HK 1234 Spitfire

[octagon]

Hey Guys,
I have just finished assembling the HK 1234mm balsa Spitfire. I know there are quite a few in the club. The plans call for a CG of 90 mm from the leading edge, but it seems on the RC groups forum, 75 is the agreed on placement. To achieve that, using a 3s 3200 lipo, I have to add 3 3/4 of lead to the front underside of the motor mount. Is that something that is normal with this plane, and is 75mm about right?
Thanks in advance

[Frank v B]

Rob,


I have not flown this one but the best advice I can offer is the farther you can get the CG forward for the maiden flight, the better, especially in a warbird.  Warbirds have smaller tail areas and are more sensitive to CG errors.
The problem with a Spit is a nose-over on landing if it is too nose-heavy.  On the positive side.  A nose-over means you have had at least a semi-successful flight and an airplane mostly in one piece. 

Pick a busy day to maiden it so at least one person there will have had experience with the plane or one similar to it.

Frank

[sihinch]

Rob,

With the same motor and a 3S 3600 I add no nose weight. Not sure where by CG is but I will bring mine when you plan to maiden yours.

[octagon]

Thanks Simon. I have solved the problem by cutting a square hole in the firewall so the battery can go farther forward. Also should make for better cooling. I am switching to an Eflite 10 motor. 1100kv. Even when I propped down to a 9/6 it was making 620 watts. I could have just flown it around at 1/2 throttle, but you know, in the heat of the moment when you really want to make it rip. It was drawing 58 amps and it only was a 60 amp HK(ish) esc. Have to say though, that little 1400 I got from you sure rips. Oh, and I had another first. I decided to try a 3 blade Master Air Screw. I thought I had tightened it enough. applied WOT and after about 2 seconds the prop adapter and prop flew off, hitting the wall and shattering! Scared the hell out of me. Very glad I was behind the plane. Another lesson learned.

[Papa]

Funny how we all have to learn that lesson, nobody listens do we?


Jack.

[octagon]

Turns out that the MAS prop did not have the countersunk hole in the back face that allows the prop adapter to seat properly. This meant that the adapter did not tighten down on the motor shaft as much as it needed. I can say that after I put the new motor in and tested it, the propeller attached to the front of the plane was not going to fly off. Valuable lesson learned, and yes Jack, if I had not payed enough attention in the past, I certainly will in the future.

[Wingnutz]

I got my lesson from a 90 mm Changesun 12 blade EDF at full song. As the hub came off the motor shaft, it released all 12 blades...really quite exciting !