rolling take-off
rolling take-off
I searched the archives but couldn't find anything : AFAIK manufacturers don't deal with rolling take-off in the RFMs. Is there any specific reason for that or is it just because of this check in hover right before T/O - which I doubt ?
ATN
ATN
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Rolling Take Offs
The only RFM that I have seen a running take off recommended was in a 1958 model 'H' Bell 47 with a Franklin engine. When I test flew it in 1978 after an engine change I found out why. This machine was very challenged in the vertical performance department.
Running take offs are a 'limited power' technique and whether you fly a skid machine or wheels don't mess with running take offs unless you have been shown how to do it properly.
For public transport ops you need to ensure you can at least achieve an in-ground-effect hover. If your Tq in-hand is zero you had better be sure you are on a runway or a big field. 5% is a good minimum to work with and 10% ideal. I've thrown pax out before now if the site is a bit on the tricky side. I go back for them later of course - well some of the time anyway.
G
Running take offs are a 'limited power' technique and whether you fly a skid machine or wheels don't mess with running take offs unless you have been shown how to do it properly.
For public transport ops you need to ensure you can at least achieve an in-ground-effect hover. If your Tq in-hand is zero you had better be sure you are on a runway or a big field. 5% is a good minimum to work with and 10% ideal. I've thrown pax out before now if the site is a bit on the tricky side. I go back for them later of course - well some of the time anyway.
G
Full pax, full baggage, full aux tank, 300nm run, so you know its going to be light enough to land, it just seemed easier to run it down the runway to get through translation without worrying about engine and transmission limits. And to hell with OEI, we'll just operate like any other Class 3.
Otherwise, running takeoffs may be done if you are taxiing towards the helipad, you call tower early 'cause you expect a delay in takeoff clearance and dang, they just come right back and say "cleared for takeoff". Now you are already taxiing at about 15-20 knots, into wind, with a long taxiway ahead of you. Are you going to stop, and then pull into a hover, move over to the helipad, the pull even more power to takeoff? Or just pull a little more collective while you are already rolling and smoothly transition to flight?
One other case for running takeoffs is if your takeoff area is littered and you want to get into the air with the least amount of FOD risk. Hovering only helps to generate a tornado of styrofoam cups, plastic bags, wrappers, paper, etc. Your compressor will love you.
Otherwise, running takeoffs may be done if you are taxiing towards the helipad, you call tower early 'cause you expect a delay in takeoff clearance and dang, they just come right back and say "cleared for takeoff". Now you are already taxiing at about 15-20 knots, into wind, with a long taxiway ahead of you. Are you going to stop, and then pull into a hover, move over to the helipad, the pull even more power to takeoff? Or just pull a little more collective while you are already rolling and smoothly transition to flight?
One other case for running takeoffs is if your takeoff area is littered and you want to get into the air with the least amount of FOD risk. Hovering only helps to generate a tornado of styrofoam cups, plastic bags, wrappers, paper, etc. Your compressor will love you.
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We used to do this alot in the S-61. When your very heavy, full fuel load etc, the ability to conduct a running take off allows you to achieve translational lift on the ground therefore reducing the power required for take off.
T'was generally done by trimming the disc to a hands breadth above the horizon as seen from the pilots seat, pulling to approx 85%-90% Torque and waiting for the aircraft to fly itself off the runway.
T'was generally done by trimming the disc to a hands breadth above the horizon as seen from the pilots seat, pulling to approx 85%-90% Torque and waiting for the aircraft to fly itself off the runway.
I did it on some occasions, mainly during ferry flights, aircraft loaded with gear and extra fuel and it does give a bonus regarding the engine power saved. I have operated with russian crews from an airstrip and never seen any Mi8 or 17 in hover, always departing and arriving on wheels.
The gist of the question was : is there anything - technical, legal or else - preventing the manufacturers to certify this procedure, with prerequisite, weight and power charts, and all ? If there is any logic behind that, I miss it.
I guess the weight should be between the certified MTOW - structural - and the max weight HIGE.
The finality would be to make it officially and legally available.
ATN
The gist of the question was : is there anything - technical, legal or else - preventing the manufacturers to certify this procedure, with prerequisite, weight and power charts, and all ? If there is any logic behind that, I miss it.
I guess the weight should be between the certified MTOW - structural - and the max weight HIGE.
The finality would be to make it officially and legally available.
