B

Bob Axsom

Well Known Member
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
 
Bob Axsom said:
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.
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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
 
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
 
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...
 
Nose Gear??

gbrasch said:
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
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What about the big ole nose gear hanging out there?:eek: Sorry, couldn't help it.
 
We will see about the NLG etc. Saturday in Denver

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
 
Good stuff

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.
 
It would be

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?
 
O-o-o-o-p-s!

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
 
Maybe you could do better?

Bob Axsom said:
... 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
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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:).
 
It's Not Bad Actually

My original best speed was 170.67 kts. I started working with the cooling drag from an intuitive perspective and it took a lot of experimentation before I got a gain of 4 kts. The wing tip configuration change was the next big improvement and it was good for 3 kts right off the bat. The NLG subfairing was the last big one and it was on the order of 3 kts. I have made a lot of other changes worth about 1 kt for the whole lot. Many changes actually reduced the speed and had to be backed out. I think the largest potential is in the engine and the prop but there are a lot of little things left to try and that is the joy of the pursuit with my own thoughts and my own two hands. Seriously, after 50 years of working in aerospace it is a very good to do this thing that requires creative thought, energy and discipline. If I thought I had achieved the best there is to be gotten from our airplane I think some of the joy would fade away.

I do pay attention to people that talk about performance enhancement especially when they are actively chasing the carrot. I meet them at the races and occassionally there is an e-mail exchange or a posting such as yours that wants to share the pain of failure, the satisfaction of success and the lessons learned. When this happens life is especially good.

Now that I found that the step removal mod gave me almost a half knot I am happy with that even though I had expected 3 kts. Mike Thompson who organized the Sport Air Racing League (www.sportairrace.org) has an RV-6 and initially he beat me in the RV-Blue Class races but he has not beat me since I developed my new wing tips. He is pressing very hard however and both of our speeds are creaping up - not in the John Huft range but respectable. He has just installed some new wing tips on his RV-6 and the race out of Front Range Airport at Denver this Saturday will be a real test. This head to head competition is hard to beat for comparing performance and stimulating the pursuit of excellence. It is the quality of the pursuit that is most important to me - more important than achieving perfection in fact.

You know the guys that really amaze me? Bruce and Steve Hammer. Bruce told me in an e-mail recently that he is working with an idea involving the modification of his exhaust to improve the performance of his fixed gear Glassair that is already outrunning Lancairs, Rockets, etc. So does Steve's very similar Glassair. Both are achieving well over 250 mph race speeds. Steve had that terrible accidental fall a few months ago but he is planning to fly in the AirVenture Cup Race with a qualified pilot in his plane as PIC. Its in their blood - true racers and brothers to the end.

Bob Axsom
 
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Bob Axsom said:
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
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I omitted the steps, not due to drag issues, but I was tired of banging my shin on it as on my previous plane. I have no problem stepping up to board. I have a small step stool for my passengers. I'll probably need one when I get older or I may decide to opt for the steps later on.
I've found no inconvenience from it. Also, the step has a history of cracking and has to be replaced occasionally.
 
Left Mine Off, Too

DanLandry said:
I omitted the steps, not due to drag issues, but I was tired of banging my shin on it as on my previous plane. I have no problem stepping up to board. I have a small step stool for my passengers. I'll probably need one when I get older or I may decide to opt for the steps later on.
I've found no inconvenience from it. Also, the step has a history of cracking and has to be replaced occasionally.
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The little folding stool from Sporty's (the wood one) is, I think, lighter than two steps and can be stowed on the floor up front for W&B on heavy loading occasions. My wife can position it just right for getting onto the wing. Less drag, cracking and potential rust. Looks better, too IMHO.
 
hevansrv7a said:
The little folding stool from Sporty's (the wood one) is, I think, lighter than two steps and can be stowed on the floor up front for W&B on heavy loading occasions. My wife can position it just right for getting onto the wing. Less drag, cracking and potential rust. Looks better, too IMHO.
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Since new readers to this list, might get the idea that leaving steps off is the way to go..... :D

I'll counter it.

Sure, it might look a wee bit better, but then those big and somewhat draggy landing gear would probably look better if they fully retracted! Same goes for those ugly tailwheels and chains. Retract those suckers too! :D

We now know that these "steps" add little in the way of drag, thanks to Bob.

Personally, I don't like the idea of pulling a step ladder out of the baggage compartment, and then reaching down to grab it; as well as putting it back in baggage.

Steps are a simple way to board, with much less potential damage to the flap area. Afterall, 7 & 9A's sit quite high. Steps are even good on the lower sitting 6A's.

L.Adamson
 
L.Adamson said:
Steps are a simple way to board, with much less potential damage to the flap area. Afterall, 7 & 9A's sit quite high. Steps are even good on the lower sitting 6A's.

L.Adamson
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I've ordered a step for the passenger side of my RV-6. The climb down off the wing and over the flap is not easy for less than athletic or short-legged guests.

After all these years, I've decided keeping a passenger healthy is more important than having to look at the step on the side of the plane. Gettin' mellow I guess....... ;)
 
Sam Buchanan said:
I've ordered a step for the passenger side of my RV-6. The climb down off the wing and over the flap is not easy for less than athletic or short-legged guests.

After all these years, I've decided keeping a passenger healthy is more important than having to look at the step on the side of the plane. Gettin' mellow I guess....... ;)
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Besides, stools have been known to tip over! :)

L.Adamson
 
Weight

Each step weighs 1.75 lbs for our RV-6A (3.5 lbs for both without attachment hardware). Sporty's advertises the step stool at 4.33 lbs. The short aluminum step ladder I am going to have to take to Denver Friday exceeds the limit of my 5 lb capacity scale. For our normal operations the steps will be installed.

Bob Axsom
 
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