powerandpassionVery interesting, thanks for the update.
No worries, pleasure.
Without taking away from the courage of Lindbergh crossing the Atlantic in 1927 and Kingsford Smith et al crossing the Pacific in 1928, both it transpires, used Gilman bearings in their ‘dependable Wright Whirlwind’ engines, so this forgotten technical innovation was perhaps critical to the success of some of the most iconic air transport achievements of the 20th century. No doubt these aviators searched for the ‘inside dope’ on any innovation that would enable success. The Gilman bearing also allowed engines in the 1930’s to move through an exponential development of more horsepower per lb of engine weight that brought us to the 1,000+ HP V12s and radials of WW2. For all this Gilman is a largely forgotten character and there is very little mention of him in Allison engine histories, and I have yet to find a photo of him. He must have been a very self effacing man.
powerandpassion[/ATTACH]
Rolls Royce Kestrel engines used Gilman bearings for the conrod big ends
Here is a wonderful chart found stuck on the wall of the workshop at Shuttleworth, which confirms the “Big end bearings were made by the Centricast process, using lead bronze on steel shells” and “main bearings were made by the Allison static cast process”.
[ATTACH=CONFIG]243609[/ATTACH]
So we have pretty much figured out he big end bearings for the conrods, what about the Main bearings for the crankshaft?
Now the crankshaft main bearings are backed by aluminium ‘blocks’, which, given aluminium’s lower melting point, could not cope with the 1050 degrees C the steel backed bearings were subjected to. So now we need to investigate whether the “Allison static cast process” was a fancy combination of steel – lead/copper-alumiunium casting.
powerandpassionIn the Kestrel rod in the photograph there was a thin sheen of oil on the contact faces when the rod was separated, so no doubt at 3000 RPM the conrod bolts are stretching and, in a fractional sense, this becomes an articulated joint. Now I am starting to think about the extravagant conrod shell bolts and their metallurgy that are a feature of Kestrel and Merlin, that have alternately thin and thick shanks, and a keyhole and pin on the head arrangement to prevent rotation. Rotation could only occur if there was a loss of clamping, consistent with stretch. I thought the thin & thick shank was light weighting but now I am thinking that this allows a factor of controlled stretch.
A wise old man told me about how the axle shafts on his 1930’s British racing car kept shearing, and this was a problem with similar cars in the car club. More powerful engines slotted in and drive trains that ‘could not take it’. Replacing an axle shaft was a real pain, worth groaning about with other club members at the bar.
He was an aircraft inspector in real life. So he pulled out the axle shafts from his car and machined down the shanks of the shafts, thinner in the middle, original thickness at both ends. This meant that the shear load, instead of concentrating at the weakest point of a shaft of standard thickness, would transfer to the longer, thinner portion of the shaft. Because there was ‘more’ thinner portion, the shear force spread out over it, causing it to twist, but not break. So he never had another breakage again. He became famous for never breaking an axle shaft on Hill Climbs. Everyone in the club begged him to explain how he had solved the problem. Surely he had found shafts made of some exotic metal, or made thicker shafts. He held off long enough until one day he explained, ‘machine your shafts thinner’. Everybody laughed and considered it a good joke, and kept on breaking their axle shafts.
powerandpassionIn respect of the manufacturing of CuPb bearings for RR Kestrel engines the following description from 1938 seems to match well :
Handbook of Aeronautics Vol II Aero Engines Design and Practice Third Edit 1938
Lead Bronze Bearings pg 26
The bearing shells are generally lined with the lead bronze by means of the centrifuging process. In this process the shell is manufactured with one blank end and left a rough machine finish. The shell is then mounted on a spindle either vertically, in which case the top is left open, or horizontally with the open end sealed by welding and rotated in a furnace, enough lead and copper in the correct proportions having been put into the shell to make a lining about one eighth inch thick. The temperature to which the shell is heated is in the order of 1050 degrees C and the speed of rotation is dependent upon the diameter of the shell, but for a normal size, say 3 inches in diameter, the rate is 800 RPM.
A small amount of phosphorus , about 0.05%, is generally added to the lead copper content and this acts as a deoxidant, having a cleansing affect on the metal and interface.
After reaching the desired temperature the shell is cooled either by air blast or oil quenching whilst the same rotational rate is maintained. The rate of cooling is important as it governs the nature of the dispersion of lead in the copper. These metals do not alloy, but merely mix and they segregate with slow static cooling. It is therefore important that the cooling conditions be such that the maximum amount of dispersion of lead in copper is obtained.
Here is a youtube of ‘centricast’ bronze casting, which incorporates what appears to be red phosphorus and water chilling, as per the process described in 1938 :
powerandpassion[/I]Method of Making Bearings US patent 2130461
The bearing resulting from the practice of the method herein set forth is made the subject matter of another application No. 575,117, filed November 14, 1931, as a division of this application.
