A/FD thought!

Someone told me that with an A/FD, the harder you load the motor, like with a wing, the faster you will go. For the record, I believe that this it totally wrong. My reply to this kind of thought is if you believe that, then pull the parachute on the starting line right before you take off. This should produce adequate load. If this theory is true, you ought to really hall ass then! But I doubt it.

 

where is nitro hawk when you really need him?

 

Wing

A-fuel cars are no different than any other type of car as far as wings go. To much wing and you scrub off speed. To little and you spin the tire. I was told by a tuner that ran 5.22 five years ago that one degree negative angle on his dual element wing would scrub off 5 mph. He was running 275 at the time.
Dual element wings are used not just because of the increased dodwnforce but also the increased drag. The drag is what helps load the motor and the downforce helps to keep the tires from spinning. With the gpm of fuel that is required to run well you cannot have any tire slippage. If you do it will immeadeatly drop cyls. A blown alcohol dragster is not nearly as sensitive to bad track conditions because of the difference in the final drive gear ratios. Thats why you seldom see a blown car smoke the tires leaving the starting line. A-fuel cars because most run a 2.90 gear and direct drive tire speed is critical but when it exceeds what the track will hold the driveshaft speed skyrockets resulting in tire smoke. Of course the wing doesn't help on the starting line but 300 feet out the same principal applies. Consider that you are running close to one hundred mph in 60 feet. At this point a dual element wing creates much more downforce than a 1000 sq. inch single element wing.
Will is right you can have to much wing and on a great track most a-fuel cars probably do. However the alternative is too little and that is ugly.
The cars will still run quick with to much wing just not as fast. If NHRA did not have a rule against changing wing angles during a run I know I would be doing it.
The reason I am not posting as much is I am back working a real job after seven years of retirment. Helping my son out building some really nice high performance fishing boats.

 

Nitrohawk,
I’m with you on everything except the part about drag helping to load the engine. How exactly is that accomplished? You certainly need enough down force to keep the tires in traction, but drag is the inevitable and undesirable byproduct.

 

Exactly my point!

 

Think of it like this. If the air flow over the wing caused a 1000 lbs of downforce it is like setting a static weight of 1000 lbs on the rear tires.
However if you look at drag, lets say at this same point it is 300 lbs. The drag is acting against the leading edge of the wing. This is basicly where the 300 lb. force is being applied. Now this is directly resisting the forward motion of the car. In effect yes it is sort of like opening a parachute but is way less force. The thing about the drag is that it is also multiplying this 300 lb force by the leverage according to the height of the wing in relation to the centerline of the rearend. In effect it is not only adding drag which will load the motor but is adding downforce because of the lever effect.
The combination of drag and downforce is what the fuel cars need to keep the large amount of fuel they burn from going out or dropping cylinders. Most of the a-fuel cars run dual element wings in the 1000 sq. in area with little negative angle. However some add a 3rd element on bad tracks to keep tires from spinning and causing dropped cylinders.
In a perfect world you would run the car as light as possible with nothing that created drag bolted on to it. But this is drag racing and a few years ago no one would have believed you could run this much fuel through a naturally asperated engine. Much less run 5.10 and 285 mph!!!

 

I remember about 1972 or so The Snake came out with his Kent Fuller rear engine car nicknamed "the yellow feather" (i believe it was about 1280 pounds) That car had a spring mechanisim which allowed the wing to change angle of attack and flatten out during the run. Was shortly after that NHRA outlawed movable surfaces. The car was a handfull as I remember a pix of it up on two wheels at Ontario Motor Speedway. It did tie low et of the world with kansas John Weibe at 6:17 at the time though.

 

OK, you explained how 300 lbs of wing drag provides additional down force for traction, but the first half of your statement above indicates drag loads the engine directly in some beneficial manner, which you did not explain, or I did not follow.

