Head in the clouds

Some well thought out posts here. I agree with Dafydd that the best way to prevent a rear engine coming into the back of your head is to catapult it over the top, still attached to a wishbone or pair of radius arms. Fairly easy to arrange in the engine pod design of a powered motorglider but unfortunately not so easy in my earlier design, and it would then have the additional problem of requiring a separate resolved structure just to carry the harness points. Sometimes when you've painted yourself into a corner you have no other options but to get your feet sticky or wait for it to dry ... To pass on the main points brought up by our US friend who has analysed literally hundreds of crash sites and broken planes - The single greatest life and limb saver of all is a 'stroker' seat. In simple terms it is a seat which is effectively a box without hard items inside it. The top of the seat is designed to break/crumple/deform/distort so that your backside breaks through the 'lid' of the box and has room to travel into the box. The ideal is at least 300mm of travel but as Dafydd mentioned this can be reduced if the box is filled with material or structures that collapse progressively and cause a deceleration that doesn't exceed 30G or so. The front of the box i.e. the part under the knees must not collapse. In the very worst crash this may mean that you get broken legs, injured knees or similar because it is the underside of the thighs which ultimately stop you from moving forward and greeting the panel or firewall. It's important to remember that a 'good strong seat structure' that doesn't deform in a crash has often been the cause of death due to shock from impact to the spine. I don't have the reference to hand but I recall reading many years ago that a person suspended in a sitting position and then suddenly dropped onto concrete from a height of just 3"/75mm, will be paralysed or killed. Someone with medical knowledge may be able to correct or expand on this ... I don't know any details but I also heard a long time ago that there was a fatality in a glider at Benalla (I think) where an apparently reasonably normal landing had been made but the pilot found deceased. I understand a deflated oleo failed to provide suspension for the wheel on landing - again someone else will probably have more details than I can recall. Based on the above, my new design has a large empty space under the seat which will be filled with a block of impact absorbing foam that will also serve as the seat cushioning. The foam will be a hybrid polymer and laminated from various densities. It resembles the foam used for yoga mats. I have a foam specialist working on a prototype for testing, I'll post more about that when we get to the testing stage. I've also arranged my underseat fuselage structure so that the strong members that support the landing gear legs are beneath the bottom fuselage members, effectively providing a double bottom of structure which would be a help in the event of putting down into a paddock which has rocks or tree stumps in it - they are another hazard to be considered as they can't easily be seen from the air when selecting an outlanding and can rip the bottom out of the plane and any part of the crew that happens to be in the way as well. A stroker seat is something fundamental to the design which must be considered from the earliest stages because it means that the volume beneath the seats cannot be used for structure or controls that could injure if the crew comes into violent contact with them. Dafydd mentioned that another problem with planes is that they lack forward volume that can be used as crumple zones. This applies to front- and rear-engined as well as low- and high-winged designs. Old K mentioned something about this, saying "I'd rather crash in a Jabiru than a steel cage. The FRP absorbs a lot of energy, and the panels do you less harm than smacking steel bars, however well-padded". I couldn't agree more about not wanting to smash into steel bars, but flying in a fibreglass plane may not be the all-consuming solution either. Statistically Jabs have protected the occupants very well but in general composite planes have a nasty habit of shattering and depositing the occupants around the crash-site. A couple of the recent Jab mishaps have shown the front of the cabin broken and it appeared to me that if the crash had happened just a bit faster the outcome might not have been so happy. The point is, as I understand it, that the well designed steel cage statistically offers the best protection from injury but you certainly don't want to be hitting the steel from the inside, so if we don't have crumple zones to absorb the energy, then what else can be done? Our expert in the US pointed out that if you don't have crumple zones then you have to do something about preventing the sudden stop instead. The solution to that, which has been adopted by a number of aircraft manufacturers, is to get rid of the sharp bottom to the firewall. Instead of being a sharp corner the bottom of the firewall can be given a large chamfer (or radius) and that extra space which is generally not used internally because it is behind the pedal arc, can be used for better cooling airflow out of the cowling. The crashworthiness benefit is that the plane won't tend to 'dig in' if it impacts in a nose down attitude and instead it tends to bounce off and dissipate the energy in a series of skips along the ground. Anyone can imagine that the consequences for the occupants will be much less than they would be if it digs in and comes to a sudden stop. That chamfer also has a huge benefit when employed on a low-wing aircraft, in prevent it digging in an flipping over - the bigger the chamfer the better. There's more but I'm out of time so it will have to wait for later. Keep posting your ideas please folks, this subject is important stuff that will save lives.

