LowtimerYak 52 – Had a couple of goes in one last year. PHWOOOOAAAAARRRRR!!!!!! What a fun piece of kit. Quite happily do that again, but unfortunately bank balance and Julie are unlikely to let me indulge long term. 🙁
You can come for another trip whenever you like, providing you think your feet can take it! 😉
LowtimerI’ve got the Yak booked for Sunday morning, so may be able to make a brief visit, weather permitting.
YR
Me too, will probably be there in a different Yak just before 12.
LowtimerJust a thought, but Yak 52’s / 50’s are loud, radial engined and can look very much like WW2 fighters compared to your average spamcan.
Steve,
It’s only loud on the inside! Honestly… if you hear four or five Lycoming engined types fly overhead, or climb out from the end of the runway while you listen from the pub in the village, and then hear a Yak rumble over, it’s a lot less prominent than the Arrows and Pittses of this world. Big slow-tunring prob and big exhaust manifolds, relatively even flow of exhaust gases.
Inside though as you know, it’s a VERY noisy eroplane.
How’s the foot coming on, then? 😀
LowtimerSo, are we saying that with the right engine and fuel system specifically designed for flying inverted, it would be/is theoreticlly possible to fly inverted for as long as the fuel lasts (before flipping over and landing normally !! thought I’d better add this before anyone else did).
Also with the right wing…
If you have a cambered wing (most are) and/or something with washout, dihedral, possibly also with differential or Frize ailerons, all these things which make life more pleasant in positive G make it worse in negative G. The Yak, for example, does not have a symmetrical wing so its inverted stall and inverted climb are both less advantageous than the positive G equivalents.
Some wings, e.g. anything with lots of undercamber like a Tiger Moth or vintage sailplane, have the inverted characteristics of a toilet seat.
A really modern unlimited aerobatics has all symmectrical everything, and really doesn’t give a hoot whether the G is + or – .
Lowtimer11s. 3s are different animals entirely. Perhaps they should be called ‘Yak-11 (mod)’ or some such.
Before long, someone will be claiming combat history for them 🙁
But the Yak-11 did start life as a development of the Yak-3 airframe, being originally designated Yak-3UTI when it first flew in 1945.
LowtimerInverted duration limits? It depends mostly on the fuel and oil arrangements for negative G. If you have a proper inverted oil system then that should run more or less indefinitely, but most aircraft with inverted fuel systems have a limietd endurance in negative G as they feed from a small inverted tank within the main fuel system. It’s usually good for a couple of minutes continuous power, and, if you use it all up, you generally have to return to positive G for several minutes for it to refill. So the POH will say something like “continuous inverted max 2 mins, aircraft must be flown erect for 5 mins before further inverted flight”.
One of Neil W’s concerns in the Zlin wing breakage episode was the short amount of time he had available for his inverted climb away and subsequent inverted circuit down to the round-out and negative G half barrel roll that he used to put her down on the ground.
If setting a negative G record you would have to modify the system a lot further than you need to complete an Unlimited aerobatic sequence, in which you are changing between positive and negative G all the time, so you never run out of inverted fuel.
LowtimerSlight digression, but qualifies as a strange-but-true…
For anything with a two-blade wooden prop (not on a Merlin engine, I know!) it’s quite important to leave it with the prop blades horizontal. Otherwise the moisture in the wood seeps down into the lower blade if it’s standing for any length of time, and this will cause quite significant out-of-balance vibration.
Has anyone noticed what the BBMF does with its four-bladers and five-bladers? the idea of leaving one of the blade apertures pointingstraight down is a good one, it lets out he water if water there is, and also makes it less likely that some small creature can make a nest in there!
LowtimerI can’t see the point in building new Mustangs from sratch when there are so any around already that could be rebuilt. The energies, money and material would, in my opinion, be better spent on recreating something rarer and more interesting than just more Mustangs.
Well, Ican see that point of view from the airshow audienc’s point of view but it’s not their money that pays, and the people with the money to buy the things might have their own views? Quite a few wealthy aviators want a P-51D not because it’s a rare aeroplane, but because they want to fly a P-51D, full stop. Come to think of it, if I had pots of money I could well fancy a new-build TF-51D, all built to personal spec, and all brand new structure, a) because I could feel a lot more comfortabel about flying it to its limits, and b) because I would feel psychologically a lot less nervous than if I were flying a genuinely historic artifact. (Just as Mark Hanna used to say he enjoyed flying his Yak-50 more than MH434, he has always so conscious of the weight of heritage he was taking responsibility for in the Spitfire.)
LowtimerYep, it was P/UT and you logged it correctly. If you had done it as P1, not at that point having been signed off for tailwheel differences training, you would have been exceeding the privileges of your licence. Same comes when you are doing your retract gear, supercharger, CS prop, etc etc. Obviously also the case for IMC training, MEP, night, or anything else that varies your licence, rating(s) or counts as part of your licence in that sense.
You may point out to whoever said “students only” that that one may on many occasions be a student with a licence.
LowtimerOr you could have a new 120 hp six-cylinder Jabiru 3300 for about £8600.
