Kitfox Iv 1450 gross

[Dave F]

did not know they went this high on Gross weight ?

[rogerh12]

Regarding increasing gross weight on a Kitfox-4:

A while back, I proposed building a Kitfox Model 4-1200 with a gross weight of 1250 lbs. I justified this because the current load specification with an ultimate wing loading of 7200 LbS (1200 lbs x 6 G’s) would become an ultimate wing loading of 5.76 G’s at a gross weight of 1250 Lbs, which still placed the kitfox within the “NORMAL “ category for wing loading as outlined in FAR Part 23. For example, if this was a certified plane and the Kitfox was designed to comply with the FAA specification for NORMAL category, it would need to operate at 3.8g’s, and be built with a safety factor of 1.5 (as outlined in FAR 23.303), which corresponds to a ultimate positive G load of 5.7. As mentioned above, at a gross of 1250 Lbs, the model 4 would have an ultimate wing loading of 5.76 G’s. However, having said all that, a 1250 Lbs gross kitfox was kind of boarder line. But then I had a better idea, and it relates to the float plane:

I have an old Denney news letter outlining the evolution of the kitfox, starting with model- 1 and ending with the model 4 speedster. This document outlines the speedster as being “capable of positive G aerobatics, ultimate load limits of 9 G + and 4.5 G –“. I noticed that the model 4 speedster has a shorter wing, and that it is rated with an ultimate load limit of 9 G’s at an operating gross weight of 950 Lbs (for aerobatics). This corresponds to an ultimate wing loading of 8550 lbs with the shorter wing. So, if I figured on using the shortened speed wing, the kitfox- 4 at a 1250 lbs gross would now have a ultimate positive wing loading of 6.84 G’s, which places it well within the NORMAL category with a safety factor of 1.8. In fact, with this level of safety factory, the kitfox 4 COULD be operated in the UTILITY category of 4.4 G’s, and still have a 150% safety factor.

Regarding the float plane: Using these calculations, a Kitfox Model-4 could be operated with a 1450 gross, but only with the speedwing (5.9 G ultimate). Of course, whether or not the landing gear would take it is another question. Though, with the speedwing installed on a 1450 gross plane, it might take you a while to get off the water !!!!

Hope this helps
Roger

[DBVZ]

Odd it got to 1450, unless it was a mistake or before LSA. I would have expected the builder to keep it LSA legal. Builder sets the max gross. Whether it is reasonable or not is something else. That engine should be able to make 1450 get up off the water, so it becomes an issue of if the reduced structural margins are reasonable. And if the extra weight will give it a higher than normal stall speed. Again, under LSA rules no more than 45kts.

As you know, the definition of “light sport aircraft” is found in FAR 1.1

Light-sport aircraft means an aircraft, other than a helicopter or powered-lift that, since its original certification, has continued to meet the following:
(1) A maximum takeoff weight of not more than—
(i) 1,320 pounds (600 kilograms) for aircraft not intended for operation on water; or
(ii) 1,430 pounds (650 kilograms) for an aircraft intended for operation on water.

[rogerh12]

Good Catch Dwight;

Oh what a difference that extra 20 lbs can make !!!!
Now it can NEVER fly light sport again (at least not in the USA).

Roger

[DBVZ]

PS: I have seen an Avid Mk 4, Heavy Hauler, with a max gross of 1320. The HH wings are supposed to be 1150. People often go to 1200 to match the Kitfox 4, or even 1250; but 1320 seemed rather high. Builder decision though. In that case it was powered by a 582 too.