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topic: drogue (4 articles)

Larry landing today

Thu, Feb 10 2022, 9:33:03 pm MST

The drogue came along for the ride

drogue|landing|Larry Bunner|Peter Hall|video

Video by Peter Hall.

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Krys' Drogue Incident 8-15-21

Thu, Oct 7 2021, 10:43:50 pm MDT

New and untested chute

bridle|drogue|Greg Dinauer|Krzysztof "Krys/Kris" Grzyb|Larry Bunner|Moyes RX|triangle

Larry Bunner reports:

On 8-15-21 Krys Grzyb and Greg Dinauer set an 83km triangle task from Twin Oaks airport in Whitewater, WI east to East Troy, northwest to McDermott airport and then southwest back to Twin Oaks. Greg aborted the task early and flew back to the airport. Krys was doing well getting over 5200’agl on nine climbs. He tagged the first two turn-points and was headed back to the airport.

To this point he had been in the air for 2hr 15min of which over 1½ hours was above 4200’. The winds were 5-9mph from the southeast. Sustained climbs over 1000’ were averaging about 350fpm with one climb averaging 770fpm. He found a thermal just past the last turnpoint 18km out and climbed 300+feet to ~4400’. He needed about a 12:1 glide to get back with a crossing tail wind. He confidently left the last climb knowing he could make it and even if he hit increased sink, he would hit a thermal soon enough.

He went on a long glide sinking over 300fpm and was soon down below 1000’. He selected a narrow field of grass along a farm for his LZ. Approaching from the southeast at 500’ he unzipped the drogue pouch and began extracting it from the pocket. His intent was to deploy it near the ground but the drogue slipped away and accidentally deployed.

Immediately the glider turned right and his sink rate increased to 600+fpm. He pulled in on the control bar, the glider began to pitch down and the sink rate increased to over 900fpm (peak). Thinking the drogue malfunctioned, he reached back to grab the bridle but couldn’t find it. He instantly began to correct for the turning dive. With extreme effort the glider rounded out pointing downwind and just above the corn. The glider, slowed somewhat by the corn, whacked in hard but the glider and Kris were miraculously unharmed. Pretty shaken, he called to the airport to get a retrieve; Greg and Chico showed up quickly to help get the equipment out of the corn.

Krys has used a drogue chute for many years. This particular drogue was developed to train runners to improve their speed. It has one long bridle that runs back to the chute shroud lines. These lines are short relative to the length of the bridle. He used this type of chute for several years with the drogue deploying aft of the keel. This spring he purchased a new drogue from a different manufacturer and replaced his old worn one. He did not compare bridle lengths before installation. Up to this flight the new drogue had not been tested/deployed. After landing, Kris discovered that the keel had penetrated between the shroud lines and the drogue was affixed/centered around the keel.

The bridle length was a couple inches shorter than his previous drogue. When the drogue accidentally deployed, the position of the drogue effectively provided a lifting surface on the end of the keel. When the control bar was pulled in to increase sink rate, the forces on the aft end of the keel decreased the nose angle further thus progressively increasing the sink rate (to the point the nose was pointed at the ground). It took close to all of Krys’ strength to push the bar out far enough to overcome the resistance to level out the glider before entering the tall corn.

In the moment, he focused entirely on recovering the glider turn and descent and felt there wasn’t enough time or altitude to throw his main parachute. His Moyes RX 3.5 sprogs were at the factory settings. Corrective actions that Krys has taken or intends to take include: shorten bridle to prevent keel interaction, add an extra line to one of the shrouds and the harness loop to give access to the pilot to deflate the drogue, and adding a drogue release so the drogue can be cut loose from the pilot.

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Final approach

June 11, 2018, 4:27:38 pm MDT

Final approach

With a drogue chute

drogue|Facebook

Aerotow paragliders

Sun, Jun 1 2003, 2:03:03 pm EDT

aerotow|altitude|bridle|David "Dave" Glover|David Glover|drogue|electric|government|harness|job|Lighthawk|Mark "Forger" Stucky|Oz Report|payout winch|PG|power|powered|powered PG|PPG|Quest Air|sailplane|Stuart Caruk|Stu Smith|tail|technique|tow|towing|trike|tug|winch

Mark Stucky <stucky_mark@hotmail.com> writes:

I just noticed the discussion on the bigair paragliding forum regarding the recent paraglider aerotowing shown on the Oz Report. For several years I've occasionally put thought into the conceptual design for aerotowing a paraglider. I really think the future is in aerotow and discussed the issues some with David Glover (who is also very interested in it for big meets) last September at the Tehachapi sailplane fly-in. I wish we could have talked more but most of my attention at the time was dedicated to the Lighthawk flying debut.

The obvious issues with aerotowing are the slow flying speed of a paraglider and the relatively small amount of pitch and airspeed control available. Some comments on the web about concerns with the vertical distance of the canopy from the tow point are not that big of a deal due to the low thrust and drag forces involved. After all, if a paraglider couldn't handle 80 lbs of thrust near the CG of the pilot then powered paragliders would not work either!

I see three methods for aerotowing a paraglider.

Method 1: The obvious solution is a tug that tows at a compatible speed and climb rate. This method would involve conventional "follow the tug" procedures and a fixed length of towline. While having a PPG or powered PG trike arrangement has some appeal due to their slow flying speeds, I think they will cause more problems than they solve. I think a better tug would be a fancily flapped ultralight or a very large yet lightweight hang glider trike. Until such an exotic tug is designed we will have to make due with exotic procedures.