Thanks Dafydd, an excellent subject for discussion. Rather close to home for me too. Where small aircraft are concerned I had always held similar thoughts to those of SDSQI and Chird. From my earliest sport flying days and then into the first part of my commercial career, which was mustering in small helicopters, it seemed that those who crashed generally died or were severely maimed, so the message was clear - don't crash. Or if a crash becomes inevitable then have a well pre-planned procedure which hopefully keeps the aircraft under control throughout the event and dissipates the energy away from yourself. Not often likely to happen, of course, but better to have a plan than not, especially when your working days are spent low and slow over frequently unfriendly terrain. About 5-6 years ago I started the design of a new plane that is rather different from the majority of the LSA types that predominate these days. The design is driven by the need for quick folding wings, retractable gear and forward side-by-side seating for best visibility. The design has loose parallels to a folding Drifter (love Drifters!) but with speed and comfort. True to my form I gave little or no consideration to crashworthiness, I just accepted that it was a design to be flown conservatively in terms of having large smooth places to put down in case of power failure, as I do as far as possible in any case. Compared to a Drifter this one would need quite large paddocks though, and that would mean flying higher on most flights which to a significant degree would negate the value of the terrific visibility provided by front seating. And so the first dilemma presented itself. All of the components of that plane were made about three years ago and the assembly of 60-70% of it completed by about 12 months ago. During the assembly I posted an open log on a US forum site and it attracted a lot of interest and comment. Most of that comment had to do with the folding aspects and the rear engine installation. There was also a lot of discussion about the less than optimal aerodynamics at the wing centre-section, tapering aft fuselage, cooling airflow and airflow to the prop. Some people predicted dire consequences for the stall characteristics due to the double divergence on the top of the wing from the combination of its own curvature and the fuselage taper, others opined that it would have little or no adverse effect as the tailbooms acted as effective spanwise flow fences. The point is - in hundreds of posts absolutely no-one at all mentioned the very poor crashworthiness of the design from the points of view of frontal impact or rollover. Any significant frontal impact would result in the engine and its mounting structure - which carries the shoulder harness - to come forward and the first point of resistance would be the backs of the crews' heads. No problem though - just don't crash ... From some time beforehand, and during the build, there was a character on this other site who was generally considered to be a ghoul and also a bit of a pest. He was/is at Uni studying everything to do with crash trauma and apparently has the world's largest private database of crash information. He is often consulted by the NTSB and similar, and he visits as many crash sites as possible adding to his collection of data. His fervour in the matters of crashworthiness bordered on obsession and he drove many of us to despair but as the numbers of fatalities grew exponentially over a few years there, and in Australia too, I started to become affected by his insistent 'preaching'. The final straw for me came when I lost more friends apparently needlessly as their aircraft folded up on them in relatively minor impacts. This influence caused me sit back and have a long and hard think about what I really want and need in an aircraft, and how I could achieve as many of the original design goals with an airframe that would provide the occupants with the very best possible protection in event that the worst happened. Our Nemesis on the other site didn't just preach about the need for crashworthiness, he generously and helpfully spelled out all the design features that would contribute to occupant protection in a crash. In high wing aircraft the majority of them are common sense and most of them add little or nothing to cost or weight, for the most part they are just a matter of re-configuring minor aspects of the layout. I also benefitted greatly from talks with Bill Whitney about his experiences with the crash-cell developed for his Boomerang design. As Dafydd has mentioned, the structural aspects of maintaining the integrity of the cabin space in low wing/canopy designs is very much more difficult and likely to add considerable weight or lose a lot of space to achieve successfully. It might be that I'm just getting older and more conservative now, but resulting from this I've now had a very frustrating turnaround in the middle of my previous project. Consequently I am now about 80% through CAD modelling a completely different design that I hope to begin to build in perhaps six months, and which will probably provide more fun, definitely more utility, and certainly vastly less risk of injury or death if things go wrong. It's a STOL design and I've moved away from sheetmetal for this one and gone back to a welded CRMO steel and fabric fuselage. Properly designed they arguably provide the best crash cage at any given cost and weight.

