Randy Haskin wrote:
Quote:
The racers are all trimmed prior to entering the course with a large nose up trim bias, the idea being as they approach the race speeds they can relax the push, as the trim will be correct for the speeds, 400 plus, so one less item to think about, in what would be a pretty intense environment.
The problem with that, James, is that at speed an aircraft has nose DOWN trim, not nose UP. Speed increases, nose
down trim increases.
If the racers were set up for "race speed trim" as they were entering the course, that would require putting
back pressure on the stick to keep it in level flight, with the back pressure decreasing as speed increased...not the other way around, as indicated in this passage.
I understand the idea of a little back pressure trim to assist with the control forces while making the turns, but this, too, would be a comparatively nose down trim condition while they were forming up for the start.
For the airplane to be somewhat manageable in the straight stretches when not in a bank, it would still require a significant amount of nose down trim when compared to "neutral".
Hi Randy - not my original data (I'm definitely not qualified enough to comment!) and the OP on Key has posted this response after similar comments to yours, made over there.
Quote:
Trim (and CG)
"surely nose down trim and not nose up then as per Canadairs post? or am i miss reading his post on the techno side?"
Sorry, not meaning this to be confusing, the difference is the way I described trim tab position vs what effect the trim tab is meant to produce.
The intent on the course is to use trim to induce a nose down effect, increasing with speed, ie the trim works harder to push the nose down the faster it goes.
But then as mentioned, the loss of the trim, which is pushing nose down, the nose will dramatically and rapidly rise.
So the tab position is UP, the Elevator TE position is DOWN, which pushes the nose DOWN. if the tab lets go, the Elevator TE goes UP, the nose goes UP.
This is much easier to explain with my hands and an imaginary stick, than via words!
On the subject of CG, basic aerodynamics says that the further aft the CG the faster the aircraft will go and the more manueverable it will be, (to aft CG limits vs weight) but this speed is gained at a price, as the further aft the CG, the less pressure required on the elevator for a given result.
So more simply put, it would be very easy to exceed the design limits of the surface with an Aft CG, and near VNE speeds.
This may be a factor regards this accident, as the elevator without trim would have a free float angle which is relative to the speed, with trim it is forced to an angle, but take the trim away and it will return to this angle, but with an aft CG it will induce as perhaps seen, a massive G as a result of rapidly returning to this point, as well inducing a large accompanying "stick force"
As mentioned, the only way to change CG in flight is to consume some weight, in most cases just fuel, but as GG had a boil off cooling system water would also be consumed. Both would affect CG, and I have no doubt they would have biased CG to move aft as both are consumed, as this would have a dual effect, the weight reduction and CG moving aft would essentially increase the speed with each lap.
They were in lap 3 when the accident occurred, so less than 1/2 way, and I would guess that they still planned to burn and boil off quite a bit more, so the CG was not as far aft as it may have been planned to end up.
The ethos of GG was to use aerodynamics to go fast as opposed to MP. While Strega, etc would be running over 100" to get to 490+ speeds, the theory of no radiator scoop, and the other clean up items was that GG could match or exceed those speeds but on 60-70", which has the add on benefit of not working the engine as hard, less fuel required, lower temperatures, etc, all good stuff and certainly excellent thinking.
I think GG was the best designed, best performing, most efficient Unlimited ever developed, it was such an incredible machine, and all involved should be commended for its development, and operation. Its last lap was showing just what it could do, and I bet the telemtry will show it did it at less than 70"
Oh, as also mentioned, I would assume that any telemetry gained or qouted was real time feed already saved, I would not think any useful data will come from the aircraft parts salvaged, but again that is the domain of the NTSB, not me.
I certainly do not want this to in any way take away from the obvious focus, the human tragedy, like everyone else I am just trying to make sense of what may have happened. None of this means a thing to anyone personally affected by this.
http://forum.keypublishing.co.uk/showpo ... tcount=190Hope its of interest, I have no angle on the details...
Regards,
Login
Register
FAQ
Search
