Robin DR400/180 stick back at start of the roll
Ah, ok, BP'er, that is a solid point against my little bit of wisdom, for this particular plane. As an (amateur) mechanic, I can't help feeling some doubt about the "virtually" no weight - I reckon there must be an adjustment to that, and how fragile is it? And how much care is taken on the average annual? It might be a good idea but it sounds like delicate.
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A&C is more qualified to respond to that question that I am. All I can say is that at my club we've had at least one runway excursion (with damage) because of this locking mechanism, and probably quite a few near misses. Because of this, it is a specific item that needs to be covered during the checkout and club checks.
It's also a bit of an issue when manhandling the aircraft on the ground. If you push against the prop to move the aircraft backward, you also push up and thereby engage the lock. This makes it impossible to move the nosewheel with the towbar. You need to stop the aircraft, pull the nose down (by the prop) again, move the towbar to the desired steering angle, and then start pushing again. It helps a lot if you have a helper or two, pushing against the wing leading edge.
Oh, and come to think of issues, we've had two brake fires lately. One of which ended up with a burned wing that needed to be replaced in full, the other was fortunately contained to the wheel spats only. Reason? Wrong feet position during taxi. In the DR400 it is extremely easy to place your feet too high on the pedals, resulting in constant brake activation. When after the incident the club pulled the data from the engine (DR400-135CDI with the Thielert/Centurion engines and full FADEC) they found not just that incident, but actually several occasions where people were inadvertently riding the brakes and needing, in some cases, as much as 50% power to get the aircraft moving from standstill. This has now also been added to the checkout and club check lists.
It's also a bit of an issue when manhandling the aircraft on the ground. If you push against the prop to move the aircraft backward, you also push up and thereby engage the lock. This makes it impossible to move the nosewheel with the towbar. You need to stop the aircraft, pull the nose down (by the prop) again, move the towbar to the desired steering angle, and then start pushing again. It helps a lot if you have a helper or two, pushing against the wing leading edge.
Oh, and come to think of issues, we've had two brake fires lately. One of which ended up with a burned wing that needed to be replaced in full, the other was fortunately contained to the wheel spats only. Reason? Wrong feet position during taxi. In the DR400 it is extremely easy to place your feet too high on the pedals, resulting in constant brake activation. When after the incident the club pulled the data from the engine (DR400-135CDI with the Thielert/Centurion engines and full FADEC) they found not just that incident, but actually several occasions where people were inadvertently riding the brakes and needing, in some cases, as much as 50% power to get the aircraft moving from standstill. This has now also been added to the checkout and club check lists.
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nor why a hard runway should make any difference
Last edited by foxmoth; 17th Jul 2016 at 13:03.
But is "getting away" sufficient? It stays well apart from "as high as possible as soon as possible, in safety (i.e. without risking stall)" which I still believe in.
The rest of your phrase is a bit confusing to me, I'm afraid, do you mean that lifting the nose as much as possible will increase wear and stress on the nosegear? That is hard to imagine for poor little me.
The rest of your phrase is a bit confusing to me, I'm afraid, do you mean that lifting the nose as much as possible will increase wear and stress on the nosegear? That is hard to imagine for poor little me.
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Nose gear centering
As Backpacker says the final inch or so of nose gear extension results in the nose gear centering lock engaging and locking the nose gear steering in the Neutral position. If this should happen at low speed the aircraft is almost imposable to steer as there is not enough rudder authority to overcome a well planted and unsteerable nose wheel.
This situation is a result of a lack of or bad maintenance practices and will not occor in a well maintained aircraft.
Unlike American aircraft Robin landing gear legs require a measured amount of oil, American practice is usually to fill the compressed leg with oil and then compressed air, the Robin leg requires to be overfilled ( in American terms ). This oil quantity is critical along with the correct air pressure to obtain the correct rising spring rate when the leg is in service.
I have seen nose legs over inflated presumably to increase the propellor clearance and main legs under inflated ( for a softer ride?) but both of these defects are an accident going some place to happen as premature nose gear centering lock engagement is likely to occor.
The later DR400 maintenance manuals offer very clear guidance on the servicing of landing gear legs ( the first edition of the manual was a less than understandable translation from the French language ).
The maintenance data is different for all the DR400 variants and should be strictly adhered to to obtain the correct Spring rate for that DR400 variant, of this is not done there is a danger of the nose gear steering locking.
The technique I described in a post above is intended to keep some of the weight off the nose gear but not to have it pointed skywards, initially on the takeoff run the thrust vector ( the only vector at the start of the takeoff ) is trying to dig the nose gear into the ground and full up elevator counters this and keeps the aircraft in a level attitude, as the aircraft gathers speed and elevator authority increases the stick should be moved forward towards slightly aft of neutral to maintain this attitude until about 50 KTS when a smooth rotation should start aiming to lift the main wheels off the ground at 55 to 60 KTS.
Keeping the stick hard back throughout the take off run is going to end in tears, the aircraft is more than capable of getting off the ground well below normal stalling speed and therefore without full control authority due to ground effect...........it is an interesting flight regime that is best left untried by all but test pilots.
This situation is a result of a lack of or bad maintenance practices and will not occor in a well maintained aircraft.
Unlike American aircraft Robin landing gear legs require a measured amount of oil, American practice is usually to fill the compressed leg with oil and then compressed air, the Robin leg requires to be overfilled ( in American terms ). This oil quantity is critical along with the correct air pressure to obtain the correct rising spring rate when the leg is in service.