NORMAN H. GILMAN.[/I]
Just to solidify the chronology of the adaptation of the Gilman bearing the following extract from the SECRET ” Historical Summary of the Royal Aircraft Establishment 1918 -1948″ by CF Caunter Report AERO.2150A Nov 1949 details, under Metallurgical developments for 1931 :
“Following an examination of Allison steel backed bearings, experiments on methods of producing lead bronze bearings in steel shells were initiated. The method of pouring molten lead bronze into rotating steel containers and allowing the metal to solidify in situ was developed… The preparation of bearing shells on these lines was demonstrated to interested firms, and a period of vigorous development followed in connection with aero engine applications”
So we have confirmation of technology transfer from Allison to the British aircraft engine manufacturing industry in 1931, consistent with Gilman updating his original patent in 1931.
So I would guess that the Bristol Pegasus, as a development of the Bristol Jupiter, went to Gilman bearings, and the Nappier Dagger too. This is an engine technology that persisted in designs from 1931 to 1938, and as few of the engines remain from this era to be rebuilt, fairly obscure today. Still you never know when you might need to rebuild a Napier Dagger…
powerandpassionhow did Capt Audy nose over the Bulldog?
Not knowing the circumstances of the nose over I can only guess at the following :
1. The Bulldog was originally designed with no brakes, certainly Bulldog IIs supplied to Australia in 1930 had only spoke wheels with no brakes.
2. The CoG of the Bulldog, with a heavy Jupiter out front and ultra lightweight rear fuselage, would make it prone to tip over if brakes were fitted and applied excessively.
3. A recent trip to Shuttleworth elicited a comment from a pilot familiar with the Demon I, fitted with hydraulic brakes and Hind, fitted with pneumatic brakes, that Demon hydraulic braking was sluggish and Hind pneumatic braking ‘bitey’. So two similar aeroplanes with different braking systems create the option of riding into a hedge or nosing over.
Don’t hold me on this but I think Hind was 15 inch wheel and Demon 19 inch wheel but both use the same expandable ‘bicycle tube’ with friction pad mechanism, one expanded with hydraulic fluid and one with air, so they are a reasonable ‘test and control’ for considering fluid mechanics. This is Limey technology while Yankee technology of the day is the Bendix type brake shoe.
4. I do not know if Bulldog K2227 was fitted with hydraulic or pneumatic brakes. From photos, it was fitted with 19 inch Dunlop braked wheels in 1962, which could be either hydraulically or pneumatically driven.
5. My punt is that the Bulldog was fitted with pneumatic brakes which combining with a CofG closer to the engine than most types and a test pilot more used to trying to stop supersonic jets from coming off the end of short runways gave us a nose over.
Stearmans seem to nose over, from what I see on youtube. Hydraulic or pneumatic?
Maybe fit hydraulic brakes ? Don’t call me if you hit the fence !
Ed2
powerandpassionI just laughed so hard that a bit of donut out came out of my nose.
Talking metallurgy, unless you are into the joy of crystal formation, can be mind numbing, so I try to spice it up ! Causing donut to pass through the nose of a fellow human being while talking about BAC.A 1021 & BS 970 301S21 I will consider as one of my most eminent achievements in this field, thank you !
powerandpassionIf the T188 contained BAC.A.1021 then Bulldog K 2227 was repaired using bits of supersonic jet ! Below are engineering notes from the second rebuild of the Bulldog by Bristols in 1963, when parts of the original structure were damaged in the 1962 nose over :
[ATTACH=CONFIG]243036[/ATTACH]
This note deals with the replacement of a roll formed fuselage strut, originally made from DTD 99, 55- 60T nickel chromium alloy (the note specifies the same strut being originally made out of the stronger DTD 54a, 65 – 75 T nickel chromium alloy, as an alternate. New question – were later Bulldogs, with more powerful engines, given uprated, stronger fuselages, by replacing DTD 99 with DTD 54a? There is a precedent in Bristol’s original 1920’s drawings for the Bulldog specifying S40 spars, later uprated to DTD54a in the Bulldog II….)
Anyway the 1963 engineering allows BAC.A 1021 at 26 SWG to replace the original nickel chrome member at 28 SWG, a pretty close match. What was BAC.A 1021?
A 1957 Report by the Air Ministry on work conducted by Bristols on ” DTD 166 Type Austenitic Chromium Nickel sheet – a summary of Properties” describes BAC.A 1021 as a proprietory Bristols specification for, effectively, Staybrite with a touch of titanium. DTD 166 may be familiar to aficionados of Hawker Hart biplanes and Hurricanes as the stainless steel fish plates used to join the tube fuselages together. It is a ‘work hardening’ type of stainless steel, not for heat treatment. It seems a further twenty years of research and development, and the addition of titanium, allowed it to be weldable, as the report describes its chief characteristic is being amenable to puddle weld to FV 448, which the T188 was clad with. So BAC.A 1021, a lower cost material than FV 448, may have been part of the T188 structure, under the low creep (low expansion under the heat of friction from smashing through air at high speed) FV 448 skin.
