
Also with roof box on car roof
https://m.youtube.com/watch?v=sweZltfD-no
Every setup will be different, but it gives some indication of what is happening.
Isn't a problem with pop tops is the extra weight up high to strengthen the pop top structure.
Swings & roundabouts!
I have a crap on my roof but have done my best to tuck it all in as tight as possible. Also thinking of getting a wheel cover to have a smooth front surface.
I suggest that the greater the ground clearance, the worse the aerodynamic drag will be, and by a significant margin.
Cheers,
Peter
Perhaps you should plan regular stops Whenarewethere or was that just a typo?
Gangplank, suspended bucket & paper on the end of the flagpole!
It would be interesting how a bullbar affects overall airflow.
You could put a aero foil on the tug, air goes right over van, less drag, no bugs on van, do not even feel a road train go by and better fuel economy
Cheers Bob
Or you could join the tug to the caravan and call it a motorhome....
Cheers,
Peter
Yes Peter, been there and done that, Jayco Conquest years ago.
There isn't a truck on the road without some sort of aerodynamics, like your in-built air foil at the front of your rig.
Cheers Bob
I would be very interested to receive input from someone who knows the answer to Peter's 'question',as my van has underfloor clearance of over 700mm.I had an aerofoil fitted to the roof of the car,but got rid of it because I was advised that,being over 2 metres from front of the van's sloping front roof area,it would have very little effect,as a result of turbulence between the vehicles.Cheers
-- Edited by yobarr on Sunday 22nd of November 2020 06:45:48 AM
In my opinion, there is a good chance, that wind may be a contributing cause of RV accidents, and/or alter the weight distribution
I have no idea how the RV manufactures could plan for it, except to put a sticker on, saying slow down in high wind, etc
I certainly feel the wind in my RV, as it has a high roof
I can tell if it is a headwind, tailwind, or which side it is coming from
I also know that going slower, with noticeable wind around, is the safer option
Tony you stand on the roof of my van when we are moving you will find there is wind up there.
p.s. could be down your way next year with a house sit.
Ian
To get back on track, it will be a pleasure to catch up with you again, when you are down this way
Hi iana
The varying size and shape of trucks, semi trailers and their respective loads will cause varying effects on the lighter vehicle while travelling in proximity.
It is my experience that when both vehicles are travelling in the same direction there is created a low are pressure area between the two vehicles. The effect of this may be magnified with road train configurations and may also result in an extra buffeting from wind or varying air pressure due to the gap above the dolly between the two (or more) trailers.
When the two vehicles are travelling in the opposite directions the shear volume of air created by the moving truck manages to buffet the lighter caravan at the moment the two vehicles meet and then as they pass each other the movement creates a lower air pressure area between the two vehicles which will cause the lighter vehicle to be drawn toward the heavier one.
These situations may also vary with speed which is obvious but also with wind direction and speed.
All these situations need to be taken into account when towing a caravan at speed when operating with trucks and in particular, large volume semi trailers and combinations.
Apart from being a professional driver for my working life I have also owned various caravans, campers and tow vehicles.
My current van is classed as off road and is higher off the ground than any other van I have ever owned. My observation when towing this new van is that it is a lot more stable in the passing truck situation than was any other van that I had owned.
Now without more research I can not comment on wether the height is actually creating the situation of a lesser effect from passing trucks but I strongly suspect that this is so. This not only comes from my personal experience with my current van but from my observations when actually driving large truck trailer combinations.
From these observations my thoughts are that the vacuum is broken to an extent from the air flowing more freely under the van and helping to balance the varying pressures from each side of the van.
The same applies from the truck combination as well with for example a two trailer road train or B Double with irregular shaped tarped loads and on standard semi trailers will have a lesser effect than one of these newer aerodynamically designed and built combinations with large pan tec bodies with wings and wind deflectors between each unit of truck and trailers. As a driver this is a very noticeable difference between these various truck combinations. Many of these trailers are also built closer to the ground to assist with wind deflection and fuel economy.
I am probably guilty of going away from your original topic contents and enquiry but with your original observatIons of the instability varying with speed and movement is a fact and with a caravan and tow vehicle combination this situation is probably for the worse due to the simple fact that most of these combinations are a balancing act using near maximum allowances on both vehicle and caravan suspensions.
It is such a shame in this country that we as a consumer have to the most extent Boo Hooed 5th Wheeler caravans when in all honesty these combinations are just so much safer than our pig trailer caravans.
I am as guilty as anyone else as I chose to buy a conventional caravan mainly due to the cost and the general unavailability of Aussie built 5th Wheeler vans. Having bought this new van I am aware of the limitations being put on me by towing a pig trailer as opposed to a semi trailer but in the same breath I am not in a hurry and fully aware of the instability when operating a caravan in windy conditions, uneven road surfaces and in the proximity of large trucks and combinations.
