Bob Llewellyn

2,2,4 trimethyl pentane is not a fuel line solvent; nor is tetra-ethyl lead, even with bromide added. I don't see how comparing contaminated avgas with uncontaminated PULP is valid. The soft flaky carbon is indicative of the high proportion of aromatics used to elevate the "octane" number of the PULP, and indicates combustion lag, with corresponding (slightly) reduced efficiency. If you can live with the low vapour pressure, and your supplier reliably meets your engine's octane requirements, fine and good. 100LL (iso-octane + TEL) does have a higher octane rating than PULP, and the combustion process typically yields a somewhat higher thermodynamic efficiency - if you need these, or your fuel system is sensitive to vapour lock, then PULP is not a substitute. Personally, I'd like to have enough money to do the fuel research the engine manufacturers didn't try... though I probably wouldn't spend it on that!

Hmmm CAR 3 did not require a positive rate of climb on one engine for aeroplanes with stall speed less than 61 knots...

...even early CAR 3 aeroplanes are, ummm, a bit off... the Cessna 172B has an Indicated stall of ~32kts at light weight, which is horseapples... mind you, if you drop it in with the flap, it'll land very short...

We owned RSV for a while; I think VGs would have been a big help!

As you may have gathered, I've been considering design issues for recreational twins, on and off, for a while - but reading the POH etc is not a substitute for flying them! I do feel that there is considerable potential to make smaller twins rather less touchy than they are - from a design aspect, certification in a commercial role has limited the design options chosen. The improvement in payload given a 402 via a VG kit is an example, to my mind, of the prosaic design choices made. I read from your comments, that quite a considerable improvement in the engine-out handling would need to be made - is this correct? Perhaps a tandem 336 layout would be the preferred option...

Erm, the development of twin-engined design standards occurred in the light of pre-existing big Bellancas, Lockheed Sirius/Vega/etc; as the twins carried more metal, they had smaller payloads, so the design standards had to impose the minimum requirements - remember, the FAA must foster aviation... such things as flying with so much yaw and so much roll on one engine, tongue against the molars and hat off come to mind... There is no reason that a non-commercial twin shouldn't have a better power-to-weight at MTOW, so giving the extra power required to overcome the corrective drag in the engine-out situation. The Anson was a mongrel for getting separation off the back of the nacelles, esp after the fan stopped on that side (and the 336/337 is a mongrel for separation off the underside of the rear fuse if the rear donk stops, too). The Speed Twin is an interesting study for life without feathering. The main problem I see, is that a mutli engine rating is the holy grail for commercial pilots, so the ones in CASA aren't going to let any recreational pilots share their grandeur, no matter what... The Cri Cri seems to work...

I'd like an RAAus-registered Twin Commanche ... The history of the NACA laminar-flow faction makes for interesting, if tedious, research - it wasn't until Prof.Ing Hoerner did his global tunnel turbulence tests that the full iniquity of the Variable Density tunnel came to light; and by then Abbot & von Doenhoff had popularised the misleading data. Briefly, the base natural turbulence of the VD tunnel is about 3 times that of free air (below ~10,000ft); which means that the Clmaxes of the 6-series airfoils as published are significantly higher than can be achieved outside that tunnel! This means that lighties like the Cherokee need so much acreage of wing, that the ~15% achieved laminar flow drag reduction, is obliterated by the sheer area. The Commanche has less parasitic drag in cruise, simply from the higher wing loading achievable (the Bonanza, also with 23012, likewise...). If you get up above ~10,000 ft, into the non-turbulant air (on a micro scale), the cruise drag comes down for laminar sections; and if you use quintuple slotted flaps and a redundant engine for takeoff/landing, the area does not get too big. Similarly, for gliders - mostly wing - laminar airfoils make a small profit. For your avergae lighty, no. Interestingly, the PA28-140 airfoil puts an 18% thick (so deep & light) spar behind the rear seat passenger's knees, which 23012 does not on both counts; as the original Cherokee, with Weick in charge of the design team, was overweight (and had too many parts), one can reasonably surmise that Thorpe chose the airfoil for other than aerodynamic reasons.

FAR 23.67(b): "The steady gradient rate of climb at an altitude of 400ft above the takeoff must be measurably positive... TO power; must be not less than 0.75% at an altitude of 1,500 feet above takeoff... max continuous" these are the engine-out requirements for piston multis above 6,000lb TOW, and all Turbine multis, that fit FAR 23 (i.e. less than 12,500lb / 5,700kg MTOW). The Dornier -27, -28 twins blue line below stall...

FAR 23 can be applied to such an aeroplane; it's just that, from a marketting aspect, most manufacturers seek an erroneously low reading at the slow end (to make it look STOL-er), and achieve a free safety cushion by doing so. Design Standards are minimum standards; anyone is free to exceed them, but may not fall short (enforced up front, in the case of Certification). I have personally investigated one (double) fatality which would not have happened had a different design standard been used (Type certified aircraft).

John Thorpe specified 6061-T65tiddlypom spar extrusions for the PA28-140; Piper reverted to 2024-T3511 once the batch of 6061 caps ran out. The early caps don't rot, making wing root rot far less of a drama than the later caps. But Piper saved a few bucks per aircraft on 2024, so let them rot... Yes and amen. The story of Taylor and his accountant should be a warning to us all... The Commanche has its roots in the WW2 research into 23012 and fighters; it would be seriously challenged to meet the current handling standards! (esp. the -400) The Cherokee /Sneekers etc used semi-laminar airfoils, which handle like soggy marshmallow, perform like soggy marshmallows, and were just like the jet fighters used (i.e. cutting edge).

