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Twitchy handling on rollout

Cloudboy

Active Member
I built an RV-8 several years ago. It was hard to handle on rollout until I put an angle shim on the landing gear. I used advice from an article Budd Davidson wrote years ago where he explained that toe out is better than toe in and straight ahead is best. It worked for me and the 8 handles well now.
I recently decided I needed an RV-3. The wait time for a kit is 18 months and I'm too old to wait that long. I just bought a flying RV-3. Now I am back where I was initially with the 8. Too squirrelly on roll out. I checked the alignment and I have toe in. I would like to straighten the alignment and wonder if any one has found a way to change the alignment short of installing new gear legs?
 
Alignment

Steve Wittman, designer of the round spring gear, called for 1/16" toe in measured in the length of the axles. No information on weight or angle of fuselage to ground when doing this.
Do you have camber? Specified camber from Wittman plans is 3/8" in length of gear.
The reality with the round gear is that the proper alignment only occurs for one gross weight and one fuselage angle.
A tailwheel link with a spring cartridge may help you.
Changing the gear alignment on the round gear is a major job.
 
I agree it looks like a major effort. New gear legs are back ordered and maybe I'll have to live with a little toe in. With my other plane toe out worked better. I have a single tailwheel control arm with single spring cartridge link. I think I will change back to the original with some slack in the chains. Years ago I talked to Ken at Vans and he suggested slack in the tail wheel chains to help prevent overcontrolling. It worked for me. I wish they still had the taillynx available.
Thanks for confirming what I was afraid of regarding adjustment.
 
From those with actual, significant experience in multiple RV types, is it possible that the RV-3 is just a little more sensitive on the ground than the RV-8? I've flown everything but the 10 and the 14 and I can say with certainty that the -3 is much more sensitive in the air than the other models. I can't say, however, that I've got a bunch of experience going back and forth between the models with enough landings to give a qualified opinion of any differences in ground handling.

Anecdotally, I let a friend fly my RV-3 not long after I bought it. He finished his RV-8 back in the 90's and has been flying it ever since. He took one flight in my RV-3 and said he didn't want any more of it. Admittedly, he was 77 years old at the time and said he was too old to make friends with a new plane, but he's been flying tailwheel planes since he was 15 years old in 1956.

I owned my Midget Mustang for about 6 months after buying my RV-3 and can say that the RV-3 was a much more docile, honest ground handling aircraft than the Midget Mustang could ever hope to be! I've never had a reason to measure or even question the alignment of my RV-3 because ground handling always seemed great to me!
 
-3 ground handling

FWIW, I am just a PP with over 1100 hours TW. Champ, Luscombe, Rose Parrakeet (very light with tail skid ), RV 3B w/ 250 hr. The 3 even had the Flyboy accessories geometry tail wheel. I always found it sensitive to the extent I did not use much power for takeoff until the rudder had significant authority. IE, a lot of tap dancing . That said, I can’t imagine anything sweeter in the air ��
 
3's and 4's are more twitchy than 7's and 8's. Especially with a steering link instead of chains.
That being said, My second RV-7 had a very bad shimmy that I tried everything to fix. The right gear was toed out 1/4 degree, and the left was toed in 1/2 degree. There is some variation in the "Heat and bend" from Lance, the supplier. I spent $600 on a new set of gear, and there is only a very slight shimmy right at 23 mph in the left gear, vast improvement. However.... many of the 3's required the builder to align the gear before drilling, so there is some variance!
Best of luck!

DAR Gary
 
Tailwheel aircraft.............

As has been said, "0" toe is best. Toe-out is better than toe-in. Think of it this way, if the airplane starts to veer to the left, more weight is transferred to the right wheel. If it is toed-in, that wheel will take you even more to the left. If it is toed-out, it will tend to pull the airplane back to the right. ref: "Landing Gear Design for Light Aircraft" by Ladislao Pazmany.

If you will notice Van recommends "0" toe with the airplane off the ground. With the Wittman style landing gear, by design, any weight on the gear causes a small amount of toe-out.

