Lecture - 25
Canards and Flying Wing
(Refer Slide Time: 00:15)
Another feature that we would like to understand is a canard, a canard is basically a tail mounted ahead of the aircraft rather than a conventional tail mounted behind. One of the advantages of providing a canard is that the trim surface or the canard carries a positive load for positive g maneuvers and that helps in reducing the load that the wing has to carry.
Secondly a canard reduces the subsonic supersonic aerodynamic centre shift.
We all know that the aerodynamic centre shifts from around a quarter chord location for subsonic flight to approximately 0.5 chord location in
supersonic flight. This causes a huge stability issue and if you have a forward swept wing, then by putting a canard this particular
subsonic supersonic aerodynamic centre shift is minimized and if you make it if you design it properly, then C L on the canard can be much higher than on the wing and that is very much beneficial.
But there is an always a drawback one drawback is that your primary lifting surface which is the wing is now going to be in a downwash or a disturbed flow from the canard and with the canard it is not easy to obtain high angle of attack and lateral directional characteristics. So, the question is when do we use canards, canards are recommended when you have a severe
supersonic cruise or transonic maneuver requirement and also is not a consideration because the canard in the front is going to reflect immediately and it is going to reduce the stealth characteristics of the aircraft.
(Refer Slide Time: 02:14)
Then, there is a question that many people want to know is why we have something like a flying wing where there is no fuselage or there is no distinctive fuselage as can be seen in the photograph of this B 2 stealth bomber the spirit aircraft. But flying wing concept is not a new concept. Actually, Northrop has been trying to advocate use of flying wings since many, many years. Let us look at us historic film about a flying wing configuration.
(Video Starts: 02:52)
Germany is a machine of color it did not affect a pair of rigid wings or to turn it off another famous machine 500,000 pounds if necessary, is being tested for stability. A striking picture of the machine in flight before the fuselage landing on a single wheel completes a successful experiment.
(Video Ends: 03:43)
So, it is not a new concept as many people think, by removing the fuselage, you improve the aerodynamic efficiency. However, distribution of the payload volume is still a problem, because you will have a bulbous thing a bulbous area in the centre where you need to distribute the payload. But if you are providing a relaxed static stability, then this configuration gives you a synergistic effect in military aircraft.
A flying wing gives us stealth and that is the principle the reason why the B 2 bomber has a flying wing configuration in commercial aircraft a flying wing allows us to distribute the load all over the structure and that can lead to reduced weight. However, the centre of gravity range is a huge compromise and that can be a real problem. Thanks for your attention we will now move to the next section.
Lecture - 26
Three Surface Aircraft
(Refer Slide Time: 00:15)
Now, one more option that you have and you see sometimes is a 3 surface layout or a 3 surface aircraft. Now, the question that somebody will ask is that if you can make a design with only 2 surfaces, then why use 3 surfaces, because it adds cost, it adds weight and it gives you a larger wetted area. So in a 3 surface layout as can be seen in this picture, you have 1
surface in the front which is a canard, the second one which is the wing and the third one, which is the tail, this is why we call it as a 3 surface layout.
So obviously, there must be some benefit and the principal benefit is that because there are 3 surfaces, you are able to trim the aircraft with near minimum drag over a much wider centre of gravity range. Because you can load or unload each of the 2 extreme surfaces to allow creation of the moments required to balance about the centre of gravity. And secondly, if you do it very carefully, and if you design it very carefully, efficient component integration can actually save weight.
If you notice in this picture, for example, the wing of this aircraft Piaggio P 180 Avanti seems to be a much slender and smaller compared to a typical wing that would be needed for an aircraft of this particular type.
(Refer Slide Time: 01:46)
So this particular aircraft GP 180 has earned the epitaph of the Ferrari of the skies. This is a image of the aircraft taken from the bottom and many people would think that this aircraft is flying from right to left because they see the engines mounted in that fashion. But actually it is flying from left to the right So I think it is very important for us to get familiar with this very interesting aircraft is one of my favorites, so I thought it is better we watch a short promotional film about this aircraft.
