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Landing a DR400 issues

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Landing a DR400 issues

Old 30th Oct 2018, 12:30
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Landing a DR400 issues

I am having difficulty in successfully keeping a Robin DR400 rolling straight down the runway after landing. The traditional method I was taught, is to flare and land on the main wheels and then let the nosewheel come down and then roll down the runway slowing down naturally before applying brake. This is fine, but once the nosewheel is down, the aircraft is unsteerable and I have had a few hairy moments where the aircraft has rolled to the right and virtually left the runway.
I am not sure if this is a mechanical issue or if this is a technique issue, I'd like to get it sorted as I am running out of underpants

Any Advice would be greatly appreciated
Paul M
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Old 30th Oct 2018, 14:11
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Sounds like something amiss with the aircraft unless there's a nasty crosswind you're not telling us about
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Old 30th Oct 2018, 14:25
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Welcome Paul,

Hold the nosewheel light as long as you are able, it's better for the nosewheel, and will make steering a little easier. Might you be unintentionally be applying brakes? Focus on keeping your heels on the floor, just as takeoff, until you need to apply the brakes. Unless the runway is short for the aircraft, it is likely that you can roll out and maybe not even need brakes, so don't be too eager to apply them, just be ready.

If the airplane will taxi straight, it'll land and roll out straight. So if you're having trouble taxiing, analyze the problem then. If you have no problem taxiing straight, but a problem on the roll out, pay more attention to your use of the pedals. If you've landed well, with good directional control to touchdown, it's unlikely that a crosswind is fussing your rollout.
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Old 30th Oct 2018, 15:21
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The aircraft has a problem !

Clearly the landing gear shock strut oil level and or air pressure has not been set up in accordance with the maintenance manual. At a guess I would say the nose gear is over pressurised resulting in the centering lock remaining engaged and / or the main gear is under pressure with not enough oil in the leg to get the correct rising spring rate to keep the correct extension of the legs hence the nose stays high and the centering lock stays engaged.

The only answer is to jack the whole aircraft up and do an oil air service IAW the MM. Robin are very clear as to the oil quantity and air pressure required for EACH aircraft variant so a -180 has very different settings to a -120.

The aircraft needs to return to the maintenance hangar before there is an accident involving the aircraft departing the runway side, I once saw a DR400 depart the runway at LFAT, it hit the PAPI lights and the leaking fuel caught fire destroying the aircraft, I offered the pilot a lift back to the UK and during the conversation he reported exactly the same symptoms as detailed above by Paul M.

It is important that this aircraft is not flown until this defect is resolved.




Last edited by A and C; 30th Oct 2018 at 15:29. Reason: Predictive text issues
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Old 30th Oct 2018, 16:18
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Hold the nosewheel light as long as you are able, it's better for the nosewheel, and will make steering a little easier. Might you be unintentionally be applying brakes? Focus on keeping your heels on the floor, just as takeoff, until you need to apply the brakes.
Normally yes, for most light aircraft I agree fully, but the DR nosewheel at full extension is locked fore and aft. It needs some (not a lot) of weight on the nosewheel before it will turn. It's aircraft specific, and the OP has been taught correctly. "Let it come down" BTW, the brakes need a good bit of rudder in a correctly set up aircraft before they come on. To brake both sides together involves pulling on a handle.
If it needs more than this, then there is a problem with the aircraft and it shouldn't be flying. You can see how much it needs by pulling down on the prop at some convenient point in the hangar or elsewhere. You may need to do this when pulling it out of the hangar anyway
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Old 30th Oct 2018, 20:01
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Pilot DAR / Piper classique

This is not a pilot technique issue, itís bad maintenance pure and simple, at one time the MM advice was poor and lost a lot in the translation from French to English but Robin have cleared up their act and the MM gives very clear advice on landing gear maintenance.

Setting up correct oil level is nothing like the way the Americans do it and if the American technique is used it results in a much less aggressive spring rate rise and so a very soft main gear , the result of this is a nose high attitude on the ground and the nose centering lock remaining engaged far too long preventing the rudders from actuating the nose gear steering.
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Old 30th Oct 2018, 21:05
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Well, I only fly them, but I thought I said it was a maintenance issue. Maybe I wasnt clear enough. If the lock doesn't disengage the aircraft won't steer. If the leg doesn't compress then the lock won't disengage. The wheel needs to be on the ground with some weight on it to compress. It doesn't need brakes to do that if the leg is properly set up. It does need the pilot to relax back pressure on the stick as the aircraft slows down after landing.
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Old 30th Oct 2018, 21:34
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Leaving aside the charge to castigate the LAE looking after the aircraft that the OP flies, I think it prudent to share this with the rest of you,

Some of the Robin DR400 range have no toe brakes. To apply braking, you pull a lever on the centre console, and brakes are evenly applied. Large rudder inputs, or indeed steering angles while moving the aircraft on the ground, results in the brakes coming on, (possibly one sided) and this makes pushing or pulling it around on concrete tough going. This also exacerbates the large inputs issue when steering with the rudder during roll out.

