Best FA tunnels

[Jorma]

Is there a general consensus of which Atlantic car had/has the best most efficient underbody aero of all time? Either opinion or hard empirical evidence.
Mike M.

[Charles Warner]

Is there a general consensus of which Atlantic car had/has the best most efficient underbody aero of all time? Either opinion or hard empirical evidence.
Mike M.

I assume you are asking which tunnels have the best (most efficient) lift/drag ratio. You also need to consider the power available to pull the car through the air. 1987 Ralt RT-4/5 cars had tunnels that created so much drag the motor couldn't overcome the drag at high speeds. The RT-5s were especially hampered.

[Jerry Kehoe]

According to Bahner the original 80 RT4 tunnels worked extremely well, after that the 86 coke bottle versions became the preferred units. The key however was sealing them properly to the tub so there would be no leaks of air and very thin spring steel and thick delrin skirts. When they were right you would about replace the 3/4" delrin every race as it was worn off while being perfectly legal when stationary. My experience with the 87 tunnels had them develop too much understeer and had the center of pressure too far back. Everybody got rid of those!

[Charles Warner]

The 1980 tunnels were good. The 1983 tunnels were better as the tub was narrowed quite a bit at the bottom which gave better airflow. Critical to all RT-4/5 tunnels was the vortex generator just at the front inside of the tunnel. It was easy to break these off and people tended not to replace them. The sidepods up to 1983 were flat sided and gave a higher top speed, with the 1983 RT-4 being the fastest of all models. From 1984 - 1986 Ralt experimented with the tunnels and sidepods. The result was the 1986 coke-bottle sidepod which had a very similar tunnel profile to the 1980 units but restricted the exit airflow with the coke-bottle shape intrusion. In 1987 they kept the same initial profile but opened up the exit airflow trying to recover lost exit airflow control. It was overdone and this produced way too much downforce and (as mentioned) moved the center of pressure to the rear, making the car worse. According to Brian R. these tunnels produced so much drag that top speed could not be reached at fast tracks. The fix was to refit the 1986 sidepods as they used the same mountings.

[reynard55]

Hello Charles
"Critical to all RT-4/5 tunnels was the vortex generator just at the front inside of the tunnel. "
Can you point me to a picture of these on the net somewhere?
I don't remember seeing anything like these on my sidepods, they are currently in storage so hard to get at to check
Thanks
Russ

[RussMcB]

Hello Charles
"Critical to all RT-4/5 tunnels was the vortex generator just at the front inside of the tunnel. "
Can you point me to a picture of these on the net somewhere?
I don't remember seeing anything like these on my sidepods, they are currently in storage so hard to get at to check
Thanks
Russ

Thanks, Russ. I was about to post the same question. :-) - Russ.

[Charles Warner]

Sorry guys,

Out of all the pictures I have there isn't one that shows the vortex generator. If your sidepods were equipped you should see an aerofoil shaped repair patch just outboard and rear of the forward lower sidepod dzus/attachment point. These were not on all versions, and I don't know exactly which ones had them. Probably about 3-4" long with a max aerofoil thickness of somewhere around 2". Typical symmetrical shape. Designed to deflect the tunnel airflow into the tunnel and not under the car.

I may have an old sidepod in storage. I'll check that tomorrow.

[M.Sauce]

I have a pair of RT4 tunnels from 82-83 if anyone needs them I also have some Swift 016 tunnels much better than the older Ralts I would suspect.