Great thread.
Thanks for the graph, I’ve been interested in this exact topic for some time and this is interesting.
I’d also be curious to see the graph of fatality rate over stall speed.
Interesting. I have never thought of cruise speed as a factor. I would also think stall speed. But, there is an obvious correlation between cruise speed and stall speed. I would think though, that using stall speed would give you less spread of the data.
The concept of a stall speed is less well defined on a non certified type. A certified type has to meet a raft of tests around Vs.
“The concept of a stall speed is less well defined on a non certified type”
Both the Annex1 aircraft I fly on LAA Permit were previously Certified.
Most identical examples of one still are.
The UK LAA annual permit test is required for all Permit aircraft, and stalling has to be done, at near max AUW, in several configurations, stall speed recorded and characteristics noted.
I’ve noted more difference before and after a wing repair and recover than
between different example aircraft.
The LAA inspectors are fussy 
but I do not believe that every Annex 1 SEP, for example, meets all the various handling requirements, at Vs.
For example does it have sufficient aileron authority to counteract propeller torque at Vs (which is 60kt max for a SE plane)? Of course not. To take an extreme example: a Spitfire absolutely doesn’t meet that requirement, and probably neither will any of the Lancairs (320 360 IV etc). That’s why they are fast (short wings and a small elevator). There is no free lunch.
Obviously some will take this the wrong way (have done so in the past, and some things are off-discussion “by convention”) but it would be irresponsible not to.
LeSving wrote:
Interesting. I have never thought of cruise speed as a factor. I would also think stall speed. But, there is an obvious correlation between cruise speed and stall speed. I would think though, that using stall speed would give you less spread of the data.
Yes I think lot of the elements in the graph will gets scaled by VS0, but this is barely similar to flying power-off? you could argue that your fatality factor is something like MTOW*(VS0*VS0), but there is something about safety that relate to “drag”, “stability” or “overpower” these relate to 100% power cruise speeds and best glide speeds, to me any aircraft where the backside of the drag curve is wide as much as 40kts need lot of “special attention” this includes high performance Gliders, Cirrus and Mooney
IMO, anything heavy with lot of power, high cruise/glide speeds will need more pilot skills to get it to touchdown at MTOW*(VS0*VS0)
Ibra wrote:
you could argue that your fatality factor is something like MTOW*(VS0*VS0)
Shouldn’t it rather be (VS0*VS0)/MTOW? A heavier aircraft will decelerate slower and absorb more energy into the airframe?
Looking at another graph in that document, it shows manoeuvring at low alt to be the largest factor. Loss of control the next largest. This suggests that “manouveribility” is important.
Peter wrote:
The LAA inspectors are fussy
A lot more pragmatic in my experience than anyone involved in certified aircraft work!
Airborne_Again wrote:
Shouldn’t it rather be (VS0*VS0)/MTOW? A heavier aircraft will decelerate slower and absorb more energy into the airframe?
Interesting remark, once you have crashed all matters for survivability is speed and distance to stop (overall Gs) and how that get transmitted to the body (to Brain & Co via cushions, straps and moving parts), on MTOW you could argue it is beneficial as there is a high interlink between airframe mass, it’s strength and the resulting stopping distance for survivability if you are crashing in open space
If crash distance is constrained one can’t argue much about having higher MTOW?
