SC-7 Skyvan Skydiving Aircraft
Just like the Twin Otter, the Shorts Skyvan is a very purpose built aircraft! Ruggedly built to haul bulky loads out of short unimproved strips. Affectionately called “the shed” by pilots and crew the Skyvan is a strut braced high wing aircraft with a fixed landing gear. It features a 18ft 7in long and 6ft 6in high by 6ft 6in wide cargo hold with an equal size in-flight opening cargo door.
Most Skyvans are SC7 Series 3 Aircraft with a MTOW of 12.500lbs, other Variants like the 3A and 3M sport up to 13.700lbs MTOW. There is also 2 different versions of Engines on the Skyvan. The original engine is the single shaft Garret TPE 331-2-201A. Some Skydiving Skyvans have the Super-2 or -6 Engines that feature a larger Compressor which greatly enhance hot-and-high performance of the A/C, as well as climb rate.
The Weight and stability of the A/C, as well as the incredible low speed performance (Stallspeed@8500lbs and Flaps 50 is as low as 49Kts) make it a pretty easy to fly aircraft. However to fly the Skyvan efficiently there are a few things that differ from other skydiving aircraft.
Weight and Balance
The placement of the wings on the fuselage was designed in such a way to give a very wide allowable range of CG and thus maximum flexibility for loading the airplane. It also means there is about the same amount of cabin ahead as is is aft of the center of the CG range. For the Jump Pilot this means the less jumpers that are on the plane the closer to the door you want them, to ensure that the C/G is not too far forward and thus your climb performance suffers. In a no seats/sidewall bench configuration, seating 3 abreast looking aft you will not be able to physically put too many people too far aft (unless they sit on top of each other) so there is no need to worry exceeding the aft C/G limit. The Step into the cockpit is a favorit seat for a lot of skydivers, but remember it’s a two man cockpit and you really don’t want anybody sitting there. Aside from the lack of a seatbelt, a person sitting there can reduce your rate of climb by 200ft/min!
The airplane has also 2 structural weak spots that any pilot should be mindful of. The first being the Nose landing gear attachment points. These get a lot of stress when using differential brakes, whenever the tiller angle doesn’t match the rate of turn, nose wheel shimmy or during towing.
80% of skyvans got written off with a broken Frame 22 where the nose landing gear attaches. Taxi carefully and corner slowly and generally treat the nose wheel like a raw egg and the aircraft owner / maintenance will be happy with you.
The second weak point is the Flaps. Specifically the way of where the flap actuation push rod attaches to the flap. Apparently the flap actuation was design for a large single flap which later on got split into 2 flap panels which now have very asymmetric actuation. Do not use flaps at high speeds, it is strongly suggested to reduce flap extension speeds well below the allowable speed as per the AFM. Don`t use flaps more than neccesary.
The Engines have very nice handling qualities being single shaft. But you have to take extra caution not to exceed EGT limits on takeoff due to the lag in indication. As a rule of thumb above 15°C OAT you will most likely be limited by EGT and not MAX Torque. The aircraft has “Scheduled Inflight Torque” Placard in the cockpit, this can be used to estimate the target Torque for takeoff by using teh inflight scheduled torque for the indicated temperature and altitude and subtracting 2 PSI. This Torque setting should get you right at the EGT limit but not over it.
Speed Speed Speed! Like any big aircraft it takes a while for a Skyvan to accelerate from unstick speed which should be never lower than Vmca, to take-off safety speed. Depending on Weight and flap setting on departure KNOW YOUR SPEEDS ! We have made a placard that fits into the recess of the instrument panel just forward of the control column that contains all the necessary speeds at 8, 10 and 12.500lbs. At MTOW your performance margins are pretty slim when you lose an engine..
Another area where pilots mess up is that they climb at the wrong airspeed for Best Rate Vy. Not too fast and not too slow. In general Shorts did a real good job when they wrote the Airplane Flight Manual, the speeds and procedures laid out there will give you max performance in all relevant situations. Coordinated flying is extremely important as the huge fuselage side area of the “Shed” will produce tremendous amounts of drag with any slip or skid. Climb performance is better if you keep your bank angles low, apart from making it a more comfortable ride for your passengers. If you can, stay away from built up areas as much as possible, because a Skyvan with 100% RPM produces quite some noise.
Depending on Weight the jump run can be flown at an indicated airspeed of 95-75KIAS. Normally you would start the jump run at the climb speed for the appropriate weight and set it up so that the airplane is slowly decelerating throughout the jump run, getting to about 80-75KIAS as the airplane gets empty. with this procedure the use of flaps is not necessary.
Now that the jumpers are standing up in the airplane you need to worry again about your C/G! Maximum number of people in the door should be 10 Jumpers! This number is already pretty uncomfortable as you will be very close to the forward stop of control column travel. Generally you can say as many people as in the door should be behind the mid cabin for balance reason. This requires a bit of briefing for larger RW exits. To get anything bigger than a 10 way out of the door at once you need the ones further back in the plane start towards the door at SET, so that they all leave the plane at GO, without making the plane uncontrollable.
And that is what happens if you put more than 11 poeple into the door, you will hit the forward stop on the elevator, with the airplane continuing to pitch up. Eventually the jumpers will exit/fall out but by that time you’re most likely fully stalled and part of their formation.
Jump run power settings are typically around 30 lbs. Torque. I usually reduce RPM to 90% thus cutting drag when you gradually reduce Torque when the plane gets lighter as well as for noise abatement.
If you do any maneuvering during your jump-run be gentle on the controls and remember that coordination is essential! 25° bank does not bother when you are standing up in the back of a skyvan, an uncoordinated turn makes you want to have handles to keep upright.
Descend at Flight Idle, 90% RPM and Vmo of 173Kts. You will find yourself in a 25° nose down attitude with 5500fpm rate of descend with your elevator trim in neutral (That’s how heavy that nose is). You can get even better rate of descend with a higher RPM setting but anything more than 90% will make folks on the ground go berserk (at least in Europe), i even go to as low as 85% RPM which is the minimum in flight setting. Be careful though when you come in for landing with reduced RPM, you will have less drag so you need to plan a bit further ahead to get your speed down for flaps extension. Also coming in light for landing 90% RPM is quite sufficient for a go around, at 85% you will not have enough power to go around and when you increase RPM you will momentarily increase drag quite a bit, so take care if you reconfigure.
If you think you are way too high for landing just go full flaps, 80Kts and 100%RPM. The result is spectacular but beware you will need most likely power to arrest descend rate and the A/C will not flare with 100%RPM but rather you only rotate to touch down attitude.
Lastly, PROCEDURES, PROCEDURES, PROCEDURES!! Know your procedures for all emergencies and malfunctions.
Our Operation is based on a “flow” where you basically start at the ceiling on startup and end up having all systems switched on and ready for engine start. After shutdown go the same way back. The A/C is extremely simple to operate and during normal flight ops you will only need the column, power levers, rpm levers, flap lever and the nose wheel tiller. However any abnormal should be handled with a checklist and the essential tasks of Emergency and Abnormal Checklist have to be memorized! Learn your airplanes systems with special attention to the electrical system. It’s the most complicated and failure prone system on the Skyvan but also when you understand its operation it gives you incredible redundancy.