When I designed the conventional gear for the Moni Motor-glider back in the 1980s, I discovered quickly that any amount of toe-in makes the airplane quite squirrelly on the ground. Once I added a minute amount of toe-out, the airplane became a pussy- cat.
 
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Things I have noticed about my RV3 compared to other RVs, and I have flown all the tail dragger variations except the -14.
For me, my RV6 was the best landing plane followed closely by the RV7. The RV3 is a little harder to land well.
My RV3 is easy to land consistently, once you get the hang of it. Being a smaller airplane can make it a little twitchy, especially if you tend to over control.
Some things that might make your RV3 less twitchy would be:
-Install VANs regular springs or the Tail Lynx with the chains/cable not quite taut. I do not care for the single arm tailwheel springs. To me they are too touchy, and I have seen several of them break.
-VANs standard tailwheel assembly is a little more stable than the angled assemblies available. Even though it has less clearance at the front of the socket. I have never had any issues with VANs standard offering or the angled variety, but just saying.
-Less air in the mains (Don't know what you are running now but 28 to 32 psi is what I like to run on the 3.)
-You might work on your landings so you make slower touch down speeds. I see a lot of RV guys come blasting in faster than they need to.
-I don't do full on wheel landings in the RVs much but prefer tail low wheel landings, almost a 3 pointer. My RV3 does really good 3 pointers so I do a lot of them. Probably a little easier to control, in my opinion, if the plane is touchy.
-Let the plane roll out a ways before you use the brakes unless you are doing a short field landing. Saves on the brakes and is easier not to over control.

These are just my observations, YMMV.
 
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I agree on all counts!

I am really happy with my Tail Lynx.


Things I have noticed about my RV3 compared to other RVs, and I have flown all the tail dragger variations except the -14.
For me, my RV6 was the best landing plane followed closely by the RV7. The RV3 is a little harder to land well.
My RV3 is easy to land consistently, once you get the hang of it. Being a smaller airplane can make it a little twitchy, especially if you tend to over control.
Some things that might make your RV3 less twitchy would be:
-Install VANs regular springs or the Tail Lynx with the chains/cable not quite taut. I do not care for the single arm tailwheel springs. To me they are too touchy, and I have seen several of them break.
-VANs standard tailwheel assembly is a little more stable than the angled assemblies available. Even though it has less clearance at the front of the socket. I have never had any issues with VANs standard offering or the angled variety, but just saying.
-Less air in the mains (Don't know what you are running now but 28 to 32 psi is what I like to run on the 3.)
-You might work on your landings so you make slower touch down speeds. I see a lot of RV guys come blasting in faster than they need to.
-I don't do full on wheel landings in the RVs much but prefer tail low wheel landings, almost a 3 pointer. My RV3 does really good 3 pointers so I do a lot of them. Probably a little easier to control, in my opinion, if the plane is touchy.
-Let the plane roll out a ways before you use the brakes unless you are doing a short field landing. Saves on the brakes and is easier not to over control.

These are just my observations, YMMV.
 
