gandalph Posted February 24, 2014 Posted February 24, 2014 Meh, it will use 2 wings, a cockpit, a fuselage and a tail so it will look like something I wish you well with your projects Bex. But .....there's been so much sizzle, when do we get to see some steak? Might you be (Bexr)better to get both feet on the bus before you announce to the world that you're travelling?
dlegg Posted February 24, 2014 Posted February 24, 2014 Sadly, more happens on internet forums than real life. Engine promises over 2 years late, now an aircraft apparichian.........buyer beware.......I know this Ghananian bloke .......
bexrbetter Posted February 24, 2014 Posted February 24, 2014 I wish you well with your projects Bex. But .....there's been so much sizzle, when do we get to see some steak? Might you be (Bexr)better to get both feet on the bus before you announce to the world that you're travelling? It's an interesting point and something that has changed in the world a bit in modern times, i.e. the insatiable need for some people on the Internet to have information now and all of it. Me, I enjoy and appreciate people going out of their way to inform me of what they can about their progress and watch and encourage them in build or update threads quite patiently. I suggest anyone who is the former to put me on your ignore list to avoid frustration. Sadly, more happens on internet forums than real life. Engine promises over 2 years late, now an aircraft apparichian.........buyer beware.......I know this Ghananian bloke ....... You are not refering to me of course.
rgmwa Posted February 24, 2014 Posted February 24, 2014 Did you say that about Jabiru at the time? They scratch built everything whereas I am taking considerable shortcuts in comparison. Neither at the time nor since. They've done well overall but it's taken them a long time to get to where they are. If you're taking shortcuts, I hope they're in the right place. Not criticising, just interested in seeing the end result. Good on you for having a go. Meh, it will use 2 wings, a cockpit, a fuselage and a tail so it will look like something and that should be enough ammunition for copying accusations, right FT? Oh, no! It's going to be an RV clone! Maybe I should notify Vans? rgmwa
bexrbetter Posted February 24, 2014 Posted February 24, 2014 Neither at the time nor since. They've done well overall but it's taken them a long time to get to where they are. If you're taking shortcuts, I hope they're in the right place. Not criticising, just interested in seeing the end result. Good on you for having a go.rgmwa "Shortcuts" have been outlaid in the engine thread, e.g. production 'off the shelf' crankshafts and cylinder heads whereas Jabiru developed everything themselves from scratch - that was my meaning. Oh, no! It's going to be an RV clone! Maybe I should notify Vans? I think Vans sleeps quite well at night and has no concern over yet another "Challenger", he has seen plenty of them come and go!
Oscar Posted February 24, 2014 Posted February 24, 2014 "Shortcuts" have been outlaid in the engine thread, e.g. production 'off the shelf' crankshafts and cylinder heads whereas Jabiru developed everything themselves from scratch - that was my meaning. No, they didn't. They produced their first aircraft using a KFM engine. Then KFM pulled the rug from engine production and Jabiru were forced to either completely redesign their aircraft for a different engine or build an engine that could fit their aircraft. They decided to go the 'produce something that will fit' route; in the light of the success of the airframes, just possibly they were justified in making that particular decision - though quite obviously the engine has been far more troublesome than the airframe. Can you name me a manufacturer that produces both their airframes and their own engines that has had the sales success of Jabiru in this class? Textron couldn't - despite its massive presence in other classes. Bombadier don't, yet they have a hugely successful engine sitting on their corporate shelf. Savannah have announced their intention to produce their own engines - this is a road to be traveled. Bex, if you can provide an airframe and engine package that gets people in the air for low cost, safely and reliably, more power to you. In my opinion, the two best aircraft designers of high-performing, excellent small aircraft for low cost have been/are Walt Wittman and John Monnet (Sonex). If you can manage something similar, you will indeed be in line for 'legend' status - go for it. However - and I say this with respect for what you are seeking to do - the allowable by regulations gap between a Homebuilt-spec. aircraft (basically, 19-reg here) and something eligible for 24-reg, is very, very considerable, and you can't just blindly state that a 24-reg aircraft should be cheaper because a 19-reg aircraft can be produced for so much less. To get the necessary ticks in the boxes for different levels of regulatory acceptance is not at all trivial. Just to do a few modifications to a 55-reg aircraft and have it still eligible for 55-reg requires a complete engineering justification to the original standard - in our case, BCAR S. Every damn para. of BCAR S. I just spent a weekend doing a Limit Load test on a new fin on our Jabiru - recorded deflection of the fin with a load of 69 kgs at 43% fin span. Would you like to have a guess at how much engineering time went into determining that 69 kgs @ 43% span is what is required by the BCAR S standard for that particular aircraft? And how much time was required to develop a test regime to demonstrate that that could be achieved? Then, multiply that by ALL of the requirements for BCAR S for the entire airframe. Bex, anyone can build a billycart. Some of those are really rather clever machines. But to build a car that meets the various standards is a whole different ballgame. Same applies in the aviation world. 1
turboplanner Posted February 24, 2014 Posted February 24, 2014 I wish you well with your projects Bex. But .....there's been so much sizzle, when do we get to see some steak? Might you be (Bexr)better to get both feet on the bus before you announce to the world that you're travelling? Last I saw, from photographs he's travelling at a speed I would expect, encountering the problems I would expect, and hopefully solving them one at a time, and he isn't doing it on a 600,000 hour budget. 3
bexrbetter Posted February 25, 2014 Posted February 25, 2014 Would you like to have a guess at how much engineering time went into determining that 69 kgs @ 43% span is You got skinny bloke or a tubby sheila to walk almost halfway up it? I feel my future analogy coming in 3, 2, 1 .....
