IBob

Really enjoy that footage. And that's really cleaned up and fast for a Jodel. Very small air intakes......

Garfly, that's a really nice innovation! Also sort of mesmerising footage: they're certainly flying through the hills, not over them! I know another user here who always pops his oil filler hatch after landing. In his case he is concerned about the possible effects of heat on the ignition modules (as the earlier ones had a history of failing over time).

Yes, you keep saying that, kgwilson, and nobody is disagreeing with you. We are talking now about the solution......which for many thousands of happy users does not involve buying a different engine........)

Mike Gearon, I don't know what the stats say now, but it used to be that a significant proportion of forced landings were due to pilot error in not understanding or correctly operating the fuel system of the aircraft they were in. Some years ago I was at a BBQ in Napier when, to our astonishment, a Spitfire came through fast, low and banked. About 10 minutes later, the same aircraft was down in a plowed field: it transpires that Spitfire fuel must be pumped between tanks, and the pump is engine operated: the engine stops, you've got no way of transferring fuel. Unlikely that he'd have had time anyway, but the reason for the crash was fuel exhaustion with fuel still onboard. And somewhere in outback Australia there is a twin whose pilot lost an engine, then lost the other perfectly good one because he hadn't read the fine print saying not to put on multiple fuel pumps. So, those and other events, I've taken a special interest in the detail of my own fuel system, which is exactly as spelled out in the Rotax link within your link above: http://forums.matronics.com/files/912_fuel_fig_54_941.jpg but with the addition of a receiver tank taking fuel from the wing tanks, as mentioned previously. Regarding the conversation in your link, I think if I experienced heat related fuel pressure problems in normal flight (and that could not be fixed by changing pump and filters) I would be looking very hard at ways to reduce the heat on the fuel system. And while I would be adding a fuel return if that was not fitted, I would not be relying on that to fix the problem. Regarding my Plane Crash YouTube links above, the pilot has not thought it through. The reason his fuel has gassed in the pipes is the elevated temperature in the engine compartment. Ideally, his fuel system should have a return that moves that gas, and the heat it contains, out of the engine compartment (as per Rotax recommendations), replacing it with cooler fuel. But what he has put in is a short loop that simply recirculates gas and heat under the hood, because somebody has told him this will fix the problem. That's what's called magical thinking. Finally, since I wrote 'detail': note the fine fuel filter before pump and return etc in the Rotax recommended fuel system. This prevents not only carburettor jet blockage, it also prevents blockage of the orifice in the fuel return, and ensures the pressure relief bypass in the electric pump seats properly.

That certainly seems like a reasonable suggestion, RFGuy. In conversations like this I think we have to be careful that we are not chasing ghosts or tilting at windmills. For instance, Facthunter's assertion that a high mounted carburettor is not ideal placement (for at least two good reasons) is absolutely correct. However, we also know that many thousands of aviators have top mounted carburettors, which they cannot alter, but which fortunately do not seem to have resulted in a history of problems. I would be starting, if possible, by asking what observed problem are we working to overcome here? Or in the plant automation world where I used to work: what have been the practical experiences of others that I can benefit from? That does not mean we cannot use our own imagination and ideas, but it helps keep us grounded in the current realities.

Ops, that should have been: But it's not well presented: what he doesn't show is that he landed and turned off his engine before restarting and attempting to take off. You see a bit of that here: But at the end of Part2 he focuses on his fuel pump replacement and his (in my opinion inadequate) attempt at a fuel return, with only a fleeting mention of grounding running to cool the engine bay: which would probably have saved him the cost of a propeller etc.

Nev, I don't think anyone is trying to argue that having high mounted carbs is a good idea. The title of this thread is Prop Stopped, and I thought the discussion was around practical means for avoiding that. That said, I'm (also) not trying to argue that the Rotax fuel return answers all our fuel delivery prayers. But what I would suggest is that with the 912, it does a good job of reducing the possibility of vapour lock in a heat soaked engine bay. To dismiss that by saying the carbs shouldn't be high and that an orifice won't pass much liquid adds nothing useful in a practical sense to the conversation. Here is a heat soaked event......the EFATO is at the start, but the analysis (if you can call it that) is at the end. And to my mind the guy displays little understanding with the 'return' he has now piped in (that is not a return at all): https://mail.google.com/mail/u/0/#inbox/FMfcgzGpGTHLQrlpggWzXQjxQlPfnzsr?projector=1

