u870234@daimi.aau.dk (Anton Norup S|rensen) (01/22/91)
From: u870234@daimi.aau.dk (Anton Norup S|rensen) I would like an update on the latest Soviet combat helicopters. The Mi-28 Havoc was seen in Paris, impressive and well-flying. Has it become operational? In what numbers? What about development of add-ons as FLIR etc. The design of the Ka-34 Hokum seems interesting. Has it got beyond the drawing board? What are the pros and cons of the counter-rotating main rotor & no tail rotor principle? In connection with these choppers, I have read about IR-jammers. How do these work? I find the name a little strange, as I associate jamming with radio- frequencies only... Anton Norup Sorensen, University of Aarhus, Denmark Flying - the best to do with your pants on...
urbanf@yj.data.nokia.fi (Urban Fredriksson) (01/24/91)
From: urbanf@yj.data.nokia.fi (Urban Fredriksson) u870234@daimi.aau.dk (Anton Norup S|rensen) writes: >From: u870234@daimi.aau.dk (Anton Norup S|rensen) > In connection with these choppers, I have read about IR-jammers. How do these work? I find the name a little strange, as I associate jamming with radio- >frequencies only... Most IR missiles uses scanning seekers (something like a telescope), and never get an image of the target, only relative signal strength when the seeker points in (very slightly) different directions. Under ideal conditions, you get maximum signal when the seeker is pointing straigth at the target, but with at pulsing jammer you just might be able to get the seeker to record maximum signal when it's slightly off-angle, thus you fool it to turn in the wrong direction. I guess the pulsing had better be matched to the scanning period. - Urban ___________________ \--------------------------/ Urban Fredriksson \--------------------------/ \ My opinions are my own, \-------------------/ I do NOT, and is not / \ but you may share them. \ Nokia Data AB / allowed to, speak for / +---------------------------+ Stockholm / my employer! / |"So, you think he deserves |___Sweden____/-------------------------/ | to die. Those that died, | | but deserved to live, can | | you give them life back?" | +---------------------------+
dnwiebe@cis.ohio-state.edu (Dan N Wiebe) (01/25/91)
From: dnwiebe@cis.ohio-state.edu (Dan N Wiebe) Anton S|rensen writes: > What are the pros and cons of the counter-rotating main rotor & no tail rotor >principle? Counter-rotating dual main rotors have at least one big advantage: a higher maximum airspeed. Possibly the biggest aero- dynamic problem with helicopters is that when they're moving forward (or in any other lateral direction), blades on one side of the rotor disk (the forward-moving side) encounter the air at a higher speed than those on the other (rearward-moving) side. Therefore, there is a lift imbalance that tends to flip the chopper over. This has classically been dealt with by increasing the angle of attack of a blade when it's moving backwards, and decrease it when it's moving forwards. However, as the helicopter's forward airspeed increases, this solution becomes less and less effective--especially when you are moving fast enough that the blade tips are entering the transonic region on one side and falling to near zero airspeed on the other. Counter-rotating main rotors provide an elegant solution to this problem--there are forward-moving blades on both sides of the heli- copter, rather than just one side, which eliminates the lift imbalance. Coincidentally, the net torque is also zero, which obviates the need for a tail rotor (although it seems that a directionally-adjustable ducted tail fan, or even exhaust pipe, would be nice to provide yaw control at low speed or hover). What's the advantage of not having a tail rotor? Dono--except that if you don't have it you can't get it shot out. Now I have a question. I don't know a whole lot about real military helicopters, but I have a couple of attack-helicopter simulators for my computer--Gunship and LHX Attack Chopper. One of the features of both of these simulators is a pair of EWRs (one for radar, one for IR) each with three warning lights--search, targeting, and guidance. The search warning comes on when you appear on somebody's screen, the targeting warning comes on when he paints you with target-acquisition, and the guidance warning comes on when a missile is launched and begins homing. I understand basically how an EWR for radar would work; obviously, the signals emitted for different purposes would have different characteristics. But how does the IR thingy work? I was under the impression that IR homing devices are passive, rather than active. How do you tell when IR energy from your aircraft is being absorbed by a missile's seeker head, rather than by the ground or air? Beyond that, how do you tell what it's being used for once it's absorbed (search, targeting, guidance)? My roommate used to fly as an observer for scouts for AH-1 Cobra attack choppers in the National Guard, and he says that these IR warning devices really do exist, and are not merely an invention of Electronic Arts. But he doesn't know any better than I do how they work. Help! Shalom, Dan Wiebe dnw@rsch.oclc.org
dnwiebe@cis.ohio-state.edu (Dan N Wiebe) (02/04/91)
From: dnwiebe@cis.ohio-state.edu (Dan N Wiebe) Mike DeMetz writes: >You info about counter rotating blates sounds good but the fastest >copters are all of conventional design. Dono 'bout that. Seems I've heard just the opposite, although I must admit that the most authoritative source I can come up with at the moment is the user's manual to LHX Attack Chopper for the PC. Most of the information in this program is probably just educated guesswork, because the Soviets probably aren't talking much about the Hokum, and anyway the LHX doesn't even exist yet. But here are the numbers they give for various Soviet and US helicopters for top speed at sea level: MIL Mi-8 Hip-C Assault Transport 250 km/hr Sikorsky UH-60A Blackhawk Transport 296 km/hr MIL Mi-28 Havoc Attack Helicopter (Apache copy) 300 km/hr MIL Mi-24 Hind-D Armed Assault Helicopter 310 km/hr McDonnell-Douglas AH-64A Apache Attack Helicopter 330 km/hr LHX (Light Helicopter Experimental) 365 km/hr Kamov Ka-34 Hokum Attack Helicopter 374 km/hr Bell/Boeing V-22 Osprey multi-mission VTOL Aircraft 645 km/hr The first five are all standard single-rotor, conventional helicopters. LHX has a single main rotor, but replaces the tail rotor with an in-fuselage ducted fan (air is blown out to one side from the end of the tail). The Ka-34 has twin counter-rotating main rotors and no tail rotor. The V-22 has twin counter-rotating tilt rotors, mounted side-by-side rather than coaxially. So, if we are to take the manual at its word, after about 350 kph, you have to start getting fancy with the technology to go any faster. Dan Wiebe dnw@rsch.oclc.or