Mel, Steve and Steve. Thanks for the replies. It is good to have conformation on what I've been thinking. So many people advocate toe in that I've felt like a flat earth believer. My 3 acts just like you would expect with toe in. Once it starts to the left, the right wheel is weighted, pushing the plane harder left. Then I overcontrol and it's Mr. Toad's wild ride. Toe out tends to self correct. That being said, the toe in is only .9 degree and it is hard to blame that for all my problems. I measured the toe with the wheels on the ground but no weight in the plane. I had even drained the fuel to update the weight and balance. I should probably have checked it with some fuel and me in the plane.
I also agree with slack in the control chains. Years ago Ken at Van's explained that on roll out when you are still moving fast, air over the rudder gives you plenty of control so a tight tail wheel gives you too much. Some slack helps that. I'm in the process of going back to lose chains.
Ken also suggested lower tire pressure. I'm down to 26 psi. If I go much lower, it will be too hard to push around.
That leaves landing speed. I'm probably landing too fast and I'll work on slower. I usually wheel land because it works so well in the 8. I've been carrying a little power on short final to keep a really minimal decent rate and avoid bouncing. I also use two notches of flaps to keep the nose down and improve visibility. Maybe I can lower decent rate using one notch of flaps instead of power to keep decent rate low. I fly final about 80 mph. What do you guys suggest.
I always tend to blame myself for problems like this and just attribute it to inadequate skill. But, I've had Stearmans, a Pitts S2S and a Cessna 140 with misaligned gear on one side. The Cessna was twitchy and unpredictable in which direction it would dart on landing. The 3 is by far the worst so I don't think it is just me.
Mel, thanks for the help with amending my operating limitations. I discussed the change with my PMI and we are on the same page now. Unfortunately, there is now an online form to fill out to apply for an airworthiness certificate. You probably knew that. There are 271 pages of instructions for what used to be the one page paper form now that it is online. After a couple hours I realized that I can't apply until Okla City gets the plane transferred to my name. That will probably take a few months given the backlog. It's too cold with too much snow on the runway for aerobatics anyway.
Happy New Year, Blue Skies and Tail Winds of 2022.
 
WHAT diameter are the main legs at the gear sockets in the engine mount?

Any chance you can have a machine shop mill the holes in the gear legs oversize to 5/8 or 3/4" and then press in solid shaft, then clean up turn the ends the same dia as the gear leg. You would have a clean leg to put holes in with zero toe in.
 
Twitchy -3

I have a -3B and it’s a total pussycat. I’ve run the tire pressure from the mid 20s to 50 psi and see no difference. Full flaps stabilized on final at 70 knots, I probably flair about 55-60. Since you have a lot of high performance tailwheel time, I suspect it’s not you. My plane is based just over the hill (Cascades) at Skagit, BVS; looks like about 200 nm. If you want to come over and to some side by side comparisons, you’d be most welcome.

PM me if you wish.

Dan
 
I'm home sick so I've had time to continue researching my handling problem. I've found 3 friends who have flown RV-3's and all report them stable and easy to handle on rollout. They are probably better pilots than I am, but still, none reported any problem. I measured the toe in of the main gear. The left main is toed in 1/8th inch or .72 degrees. The right main is toed in 3/8 inch or 2.15 degrees. The building instructions state be careful to get the gear straight when match drilling the leg to the socket because it is difficult to fix. That appears to be an understatement. There is no ability to shim to the correct angle.
The mothership referred me to Harmon Lang, who builds the gear legs. Mr. Lang suggested I remove the legs and check them for straightness first. He is able to straighten bent legs. He also suggested I could drill the holes oversize up to 3/8 inch if it would correct the misalignment. The plans are inconsistent about the diameter of the hole to be drilled, some places 5/16 is specified and others 3/8. Until I can get to the hanger, I don't know what I have. Mr. Lang was very specific about not welding on the gear legs to fill and redrill the holes.
The bushing suggestion is good but a machinist suggested I may be more difficult than it appears to ensure adequate wall thickness for the full diameter of the bushing after redrilling.
A very good welder said he could fill in the holes in the socket for redrilling. He was concerned, however, that the welding would affect the id of the socket and prevent gear leg insertion without reaming.
As soon as I can take things apart I'll have a better idea how to proceed. The instructions appear to be accurate, misalignment is difficult to correct. If all else fails, new gear legs ight be necessary.
 