All this theorising is all very well, but thousands of aircraft have a fuel return, via a small orifice, as per the Rotax installation spec. and it apparently works very well. Yes, it's a pity if it mucks up your fuel flow readings. No it's not difficult to arrange to vent it back to tank. And in a vapour lock situation (which you potentially have with a heat soaked engine bay after a recent stop) what you are expelling via the orifice is not liquid, it is gas......and so passes far more freely. How do I know? Shut down on mates strip, nobody home, set up for restart after 5mins, activate fuel pump and it chatters away for 10 to 15 secs before settling down to it's usual rate and fuel pressure is established. PS: in that scenario we also don't take off immediately. We allow a few minutes of engine running to lower the temperature in the engine bay. Or you could thermally insulate everything, and hope for the best???

Thruster88 are they, strictly speaking, vent lines? In my Savannah, which has an air box with filter, they are plumbed into the box downstream of the filter. I had the impression that the object was to have the pressure in the float bowl match the pressure of the incoming air. Though I am not sure what the arrangement is on engines with no airbox, and filters fitted directly to the carbs; maybe someone can clarify that?

Hi Steve..great to see, and congratulations! One passage ends, the adventures begin. And you get to pass it all on to those coming after you too.....)

Thanks facthunter. I'm a bit surprised, I thought the engineers here would be all over, the question, which was; How is the C of G range of an aircraft originally established? A short search did turn up this, which makes sense: From faa.gov/regulations_policies/handbooks_manuals/aviation/phak/media/12_phak_ch10.pdf The forward CG limit is often established at a location that is determined by the landing characteristics of an aircraft. During landing, one of the most critical phases of flight, exceeding the forward CG limit may result in excessive loads on the nosewheel, a tendency to nose over on tailwheel type airplanes, decreased performance, higher stalling speeds, and higher control forces. Control In extreme cases, a CG location that is beyond the forward limit may result in nose heaviness, making it difficult or impossible to flare for landing. Manufacturers purposely place the forward CG limit as far rearward as possible to aid pilots in avoiding damage when landing. In addition to decreased static and dynamic longitudinal stability, other undesirable effects caused by a CG location aft of the allowable range may include extreme control difficulty, violent stall characteristics, and very light control forces which make it easy to overstress an aircraft inadvertently. A restricted forward CG limit is also specified to assure that sufficient elevator/control deflection is available at minimum airspeed. When structural limitations do not limit the forward CG position, it is located at the position where full-up elevator/control deflection is required to obtain a high AOA for landing. The aft CG limit is the most rearward position at which the CG can be located for the most critical maneuver or operation. As the CG moves aft, a less stable condition occurs, which decreases the ability of the aircraft to right itself after maneuvering or turbulence.

Question, then, for the aviation engineering gurus: The Savannah C of G limits are quoted as 25% and 38.5 of MAC. This being a constant chord unswept wing equates to 25% to 38.5% of the wing chord. How is this range originally established or worked out?

Hank, the jig provided with the kit has 0deg and plus and minus 15deg: these are used for setting up and checking the deflection of the flaperons with no flap selected. It also has FF, and this is used to check/set up the Full Flap position. My flaperon setup is exactly as per the jig. I have not measured the actual FF angle, it looks to be slightly less then twice the 15% marking, but the flaperon pivot points are under the flaperons, so that may be deceptive. I believe the standard flaps are usually quoted at 15deg and 30deg. Since I have a 3 position setup, mine will be 10/20/30deg or thereabouts.

My mistake then, Andy....though I'm greatly surprised, and the more so as the Zenith 701 seems to have 15 and 30deg flaps.

That is a curious accident report, though probably due to inaccurate press work, or talking to the wrong person: The Sav flaps are 15 and 30 degrees, not 20 and 40. If the bump occurred 2/3 of the way down the strip it must have been a big one, as the flaperons would have had air and prop blast under them, and would tend to go to 0 degrees if not latched properly. And if the left wing was stalling, the best response (aside from also getting the nose down, if possible) would be right rudder. Not left, as reported, which would only aggravate the left wing stall. Maybe I'm being picky, but I think the last item needs correcting, if nothing else.

Let me know when you are up for a visit..)

How's progress with your build, Hank?

Not at all, Hank.

