The standard RoC formula (using FPM and LBS) usually shows the excess HP at sea level at max gross to be around 33% of the rated HP for most GA propeller aircraft.
The formula is ROC in FPM = ExcessHP*33,000*Propeller efficiency divided by All up Mass in LBS. The formula is derived from the power available and power required curves.
However, something must happen to the curves as you climb, assuming that the only change is density altitude, not mass. The TAS of Vy will increase (and Vy converges on Vx with altitude, becoming the same at absolute ceiling), and Power required is linked to TAS, but as density decreases parasite drag will reduce for a given IAS. At the same time as you reduce Vy with density altitude it presumably doesn’t move up the backside of the power required curve, but conversely Vx is presumably moving down the curve – induced drag increases at a much faster inverse rate than parasite drag.
If this improvement did not occur then most normally aspirated propeller aircraft would have a service ceiling of around 9 – 10,000 feet, which is roughly where full throttle 65% power lies (ie 1 minus the 33% excess power at sea level). However most of the NA class manage around 13 – 15,000 feet as a service ceiling, and some draggy aircraft, the 150 HP Super Cub, have a 20,000 foot service ceiling. Don’t laugh, a 135 HP Super Cub held the altitude record for many years for one of the SEP classes (around 31,000 feet).
The calculus for figuring out a service ceiling must be quite interesting, if you are that way inclined, and hopefully someone comes along to help understand this.
I have just fitted the EI CGR-30P system in a TB20 and was wondering how other people have their fuel flow systems calibrated.
The one thing that you don’t want is your system gauges showing more fuel than is actually in the tanks. To that end I was wondering how accurately other people have their systems set up.
I am currently re-calibrating the fuel transducer K-Factor every time the tanks are filled up. This has only happened once since the refit and required changing the K-Factor significantly. It is my intention to get to a point where the FOB as calculated by the CGR is 1 to 2% less than is actually in the tanks. In other words there is 1 to 2% more fuel in the tanks than is showing on the instruments.
The fuel temperature and expansion/contraction is going to affect the accuracy of the system. Full fuel left in a parked aircraft for several hours in very hot weather will expand, or even vent out of the tanks. The opposite is true as well if fuel is loaded at say 15C and then the aircraft is flown in the cruise for several hours at -5C.
How do other people have their own systems set up?
Is a 1-2% under reading of FOB a reasonable assumption?
I am just wondering… How come Eurocontrol has its own set of rules despite SERA/NCO etc?
For example >FL095 B-RNAV is required by Eurocontrol. Where can I find the law that actually contains this rule? Or can they just require whatever they like?
I thought I just got the hang of reading EASA/EU rules… Hope somebody can point me in the right direction. Thanks!
Automatically generate highly optimised IFR routes in the Eurocontrol system.