Those Steps - Draggy - What Do You Think?

[Bob Axsom]

I just completed a mod on our RV-6A to make the steps removable for racing. Those steps are wonderful for getting into and out of the plane but I can't tolerate such an obvious source of DRAG! The modification took many hours and a LOT of tedious careful work to implement. So today the wilds were relatively light and very steady. I flew the test at 6,000 ft density altitude with five 20 second interval recordings on tracks or 000, 120 and 240 degrees, wide open throttle leaned for max power, 2720 RPM, MAP 25.8 ... The average of each track was plugged into the NTPS spreadsheet and the results were 179.3 kts or 1.5 kts slower than the test before removing the steps (yes there is a tight fitting cover over the step holes). My mod allows me to reinstall the steps with screws for travel thank goodness. If you are thinking of building your RV without steps because of a perceived big difference in speed, I would advise installing them with screws and plate nuts so you can make the airplane convenient again for normal operations.

Bob Axsom

[L.Adamson]

Originally Posted by Bob Axsom

I just completed a mod on our RV-6A to make the steps removable for racing. Those steps are wonderful for getting into and out of the plane but I can't tolerate such an obvious source of DRAG! The modification took many hours and a LOT of tedious careful work to implement. So today the wilds were relatively light and very steady. I flew the test at 6,000 ft density altitude with five 20 second interval recordings on tracks or 000, 120 and 240 degrees, wide open throttle leaned for max power, 2720 RPM, MAP 25.8 ... The average of each track was plugged into the NTPS spreadsheet and the results were 179.3 kts or 1.5 kts slower than the test before removing the steps (yes there is a tight fitting cover over the step holes). My mod allows me to reinstall the steps with screws for travel thank goodness. If you are thinking of building your RV without steps because of a perceived big difference in speed, I would advise installing them with screws and plate nuts so you can make the airplane convenient again for normal operations.

If I'm reading this right, I get the impression that removing the steps, lowered the aircraft's speed by 1.5 kts. Buf if that isn't the case, then I feel good that steps only make a small difference.

One thing for sure; I don't care to carry a step ladder in the baggage compartment, and going without steps or a ladder on "A" models is a sure way to eventually get flap damage or damaged humans.

L.Adamson -- RV6A

[gbrasch]

Bob, what timing. I just today nearly completed installing my steps using countersunk screws. I will probably never take them off, but IMHO they sure look a lot better with the flush screws than with those big rivets sticking out! Fly safe, Glenn

[LifeofReiley]

From my conversations with Van's, the steps are designed to not to really affect speed on the (A) model 7's and 9's. I think its location...location...

[RV7Guy]

Originally Posted by gbrasch

Bob, what timing. I just today nearly completed installing my steps using countersunk screws. I will probably never take them off, but IMHO they sure look a lot better with the flush screws than with those big rivets sticking out! Fly safe, Glenn

What about the big ole nose gear hanging out there? Sorry, couldn't help it.

[Bob Axsom]

I have that nose gear slicked down so much that I can take on the tail draggers on an even footing now. I need more power and a prop specifically suited for racing with this airplane but those are high dollar items that I can't deal with in the short term. The nose gear with the new subfairing is not a speed handicap.

Now back to the steps - today's test result was a false negative obviously but it shows to me that the steps are not the big drag item that I thought they were. When we race at Denver's Front Range Airport Saturday I will have a step ladder for my teammate (Jeanine) to use for boarding but I now know that the no step mod is not a significant improvement and certainly not worth the inconveinence in normal operations.

Bob Axsom

[RV7Guy]

Hi Bob,

I thoroughly enjoy your enthusiasm on improving the "slickness" of the airframe. I have felt for a long time that a clean plane will do much more than horsepower and lead to more speed and overall efficiency.

Keep up the great work. My next one will be even cleaner!!! Thanks for the tips.

[hecilopter]

interesting to know the drag produced from a well faired nose gear/intersection fairing A model VS an unfaired TW/springs/etc dragging back there. I wonder if there is much difference or maybe even an advantage to the well faired nosewheel?

[Bob Axsom]

I forgot that I had not reinstalled the race plates blocking all the ports at the rear of the plenum after our trip to Baltimore. A retest today with the race plates installed (bringing the plane back to the identical configuration) increased the speed 0.4kt over the step configuration.

The nose wheel fairing work I did to my old style (flat sided) NLG faring made significant difference in speed. The result is certainly competitive with the tail draggers I have raced (John Huft and others excepted).

Bob Axsom

[hevansrv7a]

Originally Posted by Bob Axsom

... I flew the test at 6,000 ft density altitude ...wide open throttle leaned for max power, 2720 RPM, MAP 25.8 ... ...the results were 179.3 kts ...

Bob Axsom

Bob, I used the spreadsheet for engine power that Kevin Horton kindly contributed some time back and got 94% to 98% from these numbers, depending upon temperature. His spreadsheet uses pressure altitude.

I have not verified this 100% but I think my -7A can do at least 180 kts under those parameters. It does 175 GPS verified on 75%. I did try lower altitudes once and got 180+ on my GRT with TAS calibrated to 175. Looked at another way, comparing power, 94% / 75% is 1.2533. That's the increase in HP. The cube root of 1.2533 is 1.078 so that's roughly the speed gain that a 25.3% increase in HP can produce. 175 times 1.078 is 188+. That should put me in the 180+ ballpark even in thicker air.

As much as I truly admire all the work you have done and the testing that you follow up with, I wonder why you are not going faster. Maybe you should listen to George and try a SJ cowl, etc? I mean this in a friendly way, just in case it doesn't come through.