Question I cannot resolve from the internet is a) Do the bolts have a shoulder, is the washer back undercut? b) the photo above of the lower spar boom with the 4 holes looks as if the web is thicker than the top boom.
Now with my basic stress knowledge, I agree that the 3 bolts in the top boom are due to lack of linear space, and the strength of the top boom bolts could be less than the strength of the bottom boom as the stress would have been (I think) calculated on the basis of a 6g positive loading & a 3.5g negative loading times the military safety factor of 1.25 from AvP970 or equivalent in mid 1930’s.
As for the friction relief gained by the overtightening of the bolts I have not heard of that being employed in stress calculations. In any case as flight loads would be oscillatory in nature, & I think this action could negate any gain from friction, so relying purely on the bolt (double) shear strength & the spar boom holes bearing strength.

4 bolts would give a more gentle load distribution from one part to the other, so could also then be a smaller dia.

Another question then, with the ever increasing weight & performance of the Spitfire, was the spar joint overstrength in the first place or how was it strengthened
with each increase?
Interesting thread.
Keith

I wonder if 154 still carries the Llanbedr TV camera & Tx modifications, and was it upgraded to have new wings & fuselage frame? It also had a BAe designed Rad Alt installation for trials use.
Keith

Cannot help with ‘HNA as the Journey Log book I have for the aircraft only goes to 1959, & I do not have anything on ‘KWJ.
Regards
Keith

Hmmm….Memories of riding my 125 BSA Bantam flat out down Hangar straight (55 mph lying flat on the tank!), going as fast as possible round the bend by the strato chamber & scaring the life out of the pedestrians at lunch time……Going up & down the banking & Test Hill….1955 & all that! Typical teenager…..My uncles ashes now reside in the rose garden – & my father was another old apprentice! I am glad though that someone is managing to keep some history of the place.
Keith

Keith, it might be worth looking at air temperature parameters if altitude isn’t there.. .though that surprised me.

Nothing that one can vary, the standard temperature & pressure lapse rate is built in as far as I can see. So it will need someone with a lot more knowledge & capability to try a fix. Not having P3D, I can’t tell if that is any better. ( Throws in towel!) 🙁
Keith

Keith, have you got to the bottom of what was happening with the Proctor?

In real life or in M$ Flight Sim?

I’ve no way of checking real life until I can ask Tango Charlie, when he gets one of his airborne!
I did once persuade my father to coarsen pitch in one air race, but he went from full fine to fully coarse, which was more than I wanted to experiment, as the RPM dropped from 2400 down to 1700, & thats not good on the engine, I think 1900 is the minimum recommended, so he went back to fully fine very quickly, so did not see any other result!

As for M$ Flight Sim, I’ve not found a way into the inbuilt programming.

Your explanation at the top of your message is what I would expect, re: manual intermediate setting of a two position prop. But fiddling with the throttle in fine & coarse still needs to be used to avoid over or even underspeeding as far as I can see.
So I think stalemate at the moment, unless I can stir up some of the few grey cells remaining & get a flash of inspiration!
Keith

If we are talking Flight Sim prop action, then its a case of how the creator of the model addresses the prop efficiency, prop Power coefficient & engine power curves in the models .air file, and the prop angle limits & the rpm at which the constant speed cuts in, in the aircraft.cfg.
How accurate they are is any ones guess, unless the designer has the appropriate original design data. I must admit that in my models I try to get rpm, power output & airspeed as close as I can get at say take off, cruise & flat out, anything in between is a pure guess. I don’t have the mathematical knowledge to calculate these curves even if I had the necessary data!
How the M$ software calculates all of that is also unknown to me.
As noted above, the Proctor using the DH counterweight prop in real life should be started & stopped in coarse pitch, but that is not programmed in Flight Sim!
My model will start controlling at 1400 rpm, & one can move the pitch control that will change the blade angle (as seen using Herve Sors AFSD program), this will also affect power output & thrust when static. In flight likewise & flat out fine pitch will give max IAS & if one changes the prop lever towards coarse, the rpm drops, HP & IAS also, but I think that’s because its following the curves for ‘J’ vs efficiency as well as the curves for HP & Propeller power coefficient vs Blade angle & ‘J’ – the advance ratio.
There is a complex .xml programme that has been developed by a genius that can apparently replicate a VP prop, but is very complex & IIRC does not use a 3 position valve, i.e. resulting in the two position device.
Back to square one I fear! Very interesting discussion though.
Keith