Personal experience is that PA28 and Cessna drivers struggle to keep the DR400 in a straight line as it needs flown all the time that it is moving.


I love the DR400.
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Old 30th Oct 2018, 23:41
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I think there was an article in a UK flying mag earlier this year in which flying both the Regent and Remorquer were discussed. One had the handbrake system and the other toe brakes, but I don't remember which was which. However, I don't recall the article flagging up the ground handling as being particularly difficult (it does have a nose wheel after all) so suspect A&C is correct. Something is fundamentally wrong with this particular DR400.
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Old 31st Oct 2018, 06:44
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Airpolice

Having owned a number of DR400’s and been responsible for the maintenance of many others I have seen this Problem repeatedly.

The temptation to just blow the leg up and send the owner always present, I had one owner come to me and ask me to just top up the legs, When I told him what the problem was and the work required to fix it he just muttered about being ripped off, got back in the aircraft and went away ( while having difficulty staying on the taxiway ).

Im sorry if it sounds like I’m castigating another LAE but the situation is clear, the aircraft is in an unsafe state, be this because of bad servicing or leakage from the legs, ether way it should not have escaped rectification at its last 50 hour inspection.
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Old 31st Oct 2018, 11:07
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I've flown a number of DR400-180R aircraft. The ones I've flow all had a hand operated brake that applies braking equally to both mainwheels when applied. There have been no toe or heel brakes. However, when you apply rudder to turn when taxying there comes a point where the pedal you are pushing applies the brake to the mainwheel that side to assist with turning. If applying the handbrake (with the pedals central) causes a significant deviation then there is a brake problem to fix.
The other consideration is that in the air the nose wheel extends fully and disengages from the rudder controlled steering. When weight is applied to the nosewheel after the nose is lowered to the ground on landing nosewheel steering should reengage. An overinflated nose wheel olea may prevent this from happening - or a mechanical defect. Finally wear in the steering mechanism can make keeping it straight 'interesting', if there is wear it needs fixing.
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Old 31st Oct 2018, 13:20
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I certainly defer to those with type specific knowledge, as I have not flown, nor maintained a DR-400 (I'm not aware that there are any in Canada). If no toe brakes, then yes brake steering, and differential setting becomes more critical. Some early PA-28's I have flown, and the Tiger Moths have brake levers, rather than toe brakes. I think that the Tiger Moths I flew had a differential brake set up, but the Moth on wheels did not seem to have much noticeable function in this regard, and the other Moth was on skis, so it was moot.

Improperly serviced landing gear will introduce problems. That said, at faster speeds on the runway (let's say 30MPH and faster for many types), the rudder is really doing the work to steer, rather than the nosewheel. If the nosewheel is held light (or off) directional control can be maintained with the rudder alone. If the nose tire is in contact with the runway lightly, it will just scrub a little.

When I train, I teach this by lifting either the nosewheel or tailwheel off the surface, and demonstrating that control can be maintained. No, one should not fly unairworthy aircraft, get it fixed! But, don't give up attempts to maintain control either, use what you've got, including ailerons, in a crosswind. If you're really worried, choose a wet grass runway for arrival; story:

I was once asked at the last minute to ferry a 172 from a grass runway, where a junior mechanic had performed maintenance, back to the main base for the aircraft (which had one grass runway. I did the walk around, everything seemed to be where it should be, and tightened, so I started it up, and taxiied out to the runway. It was not taxiing well, but with steering, brake and rudder effect, I could taxi as needed. While backtracking, I noticed that the left mainwheel was not turning, just sliding on the wet grass. I thought about taking to plane back, and undoing everyone's plans for the day. But, I could taxi with no problem, so takeoff should be okay. It was, and I landed with no difficulty on the grass runway at the destination. I stopped short of the paved apron, and shut down. The boss asked why I'd parked it there. I told him to have the mechanic taxi it in, and he'd figure it out. The mechanic had reassembled the left brake incorrectly, and the brake pads were bolted hard to the disc - he had not checked his work. Okay, one more landing gear maintenance story;

I flew the perfectly fine 152 for it's annual inspection. Upon completion, I flew the post maintenance check flight. It did not want to taxi straight. When I took off, the weight came off the nosewheel, and the rudder pedal when slack. I could pick it back with my toe, and it just flopped around. I landed back, paying very careful attention to keeping it straight on the runway. I taxiied back the hangar, and explained to the mechanic that I was not satisfied. He was unconvinced. I told hi to get in, and flew it again. Once in the air, with a flopping rudder pedal, he could not dispute my objection. 'Turns out that the two nosewheel steering pushrods, which contain springs, are different lengths L for R, to account for the rudder bar offset under the floor. He'd installed them L for R. Once the weight came off the nosewheel, and it centered on the cam, all the springs in the system started fighting each other, and the rudder pedal function was lost on one side, as the springs took up what should have been rudder cable tension. The maintaner had not checked his work. A few hours of remaintenance later, and it flew just fine!