RV-3

I've been flying my -3 for 10 years now, and I've had no problem with the toe in. I've found that a lot of times if I land straight, I don't have to touch the pedals for the entire rollout. Of course, I don't always land straight :eek: so this is not an all the time occurrence. Also when I was doing my transition training with Jan, that the -6 seemed hard to land, and control on rollout. Every RV is different in the way that they handle, so I would suggest that you find what works best for you. :D
 
Fix

Perhaps the easiest fix is to have the gear legs annealed, reinstall them, heat the bend red hot and reset the toe. After they cool of recheck. Remove the gear legs and send them to Harmon for reheat treat.
The alternative method requires eventual removal of the mount. Also requires a TIG welder and an operator who can weld in tight places. Suspend the airplane with a hoist with straps around the upper mount tubes. Elongate the mount holes until the toe is where you want it. Fabricate some washers at least 1/8 thick from 4130 flat or 4130 tubing, just large enough to cover the holes. With the gear legs clamped at the axles very lightly tack weld the washers in place. One tack weld, let the weld cool, then the next tack weld.
It is almost certain that the engine and mount will need to be removed to finish welding all around the washers.
Both methods have been used successfully on Wittman Tailwinds. I favor the first method.
Obviously it would be best to purge all fuel from the system before welding/or bending the gear. The round spring gear was designed and patented around 1950 by Steve Wittman. He called for 1/16" toe in measured in the length of the axle. When the airplane is loaded this likely becomes zero toe.
 
I agree with the bending adjustment solution idea.

One more idea.. Not knowing how much length of straight socket and shaft are available, try and achieve the desired alignment with the through bolts removed while suspended as described above. Perhaps there is space and a location in the gear socket to allow a new hole to be drilled & reamed . No heat treating and no welding required.
 
Here is an update on my gear leg adventures. I took the wheels, brakes, etc. off the legs and checked alignment against a heavy steel I beam. There was some toe in with the gear hanging in the air. With wheels on the ground the toe in was lessoned, as Mel said. I was able to take the suspended toe in out, reassemble and test taxi. The plane behaved better but still I tended to overcontrol. I disconnected the tail wheel steering and handling was even better. I may remove the one sided arm and put the original chains and springs back on with some slack. But they are so ugly. Tail Lynx are no longer available. The best option may be simple cables with slack and no springs. We'll see.
Thanks for all the input.
 
Similar experience in a -4

I've been watching your post, and not sure what direction your headed (no pun intended ), and it reminds me of a -4 I flew from Fla to NC for a friend. I have a -4 I built, and it handles like a dream..at least to me, with the non-full swivel old school OEM tailwheel. While doing the walk-around of the subject -4 I ferried to NC, I noticed lopsided tailwheel tire wear, and a "rocket link" on one side as many have chosen to switch to. Taxiing was more difficult than mine, and the departure roll for take off made me wonder if I should abort. I was following a Cirrus home (had had ADSB) and figured I just had a crosswind biting me a bit. Stopped for fuel and did a 3 point as I usually do..JEEZ..left/right/left..ugh,near disaster.Take off from there I lifted the tail ASAP, and performed another horrible 3 point back at home field. I have 700 plus TW hours, and this one worried me. The previous owned never flew off pavement, so he didn't have complaints about it. the new owner in NC had zilch TW time, and while he was doing his training (in a different plane) , we reworked the stinger holes and squared up the tailwheel, replaced the tire and ditched the rocket link. All is well and good now !
 
Bill
Thanks for your experience with the Rocket link. It confirms my belief that it is too direct a link. Lots of people swear by them and say they get better control. Me, I overcontrol. I'm going to have some sort of hookup to the tailwheel so I don't have to use brakes all the time to steer on the ramp but I will have plenty of slack in the cables.
 
Good news, the twitchiness is resolved. First I aligned the gear straight ahead by the method in the plans. Then I reinstalled a two sided control arm for the rudder with slack chains. The plane still turns quickly but it is far more stable.
It's no longer scary on rollout.
 
