Shortening a "stock" kit's nose...

[rafe_b]

I'm putting together my 2nd Blitz 400 kit (link) (http://www.steelheadproducts.com/Blitz400.htm) . The kit consists of three pieces of foam, two of which resemble wings, and one of which resembles a fuselage.

I'm working out the CG for this guy, and finding that the plane would balance better if I shortened the nose by an inch or two. At present, the fuse extends about 8" in front of the recommended CG line, and 6" from the wing's leading edge. (The wing chord is 8", wingspan 44", fuse length 27")

Anybody see any problem with shortening the nose? If anything, it seems to me that it would be desirable to minimize the inertial moment (from the mass of the motor, motor mount, prop and ESC at the front of the plane.

Generally speaking, with electric planes I set the final CG with battery position, but ISTM it's best if the battery (being heavy) can be located as close to the CG as possible. Shortening the nose on this plane would allow me to move the battery directly over the CG.

[HX3D014]

where are you going to put your tail servos? two or one ?

[rafe_b]

where are you going to put your tail servos? two or one ?

Ahh, good question. Two HXT500s, will be mounted near CG. First model of this type had (two) tail HXT500s, way aft; I think this was not my brightest idea.

So do you have response to my question?? Any adverse effects from shortening the nose (aka, bringing the motor/prop a couple inches aft?)

[JetPlaneFlyer]

There should be no adverse effect providing you are sure that you will still be able to achieve the correct CG without adding ballast.

[rafe_b]

There should be no adverse effect providing you are sure that you will still be able to achieve the correct CG without adding ballast.

Gotcha; the whole point of shortening the nose would be to help balance the plane. The weight distribution is like this: basic airframe is 6 oz. Motor, prop, motor mount and ESC are 4 oz. Landing gear about 1 oz. Battery is 2 oz. Four servos, about 1 oz. total. Aileron servos are on (or very close to) the CG. Rudder/elevator servos on fuse, near "cockpit."

When I do a mock-up/test run of this weight distribution, the plane is quite nose-heavy. I'd need to put the battery well behind the CG. If the nose was, say, 1.5" shorter, the battery could come forward to where it sits right over the CG.

ISTM, moving weight towards the CG is always a good idea, but I don't know what rationale there might be for having the motor/prop in a given (fore-aft) position.

[steelhead]

The beauty of the BLITZ airframe is that you can tweak it to your liking. The nose can be easily cut to your desired length. Because many people have different weight electronics, some have to tailor their noses to balance.

The original nose length was to be able to balance the plane with a geared speed 400 (see red/ pink plane pic)

Also, the twin prop version as seen in below photo had both motors and props closer to CG. (see black twin pic)

One thing that I think was talked about in a different thread of yours was to only use 36 inch long wing. Otherwise, you need to increase the tail surface areas. Too little tailfeather surface area will screw with stability. The plane's tail dimensions and moment were designed for 32 to 36 inches of wing.

If you still want some extra stability, add some dihedral.

Looking forward to seeing how the build turns out!

Dean

[rafe_b]

Hi, Dean -- thanks for that input. Dang, I didn't think to increase the area of the tailfeathers (except for the rudder)... but... Blitz #2 has a 44" WS (vs 48" for B-1), and B-1 is flying reasonably well these days (if a bit underpowered.) B-1 was a terror when I first started flying it, but I seem to be getting the hang of it.

I notice the white plane in the last photo does almost the same thing I want to do. Its motor is much farther aft than if it were mounted at the end of the stock fuselage.

[rafe_b]

Flew like a champ, in spite of a 3-8 mph breeze blowing most of the day. All-up weight is just a smidge under 15 oz. I ended up taking off about 1.25" of the nose, so battery sits smack dab over the CG. Landing gear still needs a bit of work.