As a few folks have mentioned, knowing how a wing generates lift really doesn't make any difference at all to someone flying the aircraft, except in the case of the fundamental differences between helicopter/VTOL operations and those of fixed wings. Consequently this discussion doesn't really belong here in student pilot forum. Earlier mention of persons attending ATPL courses and discussing this is also a bit bewildering since the very basic aspects of aerodynamics are covered in BAK during ab-initio training and are of little consequence further down the track. Whether an airline jock is atop a supercritical airfoil or a Clark Y makes no difference to him, he operates according to the POH. Further - at the end of the day the generation of lift via varying methods and foil types is a subject for the trainee aeronautical engineer and really doesn't matter a jot to the trainee pilot. The only relevance to the pilot is the slightly differing stall characteristics between them. What is of far more concern though is the sort of mythology that I questioned a few posts back and which is clearly still being promulgated by those very same folk whose mission is claimed to be to debunk the flawed teachings. I asked our worthy Prof (see post #70) to expand on a comment in his course notes which states - Here the aircraft is rolling and turning to the left. Ailerons work opposite to each other to roll the aircraft. Rudder is used to assist the turn and prevent skidding. As the regular readers of this site will be well aware, the above seeks to promote the use of mishandling techniques which are statistically our biggest killer of all. Though he's buried his response in my quote, the Prof responded - I'm not sure whether my tears were from mirth or sheer bloody frustration that this sort of fatally dangerous mythology is still being taught - and by a University lecturer to boot ... but it does amply demonstrate the dangers of having people teaching theory who, by their own admission, have no practical knowledge of their subject. aerogeek, operating according to your statement promotes these kind of events - In what way can the above be in any way described as "most dangerous"? There is absolutely no danger whatsoever in a pilot having no knowledge of at all of Bernoulli, Transit Times, Venturis or any other matters of flow across a foil. It doesn't matter to pilots, the most they need to know is just a little about the various stall characteristics that different foils and surface conditions might cause. You should be lecturing to aeronautical engineering students ...

I'd rather not be called your friend if you don't mind, we've barely met. Yes, I know adverse yaw very well, I thought you might like to explain how countering it with rudder assists the turn. If I was writing your course notes I'd have been more specific to aid understanding, and said it prevents adverse yaw caused by use of ailerons, or even that it assists rolling the aircraft, it certainly doesn't assist the turn. How about the rest of your statement concerning using it to 'prevent skidding', would you care to have a go at expanding on that one? I take it you're not a pilot/flyer yourself are you?

Yes, I was suspecting another Troll so did a quick Google before heading off to the ignore list. I think I found out the reason for the apparent need to offer denigrating remarks and make it personal rather than accept and address the comment. It seems Prof geek is mainly used to lecturing ab-initio kids in the cadets and no doubt they're supposed to sit up and pay attention. Prof aerogeek - I came across another set of your cadets lecture notes and although I see they mainly consist of diagrams lifted from various publications (with appropriate credits) I am interested in what I think is your own statement on Page 36 about the purpose of rudder where it states - Here the aircraft is rolling and turning to the left. Ailerons work opposite to each other to roll the aircraft. Rudder is used to assist the turn and prevent skidding. I must have the whole idea of use of rudder during rolling and turning quite wrong. Can you explain how we are supposed to use it to assist the turn please?