The other aspect of the report deals with a new process called “Modulus Recovery Heat Treatment”, where this hitherto non heat treated material was subject to heat treatment at a very specific temperature range to significantly increase its strength. So BAC.A 1021 was a very clever material, described in the 1957 report as ‘high grade aircraft material’.
So certainly we have proof that ‘high grade aircraft material’, suitable for welding to the skin of the T188 was used in Bristol Bulldog K2227 in 1963.
Interestingly, BAC.A 1021, supplied by Firth Vickers, is described in the report as ‘basically Firth Vickers FDP’.
Climbing out of the Chesterfield* in front of the crackling fire* and reaching over to the oak* panelled bookshelf for my 1962 Firth Vickers “Rust, Acid and Heat Resisting Steels” sure enough confirms that the chemistry of BAC.A 1021 and FV FDP match. FV FDP is in the same section as Firth Vickers 301, Austenitic stainless, work hardening, basically Staybrite.
Ringing the bell*, I ask my man* to fetch my CAA AANs to refresh myself on the wing spar materials used in the restoration of Hawker Demon G-BTVE in the 1990’s, which show 301S21 as the material selected by Ron Dack, known to some as Yoda. I have to grab my Nachschlagerwerk Stahlschlussel from out of the hands of Brigit*, the 18* year exchange student from Germany, who is using it to set up a line of coke*, to confirm that BS 970 301S21 is the same as FV 301, which it is, basically Staybrite.
Understanding that the titanium in BAC.A 1021 was only there for weld stability, and that the roll formed sections in the Bristol Bulldog and Hawker Hart biplanes did not require welding, it appears to be entirely logical to use work hardening Staybrite for 1930’s roll formed strip steel structures, as long as you know what you’re doing. Most fascinating in the story of the Bulldog made out of T188 jet is the connecting thread between the work of the 1930’s builders of biplanes who became the 1960’s makers of steel based supersonic jets and on to the 1990’s restorers of old 1930’s biplanes. Who was Yoda’s Obi Wan Kenobi?
Certainly it would be good to continue the thread. Yoda is no longer with us, but I feel the Force. May the Force be with you.
*NB – Some aspects of the descriptions given above are not true.
powerandpassionNapier Rapier.
Happy new year.
Andy
One pint of the best served with a wink by a buxom wench ! Knew a Napier Man would be along sooner or later, well done !
Napier Rapier at Shuttleworth below :
[ATTACH=CONFIG]243008[/ATTACH]
[ATTACH=CONFIG]243009[/ATTACH]
So there is a spare cylinder available in case one ever falls off a Rapier on a…um…
powerandpassionEarly low horsepower flat four lycoming?
No beer!
powerandpassionDone deal !
Not a Le Rhone or Jupiter, not a radial……
powerandpassionWith the cylinder fins appearing to have ‘squared’ off sides is this off a an air cooled inline engine?
John
OK, you win a beer coaster but more work required for beer !
powerandpassionVersuch, no daggers for you my friend, just the compliments of the season.
Thank you for posting up the magneto and engine information, which gets closer to the mystery of the CSE 12- 12S and CSE-ES magnetos, which I think were custom builds for Napier, the first time I have seen the engine designer dog wag the magneto manufacturer tail !
My guess is that these magnetos were constructed on a similar principle to the two crankshaft Dagger engine they were placed on :
a central engine driven spindle geared to two new spindles driving through two piggy backed coils. It would not be hard to do this if you shifted the distributor into a separate device. What about the points. Perhaps they yin-yanged around a single lobe arrangement, necessitating a larger points cover. I have held one of these points covers in my hand and it is much larger than the standard points cover on the standard CSE magneto.
To prove or disprove this theory the driving ratio from the engine to the twinned magneto is required, then an assumption that the lobes opening the points were the usual 4 lobe arrangement, then follow this gearing arithmetic through to the distributor and engine.
In simple terms the Napier Dagger, with 48 spark plugs, had the equivalent of 4 x 12 cylinder magnetos stuck to it, optimized into 2 x 24 cylinder ‘custom’ magnetos.
It seems quite brilliant, typically Napier, typically introducing 200% more dependency on nothing going wrong….
powerandpassionAnybody ?
OK, clue : British
powerandpassionAre you sure ?
Why are there four magneto switches on the left hand side of the cockpit of the Hawker Hector ? Was this a twin engined aeroplane ? Or did it use twinned magnetos ? How do you provide ignition to 48 spark plugs, simply !?
[ATTACH=CONFIG]242941[/ATTACH]
Do you have a Dagger AP or handbook which actually describes the ratio of prop shaft to magneto and distributor drive? There is a little dedicated gear on the prop shaft which drives little bitsy magneto and distributor gears.
Sign In
