Field notes on airframes

The Ritewing Zephyr 3/Spade. Read on to see why I'm talking about this.

Well, a combination of a lot of travel time and endless challenges has led me to think a lot about the airframe we have chosen for the project. We are currently using the Skywalker 2014 platform with both the 1900 and 1800 mm wings. This is a highly capable and flexible airframe that allows us to carry a large amount of weight, bulky payloads, and fly for in excess of an hour (under the right conditions). There are also other major benefits, such as a tail that is removable for transport. This does make the plane fairly portable, at least much more so than the old Skywalker that did not have this feature. That said, working with the Skywalker extensively in the field has allowed me to observe a number of weaknesses in the aircraft. The major ones are:

• Difficulty in breakdown – The tail is removable but this involves disconnecting servos and any other electronics and antennas which are mounted on the tail, making removal and replacement somewhat time-consuming

• Large size – Even when broken down the plane is large. The wing spar is the longest piece at over 1m long, requiring large transport cases

• Narrow flight envelope – Heavy AUW requires higher airspeed. Unfortunately, as with many large foam planes, the Skywalker has a pretty low VNE. Above about 21-22 m/s we begin to get serious flutter in the wings and tail which can (and has)  ultimately make the aircraft uncontrollable. At a cruise speed of 16-17 m/s, any steep descent (>15°) causes overspeeding. This is problematic, especially in the steep terrain we encounter here in Peru.

• Heavy batteries – A large plane requires large batteries. The plane has no problem carrying this extra weight but carrying a bag full of 6600 mAhr 4S batteries gets old fast

• Moderate durability – The plane is fairly strong but it does not hold up well to repeated rough landings which are, unfortunately, an unavoidable reality of working in places like this

So, with all of the issues outlined above, I started thinking about better airframes for what we do. No doubt the Skywalker or a similar aircraft (RMRC Anaconda, anyone?) has its place with us, as it allows for quite a heavy payload while maintaining endurance, but for travel missions like Peru and Belize I think we can do better.

My requirement for a new airframe is simple, address all the above concerns with minimal compromise. To make minimal compromise more specific, I will define it as the ability to still fly >45 minutes with a usable payload (point-and-shoot camera).

I honestly didn’t think such an aircraft existed until a few days ago when Tim sent out a link to an exciting new offering from Ritewing. For those of you who don’t know, Ritewing is a manufacturer of very high quality flying wings. The only problem is that none of their previous offerings could be broken down. Enter the Zephyr 3/Spade. The Z3 is a flying wing with a 1.2m wingspan, high wing area, a lift producing fuselage, and plenty of room to carry electronics, 8 Ahr of 3S, and a point-and-shoot. The boys at Ritewing claim to have flown (or be capable of flying based on mAhr consumption rate, I can’t remember) for 90 minutes.

So, having established that it meets my minimal compromise requirement, lets see how it addresses the issues that plague the Skywalker. First, it breaks down very easily. The wings detach quickly and there is only a single servo connector in each one. At that point the longest part is the wing spar, which I have to imagine is significantly less than a meter long. My hope is that the thing will pack down small enough to go in a carry-on sized case along with batteries and transmitter, but that may be getting a little optimistic. At the very least it won't need a 20 kg, 1.2 m long Pelican case.

The flight envelope should also be vastly expanded. While high cruise speed may still be necessary, the Z3 should be much, much stronger than the Skywalker, allowing for much faster flight without control issues. This would eliminate any overspeeding issues.

The Z3 can use 3S or 4S, but the guys at Ritewing seem to favor a 3S setup. When compared to the 13.2 Ahr of 4S that the Skywalker needs, the 8 Ahr of 3S for the Z3 seems downright measly. In fact, the flight packs for the Z3 should weigh less than half of what they do for the Skywalker.

Finally, the Z3 should be quite a bit more durable than the Skywalker. Flying wings in general tend to be more durable than traditional planes, probably largely because they don’t have tails to break off. The Z3 will also be laminated which, in addition to helping flight performance, should make the EPO Z3 much more durable than the non-laminated Skywalker. Finally, the significantly lower AUW should make it more durable simply by reducing the momentum present when banging against things. My hope is that the airframe is strong enough to finally make net recovery a possibility.

So, with all of that said, I’ll let you know that I ordered a Z3 kit which should be waiting on me when I get back to the states. It will give us a chance to evaluate it and see what we think and, hopefully, develop our new grab-and-go plane.