Oscar Posted February 25, 2014 Posted February 25, 2014 I'll take that as a no, shall I? BCAR S doesn't mention skinny blokes OR ladies not suffering body-image paranoia anywhere...
djpacro Posted February 25, 2014 Posted February 25, 2014 ... I just spent a weekend doing a Limit Load test on a new fin on our Jabiru - recorded deflection of the fin with a load of 69 kgs at 43% fin span.. Just wondering what the objective was in applying a point load (rather than a distributed load) and why Limit, rather than Ultimate? ... Would you like to have a guess at how much engineering time went into determining .... I'm not Bex (nor better), incidentally, however I have done it a number of times. Out of interest I did the sums for the 69 kg bit and it took 10 minutes, takes quite a bit longer for the 43% bit so I didn't bother with that and, of course, airworthiness authorities want a nice report so that would take even longer.PS: I find this even more interesting than discussing boundary layers but I promise not to cause too much trouble in this thread.
Oscar Posted February 25, 2014 Posted February 25, 2014 DJP - we didn't use a point load, we set up a whiffletree arrangement with a main load beam with the load centre at 46% span (sorry, not 43%, I've been preparing the damn test report and I have figures floating around my head like snowflakes in a globe..), an intermediate pair beam with the inner load pad centred at 20.5% span, middle pad centred at 43% span and an outer load pad centred at 73% span - so, as you say, a distributed load. That replicated the certification set-up for the fin we are using (a UL fin on an LSA55). That original test load arrangement was justified (if that is the correct word) in the certification report by comparison of 3-pad BM, Schrenk BM, 3-pad Shear and Schrenk shear plots (or maybe it's curves??) - and I don't have the foggiest idea what all of those mean, I'm not an engineer, but I can do what I'm told and pass it back to the engineers to play with their computers. Why only Limit Load? - because that's what the engineer preparing the EO - the same one who did the UL certification tests - asked for. If the Limit Load test had raised any questions, I'm sure he'd have required more; but he knows the structures of LSA55's through to J160's at least, better than just about anybody. In fact, we actually went 20.1% over limit load because I don't have access to calibrated scales, just commercial ones (though we did double-weighing of each major load component and both scales agreed within .1 of a kg) and we felt a decent margin for measuring error was wise. FWIW, the deflection under a test load of (what we calculated as) 83.56 kgs, was 70mm at the fin tip (to within 0.5mm, allowing for parallax error on a visual sighting on the deflection pointer), and after a test load application of 129 seconds, the fin returned to within 0.5mm of its pre-test unloaded position which is (probably) to have been just from settling of the test rig frame. We don't have sophisticated gear here, but we believe that test was decently performed; mind you, the video soundtrack of it is a bit like the two grumpy old muppets exchanging unpleasantries, but if the old-fart owners of an aircraft can't send each other up a bit, life just is TOO serious. 2
bexrbetter Posted February 25, 2014 Posted February 25, 2014 I'll take that as a no, shall I? . Take as a "I don't care". Oh wait a moment, have a tingling feeling .... nope, false alarm, still don't. No, they didn't. . Yes they did, you just missed the context.
