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Questions about the step kit on an RV-9

L

Loman

Well Known Member
I am at the stage of opening out a tooling hole in the F-725 L and R baggage area floor ribs to accept the tube of the step kit. This is part of the original build rather than a retrofit.

The plans say to open out the tooling hole to 1 ? inch (RV-9 drawing 22, at A5 on the grid). The manual disagrees. On page 8-6, it says to use a 1 5/8 inch hole saw.

The OD of the tube is 1 ? inch so the choice comes down to whether the rib is supposed to:
A) offer some support to the step tube by virtue of a contact fit with the edges of the hole through the rib or
B) stay well out of the way and simply let the tube through with a 1/16 clearance all round.

I?m leaning towards B. Which would you do?

My second question is whether steps are needed for a taildragger RV-9 at all.

I have heard it said that the RV-9A rides higher on its gear than the other models but is this true of the RV-9 also? Even if the main gear is longer, the height difference at the rear spar will only be about half as much. Would anybody care to put numbers on this by measuring the height off the ground of the top wing skin at the rear spar on their taildragger?

Another consideration is the protection of the flaps. Do the steps make it less likely that your flaps will get stood on? I think they would.

Let's not discuss drag/speed. Unlike the above, I found plenty of material debating that issue and it seems the difference is slight.
 
Just for Clearance

Loman:
I've toured your country several times, mostly in the South. What a great place to fly! Beautiful!
Answer "B" is correct. The loads on the step are taken up on either end. Any contact with the rib mid-way will likely only cause the rib to distort. If you add the step, just make certain that you've used a very good barrier (anti-corrosion) paint on all surfaces, including the side that gets riveted against the fuselage. The step is ferrous and will rust fairly quickly if un-coated, especially in the salty,humid air around your coastal areas.
As to whether you need a step or not is a matter of personal preference. While most tail draggers would say "no", a step will provide some added assistance to anyone who may have difficulties getting in and out. More importantly, if you build without a step, adding one later may prove difficult, yet not impossible. Paint matching may be problematic, as may access under the baggage floor. Good luck.
Terry, CFI
RV-9A N323TP
 
Loman said:
...I have heard it said that the RV-9A rides higher on its gear than the other models but is this true of the RV-9 also? Even if the main gear is longer, the height difference at the rear spar will only be about half as much. Would anybody care to put numbers on this by measuring the height off the ground of the top wing skin at the rear spar on their taildragger?

Another consideration is the protection of the flaps. Do the steps make it less likely that your flaps will get stood on? I think they would.

Let's not discuss drag/speed. Unlike the above, I found plenty of material debating that issue and it seems the difference is slight.
Click to expand...

I built my -9 without the steps. If I were building again, I would probably add them. The -9 is just high enough that getting in and out can be a real pain. More so for older passengers and people who are not used to getting in and out of the -9.

The -9 does sit significantly higher than the -6 & -7, more so than I would think. The reason may be that the wing is narrower, thus the trailing edge may be higher up the fuselage.

Good to see another -9 going together.
 
Loman,

I remember having the same questions. I went to great lengths to make certain the hole was in just the right spot and just the right size. Months later, when it came time to actually install the steps, it didn't fit quite right and I had to enlarge this hole to give the step some "wiggle room" so it would fit right. If you decide to install steps, make the hole plenty large at this point and move on.

I documented this in my log and have photos, too:

http://www.europa.com/~swayze/RV-7A/Fuselage/20090130.html

http://www.europa.com/~swayze/RV-7A/Fuselage/20091010.html
 
Last edited:
It depends a lot on your height and age.

My wife & I are both very short and over 65. Even on my -6, the wing seemed to get a little higher every year. I didn't want to have the step hanging down so far so I built my step to come out straight just behind the flap. It works great and is somewhat stronger because of the fact that it doesn't "change" direction coming out of the fuselage.
 