I've heard two accounts of Savannah flaps not fully engaging, have also seen an instance where the rubber outer handle was fouling the button/latch mechanism, potentially with the same result. So, two things: The latch mechanism needs to be very free, almost loose in action (the latch, not the handle) so as to be free of any possible binding and: On setting flaps, get into the habit of then wriggling the handle to ensure they are fully latched.

Good point, Perry! Yep, the flaperon positions are all crack on, as per the jig provided with the kit.

Hi Mark, and thank you for your detailed input. This is all really good info. Yes, my battery is in the forward position, as now detailed in the S build manual etc, and yes I have difficulty keeping the nose off on landing (and as mentioned above, the original test pilot commented on this). SVA will sit on her tail, just, but I have never been sure about that as a measure, since fuel moves to the back of the tanks when the tail is pushed down: can you recall what the fuel situation was when you did this? At present I am considering two temporary options: extra weight to the rear of the (extended) baggage compartment, in the form of a flat sand bag. And/or a lead strip attached at the tail skid. Hank, I have the conventional lead/acid battery: the Savannah has no shortage of lift and I have no reason to be further reducing weight. Dan, I have the Condors all round and they are quite heavy, I also have the adjustable seats, so am not sitting hard back as in the original design. And so it all adds up, I think. Also, I initially had trouble with the full flaps lever position, as you mention: the angle was all wrong, and setting and releasing it was clumsy and difficult. In the upshot, I designed an angled lever that works very well. It is simple, but needs to be fabricated quite precisely. I was fortunate to have a very capable fitter do the required cutting and welding of the outer tube.

Yep, I'm looking at something very much along those lines, Perry. Have also tweaked my trim for a bit more nose up, but need to fly to check that first.

Thanks again, Andy. It would help if this were not subjective.....but I'm not suggesting anyone goes out there with a spring balance at this stage! FWIW I have the adjustable seats, am average size and fly with them on the 2nd notch back (full back is 4 notches). My tyres are Condor 6 x 6 and the build is as per the manual, with the battery forward. I fitted Stolspeed VGs to the underside of my elevator (so they emerge at start of elevator up, though JG now recommends fitting them on the TE of the stabiliser). I did this early in the piece as SVH noted his Sav VG was much easier to get onto the back wheels pre-takeoff. However, it was too soon in my own flying to be able to reliably judge the effect. My (hugely experienced) test pilot on completion of build ran SVA through a very comprehensive documented test program, with no changes required apart from a minor tweak to prop pitch. He did, however, note that the aircraft tends to drop promptly onto the front wheel on landing. I have 200+hrs on her now, with a large number of circuits and full flap landings, so the aircraft certainly works as is. However, I frequently fly alone, with no baggage and partially full inner tanks, and this puts the C of G well within limits, but somewhat forward. I am considering both the trim, and shifting the C of G back some, to see how that affects the approach handling. All thoughts and comments welcome. Thanks.

Mike, the Savannah has a 6litre receiver tank behind the passenger seat, with a low level switch in the top of it and an indicator on the panel: gives about 20minutes of warning, remedies all sorts of things like momentary unporting, allows flying of outboard tanks to exhaustion without loss of power etc. I'm sure many other aircraft have something similar, it's a terrific feature which avoids all manner of problems.

Hi Dan, thanks for your input. To clarify: First, I am not concerned about the approach attitude; what I am interested in is the amount of stick back pressure (for a full flaps approach at 40kts). Second, and to clear up any confusion over the trim indication: the trim bargraph has 10 segments. With 0 segments showing, the trim is full nose down, with 10 segments showing the trim is full nose up. So when I am cruising with 3 segments showing, I am 3 segments off full nose down, and for a full flaps approach I have 10 segments showing, which is full nose up. I am interested in the amount of (approach) stick pressure, to see if different owners report different degrees of this: I had thought most builds would be similar in this respect, but I am now getting the impression there is some real variation. If you never use full flaps, the effect would be far less for you, and with the battery in the tail as you describe, I would guess that you can fly a 40kt approach with most if not all nose down tendency trimmed out. I have learnt to fly approaches, mostly at full flaps with 40kt approaches as per the POH, but this requires more than a little rear stick, so the controls are relatively unbalanced. It seems to me that more balanced controls would allow for more 'feel', and am interested in the views and experience of others on this. Andy, I have the Mark Kyle flap handle bracket, which gives me 3 flap settings instead of the standard 2 settings.