pilotwolf Posted April 27, 2004 Report Share Posted April 27, 2004 Now before I get flamed I know limits are there for a reason and not meant to be exceeded but would like an answer to this one... The 269A has a VNE redline at 75mph but how was this determined? During my conversion training I had a few excursions above this with no noticable increase in vibration or handling problems. I know its normally retreating blade stall that determins the VNE but there was none of the usual signs of this. Neither my instructors, fellow group members or the engineer have an idea where this figure comes from. Finally how critical, bearing in mind my first paragraph, is it to stick to the limit? PW Quote Link to comment Share on other sites More sharing options...
yzchopper Posted April 27, 2004 Report Share Posted April 27, 2004 I'm not exactly sure about which method the Schweizer company used for the 300 but I was told by my Cheif CFI that there are two ways to determine the VNE of a helicopter. The R22 uses the second method as decribed below. 1) When the helicopter starts to experience the symptoms of retreating blade stall back off of the forward airspeed to just before it started the symptoms and then reduce that airspeed by 10% and now you have the VNE. or 2) The helicopter may not get into retreating blade stall (as with the R22 there actually is no VNE) because the helicopter just can't go fast enough to have this happen. Soo the FAA has determined every helicopter must have a VNE. To do the second method all you do is go full forward cyclic and then back off the cyclic 3/4 in. This will allow you to still have enough control movement of the cyclic during forward flight. When the cyclic is backed off to this 3/4 in. then read your speed and this is considered to be the VNE. These two methods I have described are what the FAA has a manufacturer go by to determine the VNE of their helicopters. I hope this helps. :thumb: Steve rotorheadsmiley Quote Link to comment Share on other sites More sharing options...
JGB Posted April 29, 2004 Report Share Posted April 29, 2004 From memory (what's left of it) the Vne limitation on the 269A was the front windcsreens which are lighter than a B or C model. Granted most A's would have had the windscreens changed by now and have aftemarket or B/C ones fitted.That's about the only difference and the aircraft was probably never certified to a new Vne. You can upgrade an A to be virtually a B although still with 2 seats but the Vne remains unfortunately. Quote Link to comment Share on other sites More sharing options...
Fly for food Posted September 3, 2004 Report Share Posted September 3, 2004 This is absolutely correct, the Vne is determined on the old Th55/269A by the bubble. ::devil:: Quote Link to comment Share on other sites More sharing options...
trdahbs Posted September 7, 2004 Report Share Posted September 7, 2004 BS, BS, BS. The 269A-1 is not the same airframe as the 269C, its horizontal stabilizer is narrow chord and long span as compared to the C or CB. Horizontal stabilizers are there not necessarily to stabilize, but to control VNE. The VNE is an aerodynamic limiter as taught at good old Fort Wolters. We had a few fatality accidents there from autorotative tuck from students pushing left pedal at the start of the auto. This was cured by increasing the area of the horz. stab. Those stabs, however are not even as large as the legal stabs for a TH-55 conversion to a civilian A-1. There are far too many in these forums that apparently don't have enough to do other than invent "new" helicopter aerodynamics. Quote Link to comment Share on other sites More sharing options...
Whirllybird8008 Posted October 24, 2004 Report Share Posted October 24, 2004 The bubble dose control VNE at low altitude, however at altitude where the air is thinner and the strength of the bubble is not an issue dissmetry of lift is the limiting factor Quote Link to comment Share on other sites More sharing options...
Fly for food Posted October 26, 2004 Report Share Posted October 26, 2004 BS, BS, BS. The 269A-1 is not the same airframe as the 269C, its horizontal stabilizer is narrow chord and long span as compared to the C or CB. There are far too many in these forums that apparently don't have enough to do other than invent "new" helicopter aerodynamics.I can only assume that as the self proclaimed guru in aerodynamics then, that you will also be telephoning Steven Gleason of Schwiezer......as he seems to disagree with you, and I quote: "the 269A was designed with a smaller main rotor diameter and slightly different blade twist. Those limitations are what set the VNE. The 269C has a larger diameter rotor and different twist which allows the increased speed. Regards,Steven GleasonSchweizer Aircraft Corp.1250 Schweizer RoadHorseheads, NY 14845607-739-3821 ext 4348607-796-2488 Faxgleason.steven@sacusa.com" Seems that we can all learn a thing or two, wouldn't you say Mr Birdsell (TRDAHBS)? ::devil:: Quote Link to comment Share on other sites More sharing options...
Gummy Posted October 27, 2004 Report Share Posted October 27, 2004 Its interesting how myths can perpetuate.Ive read in three different texts that the 269A was bubble limited. (reference texts not POH)Perhaps its a confusion with the 369A which was buble limited, or carried over from the early B47? Quote Link to comment Share on other sites More sharing options...
Fly for food Posted October 27, 2004 Report Share Posted October 27, 2004 I'm the same Gummy - and even heard it from the owner of a 269a - so you live and learn I guess. ::devil:: Quote Link to comment Share on other sites More sharing options...
medhawkdriver25 Posted December 23, 2004 Report Share Posted December 23, 2004 Whirllybird, Just a slight correction. At a higher altitude the pressure on the bubble would be the same as at a lower altitude, given the same Indicated Airspeed! Remember that the pitot tube is experiencing the same low pressure as the bubble. I like reading these posts...haven't been able to peel myself away from the computer! Fly Scared! Quote Link to comment Share on other sites More sharing options...
TH55 Posted December 23, 2004 Report Share Posted December 23, 2004 I agree, this is always interesting.It is fun to see other opinions.In the first post of this thread it was stated that the 269A had a VNE of 75mph, wrong, it is 75kts.I'm not going to pretend to know the reason for the VNE limit but remember this machine like most others has a power limit. In the 269A we are limited to 6 min. at 26" or more of MP. So 25"MP is our continuous duty limit. At 25"MP you may beable to fly alittle above the VNE but you are working the engine harder than I would want to. To fly at 25"MP and say 120kts would bring you back to earth.Another limit.TH55 Quote Link to comment Share on other sites More sharing options...
spw1177 Posted December 24, 2004 Report Share Posted December 24, 2004 2) The helicopter may not get into retreating blade stall (as with the R22 there actually is no VNE) because the helicopter just can't go fast enough to have this happen.This is true only at lower altitudes, you will run out of power before you will get into retreating blade stall. But at higher density altitudes it is quite possible to encounter retreating blade stall in an R22. I have experienced the onset of retreating blade stall in a R22 here in CO on a warm summer day. Also, I know a pilot who encountered retreating blade stall (the hellicopter rolled) on a sourching summer day in Pheonix at 5000ft MSL over the city. Quote Link to comment Share on other sites More sharing options...
pilotwolf Posted February 27, 2005 Author Report Share Posted February 27, 2005 The reason my first post states 75MPH is because that's what the ASI is marked as reading in our ship, since then I ve aqquired an upto date POH and that shows 75 knots... PW Quote Link to comment Share on other sites More sharing options...
Recommended Posts
Join the conversation
You can post now and register later. If you have an account, sign in now to post with your account.
Note: Your post will require moderator approval before it will be visible.