Terry & Bruce,

Loman is building an RV-9 not a -9A. Thus including the step or not is purely optional.

With the tricycle's, it is pretty much mandatory.

Mel,

I like the sound of your idea. That would probably put the step just far enough back and down to make it useful without it hanging down. Still, too late for me as there is no way I'm going to remove the baggage compartment floor.
 
I had to enlarge the hole on mine because of interference with the weld bead where the torque tube meets the rivet plate. I think I started at 1.5 and ran a "chip chaser" style deburring tool around the hole a bunch of times until it had a good fit. I also used pro-seal and wet riveted my steps on. I'm not flying yet, but after hearing stories about the step rusting between it and the skin, it seemed like a good thing to do.
 
Thanks guys

Some good answers there. Mel, I would particularly like to see a picture of your step if that's possible.

Just to be clear, it was the hole through the first 'upright' baggage floor rib that I was wondering about. That's the F-725 for those who remember part codes. I already know that the skin exit hole needs to be oversized.

Off-forum, I am also getting advice that this step installation needs to be beefed up, particularly at that skin exit hole. A VAF buddy of mine talks about skin doublers and strengthening the floor ribs. There is a third-party product marketed for RV-10s which consists of a solid aluminium block mounted inside the tube near the skin (can't get hold of the link just now)

I would still love to compare the actual measured height of the step up to the wing of a taildragger 9 with the same measurement of any other taildragger model. If any of you are going to your hangers this weekend, please bring a tape.

Terry, thanks for your comments about Ireland. I too am looking forward to flights over the hills of my native Wicklow but I also intend to take lots of flight training in the States and I am really looking forward to that.
 
Loman said:
Off-forum, I am also getting advice that this step installation needs to be beefed up, particularly at that skin exit hole. A VAF buddy of mine talks about skin doublers and strengthening the floor ribs.
Click to expand...

Having done my step not long ago I gave great consideration to a stiffener. I'm not sure it's completely warranted for the exterior skin. I found cleco'ing it in place I was able to step on it and nothing seemed to buckle. I'm about 230# so I didn't see any reason to do it.

My observation was that the load is really on the inside rib with the connecting block, the plate on the exterior skin is the fulcrum and it really wants to rotate when you step on it. So I think that's the majority of the force concerns with the exterior skin. The rivets should be sufficient for the shear strength.

That's not to say it's going to hurt anything to put a stiffener plate behind the exterior skin. I'm probably going to do that since I plan on using 426 rivets rather than 470.
 
niblettda said:
Having done my step not long ago I gave great consideration to a stiffener. I'm not sure it's completely warranted for the exterior skin. I found cleco'ing it in place I was able to step on it and nothing seemed to buckle. I'm about 230# so I didn't see any reason to do it.

My observation was that the load is really on the inside rib with the connecting block, the plate on the exterior skin is the fulcrum and it really wants to rotate when you step on it. So I think that's the majority of the force concerns with the exterior skin. The rivets should be sufficient for the shear strength.

That's not to say it's going to hurt anything to put a stiffener plate behind the exterior skin. I'm probably going to do that since I plan on using 426 rivets rather than 470.
Click to expand...

I like that idea, a lot. I've got a lot of sheet .040 alclad that would serve nicely for that...
 
Go with the larger hole or you will spend some time grinding the hole bigger to allow for the weld as in the earlier post. I used the 1-1/2 hole saw and spent way too much time with a grinder opening up the hole.
 
Another thing to consider when adding a step is to reinforce the step. They typically crack on the bottom rear, close to the fuselage. If you weld a strap across the back it will help.
 
Ken9

Another thing to consider when adding a step is to reinforce the step. They typically crack on the bottom rear, close to the fuselage. If you weld a strap across the back it will help.
 
Should I chrome plate my 9A steps?