fly_tornado Posted February 25, 2014 Posted February 25, 2014 Cessna problems seem minor in comparison to Boeing http://www.bloomberg.com/news/2014-02-25/boeing-said-to-seek-buyers-for-1-1-billion-of-early-787s.html
Oscar Posted February 25, 2014 Posted February 25, 2014 Yes they did, you just missed the context. No they didn't; there are quite a few ots components in Jabiru engines - Holden pistons, just for a start. OTS bearing shells, OTS shaft seals, OTS coils... 1
bexrbetter Posted February 25, 2014 Posted February 25, 2014 No they didn't; there are quite a few ots components in Jabiru engines - Holden pistons, just for a start. OTS bearing shells, OTS shaft seals, OTS coils... You mean an engine company that doesn't make their own pistons, oil seals and bearing shells??? Wow!! What a revelation ... "Ignore" button time has arrived, not for rude or offensive or similar, it's far worse than that, you're boring me to death.
djpacro Posted February 25, 2014 Posted February 25, 2014 DJP - ........- and I don't have the foggiest idea what all of those mean, I'm not an engineer, but I can do what I'm told and pass it back to the engineers to play with their computers. ......Why only Limit Load? - because that's what the engineer preparing the EO - the same one who did the UL certification tests - asked for. If the Limit ...... mind you, the video soundtrack of it is a bit like the two grumpy old muppets exchanging unpleasantries, but if the old-fart owners of an aircraft can't send each other up a bit, life just is TOO serious. Thanks Oscar, Schrenk is good. I am sure the video would be entertaining.
Oscar Posted February 25, 2014 Posted February 25, 2014 Actually, we're having a huge amount of fun doing all of this stuff, and we'll know every damn bit of what's in and on our aircraft. But on a more serious (and thread-relevant) note, thanks to the patience of everybody who has been 'mentoring' us along the way with both the airframe and engine to take the time to explain the what, how and why of things, we've gained a hell of a lot of understanding about just what goes into the design for efficient manufacture of an aircraft. We do have to ask the engineers to explain things in layman's terms but they generally sigh and comply, and we're better off (we think) for knowing this stuff.
djpacro Posted February 25, 2014 Posted February 25, 2014 ... we've gained a hell of a lot of understanding about just what goes into the design for efficient manufacture of an aircraft. .... Cleaning up my bookshelves today and came across a copy of a paper by Aussie John Hart-Smith in '98 when he was with Boeing in the USA. ... the separate minimisation of individual costs is shown to usually inevitably prevent the overall minminisation of total costs, whenever the individual costs interact with other costs. ...every false economy not only achieves a sub-optimum economic solution, it also creates a technically sub-optimum product. .... the B-29 bomber in large numbers, with the demand always outstripping supply ... the B-29A produced at renton and the B-29 and B-20B produced at Wichita ... revised design, implemented only on the B-29A .... Unfortunately, it required that the B-29A had to sacrifice HALF of the payload of bombs with respect to the original B-29 design .... the aircraft industry has become very efficient in making symmetric machined parts ... However, there is more paperwork associated with symmetric components than with ones that are common. .... There are many components on aircraft structures that are not common when completed, but which contain individual components that could have been made common .... The worst of all modern fads for aircraft design and construction is the belief that parts-count reduction will always save money. ... Parts count is simply not a sufficiently reliable surrogate metric for overall cost minimization. Interface control is a vastly superior metric. .... During the thirty years that the author has worked in the aerospace industry, he has observed two truisms that merit repeating. The first is that the least expensive way to complete a task is to do it right the first time, no matter what it costs. The second is that to complete a taskk in the shortest possible time, one should do it right the first time, no matter how long it takes! Just to give a taste of it - lots of very useful information in the presentation and, of course, John was a very entertaining speaker (haven't seen him for a few years now).Seems to me that Cessna fell foul of a few of his points wrt the 162. 1
djpacro Posted February 25, 2014 Posted February 25, 2014 The Gazelle would NOT be certified under today's rules. Do you really WANT to fly in something that, if it hits a decent gust in a turn, may well throw a wing away? Just about every aeroplane flying today would not be certified under today's rules, so what, they met the standards at the time. Doing a turn within flight manual limits, what strength gust would damage the wing? 0.5G? 1.8G? 2.5G? What was the design standard at the time?If service history indicates a problem then we have a system to fix it. Being certified there must (generally) be an organisation responsible for continuing airworthiness of the type for the fleet to retain their CofAs. The engineers who managed to get the damn thing to pass the regs. minimum requirements were pushed (how would YOU like to experience 10 seconds of aileron flutter in a test flight?) Often the case that engineers are pushed to just meet the minimum requirements of the airworthiness regulations - we don't like to carry excess structural weight. It is not the only type to experience problems like that in development. The Gazelle is a fundamentally dangerous aircraft both from an aerodynamic and a structural POV. However, it is a major improvement on its progenitor - the Kitfox. I quite like the Gazelle but perhaps I should learn more about it. I don't understand the term "fundamentally dangerous"? i.e. what situation renders it simply "dangerous"? Is operating a satisfactorily-maintained Gazelle within flight manual limits considered dangerous?