Yes, well now you're introducing qualification to your original incorrect statements, which now makes them a bit more useful to the thinking man. Yes, I'm stubborn, also very specific - and I haven't misquoted you anywhere, perhaps you might re-read what I wrote? I've read what you wrote very carefully and fully understand your meaning, there's no issue of "what you said, as opposed to what I think you said". I've never been one to accept something just because someone says it's so, and your explanation of the issues I picked on are flawed. I don't think you and I would get on in your lectures, I'd be the annoying one who keeps pointing out the flaws and inadequacies in your explanations. I don't doubt you understand your subject but you don't explain it well. If you tell a student that flying with the nose 3 degrees below the horizon results in a zero AoA - as you did earlier - then he will believe that. However he would only have a zero AoA if he was in level flight, and you forgot to mention that. And yes, I am quite aware that you went on to describe a further reduction of the ATTITUDE, to reach the zero-lift angle, which in a (positively) cambered airfoil would be at a negative AoA. I really didn't think I needed to address your kindergarten question about a take-off, some of us were teaching flight theory before you even got involved in aviation ... You say you had a student who flew an airliner and didn't know the type or characteristics of the airfoil? Was he Air Congo by any chance? Is it possible he just didn't want to argue with the teacher?

Yes, I do, see what I wrote in my previous post - Would you like me to demonstrate a stall for you with the nose 3 degrees lower than the horizon, in the attitude that you suggested is zero degrees AoA? That's surprising, most of the experienced ATPLs I know are very knowledgeable on the subject, but it takes all kinds I guess. Yup, as long as your teachings suggest AoA is related to Attitude without further explanation or qualification, I'm afraid it does.

I wasn't being narky, just pointing out that your explanation is nonsense. Raising or lowering the nose doesn't necessarily make any specific change to the AoA, for example if I raise the nose and increase speed as well the AoA will remain much the same or if I increase the speed more then the AoA will reduce whereas your (incomplete) explanation suggests it will increase. Similarly if I lower the nose but also reduce speed significantly then the AoA will increase rather than reduce, contrary to what you stated. The AoA is the angle between the chordline and the relative airflow, as you're well aware, but from what you're saying you'd have your students believing that AoA is somehow related to the attitude of the aircraft, which it isn't. You may well know your stuff but wading in and suggesting that instructors don't, and that they're misleading their students is a bit rich when you lack specificity in your own explanations. Just sayin'

Too much of a generalisation, your statement is only correct in level flight. Hmmmm professor, a little more specificity wouldn't go amiss. I have a plane with 3 degrees set angle of incidence and it flies with a full range of AoA, not 3 degrees all the time, or very much of the time come to that. If I lower the nose three degrees I very rarely reach the zero lift angle. I think you need to bring relative airflow into the discussion or your statements are a nonsense.

I agree with you about Alan Dunbar, excellent instructor. I do have his phone number and last spoke with him a couple of years ago. I don't feel it would be right to hand out folks' numbers but if you would like to PM me yours I'll pass it on to him and ask him to call you?

I have no doubt whatsoever that my LL training helped me to get out of a very sticky situation when I stupidly got myself caught in bad weather and spent time scud-running to try to find somewhere to put down. I strongly agree that LL training should be a part of the pilot training curriculum. Poteroo - when there are a lot more of them perhaps the comments on this thread might be used to strengthen the argument for having LL included in the syllabus.

GFA then?

Hey, welcome Topaz! Not sure whether Oz will help your sleeplessness but ... Nice work on the Bug Dave!

Nice one rgmwa! I have a friend who was at Old Warden two days ago and watched them there, sent me a few photos. He said the sound was enough to bring tears to your eyes. He's a war historian and has written a number of books about specific aircraft and Squadrons. He mentioned that Australia's Lancaster, G for George, was presently disassembled and he wanted to know if there are any plans to restore it to flying condition - does anyone know?

Not offhand but I'll ask around and PM you if I come up with anything useful. In the meantime other forumites down that way might know people they could recommend. BTW, I'd recommend that it should be a LAME and that you get a written condition report, have an engine leak-down test done, oil analysis etc. Such an inspection and flight test is all you'll have to seek reparation if something costly turns out to be wrong with it, and it's a LAME's responsibility to conduct these inspections and warrant that the aircraft is airworthy and in good condition. Just because it's RAAus registered doesn't stop a LAME inspecting and reporting on it. It usually costs a bit but is good insurance against ending up with a dud. Even if you don't end up buying the plane you can sometimes offset the cost of the inspection and report. I had a yacht inspected and decided against it although the report wasn't all bad, I just wasn't quite happy with the condition of the filler under the paint below the waterline. The marine surveyor's report cost me $1600 and would have been required for me to get it insured, so had to be done in any case. I kept in touch with the agents who were selling the vessel and in the end I sold the report for half price to the person who eventually did buy it, so they could could provide it to their insurer.

