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#1
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Ventus bT/cT comparison
On Tue, 17 Apr 2012 12:46:24 +0000, Jim Pengelly
wrote: Hi everyone, I fly a Discus bT at the moment and absolutely love it. However, I am thinking of upgrading to a flapped turbo in the next one or two seasons and the Ventus bT/cT would seem to be the natural choice. I have heard conflicting opinions about the various models: i) The bT has handling issues and the cT was designed to overcome these issues, with a bigger rudder and some other changes. The cT is the model to go for. ii) The cT has handling issues, can be difficult to bleed approach energy due to the brake configuration and was not a popular model, which is why there are so few of them around. The bT is the model to go for. iii) The bT and cT perform relatively poorly in 15m mode rather than their 16.6m (bT) and 17.6m (cT) modes, so competing in 15m mode is not recommended. Any thoughts much appreciated. Cheers, Jim I'll offer a few comments. My Ventus cT is a 1987 model and I've got about 1500 hrs on the ship over the past 13 years. -- One possible reason for the apparently small number of C models in the US is that at least the early C's were brought into the US as B models, and then re-placarded as a C model. My '87 cT has the original B placard still in place, but X'd out with the new C placard mounted below it. I notice that a number of Ventus B models in the FAA database are in fact C models whose owners never updated the FAA records. -- I've got no complaints regarding the handling of the Ventus C, thought I fly almost exclusively with the 17.6m tips. I've noticed no issues with handling with the 15m winglets, however. -- Unfortunately I have never had to opportunity to fly a Ventus B. The only unbiased comment I can quote is from Derek Piggott in the Dec 1992 / Jan 1993 Sailplane & Gliding issue. "Whereas the earlier model has rather a reputation for stalling and spinning if flown carelessly. the C model seemed a model of docility. I frequently pulled into steep thermalling turns, getting down to well below 40kt with only an obvious buffeting and sinking feeling clearly indicating that this was far too slow. It did not once drop a wing requiring any proper stall recovery. In spite of the extra wing span, the rate of roll is excellent at all speeds and it is easy to fly accurately rolling into and out of turns" -- Max gross with or without the engine is 500kg. The issue with the engine in place is the 255kg non-lifting limit. With the engine in place, the pilot weight determines whether the max gross of 500kg or the non-lifting limit of 255kg kicks in first. For my weight and 28 gal of water, I hit max gross just before I hit the non-lifting limit. Bottom line, with the engine in place and ballasted to max gross, you are at the same loading as without the engine, but you cannot dump down to the same low loading as without the engine. With the engine in, I can go from 10.1 lbs/ft2 max down to 7.9 lbs/ft2 min. Without the engine, W/L ranges from the same 10.1 lbs/ft2 down to 7.2 lbs/ft2 (all with 17.6m span). The B model has the same issue and limitations. -- For what its worth, only the C models were factory certified with the 17.6m tips. -- Regarding the air brakes, I have never found a situation where landing flap and full dive brakes were inadaqute. That said, they probably are not the equal of a PIK 20B or any other ship with full 90deg flaps (I've got about 2500 hrs in a 20B, before the Ventus). Hope this helps your decision. Bob |
#2
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Ventus bT/cT comparison
At 03:36 18 April 2012, Bob Gibbons wrote:
On Tue, 17 Apr 2012 12:46:24 +0000, Jim Pengelly wrote: Hi everyone, I fly a Discus bT at the moment and absolutely love it. However, I am thinking of upgrading to a flapped turbo in the next one or two seasons and the Ventus bT/cT would seem to be the natural choice. I have heard conflicting opinions about the various models: i) The bT has handling issues and the cT was designed to overcome these issues, with a bigger rudder and some other changes. The cT is the model to go for. ii) The cT has handling issues, can be difficult to bleed approach energy due to the brake configuration and was not a popular model, which is why there are so few of them around. The bT is the model to go for. iii) The bT and cT perform relatively poorly in 15m mode rather than their 16.6m (bT) and 17.6m (cT) modes, so competing in 15m mode is not recommended. Any thoughts much appreciated. Cheers, Jim I'll offer a few comments. My Ventus cT is a 1987 model and I've got about 1500 hrs on the ship over the past 13 years. -- One possible reason for the apparently small number of C models in the US is that at least the early C's were brought into the US as B models, and then re-placarded as a C model. My '87 cT has the original B placard still in place, but X'd out with the new C placard mounted below it. I notice that a number of Ventus B models in the FAA database are in fact C models whose owners never updated the FAA records. -- I've got no complaints regarding the handling of the Ventus C, thought I fly almost exclusively with the 17.6m tips. I've noticed no issues with handling with the 15m winglets, however. -- Unfortunately I have never had to opportunity to fly a Ventus B. |
#3
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Quote:
Every Ventus cT manual that I have looked at says the max weight with the engine in is 430 kg regardless of the span. With the engine out, 500kg at 16.6. and 17.6m respectively Cheers Colin Last edited by Ventus_a : April 20th 12 at 04:07 AM. |
#4
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Ventus bT/cT comparison
On Fri, 20 Apr 2012 02:59:15 +0000, Ventus_a
wrote: 'Bob Gibbons[_2_ Wrote: .... text deleted -- Max gross with or without the engine is 500kg. The issue with the engine in place is the 255kg non-lifting limit. With the engine in place, the pilot weight determines whether the max gross of 500kg or the non-lifting limit of 255kg kicks in first. For my weight and 28 gal of water, I hit max gross just before I hit the non-lifting limit. Bottom line, with the engine in place and ballasted to max gross, you are at the same loading as without the engine, but you cannot dump down to the same low loading as without the engine. With the engine in, I can go from 10.1 lbs/ft2 max down to 7.9 lbs/ft2 min. Without the engine, W/L ranges from the same 10.1 lbs/ft2 down to 7.2 lbs/ft2 (all with 17.6m span). The B model has the same issue and limitations. Every Ventus cT manual that I have looked at says the max weight with the engine in is 430 kg regardless of the span. With the engine out, 500kg at 16.6. and 17.6m respectively Cheers Colin Colin, you are correct in quoting the handbook. Several of us actually discussed this apparent contradiction with Klaus Holighaus on a visit a number of years ago. He agreed that it so long as the non-lifting limit is followed, it makes no difference whether the engine is in or out. The engine represents a fuselage (non-lifting) load on the airframe, the cause of this non-lifting load should not be a factor in the overall gross weight, so long as the non-lifting limit is observed. Bob |
#5
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Ventus bT/cT comparison
On Saturday, April 21, 2012 at 12:26:44 PM UTC+12, Bob Gibbons wrote:
Every Ventus cT manual that I have looked at says the max weight with the engine in is 430 kg regardless of the span. With the engine out, 500kg at 16.6. and 17.6m respectively Cheers Colin Colin, you are correct in quoting the handbook. Several of us actually discussed this apparent contradiction with Klaus Holighaus on a visit a number of years ago. He agreed that it so long as the non-lifting limit is followed, it makes no difference whether the engine is in or out. The engine represents a fuselage (non-lifting) load on the airframe, the cause of this non-lifting load should not be a factor in the overall gross weight, so long as the non-lifting limit is observed. Bob Sorry, but I'm still confused. To my mind, a non-lifting limit is a hard limit, defined by the mechanical limit of the four wing-root pins. If you remove the engine (and fuel tank and engine battery) then this limit should not change; you've taken weight off the pins so can add more pilot weight etc. (ignoring balance considerations for the moment). What the flight namual seems to be implying (and thanks, Colin, for the discussions) is that there are some wing bending issues. The (non-turbo) Ventus was designed for a MAUW of 500kg and the wing will cope fine with a max non-lifting weight of 255kg (for example - it varies depending on the model). What the manual seems to be implying is that SH then wanted to put a turbo in but came up against the (true) load limit of the wing pins, as well as some bending moment limitations on the wing, but the market need for a turbo version was great so they put a 430kg limitation on the MAUW. I know that there are cT/bT pilots out there who ignore the 430kg limit and ballast up to 500kg with no issues. I'm asking the Collective Wisdom of y'all whether: a) my reasoning above is correct; b) whether to take the numbers in the flight manual with a grain of salt, bearing in mind the discussions with Herr Holigaus; and c) whether it's worth asking SH to revise the flight manual to clear up the confusion; or d) to obey the flight manual at all times and loads. Answers on a postcard... DH TX |
