Nimbus 4 redline at 45000 and 55000 feet

On Thursday, February 28, 2013 3:44:37 PM UTC-5, Bill D wrote:
When Klaus Ohlmann was in Colorado a year so so back he mentioned the N4D he flew to his distance record in 2003 had been "altered" by the factory to allow higher IAS at high altitudes. At the 2012 SSA convention in Reno, I asked Tilo Holighaus what Klaus was talking about.



His answer was they had taken another look at the N4D engineering and flight test data and decided the IAS altitude limitations could be eased. Apparently, Ohlmann's "alteration" was an edit to the Approved Flight Manual.



That said, there are airframe modifications which 'might' improve flutter resistance in the flight levels. Silicon oil filled hydraulic dampers installed as near as possible to the control surfaces are one possibility. Essentially, one pays the price of 'stiffer' controls in exchange for a greater flutter margin. Of course, that does nothing for airframe flutter which does not involve control surfaces.




There were some very good discussions on flutter margins, IAS, and altitude in Homebuilder's Hall articles from the 1970s or 1980s. Searching the SSA Archive will certainly turn them up. There are some commonly used rules of thumb along the lines of x% reduction per thousand feet, but they may not be good enough for the situations you're talking about (i.e. 2% per thousand feet at 50,000 feet is...)

P3

Here's a good video for you:

http://www.youtube.com/watch?v=kQI3AWpTWhM

Boggs

Default answers:

1: Read the approved flight manual and follow it.
2: Any remaining unanswered questions, ask the factory.

Now on to something else. The articles Papa3 referred to came to a head in the August 1977 Soaring magazine. Homebuilders Hall was written by Stan Hall a Lockheed engineer and the designer of a number of homebuilt gliders. The question "which determines flutter IAS or TAS?" came up and led to a number of contradictory answers which he endeavored to resolve by bringing in Perry Hanson, a NASA aeroelastician who spent much of his career studying flutter. If you're an SSA member you can look up his full answer in that issue of Soaring online. To simplify his answer assuming the the conditions are not such that limiting Mach number is a factor, and assuming the structural characteristics haven't changed due to temperature changes a glider will always flutter at the same Equivalent Airspeed - which is nearly the same as Indicated Airspeed (assuming the airspeed indication system isn't so grossly inaccurate as to diverge significantly from Calibrated Airspeed) except that EAS is usually a little lower than IAS. The example he gives is that 120Mph. IAS at 35,000 ft. is equal to 118Mph. EAS. Essentially he says that if you're worried that the glider will flutter at 140Knots at 35,000 ft. you should be just as worried if you're going 140Knots at 2000ft.

I've found some glider manuals give no reduction in VNE as altitude increases, some do give reduction in VNE as altitude increases. The reduction in VNE I have seen in manuals frequently doesn't seem to be done in a manner which is proportional to changes in TAS. It's left me wondering whether the VNE reduction actually is done with changes in the structural qualities with temperature is the reason behind it. Or whether it's a CYA restriction. I'd love to find out for sure just to put my curiosity to rest.

For myself I always go by the first two answers I gave. As it is, I have no oxygen system in my ship and I fly in Canada where there are damn few places you can go above 12,500 ft. at will anyways so it's all kind of academic to me.

On Thursday, February 28, 2013 11:57:14 PM UTC-7, wrote:
Default answers: 1: Read the approved flight manual and follow it. 2: Any remaining unanswered questions, ask the factory. Now on to something else. The articles Papa3 referred to came to a head in the August 1977 Soaring magazine. Homebuilders Hall was written by Stan Hall a Lockheed engineer and the designer of a number of homebuilt gliders. The question "which determines flutter IAS or TAS?" came up and led to a number of contradictory answers which he endeavored to resolve by bringing in Perry Hanson, a NASA aeroelastician who spent much of his career studying flutter. If you're an SSA member you can look up his full answer in that issue of Soaring online. To simplify his answer assuming the the conditions are not such that limiting Mach number is a factor, and assuming the structural characteristics haven't changed due to temperature changes a glider will always flutter at the same Equivalent Airspeed - which is nearly the same as Indicated Airspeed (assuming the airspeed indication system isn't so grossly inaccurate as to diverge significantly from Calibrated Airspeed) except that EAS is usually a little lower than IAS. The example he gives is that 120Mph. IAS at 35,000 ft. is equal to 118Mph. EAS. Essentially he says that if you're worried that the glider will flutter at 140Knots at 35,000 ft. you should be just as worried if you're going 140Knots at 2000ft. I've found some glider manuals give no reduction in VNE as altitude increases, some do give reduction in VNE as altitude increases. The reduction in VNE I have seen in manuals frequently doesn't seem to be done in a manner which is proportional to changes in TAS. It's left me wondering whether the VNE reduction actually is done with changes in the structural qualities with temperature is the reason behind it. Or whether it's a CYA restriction. I'd love to find out for sure just to put my curiosity to rest. For myself I always go by the first two answers I gave. As it is, I have no oxygen system in my ship and I fly in Canada where there are damn few places you can go above 12,500 ft. at will anyways so it's all kind of academic to me.

Interesting comment, though why you'd say so few Canadian high altitude places exist is bit puzzling. Most eastern pilots seem to have access to a site in Vermont, and out west here there's Cowley, which has high altitude windows to 28,000 open twice a year, other times by arrangement. It is possible to go higher at Cowley by special arrangement with ATC, but given the TUC above 25,000 it's a little unclear to me why you'd want to take the risk.. This all assumes you're not transponder equipped. If you are, a lot of airspace opens up between 12,500 and 18,000.

As for altitude in Canada I was just referring to the airspace in most places people actually live and fly IN CANADA being Class B and requiring transponder and/or ATC clearance above 12,500 ft. as opposed to the number of places in the US which are open to 18,000 ft. Where I fly the times when conditions make it practical to go above 12,500 are few and far between anyways.. The wave we get seldom has any real power in it above 10,000 so even when we get to 12,500 the last few thousand takes a while:-) The good thing is we can usually release from tow at 1100 ft ASL so Silver and Gold altitude gains are attainable.

18,000 MSL is routine at Moriarty this time of year. I've had 7 or 8
flights above 17,000' in the past 3 months. We also have a negotiated wave
window so, if you need that altitude diamond, consider Moriarty.


wrote in message
...
As for altitude in Canada I was just referring to the airspace in most
places people actually live and fly IN CANADA being Class B and requiring
transponder and/or ATC clearance above 12,500 ft. as opposed to the number
of places in the US which are open to 18,000 ft. Where I fly the times when
conditions make it practical to go above 12,500 are few and far between
anyways. The wave we get seldom has any real power in it above 10,000 so
even when we get to 12,500 the last few thousand takes a while:-) The good
thing is we can usually release from tow at 1100 ft ASL so Silver and Gold
altitude gains are attainable.

On Wednesday, February 27, 2013 5:59:59 PM UTC-7, wrote:
Does anyone know the redline IAS for the Nimbus 4 at 45000 and 55000 feet? Does ballast make a difference?



Thanks



AH

Lets say the temp at 50000 is -40 and the redline on the Nimbus is 140 Kts...My E6b is showing 53 kts for the TAS. If you fly faster... than you would be a test pilot and should wear some protective clothing, in case you have to jump...bail out bottle the works. They call it the cofin corner I think.... dunno but normally AC flying up there are on auto pilot to make sure things are done right?

Dieter Bibbig

For those in the US. Class B in Canada is different than in US. So much for ICAO standards.

Canada Class B requires VFR positive control above 12,500 MSL, unless you are in really remote northern areas.

Bill T