Lots of talk about primer on the steps but with chrome plating the steps will I still have to spray primer on back mounting plate of step??/ Or Shouldn't I chrome plate the step at all?
Ron
 
Ken where do they crack? Are you talking about the tube on the outside going INTO the Plate or the under side of the plate where the tube comes thru? Ron 9A
 
Tube cracks seem to be common on the R step where the exterior tube comes out of the flange. Cracks are horizontal and typically right at the weld. Imagine pulling up on the step and envisioning the stress, and that's where the cracks happen. Previous threads on this have suggested that it has to do with poorly-annealed welds. Seems to happen most often on R step and some have suggested that this is related to the prop wash vortex around the fuselage, or something to do with vibrational nodes. In any event, check closely for this problem before you paint (after you have stepped on the step many times). I found no issues until after flying maybe 50 hours when the crack appeared (fortunately it was before painting). I also remember that some folks mentioned that the step can be welded in-place by a competent TIG or MIG welder that doesn't generate a lot of excess heat (I don't recall which and I'm not a welder so may have that wrong). I just pulled mine for welding (gave me a chance to clean up all the junk under the baggage floor!) and reinstalled before paint. 170 hours now and so far no recurrence. L side never had the issue.

greg
 
A friend has a -7A where the right step almost completely snapped off about 2 inches below the flange weld. After a couple of twists and bends, the step came free.
Boy, does he get the LOOK from wifey when he's asked to explain what happened. And she's a petite woman.
He still hasn't repaired/replaced the step. Waiting for springtime. If I had a pic, I'd post it.
 
Ken9

The crack happens on the back of the leg just after it exits the plate. You can see it when you pull out on the step. I have seen it on several planes at OSH, including Vans demo. I welded a 3/4" wide x .06 strap half way around the back side to reinforce it. My plane is not flying yet but my friend had a welder repair his with a similar strap while still on the plane. That was a couple of years ago and it is still OK. You need a very good welder to.
 
Loman,

Tried to send pictures of my steps to your posted email.
It got kicked back. What is your current email address?
 
Steps on RV9

I built an RV9A with Steps and found them useful. I recently converted my airplane from 9A to a 9 and left the steps on. I'm glad I did. It really makes it easy for me to get in and out.

Joe Ramotowski
N358JR 250hrs (RV9A) 45 hrs (RV9)
 
Chroming increases brittleness

ron sterba said:
Lots of talk about primer on the steps but with chrome plating the steps will I still have to spray primer on back mounting plate of step??/ Or Shouldn't I chrome plate the step at all?
Ron
Click to expand...

I'm not metalurgist but it has been said elsewhere on these forums that chromed steps are more brittle than painted ones and much more likely to crack.

Nonetheless, I have been thinking about chroming my steps because I think they would look so cool.

I have a few different measures in mind against the likelihood of cracking. Firstly, I would like to strengthen both steps with a strap welded to the back before chroming, in the position where most cracks occur. Second, I want to get the steps properly annealed in case that was not done when they were originally made. Thirdly, I have been considering using small bolts instead of rivets to fix the plate through the skin to a doubler plate . This would mean that the steps could more easily be replaced if anything did go wrong.

Of course these ideas may be just as relevant for painted steps as for chromed ones.

If anyone thinks (or knows) of reasons I shouldn't do any of these, I would love to know.
 
I thought chroming would be cool, but then I wondered about bumping into them bare legged after the bird beens' parked out on a hot ramp in the summer for a few hours...I'm in the high mountain desert...
 
Loman,

I wouldn't use bolts/screws rather than rivets. Rivets are relatively easy to drill out (how I know - I had to reweld a cracked step) and the real problem is the bolt through the end of the step under the baggage floor (which requires either drilling out the entire baggage floor (again, I know from experience) unless you build in nutplates and screw down your floor.

I think that if you anneal and/or reinforce the steps before installing, you are unlikely to ever have to remove them.

My two cents.

greg
 
This is excellent timing, I'm ready to mount my steps. How would you go about annealing them before installation?
 
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