LowtimerI could be wrong, but I vaguely recall being told that Coffman cartridges are getting scarce, and aren’t reccomended for piston engines which are being managed for long life. As this could be either complete rubbish or true, anyone able to correct it?
Don’t know about the scarcity but I’m quite sure you’re right about the second point.
I wouldn’t want an engine that I was paying for to be woken up by a Coffman starter if I had the choice of an electric start, especially on such a large engine as a Centaurus with such high rotating mass. (But also with a smaller engine such as a Gypsy Major, come to that.)
The power pulse of a Coffman is pretty high-impact. Obviously there are high stresses from the very high gas pressures, and the Coffman starter also accelerates the internals to quite high speed in a very short time – so there is a lot of acceleration stress. Whilst we all have a feel for the stress that high RPM puts on an engine, the rate of change of RPM also puts its own stresses into various components, and these will be especially taxing if the engine is cold.
An electric starter puts its energy in steadily over the cranking period, so there is a lot less of a thump when you press the button.
Another good solution for radials is the Russian-style compressed air starter, which meters compressed air into the cylinders one after the other. The peak pressures are a lot lower than with a Coffman and the air keeps flowing smoothly, so the Russian system also spreads the load somewhat compared to the cartridge starter.
Obviously the military had different priorities at the time these systems were engineered, so that’s no criticism. If you are expecting to write off a big engine after a few hundred hours or less, it’s not really a problem. A good comparison is the old practice of oil dilution with petrol to facilitate a cold start – if you want the longest possible engine life it’s much better to pre-heat the oil and engine, and indeed to circulate hot oil all through the lubrication system, before engine start. While this is practicable for an operator in the modern aircraft preservation / restoration world, it would not have been so practicable in wide-scale all-weather service with military and/or commercial pressures, and where engines were often semi-disposable items.
LowtimerThe Staggerwing is based at North Weald and belongs to Peter Teichman.
LowtimerExcellent collection, and interesting pics, I bet that floor gets slippery! What’s the low-wing natural metal job that looks a bit like a Vans RV series, but isn’t?
LowtimerHaven’t yet flown the Zlin, alas, but I understand that whilst a delightful aeroplane it does not have quite the Chippie’s perfect control harmony. In terms of objective facts rather than opinions, though, it has some serious advantages over the Chippie for aerobatics: the engine works under negative G, it has a wing section for more suited to negative G manoeuvres, and it is cleared for a far wider range of manoeuvres, e.g. flicks being prohibited in the Chippie.
LowtimerThe short answer is “possibly, if it’s windy”. Theory is not much use over such a short distance as so much depends on technique and small variations in the assumptions can have big effects. But it’s quite fun to see what the published data reveal and play with the figures to see what’s plausible. We need to know the speed that the aircraft needs to accelerate to, the acceleration available, and we can work out the space needed.
I don’t have an authoritative stall speed report on the IX in combat trim to hand, but I did find a copy of the A&AEE handling report on the 4x20mm equipped Vc here,
http://www.fourthfightergroup.com/eagles/aa873.html , which quotes a clean, presumably power-off stall of 81mph with heavy buffeting from 90 mph. The AUW is not quoted, alas.
http://www.fourthfightergroup.com/eagles/bf274.html is the A&AEE speed performance report for the IX, Sadly it does not quote stalling speeds but gives an AUW in military trim of 7480 lb with full internal fuel, no overload tank.
It seems reasonable to assume that the extra weight and drag of the two additional cannons on the Vc tested above would be compensated for in the IX by the extra engine weight of the 60 series engine, the four blade prop, and the wing machine guns (whether they be 2x .50 or 4 x .303). So I doubt the IX is operating at a lighter weight than the Vc tested here.
Stall speed at full power would be considerably lower than power-off, especially with a big 4-blade prop in fine pitch either “blowing” the wing roots or partially blanking them, but no sane pilot would pull off an aeroplane in heavy buffet, even if it has the gentle stall of a Spitfire. Factor all that in and let’s work with 80 mph as the lowest unstick speed we might imagine, letting the aeroplane rise by itself from the three-point attitude as one might if really struggling for the lowest unstick speed.
A 360hp Yak with a really efficient 3 blade c/s prop has static thrust of about 1,350 lb. A Spit with a Merlin 66 has 1315 bhp at sea level using the take-off settings of 3000 rpm / +12 boost. That’s 3.65x the power, so let’s say 3.65 the static thrust: 4927lb. That means that the initial acceleration in G will be 4927 / 7480, or as near two-thirds of a G as makes no difference. (It will slacken off a bit as drag becomes a factor but let’s ignore that for now).
You need about 1.5G constant acceleration over 50 yards to get to 80mph. So it’s not a goer in still air. But 0.66G will get you to almost 55mph. With a 25mph headwind component, that’s enough. (And if you have a healthy crosswind from the right, you might even be able to get full power on right from the start of the take-off roll rather than screw the aeroplane into the ground!).
None of this as ANYTHING to do with quoted take-off distances of course, which factor in all kinds of fudge factors, safety margins, obstacle clearance etc. It also totally ignores slope or runway surface, and ground effect. With the Spit’s broad wings and low wing, ground effect undoubtedly significantly lower the minimum achievable unstick speed, though not the speed at which one may climb away…
Sign In