#6
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Quote:
Too cheap to use a postcard but may I suggest a talk with Pat re his experience with OP if you haven't already. I'm sure he can add something :-) Colin |
#7
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Ventus bT/cT comparison
At 03:36 18 April 2012, Bob Gibbons wrote:
-- Max gross with or without the engine is 500kg. The issue with the engine in place is the 255kg non-lifting limit. With the engine in place, the pilot weight determines whether the max gross of 500kg or the non-lifting limit of 255kg kicks in first. You've lost me somewhere. Why does pilot weight stop you getting to max gross as long as the wing tanks are big enough? Assuming tanks *are* big enough to get to max gross without the engine then it should be a piece of cake to get there *with* the engine. PF |
#8
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Ventus bT/cT comparison
If pilot + other non-lifting parts exceeds 255kg, then you can't fly. If
you can fly, then you can water up to the 500kg limit. Indeed, it should be beneficial as water in the wings reduces wing root bending. It increses bending at the end of the tank area, but the manufacturer should have taken care of that......... At 08:43 20 April 2012, Peter F wrote: At 03:36 18 April 2012, Bob Gibbons wrote: -- Max gross with or without the engine is 500kg. The issue with the engine in place is the 255kg non-lifting limit. With the engine in place, the pilot weight determines whether the max gross of 500kg or the non-lifting limit of 255kg kicks in first. You've lost me somewhere. Why does pilot weight stop you getting to max gross as long as the wing tanks are big enough? Assuming tanks *are* big enough to get to max gross without the engine then it should be a piece of cake to get there *with* the engine. PF |
#9
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Ventus bT/cT comparison
On Apr 20, 2:56*am, Peter Purdie wrote:
If pilot + other non-lifting parts exceeds 255kg, then you can't fly. *If you can fly, then you can water up to the 500kg limit. Indeed, it should be beneficial as water in the wings reduces wing root bending. *It increses bending at the end of the tank area, but the manufacturer should have taken care of that......... At 08:43 20 April 2012, Peter F wrote: At 03:36 18 April 2012, Bob Gibbons wrote: -- Max gross with or without the engine is 500kg. The issue with the engine in place is the 255kg non-lifting limit. With the engine in place, the pilot weight determines whether the max gross of 500kg or the non-lifting limit of 255kg kicks in first. You've lost me somewhere. Why does pilot weight stop you getting to max gross as long as the wing tanks are big enough? Assuming tanks *are* big enough to get to max gross without the engine then it should be a piece of cake to get there *with* the engine. PF- Hide quoted text - - Show quoted text - The Ventus (and nearly all gliders out there) fuselage is hanging from the wings by four pins. On the Ventus they are about 15-20 mm in diameter. The non-lifting weight limit is the maximum load those pins can support and is unchanged by the extra weight water ballast adds. |
#10
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Ventus bT/cT comparison
Yes I know what max weight of non-lifting parts is.
If you can fly at all, you can fly at max gross. I'm just confused by Bob Gibbons post (See quote below) For his weight the margin on non-lifting limit is the same with or without water the 28gals is irrelevant. PF Quote -- Max gross with or without the engine is 500kg. The issue with the engine in place is the 255kg non-lifting limit. With the engine in place, the pilot weight determines whether the max gross of 500kg or the non-lifting limit of 255kg kicks in first. For my weight and 28 gal of water, I hit max gross just before I hit the non-lifting limit. End Quote |
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