Yes, that's one of the problems of being so far away but it does have its benefits too. Quite apart from the flying being better (incoming ....), as with yachts, cats and power boats, they're worth more over there when you come to the time to sell them because as you are now aware, the demand is there but the supply isn't. I've bought a number of aircraft for myself and for organisations I've been piloting for, and usually all the preliminary search and inspections has been done for me by trusted people in the industry, and completed well before me hopping on a burner and going to have a look, test-fly, pay and fly it home, usually from one side of the country to the other. I haven't bought a lemon yet, gladly. The important thing, of course, is to find the 'trusted one' and I've previously had the advantage of having had the engineers for my commercial ops scattered around the land, so if there hasn't been someone I know near to the prospect, then they've always known someone who is. An essential aspect is to have it looked at by someone completely independent and preferably someone who has never seen that particular aircraft before and is also an experienced pilot, so can test-fly it. I guess your starting point would be to find that 'someone' - so where is the plane located?

Used aircraft are always in demand in Australia so, unlike in the USA, old ones generally get rebuilt rather than scrapped. The 1960 C172A that I sold recently was immaculate because it had been rebuilt to new condition several times and during its illustrious career had sported seven wings without ever being anything other than a monoplane. The only original wing part was one of the flaps. Consequently the reason 'your' C120 wings aren't corrosion protected is probably because it has been damaged at some stage and had new wings fitted. You can often detect that by looking at the areas where the wing spars attach to the fuselage and look for new rivets, paint, panels etc. Not that there's anything wrong if it has been repaired provided the job was done by a reputable workshop, it often means other maintenance has been attended to at the same time. Another thing to look for is creases in the rear fuselage, usually on the bottom surface, indicating hard landings or sudden stops. Being a taildragger the aft fuselage is somewhat stronger than the later nosedragger models so any creases would indicate it having had quite a significant beating. Again though, not a difficult thing to remedy. I've not flown a C120 but have quite a few hours in the similar C140 and C170 and must say they are a delightful aircraft especially for those of us who like draggers and love to be able to fly s-l-o-o-o-o-w. The C120 has a slight handicap in that regard though, being the flapless version. For corrosion to occur I think you'll find you need moisture as an electrolyte. I think you were half right Shed, the 120 came out with the C-85 and the C-90 or Lyc 0-235 were options I think. I don't think the 0-200 was ever on the Type Certificate so if this has one I guess it must be on an STC.

This valve-to-guide clearance issue is interesting. One northern Australian operator of Robinson R22 helicopters had a large fleet of them used for mustering and in the earlier days almost without exception they suffered from sticking valves. This usually happened after the main part of the muster and before the yarding, when the helicopter was spending a large percentage of its time at low airspeed albeit not in the hover, so not at particularly high power settings. High CHT seemed to be the issue even though the cooling is provided by a squirrel cage (centrifugal) fan rather than by airspeed. One theory was that the hot air was recirculating through the fan, perhaps while hovering downwind. The R22 is fitted with a Lycoming 0-320 de-rated by MAP limit to 124hp though full power is available to the throttle if required in emergency. That operator had the exhaust valve guides of every helicopter reamed considerably oversize, I don't recall the actual size but I think it was a thou or two above the max wear limit specified in the manual. As far as I know they never had a stuck valve after that and all new engine changes and/or all brand new helicopters, including mine which they sometimes serviced, had the guides reamed before the machines went to work. IIRC this was done without removing the cylinders, by using thin rope to fill the cylinders through the plug holes. That was held tight against the valve head with the piston, to be able to remove the springs and cotters, dropping the valves into the cylinder and then coaxing them back into their guides afterwards with telescopic magnets - or similar. All sounds a bit bush-mechanic looking back on it but it worked well.

This is rather worrying Oscar, I trust you have filed a report with RAAus?

I guess the 206 must be a bad design then? Wouldn't have anything to do with the piloting ... would it?