(Video Starts: 02:23)
The original Piaggio Avanti P 180 twin turboprop pusher first flew in 1986 was certified in 1990 yet it is 2001 model still looks as futuristic as it did more than a quarter century ago perhaps not surprisingly this aircraft is still economically in a class of its own. The small forward lifting wing means that the rear horizontal stabilizer is also lifting surface resulting in
a 34% decrease in main wing area deepening the fuselage itself is shaped as the aircraft total lift.
The narrow chord wing ensures that the laminar flow is maintained around 50% of wing chord compared to around 20 to 25% for conventional tractor turboprops where the propeller wash disturbs the air flow over the wing and underlying reason for its ability to maintain laminar flow is the quality of the surface finish. Over the Avanti’s 90% element in alloy, the fuselage and wing look like they are molded from composites because they are constructed
with airframe panels held in place in the check during assembly by large vacuum pass.
Some frames and ribs can be riveted from the inside. This makes for an exceptionally smooth finish and reduces drag. The result is that the Avanti’s of the superb performance for turboprop, a cruise 41,000 feet with a cabin altitude of only 6600 feet, cruising around 353,360 knots in the high 30s with a fuel burn less than 300 pounds per side and a range of close
to 1450 nautical miles, which means you can fly 1000 nautical miles and a little over 3 hours burning just 1600 pounds of fuel.
The aircraft is certified to catch up to instrument landings, steep approaches and flight into known icing and the Avanti has the ability to operate on short runway lengths around 1070 meters at maximum weight. This airframe has also been recertified to increase maximum
takeoff weight to 12,100 pounds, allowing an, extra 2 passengers at the maximum fuel load.
The cabin provides a stand up height of 1.75 meters and the weight of 1.85 meters, dimensions only bettered by super midsize jets.
The cabin can seat up to 9 in a corporate shuttle out but typically seats 6 in this VIP role with a half toilet. The Avanti is certified for single pilot operation the Avanti is a DC electrical aircraft with no aptitude but you can use an external power cart to load the FMS price start or engine start and run switches are centrally located in 1 panel before the end of the centre
console just to handle the throttles.
A rotary test switch on the base of the console is used to check all ancillary systems such as hydraulics, electrics and de ice, and the aircraft can be ready to taxi in 3 to 4 minutes after engine start. Avionics include weather, radar, traffic avoidance and tours, in addition to 8.33 megahertz VHF radius precision on F and V now, this P 180 also has the optional HF radio.
Avanti was introduced this avionics upgrade of the P 180 Avanti 2 turboprop pusher.
The Avanti 1 remains; that have to proposition with its load appreciation and combining with its perfect cabin and low operating costs. The Avanti has no natural turboprop competitors this closest jet rivals being the rating premier 1 and Cessna citation CJ 1 and 2. If pure top speed is not the overriding criteria, the Avanti is combination of fuel efficiency, cruise speed,
range, sealing and cabin size are hard to beat. The aircraft deserves its Ferrari in disguise and can hold its own against a similar size jet.
(Video Ends: 06:47)
So that was about the Ferrari of the skies. What are the design features of this aircraft which make it very distinctive?
(Refer Slide Time: 06:56)
First of all, it has high aspect ratio wings. As you can see in this picture, very slender wings and the engines are mounted behind the pusher engines which result in a very quiet cabin.
(Refer Slide Time: 07:10)
It has got anhedral in the canards you can notice here, one can notice here that the canards are mounted at a slight 2 or 3 degree downwards angle.
(Refer Slide Time: 07:24)
We also see that the canards, has flaps. It is very clear in this particular figure that these canards have flaps you can see here.
(Refer Slide Time: 07:36)
You have delta fins on the aerofoil shaped fuselage. So, the fuselage itself, you know, is very beautifully shaped, as you can see, it is shaped like an aerofoil and you have these delta fins.
These fins enhance its lateral stability characteristics.
(Refer Slide Time: 07:53)
And interestingly, the passenger cabin is mounted ahead of the wings, the wings are mounted behind the passenger cabin and the engines are mounted behind the wings. So, you have unrestricted view for the passengers, you know, the view that is available to the passengers is
completely unrestricted on both sides plus the location of the engines behind results in very low noise levels. Thanks for your attention we will now move to the next section.