average_pilot Posted April 21, 2015 Share Posted April 21, 2015 (edited) I want to add more controversy on the topic :) First, I'm not requesting a feature nor a modification. It's just a little experiment. I know that in the real Ka-50 the centering force on the cyclic dissapears when you press the trim button and so it is implemented that way when using a FFB joystick. But I've never understood why is done that way in the real one because I find that it introduces a lot of unwanted input due to the force suddenly dissapearing. If you are exerting a force to place the cyclic out of the current trimmed position there is always a twitch in the moment the trim button is pressed that in most cases prevents you from trimming where you really intended at first. I wanted to test what'd happen if that feature was removed so I've modified simffb and now the centering force always exists. When I did the test flight I was astonished by how much better the control is! Not just a little better, but a completely new and better feel overall. I'm really curious about why these feature exist in helicopters like the ka-50. I mean, what is the purpose of cancelling the centering force while the trim button is held down? Edited April 21, 2015 by average_pilot Link to comment Share on other sites More sharing options...
AlphaOneSix Posted April 21, 2015 Share Posted April 21, 2015 (edited) I'm really curious about why these feature exist in helicopters like the ka-50. I mean, what is the purpose of cancelling the centering force while the trim button is held down? Because the centering springs are a lot stronger than the ones in your joystick. Also, you should omit "like the Ka-50", because all helicopters have it. Edited April 21, 2015 by AlphaOneSix Link to comment Share on other sites More sharing options...
average_pilot Posted April 21, 2015 Author Share Posted April 21, 2015 Because the centering springs are a lot stronger than the ones in your joystick. Also, you should omit "like the Ka-50", because all helicopters have it.I was unsure if that was universal or a feature in a subset of helicopters. Do you mean that the cyclic feels so hard to move away from the trimmed position that effective control is not possible without cancelling out the centering force? Why is it done like that? Please, bear with me. I just don't know the answer and I've been wondering about it from years now. Knowing that there are real helicopter pilots in this forum I hope I can have this question finally answered. Link to comment Share on other sites More sharing options...
Sokol1_br Posted April 21, 2015 Share Posted April 21, 2015 (UH-1) Magnetic brakes do the trick - items 26 & 33 http://incolor.inetnebr.com/iceman/data/specs504.jpg Link to comment Share on other sites More sharing options...
AlphaOneSix Posted April 21, 2015 Share Posted April 21, 2015 Do you mean that the cyclic feels so hard to move away from the trimmed position that effective control is not possible without cancelling out the centering force? Why is it done like that? No, it's not that bad. The force from the springs varies, but generally, very small movements (like say half of an inch) around the trimmed position are quite simple, but larger movements can have quite a bit of spring force. For example, on the Mi-8, the feel springs are preloaded to 20 pounds, so moving the cyclic more than a very tiny amount requires 20 pounds of force in any direction. 20 pounds of force is not so bad, but if you're going to keep the cyclic in the new position, you're going to want to trim it very quickly. In order to move the control to the feel spring's limits requires 95 pounds of force left and right, and 122 pounds of force for and aft. When I fly (note, I am not a pilot, but I get to fly Mi-8s fairly often), I hold the trimmer down until I get my attitude set where I want it, then release the trimmer and push against the springs for minor adjustments around the trimmed position (around 1/2 inch of movement). In a hover, I tend to just hold the trimmer in the whole time unless I'm going to be hovering for a long time, in which case I find that "sweet spot" and then release the trimmer, but I tend to hit the trimmer a lot in a hover if not just outright holding it down the whole time. Link to comment Share on other sites More sharing options...
AlphaOneSix Posted April 21, 2015 Share Posted April 21, 2015 And just to clarify, the magnetic brakes don't provide the sprint tension, they are either on or off. That is, with the trim button released, the magnetic brakes are engaged and prevent movement except through the feel springs. With the trim button pressed, the magnetic brakes disnegage and allow movement, effectively bypassing the feel springs. Note that while they are called "feel springs" on Russian aircraft, they are typically called "force gradients" on U.S. aircraft. Link to comment Share on other sites More sharing options...
Puddlemonkey Posted April 21, 2015 Share Posted April 21, 2015 I wonder if all those years ago, a couple of developers sat coding the trimmer functionality and said to each other "I bet people around the world will still be passionately discussing and debating this in 7 years time"? :-) Link to comment Share on other sites More sharing options...
average_pilot Posted April 22, 2015 Author Share Posted April 22, 2015 I wonder if all those years ago, a couple of developers sat coding the trimmer functionality and said to each other "I bet people around the world will still be passionately discussing and debating this in 7 years time"? :-)Very true :) Link to comment Share on other sites More sharing options...
Odin_74 Posted April 23, 2015 Share Posted April 23, 2015 Also, you should omit "like the Ka-50", because all helicopters have it. No, there are actually a lot of helicopters that don't. As for the technique for those with, the way AlphaOneSix described is most commonly used and gives the most comfortable ride. Link to comment Share on other sites More sharing options...
AlphaOneSix Posted April 23, 2015 Share Posted April 23, 2015 I guess I should have said "all helicopters with hydraulically-boosted flight controls", but I'm sure someone would sharpshoot that, too. Link to comment Share on other sites More sharing options...