They're very far from pointless. If you have a jammed float valve, which is surprisingly common, often caused by a tiny piece of fuel tube sliced off when fitting the hose to the hose barb - so is on the downstream side of the fuel filter - the fuel pump(s) will make the fuel overflow the float bowl and, in the absence of the drip tray (with drain), the fuel will run onto the exhaust header. At any power setting above about half throttle the header is sufficiently hot to ignite the fuel instantly. A fuel fire in-flight is no fun at all. In the photo it appears that your exhausts are lagged, that's great for not radiating heat to other components, cowling, wiring etc, but also means that the headers will be even hotter than otherwise and so will ignite fuel at lower power settings than if they were exposed. I would suggest having those cracks welded before they progress further. One advantage of doing so is that they will be less likely to crack again because the heat of the welding will anneal the aly and thus reduce its temper making it less hard and brittle, and hence more crack resistant. The fact that they have cracked like that in the first place indicates that you have a vibration resonance on the part and so you need to damp it. You could put some lines of high temp silicone (the red stuff - it's heat and fuel resistant) on the back of the part, or add a cable-tie from the tray to something else nearby. I would suggest not using a spring as it can excite the condition rather than damping it.

Oscar, are you saying that Jabs are built using E-glass? If so do you have any idea why? Given the superior strength, stiffness, temperature stability and corrosive (capillary) resistance of S-glass I would have thought that would be the minimum used in an aircraft application. Surely the 'very average' quality general purpose E-glass would only be used in aircraft in areas of extreme curvature where no other fibre is flexible enough?

Raised in the bush, all the kids climbed to the highest branches of the biggest trees and if you didn't follow suit you ended up without friends. I never had a problem getting up there but coming down was sometimes a bit of a nightmare. I've never liked confined spaces either. My high school had plenty of adventure activities so they suggested anyone with phobias should confront them by taking up an activity that challenged it. Consequently we acrophobiacs and claustrophobiacs spent the next two summer camps learning rock climbing, abseiling, caving and potholing. I thoroughly enjoyed it but it never cured the heebie-jeebies. I never noticed it when flying until carrying external loads on the hook with helicopters. That's another challenging and very enjoyable activity but the 'height' aspect is very noticeable. It was that which showed me the difference between flying and ladders, for example. When you're flying there's very little perception of height but when you look down a ladder, or the cable carrying an external load, you can see it extending away below you and it provides a perspective view of the height.

From Surfers to Bribie Island stick carefully to the VFR route marked on the VTC, depending on the day there can be significant traffic - northbound don't cut the corner at the northern end of Moreton Island. And - keep a good ear on the radio, helicopters (!) are a-plenty. Training operations out of Coolangatta, Surf Rescue out of Coolie and Carrara, joyflights out of Seaworld, Dreamworld and Marina Mirage, private regular helicopter ops out of Currumbin, Oxenford, Pimpama, Surfers (Nerang River) and Paradise Point. Recreational flyers tend to gather around Jumpinpin and the North and South Stradbroke Islands' ocean beaches - busiest on Saturdays, not much on other days. There's no problem crossing the water at 3500' between Moreton and Bribie islands, just be aware of the wind direction on the day and how it affects your glide distance in either direction.

It's good to see that you're actively seeking knowledge to improve your performance in the event that things go wrong at some stage. Well done. Unfortunately we've had an unhealthy string of mishaps in the recent past, a good percentage of which might have been avoidable. The following threads contain invaluable information among the general discussion, well worth reading, and feel free to add to the discussions if you like. Turn Smart - starts with a video that EVERYONE should see. Understanding what this very experienced Ag pilot has to say, and applying it, will prevent becoming a statistic in the all-too-frequent base-to-final stall-spin scenario. Va - Manoeuvring Speed - has some very useful information in it, about an often poorly taught and much misunderstood subject. The above Va thread came about because of discussion about the consequences of inadvertent flight into VMC which was possibly the cause of the recent Barossa Valley crash - this tragic thread is a good heads-up about taking extra care where foggy/low cloud conditions exist or may develop. Do Vortex Generators Really Work? Is interesting if you have a curiosity about STOL and/or design for spin resistance.