I found myself thinking back in the National Air & Space Museum recently. Firstly, because a friend announced that she had just visited it and secondly because yesterday we oversaw reciprocating engines at the class of the theoretical course for the private pilot licence.
The class itself was not telling nothing completely new, but it reminded me that I had a video of a demo of a radial engine recorded last year at the NASM in Dulles. I filmed it in order to upload it at some point… here it is:
For those not initiated, you may find how reciprocating engines work here, and more specifically how radial reciprocating engines work here.
I’ll never get tired of praising the Smithsonian institution.
Albi is small city close to Toulouse. It is mainly famous for its UNESCO World Heritage Site Cathedral Sainte Cécile and the museum of the painter Toulouse-Lautrec. I had been there twice, but I hadn’t yet written a post about the city. Today I’ll write about another special feature it has.
In Albi there is a car racing circuit. I have a colleague who likes cars, motor-bikes and has been already using that circuit in one of its open days.
Let me connect the dots. On Saturday, while having lunch, our colleague told us that the circuit in Albi was having an open day that precise day. He encouraged us to propose to our instructor to fly to Albi. And here comes the catch: “Why?” Because the aerodrome of Albi, our colleague explained to us, is embedded in the car racing circuit!
We gave it a try, demanded our instructor to go to Albi and succeeded. See below the flight path recorded with my Garmin:
In the following screenshot of the Visual Approach Chart (carte VAC) you may see how when the circuit IS active the runway of the aerodrome is shortened as the circuit crosses the runway! (You may download the chart here, PDF, 360KB).
Visual Approach Chart (VAC) for Albi aerodrome when the car racing circuit is active.
You may see it better below, in the Google maps view, how the circuit intersects the runway:
Albi car racing circuit and aerdrome.
Finally, enjoy the video of the final approach of our flight. If you pay attention to it, you’ll notice the cars racing in the circuit while we are approaching and how we are in fact touching down only within the allowable space when the circuit is active:
Yesterday, I wrote about a documentary on the AF447 accident. Within the video, a flight instructor performs a real stall exercises and he mentions that this is taught in the first lectures of flight instruction.
As I mentioned in the post, I learnt about the documentary while having lunch with 2 colleagues. I was telling them “I’d like to perform those stall exercises to see what feeling does your body have and how you instinctively react to it and how you have to consciously correct that reaction”. As the old adage goes “be careful what you wish for ’cause you might get it”.
After lunch, we headed to the aeroclub to have our class. Thierry, our instructor, opened by asking whether we had seen that documentary we had been talking about. Then, he mentioned “let’s do today stall exercises!”
[...] a stall is a reduction in the lift coefficient generated by a foil as angle of attack increases. This occurs when the critical angle of attack of the foil is exceeded. [...]
Stalls in fixed-wing flight are often experienced as a sudden reduction in lift as the pilot increases angle of attack and exceeds the critical angle of attack [...].
The theory of the exercise was easy: fly up to 3,000 ft, reduce the power of the engine down to idle, try to keep the altitude by pulling the stick backwards (nosing up), keep pulling the stick backwards when the stall alarm sounds off, wait until the aircraft starts buffeting, cannot maintain altitude and falls off… then push a little the stick (nose down), recover speed (above stall speed), start nosing up again while increasing power up to max rpm, get to 3,000 ft again. Easy.
The practice… well, my colleague was doing his exercises first while I was sitting at the back. I went from being warm due to the sunny weather to feeling uneasy to experiencing this cold sweat…
You may see the video below with one of the stall exercises performed by my colleague. You’ll notice the stall alarm (in this case it is just an alarm, not a voice saying “stall”):
Apologies for 1) bad quality of the video performed by my not-so-smartphone and 2) for not having recorded a video of my own stall exercises… I was too stressed with them
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Note: For the record, in the documentary it is mentioned that pupils get to practice stall in their first lessons. Yesterday’s was my 10th flight in order to obtain the PPL (private pilot licence), up to then I had completed just slightly above 6 flight hours.
As part of the preparation of a flight, the pilot shall make sure that the total weight of the aircraft (including fuel and passengers) is at or below the limits, and that the center of gravity is within a certain area. This is what is called weight and balance.
Some months ago, in our private pilot licence course we had a class where we reviewed this. I remember that one pupil asked “is it possible that the aircraft gets knocked over backwards on ground?” (imagine the aircraft “sitting” on its tail).
This question led me to make the numbers to see whether this was possible with the aircraft we are using for our lessons, a Robin DR 400.
Centrogram for a DR400-120.
For this purpose we use a centrogram, which is nothing but a small “map” where the different possible weights that can be loaded into the aircraft and its momentum are already drawn so the center of gravity can be easily calculated and checked whether it falls or not in the allowed area. This centrogram is included in the flight manual of the aircraft.
I found that, carrying 2 pilots (~154kg) plus 2 passengers (~154kg), you could never load much weight into the rear compartment reserved for baggage. As that area is the one behind the main landing gear, you wouldn’t knock over the aircraft on ground.
If instead of 2 pilots and 2 passengers, you had only 1 pilot and you would load the same weight (~231kg) as baggage, the aircraft would be unbalanced but still wouldn’t fall backwards and sit on its tail. Even if the center of gravity of the baggage compartment is behind the landing gear, the weight of the empty aircraft with a center of gravity between the nose and main landing gear over compensates our trick.
Once I had calculated this, I went one step further: in which cases being under the maximum take-off weight (MTOW, 1,000 kg for a DR400-140) given by the designer could the aircraft be unbalanced? That is, what is required to get the centre of gravity out of the allowable range?
I found that to get the aircraft unbalanced basically you would need to load it in two different ways that at first seemed quite bizarre to me:
You would need to carry only 1 pilot and 2 passengers (plus at least 25 kg of baggage and bearing in mind not to exceed the MTOW), but instead of two of them occupying the front positions and one sitting at the back, you would have a single adult piloting the aircraft and the other two at the back. I’ve never seen that.
You would need to have 1 or 2 adults piloting the aircraft, no passenger at the back plus at least 100 kg of baggage at the back. Why would one person carry so much baggage for a short trip with a Robin DR 400? Here I would add that the designer of the aircraft placed a small plaque indicating that no more than 40kg should be loaded in the baggage compartment.
Well, the two cases can be referred respectively to the following situations:
A couple formed by future groom and bride flying alone with a pilot. Maybe that flight was used by the man to propose the marriage. Well, now you know it, that’s not a good idea, it could make the aircraft unstable (takeaway: no proposals in small aircraft).
Drug-trafficking. I can imagine such small aircraft being used to carry as many drugs as possible… well, apart from being illegal, if someone would carry too much (that is over 100kg), even when below the maximum allowed weight, would make it unstable.
Today, 17th December 2011, I made my first take-off aboard a Robin DR-400-120 .
As part of my training towards obtaining the PPL licence, today we performed the 5th flight, the first in which I was fully at the controls during take-off.
My colleague, Miguel, took the following video:
You may see the route we followed from Graulhet (LFCQ) to Toulouse-Lasbordes (LFCL) aboard the Robin DR-42 (F-GORM), as I recorded it with my Garmin GPS:
