Check the grass on the day. At this time of year grass can grow fast.
greg_mp wrote:
That a common statement on almost all props planes… Even a C182 will always land shorter than it can takeoff
Not sure that’s correct or the relevance of the fact that it is a prop plane – surely the efficacy of the braking system is relevant to landing distance? DA42 and SR20 come to mind as aircraft I have flown where, IIRC, landing distance is significantly longer than takeoff, at least according to the numbers in the POH.
greg_mp wrote
That a common statement on almost all props planes… Even a C182 will always land shorter than it can takeoff.
For “spamcans” yes, but not necessarily for aircraft built out of composites. E.g. it is very much not true for the DA40.
a1650772 wrote:
– surely the efficacy of the braking system is relevant to landing distance?
Less often the braking system and more often the amount of grip between the tyres and the surface.
It’s a common misconception, and applies to cars too, that to stop more quickly you need to fit more powerful brakes. If the existing brakes are powerful enough to lock the wheels at speed (which for an aeroplane on grass is quite easy) then more braking power will not shorten the stopping distance, it’ll just make it easier to lock the wheels.
To shorten the braking distance you generally need to increase the amount of grip (more rubber on the road) so that more braking force can be applied without locking the wheels.
Graham wrote:
To shorten the braking distance you generally need to increase the amount of grip
Which you don’t really want in an aircraft, as the brutal force may wreck your tyres …
MichaLSA wrote:
Which you don’t really want in an aircraft, as the brutal force may wreck your tyres …
Sure, but you therefore remain limited to the braking force that can be supported (without locking up) by the amount of grip which exists between your tyres and the surface.
Most braking systems allow the user to apply sufficient force to lock the wheels. This being the case, stopping distance cannot be shortened by increasing the available braking force, but only by either (1) increasing grip, or (2) fitting ABS so as to allow an almost-constant force right at the limit of adhesion to be applied.
Today was the day to try this out 😊
It was a rather hot and bumpy day but I had time.
The airfield was EDMT Tannheim, which has convenient 1000m and no significant obstruction close to the field.
Having been on hard runways for the past two years, I had completely forgotten how bumpy it could be. Also, the number of bugs decorating the facade calls for essential cleaning afterwards.
I performed three take-offs and I would say I was comfortably airborne by or little before the midfield marker,.i.e. between 450-500m. With 180 litres of fuel and one onboard, it was alright for a hot day. I need to try it again on a 580m runway, but perhaps in the morning hours.
Great experimentation. I always find that you learn a lot about yourself and the aeroplane though doing stuff like this.
It’s great practice, and a valuable skill to master short takeoffs. But remember, the object is to get the airplane off the surface, and there after, clear an obstacle (if present). Clear it, not clear it by 100 feet! It is widely overlooked that airplanes generally cannot be safely landed back after an engine failure much below Vy. So if you’re climbing through 100 feet at Vx, a safe land back is unlikely. If it’s a risk you need to take, okay, but don’t take the risk of being at Vx more than 20 or so feet up for no good reason, use ground effect to be safe after your short takeoff, and accelerate to Vy.
For those who question the background of this, review the underlying principles of a “height/velocity avoid curve” for any helicopter. The same physics also apply to airplanes, it’s just rarely taught nor explained well. Flight Manuals usually have soft wording about achieving a specified airspeed (around Vy) when obstacle avoidance is not needed, but no explanation as to the reason why it’s wise….
