BK117
Guest
Posts: n/a
BK117
Has anyone else had un-commanded pitch-up occurences in BK117's(around 20 degrees)in moderate turbulence ? This has happend twice to me now at night in IMC & it feels rather uncomfortable! The CSAS has been thoughly checked out and cleared.
Guest
Posts: n/a
Could your csas have gotten kicked off momentarially? I find nose =-20 degrees is normal flight in a BK in turbulance. Seems you are always fighting to keep the nose on the horizon even in light turbulance. Of course I could have had the problem and not known. It's also possible the gust was too much for the csas to handle. It's not a very good system compared to the single pilot IFR SPZ 700.
Give me the S-76 any day.
Give me the S-76 any day.
Guest
Posts: n/a
Devon & Cornwall Constabulary Air Support Unit operate a BK117. Albeit mainly in the police role they do a limited amount of EMS when Air Ambulances are not available. if you don't have their details they're all in Shephard's 'Police Aviation Handbook'. Any more difficulty e-mail me.
Guest
Posts: n/a
I fly a BK117 in California in an EMS role. It is excellent and very popular in the states. The B2 model is very strong and performs well in high DA situations. It's great for night operations since the cabin is separate from the cockpit, no bother from the patient or the interior lights. It's a stable platform for IFR but I understand that it doesn't have the range to be very effective. The medical crews like it as well. Two patients or one. The interior is key, take your time in designing it.
Let me know if you need any more info.
Let me know if you need any more info.
Guest
Posts: n/a
the BK is probably the single most popular EMS ship in the USA. Suggest you contact Keystone Helicopters. They operate a fleet of BK's as well as an assortment of other ships (S76, A109 etc.) and are one of the premier EMS completion centers in the US as well.
http://www.keystone-helicopter.com/
http://www.keystone-helicopter.com/
Guest
Posts: n/a
Whatsarunway,
I've flown the BK and BO in EMS, if I had to make a choice I'd take the BK. But if there is an S-76 available I'd jump in that first.
With regards to the BK-117, try to avoid the "A" series helicopters, a bit weak. The B-1 or even better the B-2 have more umph on takeoff. Some of the A's do not have yaw sass I understand, you want to be sure you get a machine with yaw sass. (Yaw sass was added due to the number of med crew getting air sick) Even with yaw sass I find the patient, and often the med crew, get sick in the BK-117. It's a much more sharp edged ride in turblence then any other helicopter except the BO-105. In my experience 10 gusting to 15 feels like 20 gusting to 30 in most other helicopters.
In spite of the room in the back the patients side rubs the side wall on loading so we have had problems with a patient with a broken right arm or leg "fitting" comfortably. Lots of loud comlaint.
I'm also not crazy about the hydraulic system in the BK, same type as the BO. The no 1 system is carring all the loads all the time, then if it fails you have to rely on an automatic switch over to the no 2 system to keep the controls working. There have been a few situations during the switch over where the collective slams down. Good idea when you do the pre-takeoff hydraulic check to leave the collective up a little during the switch over check to see if it drops. An engine overspeed control system has recently been added to the BK too. I have heard of a few situations of it causing a loss of power due to a false sense of an overspeed. Also the overspeed test switches are not "locked out" at 100% N2 so if you move one to test in flight, by mistake, you can have a momentary loss of power, even a shut down in some cases.
Some one else mentioned fuel. Make sure you get the small aux tank, the early A's did not have it. Gives you 180 US gal of fuel. About 2+15 to burn out at 60% torque in the A or B-1 @ 120 kts. Not great for IFR IMO.
Hope this helps you in deciding whether to buy a BK or not. For the cost of a new one you can have a great used 76 which is a much more capable helicopter.
Fly safe.
I've flown the BK and BO in EMS, if I had to make a choice I'd take the BK. But if there is an S-76 available I'd jump in that first.
With regards to the BK-117, try to avoid the "A" series helicopters, a bit weak. The B-1 or even better the B-2 have more umph on takeoff. Some of the A's do not have yaw sass I understand, you want to be sure you get a machine with yaw sass. (Yaw sass was added due to the number of med crew getting air sick) Even with yaw sass I find the patient, and often the med crew, get sick in the BK-117. It's a much more sharp edged ride in turblence then any other helicopter except the BO-105. In my experience 10 gusting to 15 feels like 20 gusting to 30 in most other helicopters.
In spite of the room in the back the patients side rubs the side wall on loading so we have had problems with a patient with a broken right arm or leg "fitting" comfortably. Lots of loud comlaint.
I'm also not crazy about the hydraulic system in the BK, same type as the BO. The no 1 system is carring all the loads all the time, then if it fails you have to rely on an automatic switch over to the no 2 system to keep the controls working. There have been a few situations during the switch over where the collective slams down. Good idea when you do the pre-takeoff hydraulic check to leave the collective up a little during the switch over check to see if it drops. An engine overspeed control system has recently been added to the BK too. I have heard of a few situations of it causing a loss of power due to a false sense of an overspeed. Also the overspeed test switches are not "locked out" at 100% N2 so if you move one to test in flight, by mistake, you can have a momentary loss of power, even a shut down in some cases.
Some one else mentioned fuel. Make sure you get the small aux tank, the early A's did not have it. Gives you 180 US gal of fuel. About 2+15 to burn out at 60% torque in the A or B-1 @ 120 kts. Not great for IFR IMO.
Hope this helps you in deciding whether to buy a BK or not. For the cost of a new one you can have a great used 76 which is a much more capable helicopter.
