Webmaster's Note: More from Rob Lake at Lake Aviation - this time on gross weight.

Michael's Question:

Now that the XL-65 has a gross weight of 1060 lbs, do you think that the 582 will start to be taxed like the 503 was previously at 960 lbs? What do you think the performance will be if you’re on floats, two up, at high altitude on a hot day at close to gross weight?

Rob's Answer:

The challenge with all airplanes is to keep the empty weight as low as possible. This maximizes the payload and performance. However, demands and requirements have changed over the years and modern Challengers are heavier than they used to be. The manufacturer has recognized this weight growth and has responded with design improvements to increase maximum gross weights. The maximum takeoff weight has increased from the original 800 lbs to 960 lbs and now to 1060 lbs with the XL-65 model.

The original Challengers back in 1983 had no doors, no brakes, no streamlining fairings, no radio, no electric start, no battery, no lights, no heater, and so on. Needless to say they were very light weight! Many of those features are now considered mandatory by owners especially in Canada and the northern United States. Obviously this has increased the empty weights! Add to this long range fuel tanks plus pilots who aren't getting any thinner and...

The problem with all virtually all two seat airplanes is that when equipped with floats they essentially become single seat aircraft during the hot, humid summer months. Likewise four seaters become two seaters, six seaters become four seaters, etc. Performance suffers and even becomes dangerous.

The 65 HP Rotax 582 helps eliminate this problem with extra power. A Challenger with a 582 on floats flies like a Challenger with a 503 on wheels. In effect it flies like it is not on floats at all. Last fall I flew a customer’s Challenger 582 on amphibious floats with a full 17 gallon fuel tank and with him in the back seat. We climbed out easily at about 600 fpm. I was really impressed by the performance of this Rotax 582 equipped Challenger on floats. Earlier in the year I test flew a new Challenger 582 on wheels and it climbed out so fast that I overshot circuit height by 200 feet and this was before even getting to the downwind leg! It made me laugh out loud!

The more powerful engine is not the only reason for the increased gross weight on the XL-65 though. The XL-65 features a heavy load saddle kit that strengthens the connection where the main lift struts attach to the fuselage. The kit essentially spreads the pull forces from the wing over a wider area where the strut bolts attach to the longeron. So the wings are therefore able to pull on the fuselage with more force with the high load kit. This kit is available for retrofit on any Challenger but it will not increase the gross weight of older Challengers.

Very importantly the XL-65 now has the fuel tanks in the wings as a standard feature. The wings have been redesigned internally for additional strength to accommodate the two 10 gallon wing tanks. Having the fuel in the wings means that the weight of the fuel formerly in the fuselage does not have to be supported by the wing to fuselage attachments or by the strut to wing and strut to fuselage attachments.

Finally, both the XS-50 and XL-65 models have a completely redesigned landing gear. The welded steel cuffs that support the gear legs have been heavily reinforced. Formerly the steel cuffs were two separate units that sat around the two large fuselage longerons. Now the two steel cuffs are connected together with a welded steel cross brace that spans the width of the fuselage. In addition, the cuffs are supported by triangular welded steel support rods that are inside the fuselage. These supports brace the gear leg cuffs from forces encountered during landing and taxiing across rough terrain at the higher gross weights.

So, these four new features: more horse power, the heavy load saddle kit, the wing tanks and the beefed up landing gear, all add up to the higher allowable gross weight of 1060 lbs for the XL-65 Challenger model. This makes the XL-65 Challenger ideal for use on floats. It will perform better than any aircraft in its class with two people on board, even on hot summer days.

The XS-50 model has the new landing gear primarily to benefit operations on rough surfaces. Even with the heavy load kit and the optional wing tanks the XS-50 is limited to 960 lbs and is not suitable for floats due to the smaller 503 engine and the 26 foot clipped wings.

Your pilot training taught you about density altitude and its impact on takeoff and climb performance. All this having been said, it is always wise to keep a circumspect eye on your gross weight, especially when its hot, humid and/or you are operating at high altitudes.