FAR 23.1323 allows 5kt error; so the Jab in question meets Cessna's design standard. Which means it'll meet CS-VLA too - Jabiru have been using CS-VLA (rather more demanding than ASTM F2245) for some time. That being said: Short of a pressure head that incorporates both pitot and static in one assembly, be it Zahm type or Piper's neat underwing pylon type, it really is worth doing a pressure survey of the airframe before finalising a location. there is a good reason that flight testing requires the use of a trailing cone static source.

Ok, ta...so it's like a Cessna T-37(?) Dragonfly, except slightly less ROC :o)... That puts me to mind of a story told me by a GA CFI, about a bloke doing a twin endorsement in GA after about 800 hours un-endorsed twinning (naughty...); when the instructor reached down and turned the fuel off to one engine, the pilot reached down and turned it back on... the instructor spoke to him, and turned in back off. When the donk quit, the pilot shut down the other donk and dead-sticked it... he later asked the instructor to show him the reg that said he shouldn't have done that...

I'd suspect static PEs first... BEAGLE were the masters of that; one of the Austers (J5-G?) under-read by 9% at stall, over-read by 9% at VH (at the time they were allowed 10% error!). The trick is to put the pitot under the wing root, far enough aft that it's in suction at cruise and pressure near stall; and put the pitot ahead of the wing LE, angled so that the crossflow exceeds 20 degrees at about 1.15 VS0... I had my T-83 stalling at 22kts and cruising at 65 for a while...

Peter, I was taught not to fly the final right into the ground, but to seperate the final approach and the landing. I'll dare the wrath of the anti-slip crowd and say, I generally like to keep a few knots up my sleeve (in slow aeroplanes or gusty conditions) by slipping down final - the resultant steep final lets me begin the landing transition right at the start of the strip - and then fly the landing, in ground effect pretty much, waiting for the speed to bleed off until the wheels go "squip"... the spare energy is available until a few seconds before touchdown, so the window of exposure to loss of situational control is smaller than in the non-slip, 1.3Vs final approach I was first taught (same instructor, I might add). Of course, in a Blanik you just use the divebrakes and fly at 50 kts!

Got any pix of them? NACA TR 31 (1919), and Report 264 both show most all pitots having a fair accuracy over a range of ~+/- 20 degrees...

A modular aeroplane makes a fair bit of sense... look at Piper :see no evil:using the Cherokee 140 fuselage for the Warriors, and stretching it for the PA28-150, -151, -180, and -235... overlapping with the Cherokee 6, Seneca... Certainly, the lighter the aeroplane, the easier to have several sets of wings without excess weight. The Drifter / Thruster were partly triggered by the availability of low cost extruded 6061 large bore tubing; which isn't low cost anymore. The labour content hasn't gone down, so the margins have disappeared / cost of finished aeroplane skyrocketted. If you get around the labour via kit building, then yes, a Frankenlight is possible... I do not know any type that provides a big enough source of wings as to be worth the considerable effort of designing around though... Skyfoxes perhaps?

That seems a bit odd - LPG is composed of shorter hydrocarbon chains, so there's less carbon and more hydrogen - proportionally - than petrol. As hydrogen burns around 2,800C (from memory), and carbon burns around 3,400C, the flame temperature should be considerably lower, giving much more resistance to detonation.

Yes, Newton did TOD available vs weight charts for the T-500, with Catto props and 503 / 532 (note: The leaded petrol 503 claimed 58hp, so there's one set of charts for both). He also did ROC vs weight vs speed at 2,500ft density altitude. As soon as I can get my ^*&^)*^%%!!!!! scanner working, I'll be posting this stuff on the TOSG website

Nope. There's no such thing as a simple Reid Vapour Pressure tester; or a simple E-35 test engine. One of the problems is the oil companies use a wide range of additives to meet the commercial spec for the fuel, so the various properties vary wildly, including the rate of aging (both loss of volatility and loss of effective octane number can be significant within days, if dissolved butane is used; or months, if (carcinogenic) aromatics are added).

Er - 50 deg lean means excess oxygen means hot metals oxidise rapidly; 50% rich means excess carbon, so they don't.

I seem to recall an account of some cargo getting stuck on the ramp when being shoved out of a Herculese? - when drogue 'chute pallet drops were first being experimented with. And I'm pretty sure some Air America operators had a few minor load shifts... when I stick my hand in my pocket for a hankie whilst flying the T-83, there's a few % CG shift

Very long-sighted - if any 'easy entry' category threatens GA production, the US of A will never recover from the post-ww2 depression - and that was 60+ years away!

But when rotax put plastic caged bearings into the 532, and they melted, that was alright because it was german Engineering (even if a Canadian-owned Austrian company)... and the average of ~40 Service Bulletins for every significant model of Lycoming flat engine is irrelevant... if Jabiru EVER get anything less than perfect, they deserve universal condemnation and an eternity listening to Hansard... because!

I inspected the one ditched at, er, Green Island? Flameout of the mighty PT-6... and versatile Cessna had only Alodined about half the internal structure, boo hiss... an operator up there found the slot-lip ailerons resulted in poorer payload factors "hot & high" than Cheiftans...

Possibly - but since NACA did all the research on light singles in the '20s and '30s, why can't Cessna read? Designing for spin resistance was done to death - remember the Ercoupe?