I have a question from people with connection with the PAF. Mashshaaq is based on Saab Supporter which first flew in 1969, nearly half a century ago and has been in PAF service for nearly 40 years. Is PAF considering replacing it with more modern designs such as Pilatus PC-9?
Additionally Mashshaaq is a high wing trainer where most other trainers such as Tucano, Pilatus -9, Deepak etc. are low wing design. Is there any reason as to why PAF prefers a high wing trainer?
If PAF is going to replace Mashaaq it would be by Turkish HURKUS.
This is going to be an interesting read on high and low wing advantages.
High-Wing vs Low-Wing Airplanes
by Stephen Lewis
Anyone contemplating the purchase of a single-engine airplane has numerous factors to consider prior to committing to buy. Among the items that warrant attention are acquisition price, insurability, performance characteristics, hangaring, maintenance expenses (both recurring and unforeseen), and direct operating costs – among others. While all such factors are relevant concerns, another item deserving of due consideration is the wing configuration. Though many pilots believe wing position to be largely a matter of personal preference (which it is), there are several other characteristics that enhance (or detract from) a given layout. Below we'll examine the two most common configurations, high wing and low wing, as well as the pros and cons of each arrangement.
Stability
I've yet to meet the general aviation (GA) pilot intent on procuring the most unstable airplane on the market. If you're anything like the average GA flyer, you're on the lookout for a stable flying platform that responds predictably to control inputs and smoothly minimizes the occasional jostle from turbulence. As you might have guessed, wing placement and associated factors play an important role in the inherent lateral stability we can expect from a given configuration.
Dihedral: Wing dihedral is a design feature that contributes to the lateral stability of an airplane. Dihedral appears in the form of a slight “V†shape (as viewed facing the plane) that results from the gradual upward angle of the wings as they progress from root to tip. Look at a few planes and you'll see that dihedral is much more prominent in low-wing planes than in their high-wing counterparts. This difference is necessary due to the higher stability inherent to the high-wing configuration.
Why are high wings naturally more (laterally) stable? This results from the sideslip condition that occurs whenever one wing is raised (and the other is lowered) in flight. In high-wing planes, the location of the fuselage (below the wings) causes the relative wind to exert an upward force on the upwind (lowered) wing, therefore helping to return the aircraft to wings-level flight. With low-wing models, the fuselage leads to the relative wind exerting a downward force on the lowered wing, thus exacerbating the condition. Despite this inherent response of low-wing planes to sideslip conditions, the degree of dihedral designed into the wings effectively negates any issues with instability.
Fuel Load/Lateral Balance: Although dihedral can counter the less-than-ideal lateral stability of low-wing designs, it can't overcome the imperfections characteristic of most low-wing fuel systems. In terms of balancing and managing fuel load, high-wing aircraft have an advantage. Since the vast majority of GA airplanes store their fuel tanks in the wings, high-wing planes are able to use gravity to deliver gas to the engine. As such, a fuel pump usually isn't required, and gas from both tanks can be utilized simultaneously. By consuming from both tanks at the same time, the weight of each tanks remains about the same, which contributes to lateral stability.
Because low-wing planes store their fuel below the engine, they require a pump to deliver gas to the cylinders. This usually means only one fuel tank can be used at a time. While not a huge inconvenience, this shortcoming does require pilots to keep an eye on their fuel burn, both to ensure lateral balance and to avoid running a tank dry.
Visibility
Another important factor deserving attention concerns the visibility provided by each type of plane. High wings are great for spotting objects on the surface, but leave a lot to be desired in term of visibility directly above the aircraft. They also require pilots to raise a wing before beginning a turn – a precaution necessary to check for traffic at the same altitude. If your primary mission will involve air-to-surface photography or overhead inspection of powerlines/pipelines/city traffic/wildlife/etc, high wing is the only way to go. If you prefer to gaze at the stars or spot airliners cruising overhead, a low-wing model is probably worth a look.
While low-wing planes offer fantastic visibility at your altitude or above, they're terrible vehicles for checking out the activity below (From personal experience, I can attest that aerial photography flights in a low wing can be maddening). Though visibility is but one of many considerations, don't underestimate the impact it can have on your primary mission for the aircraft. (While we're on the subject, check out this
interesting story involving visibility and wing configuration.)
Obstacle Clearance
Though not a factor once airborne, bear in mind the potential for collisions during the surface phase of operations.
Taxi: High wings definitely have an advantage here. Most high-wing planes will have sufficient vertical clearance above such obstacles as fences, lights & signs, snow berms, tugs, and other low-level items. Low-wing flyers don't enjoy the same luxury, and must remain extra vigilant to avoid unpleasant encounters with nearby objects.
Ramp/Hangar: Once on the ramp or in the hangar, birds of a feather definitely should not flock together. This is especially the case at busy GA airports and in shared hangars. If high wings get too close to other high wings or low wings come too close to other low wings, hangar rash and swapped paint will be the inevitable outcome. However, a high wing the same distance (or closer) to a low wing will usually pass right over with nary a touch. If you'll be sharing a hangar with multiple planes (and whenever parking on a GA ramp), seek out the company of the opposite wing configuration to reduce the chance of an unpleasant encounter.
Landing: High wings and low wings are pretty evenly matched when it comes to landing. Low-wing planes will experience greater ground effect, which can be helpful during soft-field takeoffs & landings. However, pilots approaching with extra speed will float more during landing, in which case high-wing flyers have a bit of an advantage.
Another area to consider relates to crosswind components. Although many pilots consider low-wing aircraft to be more stable and easier to handle during crosswinds, such is only the case up to a point. With a significant sidewind, high-wing pilots are able to counter with more wing dip in the direction of the breeze. Try the same thing in a low wing and you're liable to scrape a wingtip on the runway. With this in mind, remember that you always have the option of diverting to an airport with a more favorable runway alignment.
Fueling/Cleaning/Preflighting
When it comes to prepping and preening your bird, low wings win hands down. To fuel a high-wing plane, you'll either need a ladder or should be prepared to climb (and balance) on the wing strut – not an easy task when you're wrestling a hose. Same goes for washing & waxing the wingtops. With low wings, these inconveniences disappear, as you can easily complete all of these tasks with your feet firmly on the ground.
Loading/Unloading
Though there's no significant difference between the two configurations as far as loading & unloading cargo is concerned (although it can vary from model to model), boarding and deplaning passengers might deserve extra attention, particularly for elderly or disabled companions. For limited-motion pax, climbing onto a wing and then descending into a cockpit – not to mention having to reverse the process to exit – can be incredibly difficult (if not impossible) steps. With the high-wing configuration, you're much more likely to be able to assist such passengers into and out of the plane. Additionally, high-wing planes usually feature doors on both sides, whereas many low-wing models have only a single entry & exit door. As an added bonus, overhead wings will help keep your passengers dry if boarding/deplaning during periods of precipitation.
Once of Many Factors
Ultimately, the configuration of an airplane's wings is just one of many aspects that merit analysis. Both layouts have their benefits and drawbacks, though many examples of each arrangement exhibit fine flying qualities. In your search for the ideal single-engine airplane, be sure to base your decision on the overall qualities of the options under consideration. However, don't ignore the potential advantages a given wing arrangement might bring to your unique flying objectives.
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