 

2 element wings

One thing to keep in mind is the reason there is a second or third element as opposed to one large radiused wing. The air gap inbetween each element allows the air to pass through creating more downforce with less drag. An A/Fuel car just like anybody else doesn't need extra drag.
The load creates increased cylinder temperature and pressure which allows more slow burning nitromethane to fire off. You cannot burn 27+ gallons per minute of nitro without loading the motor. I think I've proved that so far this year! ha ha.
Nitro does not have the same burn characteristics as other fuels, in fact they are quit opposite. For anyone who has towed a large diesel truck up a steep grade, if you are in too high a gear the engine will lug because too low an rpm the engine temperature will skyrocket. Cylinder temperature is up, this is what the nitro motor wants and likes.........load.
Johnny
TAD 734

 

Just a point of clarification, drag acts in the opposite direction of car motion thru the center of pressure, and, the amount of drag can be changed by the shape of the form drag.

 

for the record the majority of drag is not acting on the leading edge

it is the turbulent wake behind the wings that contributes the most drag, and form drag acting all over the surface of the wing

 

This discussion was not necessarily on air foil design. The question was about loading a fuel motor and its effects.
Question? Is a 2100 lb. car and a 2.90 gear enough of a load for an a-fuel motor. Ans. Given most track and weather conditions no. If it were you would be able to increase clutch pressure and run maxium amount of timing with as much compression you could make. Most of the a-fuel cars can spin the tires at launch under these conditions. If you could make all the power you wanted at launch and only achieve the optimum driveshaft speed I would say it was enough load. However the wing which we have been discussing and its effect has no bearing on the engine load at this point in time except for the extra weight it adds to the car.
Question? If you took the coupler out and pushed on the wing would the car roll backwards. Ans. Of course. But this only proves my point that drag is the resistance to air flow over the wing and can be measured in lbs. of force. Just as a point lets say you are a real good driver and at 330 ft you feel the tires get a little loose and grab a handful of brake and the load on the engine keeps it from dropping cylinders. Look what happened. The resistance to movement created by the brake application did two things. It increased the load the engine was seeing and slowed the tire speed down. Now if the down force by the wing and the drag created multiplied by the height of the wingstand to the center line of the rear axle had been great enough you would not have had the problem to start with. The good news is these forces are adjustable. If a single element wing would exert enough down force and drag these cars would be running them as the dual and triple element wings are way more expensive.
Question? Is the drag created by the wing parasitic?
Ans. In most wing applications probably. However when in the application where the wing is turned upside down and placed on a fuel dragster it is not.
Parasitic to me means that it has no redeeming effects. In this application the redeeming effect is that because of the location of the wing in resect to the center line of the axle it creates more down force and loads the engine to a degree at the same time. The down force created by the wing increases the coeffecient of friction between the tire and the track making it harder to break the tire loose. The drag has a side effect of increasing the down force but when view as its resistance to the flow of air acts to load the engine as any other form of drag you might add to the car.
As far as Richert and his new Gallant wing. Authurs wing is a nice piece. I don't know if the airfoil design is different from what Bill had been running or not but I was pitted next to Bill when he made those remarkable runs. We were in the stands to witness both the 5.10 /282mph run and the 5.15/285.75
run. The increase in mph on the last run just might have had something to do with a change in the wing angle. But only Bill could confirm that.
I am not an expert by any means on this subject. Take what I have to say with some degree of suspicion. The only thing I do know from living this long is the more I learn the more I realize how little I know!

 

I do wonder if some A-Fuel racer tried deploying the Chute after 60' to see what the car would do.

 

Trust me, It will slow down!

 

If the tuners in the past who developed the current a-fuel tuneups used convential thinking they would still be running 6.40 et's.
There's only two things that scare me. 1. Someone from the goverment who says they want to help me. 2. Someone who makes the statement "TRUST ME".

 

okay, have never tuned a /fuel but from my observations of this conversation if nitro needs more load why not create some on the car? larger leading edges on wings? bigger less angled struts for the wing? maybe some ribs on the body that create some downforce and a little drag? if you need to load it down for more power wouldnt some downforce make up for the drag? the wings they have on top fuel cars look like a big old bunch of drag but they work. just my 2 cents

 

How about "loading" it with gearing, not with wing which WILL slow you down!