Practice airfield hopping
You've got your XC endorsement and looking forward to doing your 50km, but the fields are full of tall standing crops. This is where airfield hopping can be great fun and a very useful skill to master.
What is airfield hopping? |
Airfield hopping means keeping the flight within glide of at least one known airfield throughout the flight. This is a skill well known to mountain pilots where the terrain is unfriendly to picking a land-out field from the air. Instead the mountain pilot uses a network of known airfields, or designated farmers' fields, as stepping stones in a cross-country flight.
It also makes perfect sense to "airfield hop" when the crops are high in the flatlands. To airfield hop, we need to know the distance to each airfield from our current position, and be able to calculate quickly if we are safely within glide. This can be done by drawing circles on a map based on 7 - 8 km per 1,000 ft. (25:1) plus a safe arrival height. A more practical solution is use the "go to" function on a flight computer to display the distance to reach a given place, whilst cross-checking this value from a map. Although flight computers will also display data about glide angle or arrival height above the target (based on the glider's polar), these readouts should be treated with great caution by early XC pilots: Its better to assume 25:1 than let the flight computer base its calculations on the polar - which could turn out to be too optimistic depending on lift/sink on the way. There are also various "gotchas" depending on how the flight computer is set up, e.g. the "safety height" setting (height of intended arrival over the place). As a result, a rapid mental calculation is highly recommended. e.g. 14km to the airfield means I need 2,000ft to get there. If I'm currently at 3,000 ft, then I will arrive over the airfield at 1,000 ft (assuming there is no big difference in field elevations AMSL). This will hold true if flying in light winds or with a tail wind. However, if there is a significant breeze, we can't rely this calculation: These are days to stay upwind of the home airfield. |
Planning and flying the task |
Before the flight, you must get a briefing from the Duty Instructor to discuss your flight, have checked NOTAMs and have a retrieve plan in case you land away.
We need to ensure our flight computer is loaded with the airfields, such as those shown in the diagram. Some airfields will be included in the files already downloaded to the flight computer. Smaller airfields may need adding manually. We will also need the radio frequency where appropriate for each airfield (many small airfields won't have one) and have done our homework on what the airfield looks like from the air (CGC Field Book contains valuable information about many of our local airfields). Also mark up a map with the airfields and note the scale (e.g. how many km is equivalent to "one thumb"). If your planned route takes you near the Cambridge radio reporting zone, then its important to call Cambridge ATC as explained in the LoA. When using the flight computer initially, cross check the displayed distance matches one's expectations from the map. We don't want to get caught out by data errors. Its usually best to plan a flight on the upwind side of the airfield, possibly with cross-wind TPs, so that we practice working our way up-wind - And have a helpful tail wind if we need to retreat. When we start the flight our "go to" will the home airfield. Once we reach the edge of the glide cone back home, we can then switch our "go to" to another airfield. At this point, we consider our flight to become a cross-country where we are out of range of the home airfield. The new airfield becomes our new base and we ensure we stay local to that new airfield - Including retreating towards the new airfield if we lose height - And we don't find lift, then make a circuit and land at the new airfield. How exciting is that! Remember to read up the details of the Cambridge LoA if you are flying between GRL and Cambridge. Go to CGC website, members, log in, noticeboard, flight operations. |