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I use rolling takeoffs whenever I am departing an airport. Lets me get my 76 off the ground with 60% Tq or less instead of 80%+
Easier on the system, through translational and almost at CDP before the wheels are off the ground.
Easier on the system, through translational and almost at CDP before the wheels are off the ground.
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Skids
Skids leave some nasty marks on a tarmac, but when you have to, you have to.
Not the greatest feeling in the world if a gusty wind causes you to skid through transition.
Not the greatest feeling in the world if a gusty wind causes you to skid through transition.
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The Cobras I flew in Vietnam were about 1200 lbs over gross weight, and the max altitude for hover was about 6 inches. We made sliding takeoffs everywhere, and gained about 10% more payload in the process.
Most helos now are performance designed around the IGE hover, so that MGW matches IGE hover weight under normal circumstances. This means you can't gain payload without busting MGW, even if you make a rolling TO.
But at altitude, it is possible that you can get an advantage. Be careful, it is quite possible then to find yourself in an embarassing position where the landing is a short squatty one as you fall through, if you forget and try to hover. Of course, you will be saved by jumping out and shouting "VRS got me!"
Most helos now are performance designed around the IGE hover, so that MGW matches IGE hover weight under normal circumstances. This means you can't gain payload without busting MGW, even if you make a rolling TO.
But at altitude, it is possible that you can get an advantage. Be careful, it is quite possible then to find yourself in an embarassing position where the landing is a short squatty one as you fall through, if you forget and try to hover. Of course, you will be saved by jumping out and shouting "VRS got me!"
What speed do manufacturers have to certify their undercarriages to withstand ? Could a running takeoff exceed this speed ? If so, the manufacturers aren't likely to stick anything about RTOs into their Flight Manual, because they'd then have to beef up the gear, with all the cost that would entail.
Perhaps.
Perhaps.
Avoid imitations
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Used to be taught as a technique by the RAF during the time I instructed, probably still is. I had to do one for real to get a Puma (AS330J) airborne during a single engined transit recovery flight after the second engine refused to start on a small offshore island. It's no big deal provided the surface is OK - we had a small airstrip of oiled rolled sand.
The only times I did it for real, was to leave all the flying dirt behind me on laterite airstrips.
I also use to occasionally practice it, but I don't remember ever been instructed on a particular technique.
I just know I must be carefull with cyclic forward input when taking off.
Since there is no graphs, nor procedure described in the RFM on helicopter type I use to to fly, my common sense tells me it's not an approved technique.
I also use to occasionally practice it, but I don't remember ever been instructed on a particular technique.
I just know I must be carefull with cyclic forward input when taking off.
Since there is no graphs, nor procedure described in the RFM on helicopter type I use to to fly, my common sense tells me it's not an approved technique.
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Robbo,
The gear has to meet a percentage of the Vy or Vauto, and must be tested both structurally and handling. It must meet bump and side load criteria, all of which can establish the llimit speed, which should be in the op limits.
The gear has to meet a percentage of the Vy or Vauto, and must be tested both structurally and handling. It must meet bump and side load criteria, all of which can establish the llimit speed, which should be in the op limits.
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I seem to remember that sometime in the 80's the RN were having problems with some cracking in the gearbox support frames (?) of the Sea Kings. The first simple solution, in order to keep operating was to try and restrict operating weight below a certain figure but if not possible, full fuel, weapons etc and above that figure then running take offs were the way to go. Straight forward and no problem if you have a runway etc.
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Rolling take-offs are the only way to go when you are doing a 0 Vis-0 Ceiling, 600' RVR take-off. Your able to gain some of the speed you need for VToss, VMini (min ifr speed)... while still touching the ground... not a bad place to be.
It's funny how times and philosophies change. Way back in the days of yore, when "yore's" truly got his pilot certificate (endorsed by Wilbur), running take-offs were taught as a matter of course. Franklin's engines (invented by Ben, I'm sure) were not known for their surplus of power, and if you didn't have enough to hover, well, sliding it off was what you did. Sliding it on was more or less a given; you had to assume you wouldn't have enough power to hover. Show of hands, how many of you recall the experience of having the throttle wide-f-open and modulating the RRPM with the collective on take-off? If anyone says they were the "good old days" I will slap you silly.