Good maintenance is worth the trouble!
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Old 31st Oct 2018, 17:11
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Jim59

You are correct I what you say until you get to the bit about the nose wheel steering disengagement from the rudder system, it does not ! The nose wheel is steered by a single rod attached to the rudders by a springs, as you move the rudder on the ground the springs apply force to the nose wheel via the springs. When the nose leg is fully extended a cam engages the nose wheel centering lock ( it is attached to the rod that runs from the bottom of the sliding part of the leg ). When in the air the rudder is still attached to the nose leg in the same way but operating the rudder just compresses the spring because the centering lock prevents the wheel from moving. I suspect part of the reason for this system is to stop over enthusiastic rudder inputs in the air, the aircraft is well balanced and the only reason I can think for using full rudder to recover from an unintended spin ( the aircraft is not cleared for intentional spinning ).

Now back to the problem, the centering lock on this aircraft stays engaged on the ground because the aircraft settles at the wrong attitude after landing, the reason for this is incorrect ( or lack of ) servicing of the shock struts. To put the aircraft in the correct ground attitude the correct spring rate is required, this is a rising rate system so it is critical that the correct amount of oil is in the leg along with the correct pressure. If you think that just sticking a bit more pressure in a leg that is low is the answer think again...... you will not get the correct rate rise.

Likewise putting too much pressure in the note shock strut to get a bit more prop clearance is a perfect way to create this problem.

Until people grasp the theory of rising rate springing and the fact that this leg requires more oil than American leg they will continue to have nose wheel steering problems with the Robin.

Last edited by A and C; 31st Oct 2018 at 17:59.
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Old 31st Oct 2018, 19:41
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What A and C said - the Robin is a pussycat on the ground if it's been set up properly. Yours hasn't.

You can sort of alleviate it by easing the stick forward after landing and gentle steering movements (ours only needs 10-15deg before the wheel brake starts coming on) but suggest you get to a shop that knows the robin. Aidan at Dunstable, or AKKI at turweston should be able to help.
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Old 31st Oct 2018, 20:02
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In my experience same problem can occur in Cessna 177RGs for the same reasons so I believe A and C is correct it should be fixed before next flight. Note if an incident occurs due to this problem the insurance investigator will be asking questions as will the CAA and AAIB, have been there. Insurance considered not paying out.
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Old 3rd Nov 2018, 16:16
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Possibly already mentioned, but when I flew a DR400 (this was 6 years ago, and only did a few flights), I was taught that the nosewheel was a bit like that on a rubbish supermarket trolley. Once it's come down, some forward pressure on the stick pushes the wheel into the ground and makes the ac a lot more controllable.
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Old 4th Nov 2018, 06:00
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Originally Posted by JustOneMoreQuestion. View Post
Possibly already mentioned, but when I flew a DR400 (this was 6 years ago, and only did a few flights), I was taught that the nosewheel was a bit like that on a rubbish supermarket trolley. Once it's come down, some forward pressure on the stick pushes the wheel into the ground and makes the ac a lot more controllable.
This is another example of people developing flying techniques to overcome poor maintenance practices, as long as the shock struts are correctly serviced this use of forward stick is not nessesary, Nose wheel shimmy is also an indication that the nose leg bearings are incorrectly adjusted.
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Old 5th Nov 2018, 12:59
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This happened to me in France a couple of years ago. Even the instructor beside me was unable to stop us wandering all over the parallel grass runway before control was finally regained. Please correct me if I am wrong, but I think on the DR400, the nosewheel is locked into the straight ahead postion when there is no weight on that wheel. On landing, when you do finally let the nosewheel down, you have to do it rather firmly rather than gently greasing it on, otherwise it does not unlock again, and you are left with only the rudder and differential braking. Instructor did not warn me about this.
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Old 5th Nov 2018, 14:44
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Tow1790

You are correct in saying the nose wheel is locked when there is no weight on it but the lock is removed in the first inch of nose leg compression.

If the nose leg is too firm or the main legs too soft the lock will stay engaged, if the legs have been properly serviced the aircraft will settle in an attitude that gives the pilot full control.
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Old 6th Nov 2018, 09:09
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Thanks for all the responses, it's been overwhelming. A lot of useful information here. The aircraft is due for its annual soon so will definitely pass on your comments to the Inspectors
Paul M
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