Fly safe.
Join Date: Jul 2003
Location: Australia
Posts: 32
Likes: 0
Received 0 Likes
on
0 Posts
BK117
The BK117 variants, whilst being superb all-round helicopters have a couple of very nasty vices which can/have caused accidents or messed flightsuits (to say the least). In particular, the severe pitch-up at high DA/AUW/IAS combinations, and the inability to recover from a steep right roll at sub 40kt airspeeds. Can anyone shed some light on the causes of these and more importantly, are there any plans/mods to have these problems alleviated in later models (EC145)?
Cheers,
The Monkey.
Cheers,
The Monkey.
Join Date: Jul 2002
Location: Up a sago palm
Posts: 35
Likes: 0
Received 0 Likes
on
0 Posts
Hi 'Love your Monkey',
Unfortunately I have encountered both the problems you describe, but cannot shed any technical light on the causes, less to say that they are aerodynamic. The pitch up is a bit disconcerting, especially at night, as it can be as high as 20/25 degrees. I had put it down to the SPAS applying a correction to the stick position as a result of the applied cyclic when correcting the pitch up, but have since come to the conclusion that it is an instability problem. When it happens you get the distinct feeling that you have no pitch control for a couple of seconds.
If your interested you can also get locked into a tight left bank in the BK. Once again I found myself in this position doing a low level exercise and thought I was about to literally slide slip into the ground from about 20 feet with full opposite (right) stick displacement. Thankfully it held its height (only barely) as it decelerated in the uncontrolled turn, from about 80 knots to 5 knots in less than 3 seconds. Scared the crap out of me. I have since found that applying a small amount of opposite pedal and forward cyclic will bring the old girl out of any high angle of bank, albeit with low G’s.
Your right, it’s a pretty well know problem and one I think we just have to deal with from inside the cockpit as it is probably inherent in high performance helicopters.
Give my best to your monkey,
Cheers
If your interested you can also get locked into a tight left bank in the BK. Once again I found myself in this position doing a low level exercise and thought I was about to literally slide slip into the ground from about 20 feet with full opposite (right) stick displacement. Thankfully it held its height (only barely) as it decelerated in the uncontrolled turn, from about 80 knots to 5 knots in less than 3 seconds. Scared the crap out of me. I have since found that applying a small amount of opposite pedal and forward cyclic will bring the old girl out of any high angle of bank, albeit with low G’s.
Your right, it’s a pretty well know problem and one I think we just have to deal with from inside the cockpit as it is probably inherent in high performance helicopters.
Give my best to your monkey,
Cheers
Join Date: Jul 2003
Location: Australia
Posts: 32
Likes: 0
Received 0 Likes
on
0 Posts
Didn't know it could happen to the right. The pitch up is (I am led to believe) caused when there is not enough fwd stick remaining to counter flapback at high blade pitch angles caused at high DA/AUW/IAS combinations, even with a servicable SPAS. Can anyone can verify this?? Lowering collective fixes the condition, but not after you lose 40-50 knots and 10-20 years off your life (double this at night). Does this happen on the EC145?
"Taught" about this quirk during endorsement training, but never been able to reproduce it operationally. I was led to believe that it was affected by the rigging, and substantially reduced/eliminated with the B2 upgrade, which revised the rigging and pitch horns. As such, I would expect that the 145 should limit the problem, but that's only a guess.
I have had instances of pitch "running away" nose up at altitude, when IAS has got on the high side, which has either needed gobs full of forward cyclic or a pedal turn/roll to reduce. Talking about DA>6000ft, though. It can be a bit twitchy up around 9-10,000 ft, but the collective is usually around the pitch limit there, anyway, so most flying is with the trim rather than brute force
(Just a late thought, but reducing collective is sometimes a solution to the pitching up problem, but not always. But it helps at high DA)
I have had instances of pitch "running away" nose up at altitude, when IAS has got on the high side, which has either needed gobs full of forward cyclic or a pedal turn/roll to reduce. Talking about DA>6000ft, though. It can be a bit twitchy up around 9-10,000 ft, but the collective is usually around the pitch limit there, anyway, so most flying is with the trim rather than brute force
(Just a late thought, but reducing collective is sometimes a solution to the pitching up problem, but not always. But it helps at high DA)
Last edited by John Eacott; 6th Aug 2003 at 18:58.
During Factory training....and demo of the low altitude, steep bank, roll coupling....no more lateral cyclic situation.....advice was to use as much opposite pedal as required to regain control. Main concern is regaining control and use of full pedal is acceptable....the little ****** is "rigid rotor" (my definition....not Lu's) thus it is tolerant of "G's" or the lack of. At least it is far more tolerant of them in the air than when making contact with the ground at a high rate of knots!
Right turns are the problem...first I have heard of a left turn presenting a problem.
Right turns are the problem...first I have heard of a left turn presenting a problem.
Hingless Rotor wrote:
Haven't flown the BK, but the MBB BO105 has a very similar rotor with similar characteristics. One day, up high and scooting right along, I caught a little updraft (I guess) and the nose pitched up. And up, and up. I kept feeding forward cyclic in, with no response, thinking, "This is a bit odd, eh what?" Finally I did lower the collective and returned to controlled flight. I came to the conclusion that my little BO-peep did not like high-altitude flight all that much.
I had put it down to the SPAS applying a correction to the stick position as a result of the applied cyclic when correcting the pitch up, but have since come to the conclusion that it is an instability problem. When it happens you get the distinct feeling that you have no pitch control for a couple of seconds.