Nowadays, most helicopters can hover at their MGW and the inability to do so would indicate that los pasajeros have fibbed a little about their personal AUW. Nowadays, at low altitude at least, we wouldn't think of taking off if we couldn't get some air under the skids. Thus, the running take-off/landing techniques have sort of fallen by the wayside.
Most pilots I've flown with make two basic mistakes: First, they try to rush the maneuver; secondly, they move the cyclic much too much.
Obviously, it works better on a helicopter with wheels. But there are dangers. New York Airways used to operate S-61L's (the kind with fixed gear, no sponsons or retractable wheels). Operating out of busy places like JFK, LGA and EWR, the designated landing/take-off areas were not in the terminal areas but out on taxiways- taxiways which were often occupied by largish jets. The helicopter pilots would sometimes "expedite" their landings by "hitting the ground running" instead of coming to a complete stop and setting down. The more comfortable they got, the faster they would touch down. This procedure had tragic consequences later on.
Sikorsky certainly had done their homework on the expected vertical loads for their landing gear. But they never really considered that such strong and repetitive fore-and-aft loads would be imposed. One day, as an S-61 was sitting on the rooftop helipad of the Pan Am Building in midtown Manhattan NYC and passengers were outside of the aircraft, one of the gear legs failed and the ship rolled onto it's side.
Nowadays, most helicopters can hover at their MGW and the inability to do so would indicate that los pasajeros have fibbed a little about their personal AUW. Nowadays, at low altitude at least, we wouldn't think of taking off if we couldn't get some air under the skids. Thus, the running take-off/landing techniques have sort of fallen by the wayside.
Most pilots I've flown with make two basic mistakes: First, they try to rush the maneuver; secondly, they move the cyclic much too much.
Obviously, it works better on a helicopter with wheels. But there are dangers. New York Airways used to operate S-61L's (the kind with fixed gear, no sponsons or retractable wheels). Operating out of busy places like JFK, LGA and EWR, the designated landing/take-off areas were not in the terminal areas but out on taxiways- taxiways which were often occupied by largish jets. The helicopter pilots would sometimes "expedite" their landings by "hitting the ground running" instead of coming to a complete stop and setting down. The more comfortable they got, the faster they would touch down. This procedure had tragic consequences later on.
Sikorsky certainly had done their homework on the expected vertical loads for their landing gear. But they never really considered that such strong and repetitive fore-and-aft loads would be imposed. One day, as an S-61 was sitting on the rooftop helipad of the Pan Am Building in midtown Manhattan NYC and passengers were outside of the aircraft, one of the gear legs failed and the ship rolled onto it's side.
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Rolling takeoffs aren't a published data chart in the FM for several reasons -
1) there is no regulation that requires it
2) it's not, strictly speaking something you want to be doing.
If you can't hover in ground effect at the height shown for the hover IGE charts, then you've probably overloaded your helicopter for the atmospheric conditions.
It's a great maneuver for teaching coordination, but a lousy lesson on performance (if one day you can't get it into the hover, you can do a rolling takeoff...)
I've been involved in at least one accident investigation where the pilot seriously overloaded the machine at sea level, and then used the rolling takeoff to get airborne. Even an hour or so later, he was still overweight, and couldn't keep it out of the water he was trying to hover over.
1) there is no regulation that requires it
2) it's not, strictly speaking something you want to be doing.
If you can't hover in ground effect at the height shown for the hover IGE charts, then you've probably overloaded your helicopter for the atmospheric conditions.
It's a great maneuver for teaching coordination, but a lousy lesson on performance (if one day you can't get it into the hover, you can do a rolling takeoff...)
I've been involved in at least one accident investigation where the pilot seriously overloaded the machine at sea level, and then used the rolling takeoff to get airborne. Even an hour or so later, he was still overweight, and couldn't keep it out of the water he was trying to hover over.
Interestingly, the S-61 FLM describes the technique, for either Cat A or B departures, in the Part 1 section 2 (2-28)
I agree that in normal CAT (public transport) operations there is no need for it. Landings though are another story......
I agree that in normal CAT (public transport) operations there is no need for it. Landings though are another story......
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In the hot summer of 1969 at MW, the Hiller Ravens of the Basic RW Flight would not lift into a hover with large student (me) and instructor on board. I was taught to apply full power, tilt the disk carefully forward, waggle the pedals to break the grip of the grass, and hope that we got translational lift before we fell into a rabbit hole. Those were the days!