Regards
Rob
-- Edited by bentaxlebabe on Sunday 22nd of November 2020 10:21:37 AM
Regards
Rob
Hi Rob,
My original post probably not clear, was that all the careful weight calculations basically go go out the window once a tug-van combination starts moving, i.e. the rotational forces created rearwards, increasing with speed. Different designs, combinations, head winds, following winds what ever. So ball weights and all change.
You bring up some interesting points paralleling with my thoughts on the effects of the passing rigs, our van is quite high off the ground. We get more buffeting effect when there is a cross wind and have rows of trees along the road, but nothing that worries us.
It would be interesting to see wind tunnel tests on some of our rigs.
PS if you travel close enough behind a truck, one can save on fuel
, don't try it, just joking.
Open source fluid dynamics software
https://openfoam.org
A video for getting started
https://m.youtube.com/watch?v=KznljrgWSvo
An apology to be still talking trucks but searching hasnt found much info on caravan aerodynamics.
I did come across this truck which has a aero wing fitted under the trailer. It appears to create a low pressure area directly under the trailer. This would be for improved fuel economy.
My thoughts with a caravan would be a system of creating downforce might be better for stability.
Here is the link.
youtu.be/8g21AofSu_E
Regards
Rob
Iana, your theory in your first post mentions both the high pressure at the front opposing the low pressure at the rear so my thoughts are by eliminating the high pressure at the front with maybe the use of a designed wing or foil, then this may help to keep the unit straight. The explanation in the video covers sway but not aerodynamics in design.
Here is the link to a video which explains a little about caravan sway or instability.
I am not a fan of linking to advertising but it does cover some interesting points.
Regards
Rob
youtu.be/PUHk6lqSKQI
It would be interesting if the rear of a caravan is too symmetrical left to right which causes an oscillation. Together with an added issue maybe just enough to cause the caravan to be unstable.
Tall towers or chimneys have a spiral so the air always goes one way & up.
If you have a look at Burj Khalifa tower the sub towers step up clockwise around the building to dissipate wind energy clockwise & up.
If buildings are not designed this way, wind will destroy them.
1st - BobDown, quote - "You could put a aero foil on the tug, air goes right over van, less drag, no bugs on van, do not even feel a road train go by and better fuel economy", do you have figures of fuel economy betterment before /after foil use? I am seriously keen to see the improvement - could be I go that way.
2nd - iana I have enjoyed all the contributions as they have been very informative.
I did a fair bit of "Aero dynamics" theory during my apprenticeship, we were taught clean was good. Have a look at the birds and fish, they can be blunt at the front, but they all taper cleanly to the rear. We tend to think in terms of say an arrow head being pushed through margarine, but the trouble is air, being a gas does not behave like that. The air swirls and eddy's and seeks out the low pressure areas. As for fitting aero foils, we really don't know what the effect is, unless it was tested in a wind tunnel in controlled conditions.
With regards the high pressure areas at the font of the van, we were taught that streamlining at the front (of an aircraft) was not that important, that there would be a pocket of Hi pressure air at the front, the on coming air would sense this, split into laminar flow streams and go around, but the rear was important. A bit of trivia, all goes well until we reach a speed of 550mph or so depending on altitude, the plane starts to go through the sound barrier, and **** hits the fan.
Ideally one would want to use a wind tunnel with a moving road & rotating wheels.
The various TV programs I have seen over the years. Often very minor changes to an aircraft can make a lot of different.
A small amount of plutonium was put in the ends of the 747 wings to add some weight to stop the wings vibrating.
Wing tips to increase fuel efficiency on various aircraft.
High speed reconnaissance Spitfire had all the rivets made flush so they could get an extra 100mph out of it.
An old 747 weighs about an extra tonne with all the ground in dirt, so more fuel used.
Ian, apologies for going off topic but your post reminded me of something that has puzzled me for a while. What is the origins of V1 and rotate when taking off. I would have thought that lift was a better description?????
Re the small things that effect airflow, back at one of the places I worked at, the chief pilot there asked me to install a big electric fan in the ****pit of his Piper Pawnee Ag plane. I refused, but we did make up an air duct on the roof of his canopy to give him fresh air. The first flight and he said it was unusable, the buffeting on the rudder made it completely unsafe.
I think you meant winglets on the end of the wings, they reduced, or effected the wing tip vortices' that also caused drag.
Re the flush riveting on the wing leading edge, and other areas, reducing parasite drag, common practice towards the end of WW2 on the very high performance aircraft that were being built.