I have seen nose legs over inflated presumably to increase the propellor clearance and main legs under inflated ( for a softer ride?) but both of these defects are an accident going some place to happen as premature nose gear centering lock engagement is likely to occor.
The later DR400 maintenance manuals offer very clear guidance on the servicing of landing gear legs ( the first edition of the manual was a less than understandable translation from the French language ).
The maintenance data is different for all the DR400 variants and should be strictly adhered to to obtain the correct Spring rate for that DR400 variant, of this is not done there is a danger of the nose gear steering locking.
The technique I described in a post above is intended to keep some of the weight off the nose gear but not to have it pointed skywards, initially on the takeoff run the thrust vector ( the only vector at the start of the takeoff ) is trying to dig the nose gear into the ground and full up elevator counters this and keeps the aircraft in a level attitude, as the aircraft gathers speed and elevator authority increases the stick should be moved forward towards slightly aft of neutral to maintain this attitude until about 50 KTS when a smooth rotation should start aiming to lift the main wheels off the ground at 55 to 60 KTS.
Keeping the stick hard back throughout the take off run is going to end in tears, the aircraft is more than capable of getting off the ground well below normal stalling speed and therefore without full control authority due to ground effect...........it is an interesting flight regime that is best left untried by all but test pilots.
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But is "getting away" sufficient? It stays well apart from "as high as possible as soon as possible, in safety (i.e. without risking stall)" which I still believe in.
The rest of your phrase is a bit confusing to me, I'm afraid, do you mean that lifting the nose as much as possible will increase wear and stress on the nosegear? That is hard to imagine for poor little me.
The rest of your phrase is a bit confusing to me, I'm afraid, do you mean that lifting the nose as much as possible will increase wear and stress on the nosegear? That is hard to imagine for poor little me.
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I very much support A & C's post above. A well maintained aircraft should not require "special" pilot technique during runway operations to optimize nosewheel steering. It you have difficulty steering the plane on the runway, while holding the nosewheel light, refer the aircraft to maintenance. I cannot think of a GA aircraft, for which forcing the nosewheel down to steer while on the runway should be required.
And then hope the maintenance people find something wrong, or it's your technique!
And then hope the maintenance people find something wrong, or it's your technique!
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The simple rule that always works is: Unload the small wheel.
For a taildragger, that is stick forward to unload the tailwheel.
For a trike, that is stick backwards to unload the nose wheel.
Then as airspeed increases, and you get "feel" in stick and rudder pedals that the air is "biting", then you can start to "fly" the aircraft to take of.
Most think that "flying" starts when the wheels leave the ground and stops when the wheels touch the ground.
That is why so many "modern" pilots get in trouble when they convert to taildraggers.
For a taildragger, that is stick forward to unload the tailwheel.
For a trike, that is stick backwards to unload the nose wheel.
Then as airspeed increases, and you get "feel" in stick and rudder pedals that the air is "biting", then you can start to "fly" the aircraft to take of.
Most think that "flying" starts when the wheels leave the ground and stops when the wheels touch the ground.
That is why so many "modern" pilots get in trouble when they convert to taildraggers.
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Oh my .... the feel is so different when you need to transfer your skills from a 900m asphalt runway to ~500m grass runway.
Holding back the control column was an easy modification to the habit, but the "light feel" of nose up and moving the control 'a bit' forward will take sometime getting used to. The difficult level goes one/two notch up as the control column is shaking on the grass runway
For today's lesson I had the Grob 115. Even though Robin is fun to fly, I think I am going to stay with Grob.
Holding back the control column was an easy modification to the habit, but the "light feel" of nose up and moving the control 'a bit' forward will take sometime getting used to. The difficult level goes one/two notch up as the control column is shaking on the grass runway
For today's lesson I had the Grob 115. Even though Robin is fun to fly, I think I am going to stay with Grob.
Last edited by indyaachen; 18th Jul 2016 at 15:19.
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I have about 20 hours on Robins post-PPL (I learnt in Cessna 152) and the stick back instruction surprised me at first too...but all experienced Robin instructors say it: stick full back always whilst taxing and at the beginning of the take-off roll, easing as speed builds to avoid rotating too early. As well as taking load off the nosewheel, the DR400/180 in particular has only a small clearance between propeller and the ground, so you need to do everything possible to avoid a propeller strike, particularly on grass runways where a bump in the wrong direction could be very bad news. I didn't fully believe this until someone way more experienced than me did exactly that... a prop strike in a DR400/180 on a grass strip...now I'm absolutely paranoid about remembering to keep that stick back!!...
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On the robin hr200 I was always taught that stick all the way back on take off for soft field, then as you leave the ground nose forward to gain your 70kts and climb out as normal. But just gets you off the ground that bit faster and stops the nose wheel acting like a plough on soft grass.
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Mr Enthusiast
The symptoms you write about have all the signs of mis -servicing of the landing gear shock struts, the likely reason for the inadequate propeller clearance is an insufficient amount of oil in the nose shock strut, the result is the spring rate fails to rise fast enough to maintain the propeller clearance. ( with the added safety if all the air is lost and a hydrulic lock stopping the leg from fully compressing to maintain a minimum safe clearance )
Robin would not build an aircraft that did not have enough propellor clearance, unfortunately they can't legislate for the idiots who don't read the maintenance manual and fail to service the landing gear in accordance with the published data.
Robin would not build an aircraft that did not have enough propellor clearance, unfortunately they can't legislate for the idiots who don't read the maintenance manual and fail to service the landing gear in accordance with the published data.
Last edited by A and C; 19th Jul 2016 at 04:54. Reason: Editing predictive text nonsense.