Method 2: Perhaps the best solution for paraglider aerotowing is to make a lightweight payout winch that can handle 2500 feet of spectra. Until we can get the tow airspeed slow enough to match the speed the paraglider pilot would like we will need to figure out how to handle a speed differential. With a payout winch you could use existing tug aircraft with procedures similar to a ground payout winch tow, the paraglider could simply climb up behind the tug without regard to maintaining the same relative altitude as the tug.

Let's assume we can get a tug that can tow at 45 feet/sec (30 mph) and have a paraglider that wants to fly at 30 fps (20 mph) for a differential speed of 15fps. I think a comfortable climb rate for a paraglider from a ground tows is 500 fpm. If the tug was also climbing at 500 fpm then the total climb rate of the paraglider would be 1000 fpm so a two minute tow to 2000 feet AGL would require 1800 feet of tow line (plus whatever amount you initially laid out). The benefit of an aerotow winch would be that you could use a small field and any wind direction instead of being tied to a long road.

Additionally, the tug could tow you to a thermal although once the line pays out beyond a few hundred feet the tug will be limited to shallow banks or short, quick turns (similar to ground circuit towing). The winch would have to have some kind of rewind capability and a small drogue to ensure it couldn't recoil into the tug's propeller.

Method 3 is obviously not for the faint of heart and requires advanced skills at both ends of the towrope. It is designed to make due with existing tow aircraft and uses a small fishing reel as a short duration payout winch. One way to manage a small speed differential is by using differential bank angles to fly concentric arcs with the paraglider flying a slower speed on the inside of the turn.

Stu Caruk's comments about delivering a bag of goods from a Cessna by hanging it out a window and flying circles around it has some merit. I was once involved in a government program that built upon that technique in an attempt to hover a small spy package several feet off the ground. The package contained sensors and fed position and altitude information back to the aircraft that was equipped with an exotic hydraulic winch which would make the fine high speed in/out corrections to the tow line while the pilot make the rough corrections by following guidance to fly an exact arc thousands of feet overhead. The program got cancelled and I sure wish I could have figured out a way to get my hands on the winch and the 10,000 feet of spectra!

To tow successfully without a high capacity payout winch, we need to manage not just the airspeed but also the climb rate, turn rate, and rope length. To manage the rope you need to first start with the proper length of towline. Too short of a rope and the workload is too high, the allowable lateral/vertical errors too small, and the probability of a lockout is too high. If the rope is too long then the turn circles are no longer concentric and havoc will quickly result.

We need to fly the proper arcs at an angle of bank that does not require extraordinary piloting skills or decrease the climb rate excessively. This means we need shallow bank angles so we can increase or decrease them as required without generating excessive turn rates that would be impossible to manage in a tethered relationship.

Successfully aerotowing a paraglider with this method requires a change to the traditional paradigm of towed flight in which the glider must dutifully follow the tug. Both the paraglider pilot and the tug pilot will have to abide by a pre-coordinated plan for dealing with the continuous corrections that will be required. In the absence of such an advanced plan, the aerotow will be short-lived.

If our 45fps tug flew at 13° bank then his radius of turn would be 275ft at a leisurely turn rate of 10° per second. To achieve the same turn rate with the 30 fps paraglider, it would use 9° of bank for a radius of turn of 178ft. At these conditions I computed a 160 ft towrope as optimal. Under these conditions the paraglider is approximately 45° off axis from the tug (i.e. with both aircraft in a left handed turn, if the paraglider is pointed north, the tug would be pointed northwest).

While this would normally be disconcerting to a tug pilot used to conventional aerotows, it is possible to tow with the line leaving the tug at a 45 degee angle (and only 70% of the tow tension providing thrust to the paraglider). As always, though, the paraglider pilot should strive to keep the towline square to the harness and canopy. Note that if the towrope was routed to the tug's tail then the drag of the paraglider would always be trying to pull the tail inline with the glider and the tug would have to have sufficient rudder power to counter the torque of the off-axis tow or else have some sort of CG/bridle hook up.

If both aircraft are climbing out at the same rate then everything is perfect but chances are there will be some errors. Here is where the pre-planning is required. If the tug is climbing faster than the paraglider, then the paraglider should decrease its bank slightly to increase its speed and climb rate. If the paraglider is climbing above the tug (more likely) he should increase his angle of bank to cut to the inside. Here is where a smart tug pilot will make or break the tow.

He needs to evaluate if the paraglider pilot has been doing a good job and if it has room to make the required correction. If the paraglider is slightly out of position but correcting back then the tug may just observe. If the paraglider pilot is already in the planned position (about 45° inside the turn) then there isn't much more he can do and the tug pilot should either throttle back or increase his bank angle to decrease the climb rate. His course of action should be based upon his interpretation of the paraglider's 3-D position and heading (if the paraglider has dug far inside the turn and the tug turns harder then the paraglider will have to deal with a huge change in heading and possibly even slack line).

If the plan is properly coordinated and well flown by both pilots then a small payout winch could be mounted on the tug. The purpose of the winch would be to handle short periods of excess tow pressure. The winch could simply be a large fishing reel with some pretty small towline (or large fishing line - depending upon your point of view). I'm not a fisherman but I think you could get a commercial product with 500 feet of line that only weighs a few pounds.

You would set the drag for say 20% more than the planned tow force and it could handle short periods of time while the aircraft are transitioning back to the proper positions to reset the planned steady-state conditions. A small electric motor could wind the line back in at the completion of the tow. The reel should be mounted in the field of view of the tug pilot and the line could be routed through guides or pulleys to route it clear of the propeller.

(editor’s note: I believe that all of these methods are being looked at and attempted in some cases at Quest Air.)

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