Oscar Posted February 25, 2014 Posted February 25, 2014 DJP - perhaps I should PM you on this one? And of course you are correct that the Gazelle is basically safe if operated within limits - but as that wing separation a couple of years ago showed, it's possible to get it outside limits quite inadvertently with disastrous results. I don't think anyone has ever suggested that the pilot was doing anything wrong, or even close to wrong, but a gust basically took the wing off due to lift reversal that collapsed the forward (I think) lift strut and the wing was gone. As far as I understand, it's a feature of the airfoil, and an airfoil that can generate a load from a change in conditions that is not wildly unexpectable, I reckon is a fundamentally dangerous problem. If the pilot had been pushing VNE, well, obviously it's not the airframe's fault, but certainly the witness reports did not suggest he was doing something silly - just got caught in a hard gust in a medium turn.
Dafydd Llewellyn Posted February 25, 2014 Posted February 25, 2014 I think Oscar is confusing the Gazelle situation with that of the CA 21, which was certificated to CAO 101.55 / BCAR S preliminary issue. The design standard (certification basis) for the Gazelle can be found by looking up its Type Certificate Data Sheet on the CASA website. The basis was JAR-VLA with some variations. I do not have JAR-VLA to hand; however from its successor, CS-VLA, gust loads and manoeuvre loads are generally considered separately; that is to say, the aeroplane is assumed to be in equilibrium at 1G in level flight when it experiences the gust. I do not consider the Gazelle to be inherently dangerous when flown within its flight manual limits; however there is a load transfer from the front wing spar to the rear wing spar due to the very high wing airfoil camber, which has the effect that the whole of the wing load is carried by the rear spar at some speed between 70 and 80 kts CAS - closer to 70 than 80, I suspect. At higher speeds, the front spar carries a download, and thus the rear spar load is further increased. For this reason, the speed limits for the type really do mean what they say. 1 1
Oscar Posted February 26, 2014 Posted February 26, 2014 Thanks for that clarification. I am under the impression that the JAR-VLA gust speed requirement is somewhat lower than is typical for 'Australian' conditions?
djpacro Posted February 26, 2014 Posted February 26, 2014 Thanks Oscar and Dafydd. I note the low design airspeeds and I understand that the manoeuvre limit design load factor is 3.8. ... gust loads and manoeuvre loads are generally considered separately; that is to say, the aeroplane is assumed to be in equilibrium at 1G in level flight when it experiences the gust... Yes. If some-one happened to be flying it aggressively, say a 2G turn with airspeed at the top of the green, it still has roughly something approaching 1.8G margin for an unexpected gust. I guess that Oscar's point is that Vne is not much higher hence reduced margins cf other types.
Oscar Posted February 26, 2014 Posted February 26, 2014 DJP - yes, I think that's what I was trying to say in my less-than-engineer way. I've noticed that, with some of (particularly) the Euro devices around, the performance claims warrant inspection - some of the ads. over here make comments writ large about 'cruise' performance (presumably quoting Vno) and sometimes (less prominently) Va, but sometimes you need to look rather hard to find Vb, and often it's quite a gap below even Va. I can think of one fairly popular one that used to claim Vno of 2 kts less than Vne (though I think that claim isn't being made any more) - which may have been completely true, but struth, that's an awfully tiny margin at 100 kts-plus.. I wonder how many pilots tend to think about selecting their flight speed for conditions in terms of what the glossy brochure said rather than a hard study of the POH? That's a pretty understandable situation, not a snide hit at pilots at all (and I'm not the one to make any criticism anyway) - if you paid the $$ for something that's supposed to get across the sky at 'X', you'd reasonably expect it to do that, I reckon.
djpacro Posted February 26, 2014 Posted February 26, 2014 I haven't used those VLA rules (been ages since I used BCAR Sect S so forgotten it all) but a quick look indicates that the flight envelope specs are very similar to FAR 23, in fact the diagram is a direct copy fom FAR 23. Seems to be the same gust velocities. No Vb, same as FAR 23. 1
Recommended Posts
Create an account or sign in to comment
You need to be a member in order to leave a comment
Create an account
Sign up for a new account in our community. It's easy!
Register a new accountSign in
Already have an account? Sign in here.
Sign In Now