Alpha-87 Posted May 6, 2015 Share Posted May 6, 2015 AlphaOneSix is quite correct, although I cannot speak for other aircraft types as I'm only rated on the AS365N3 and EC135T2 - both of which are fairly basic by today's standards. The following is a bit long winded, but hopefully it will give you some idea of how trim is utilised in a real helicopter. If you have any questions, lob me a PM and I'll get back to you. Every helicopter will have one type of trim, be it a 'mag' trim, 'beep' trim or just holding the cyclic where you want it; or a combination of all three. In the Dauphin we have parallel and series actuators on the control runs, the parallel ones are controlled using the 'beep' trim on the coolie-hat on the cyclic. This allows small movements to be made to fine tune the attitude of the aircraft, the Dauphin operates a mechanical trim system, which instills a certain amount of time delay in the servo reaction, rendering it basically useless. The 135 and most other modern aircraft use Smart Electro-Mechanical Actuators (SEMA's) and these provide an almost instant reaction to trim inputs and are much more useful. This trim system is also the one that the AFCS (automatic flight control system) has authority, once the AFCS has used up all of the parallel trim actuator it needs manually re-centred using the 'mag' trim.... The 'mag' trim uses magnetic brakes to remove centering forces on the cyclic by re-centering the series actuator on the control run - doing this will also allow the parallel actuator to recover its range of movement. They also contain the 'weak links' that you can break using force to recover manual control in the case of a trim actuator runaway. By holding in the 'mag' trim you can effectively go 'floppy stick' like the little Schweizers and Robinsons that you do your initial training on. This is unwise as when you release the mag trim your aircraft is now trimmed in whatever attitude you left it, which may be an undesired one, particularly if you are IMC. For the same reason you should never trim roll into a turn, you can trim pitch to keep the nose on the correct attitude, but if you trim roll, then you can easily become disorientated, so it is best to manually push through the roll centering force on the cyclic and keep it trimmed for level flight as if it all goes wrong, the aircraft will attempt to recover to level flight by itself, which is a much better option if you are in cloud.....which we normally are. Oh and as an aside, if you press the 'mag' trim in a simulator (by which I mean the official Eurocopter full-motion level D sims in France etc) you will pretty much end up upside down. Even the aircraft manufacturers can't get their official helicopter simulators to react the same way as a real aircraft, although they are pretty close. Real pilots stop first, then land. Runways are for models and wings are for fairies. Link to comment Share on other sites More sharing options...
average_pilot Posted May 7, 2015 Author Share Posted May 7, 2015 That's an informative post. I've found several articles on the topic thanks to the content of your post (keywords, that's all about when you want to find something useful using google), and I've reached the conclussion that the Ka-50 manual should have a little introduction to helicopter controls in general that would make thinks a lot more understandable. Link to comment Share on other sites More sharing options...
Alpha-87 Posted May 7, 2015 Share Posted May 7, 2015 That's an informative post. Thank you, and I agree about the lack of information and also about the addition of a little more info in the manual. However, if you or anyone else have any questions regarding helicopter systems in general, feel free to send me a PM and I'll get back to you as quickly as I can. I won't be of any help regarding military ops as I've never been a military pilot, but I do have around 3000hrs of commercial flying so I've got a rough idea how a helicopter works and I can hopefully help with those type of questions i.e. systems, principles of flight, emergencies, instrument flying etc. basically everything but the deployment of weapons. Cheers, Roy Real pilots stop first, then land. Runways are for models and wings are for fairies. Link to comment Share on other sites More sharing options...
Catastrophy Posted May 11, 2015 Share Posted May 11, 2015 [...] I won't be of any help regarding military ops as I've never been a military pilot, but I do have around 3000hrs of commercial flying so I've got a rough idea how a helicopter works and I can hopefully help with those type of questions i.e. systems, principles of flight, emergencies, instrument flying etc. basically everything but the deployment of weapons. Cheers, Roy I know there are birdstrikes with planes but what about helos? Aren't birds scared and rather try to get away or evade? Link to comment Share on other sites More sharing options...
AlphaOneSix Posted May 11, 2015 Share Posted May 11, 2015 Birds are generally pretty good at avoiding helicopter strikes, but it does happen on occasion. I'm sure Google will oblige you with pictures. Link to comment Share on other sites More sharing options...
Alpha-87 Posted May 11, 2015 Share Posted May 11, 2015 As said above; you do get bird strikes, but they are not particularly common. We have had a few over the years on base, but they generally disappear in a pink puff through the blades or they bounce off the side. The engine intakes are protected in a few ways to prevent ingestion depending on the aircraft type - we have mesh covers over the front of our air intakes, whilst other aircraft have air intakes on the side of the engine compartment instead and some others have curved intakes. However, losing an engine (if you have two) really isn't a big deal and is something we practice regularly both in the sim and real aircraft. The biggest issue would be intrusion into the cockpit, which thankfully is rare. And again as said above, Google will show you the effects of cockpit bird strikes. Real pilots stop first, then land. Runways are for models and wings are for fairies. Link to comment Share on other sites More sharing options...
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