I think that almost every tailwheel airplane out there flys differently and you pretty much have to sort out what works best with time. I find my 3 to be an easier airplane to fly than most of my prior TW experience. It's very sensitive and small corrections work well and I prefer that. For me I typically fly my approaches half flap, over that numbers around 75-80, tail low wheelie, slight forward pressure on the mains to plant them, flaps up, as soon as the tail stops flying I plant it stick back and NEVER let up till the mags are off. I think Van got it so right with these little airplanes and they make us look good. I came home from a long trip the other day and had a runway closed at my home airport leaving me with 18Kt gusting 24 direct crosswinds as my only option if I wanted to tuck my little guy in that same night. The PC-12 in front of me was complaining and it gave me terrible anxiety. It took a ton of aileron down to the pavement and once I had the mains on it took full deflection and a lot of rudders to maintain centerline but it was amazing, I NEVER felt like the airplane was out of control or that I lost authority. It was a huge confidence builder in the airplane and its ability. I don't think I would ever go search for these conditions again but it certainly made me feel better that its not a problem for the airplane. I think the one big thing I do is run a lower PSI in the tires, which seems to help my bird.

I look at TW flying like golf, the secret is in the dirt. When I go fly my 3 I usually go to another quiet airport and fly patterns for 20-30 min. You can literally make 10 landings in that amount of time in a 3. If you want to get really good at something you have to go do it a lot. At the end of the day you should not fear landing these little airplanes, its one of the most fun things you can do with them IMO. Learn how to land it power on, power off, full flap, half flap, no flap. I hope I never experience it but I no longer fear the off-airport scenario in my 3 like I did when I first bought it.
 
Sounds like you have discovered the problem as poor build from the beginning with too much toe in/out. I'm not sure what you mean by "twitchy", but If you encounter a gear "shimmy" on one side; make sure to check the engine mount for a crack on a lower cross tube. My 3A developed a shimmy that a friend also noticed when I took off, and a careful inspection found a crack on the mount, and once that was repaired the shimmy went away.

Doug

RV-3A sold
RV-9A FWF
 
Bill
Thanks for your experience with the Rocket link. It confirms my belief that it is too direct a link. Lots of people swear by them and say they get better control. Me, I overcontrol. I'm going to have some sort of hookup to the tailwheel so I don't have to use brakes all the time to steer on the ramp but I will have plenty of slack in the cables.

I think you are jumping to conclusions. He changed several things at once. If the basic alignment was off there will be directional control issues. I don’t think this proves that the rocket link was the culprit.
 
What are the springs for ?

ok, we are all up to speed on caster, trail, toe in/out, friction damping etc.
Loose springs vs tight springs ?
I have flown TW ships with cables and no springs, slightly loose and slightly snug springs. They all work, so WHY are the springs the standard for tailwheel assemblies ?
 
I disconnected the tail wheel steering and handling was even better. I may remove the one sided arm and put the original chains and springs back on with some slack.

YES! There MUST be slack in the tail chains, I see this often (it was on the last RV I bought) and while it makes it slow taxi on rails, it will definitely make it twitchy exactly in the dangerous mid-speeds. You don't want it, the chains should sag a good inch and you should need about 1/4r of rudder travel before it tightens.
 
Springs

Just as the rudder is losing effectiveness if you get a significant crosswind gust you will wish you had properly kept the steering springs tight.
 
YES! There MUST be slack in the tail chains, I see this often (it was on the last RV I bought) and while it makes it slow taxi on rails, it will definitely make it twitchy exactly in the dangerous mid-speeds. You don't want it, the chains should sag a good inch and you should need about 1/4r of rudder travel before it tightens.

1/2” per Van’s:

i-RJJssKd-L.jpg
 
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RV3 Twitchiness

As a previous owner of a RV8, a RV4 (owned the same one twice !), and 2 RV3Bs one of which I currently own, I can say the 3 is a twitchy bird simply by its nature of being a lightweight short little airplane. Mine had the Rocket steering arm which I just replaced with the traditional spring setup (Thanks Paul for the parts !!).
I like having just a little play in the tailwheel steering which helps avoid the twitchiness of the instantaneous response of a steering arm like the Rocket.
My 8 was unusually twitchy on the ground, so I toed out the camber slightly, and I also changed it back to springs immediately after my solid steering arm went over center once on a crosswind landing and locked my rudder pedals out. Almost lost the plane (with wife in the back) and deposited lots of rubber on the runway to prevent a nasty groundloop!
 
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