Crofter 24" simple glider: revisiting my first ever model plane

Most aeromodellers seem to have memories of one sort or another about the first plane they ever built. As advertised in a previous post, my first attempt was a Crofter glider by Ian Barret published in Aeromodeller in 1973.

 

As a boy, the build felt like I had slaved away for ages to produce a small glider. While I had a sense of satisfaction, trimming and launching it properly evaded me. I had no real support for that, and didn't know who to ask. This was obviously pre-internet. I was 11y old and although I managed to get it to release off a hand tow launch, the overwhelming feeling was of frustration. 

I've always wanted to revisit this model. With the benefit of some years of experience of full size gliding, building chuck gliders and many other models, construction this time round was really easy, taking me essentially one evening. The decoration and ballasting happened the next day. Here's a picture of the final model. 

Who doesn't like tissue flames?! Perhaps they signify my boyhood frustration with this thing! 

Today, I'm an experienced aeromodelling chappie and I see two main issues with this design. Let me start with the weight: 

Wing: 12.3g

Fuselage: 11.9g

Stab: 2.3g

Ballast and rubber bands: 13.9g!!

AUW ready to fly: 40.4g

The built weights of the wing, stab and fuselage are pretty good, but that is a massive amount of ballast required to achieve the plan-marked CG of 38mm behind LE. It indicates a heavy tail, a long lever arm, a short nose, a forward CG, or all of them! 

Not surprising then that first glides from the shoulder indicate to me a higher wing loading than even most of my chuckies! It's stable due to the CG and dihedral, but has to glide relatively fast compared to really lightweight tissue and balsa gliders. On the other hand, it seems to react well enough to the air, so it should thermal - that is if I can get it to launch and turn on the glide (without using auto-rudder and such). I've started with the tow hook a little bit further forward than indicated on the plan:

The second issue I see with the design, is the ease with which this wing can warp. Nothing wrong with a Jedelsky style wing (reminiscent of the Cloud Tramp rubber model, but also some really high performance free flight models of the past), but the Crofter's wing is not very "stable". Trimming becomes interesting, as one day it will turn left, and the next day right. This is purely because of the twistability of the wing design. It's like it has random ailerons! On the plus side, you can eyeball it quite easily, and steam changes in. Whether the changes stay in, only time will tell! But at least I know what I'm doing now with trimming, balance and warp changes. You can see a little stab shim in the photo above. If I had the trimming information guidance or sources as a kid, I think the model would have been a good teaching aid for aeroplane control surfaces. 

As I write this blog, I wait for good weather to maiden it on a small high start. It's gonna be fun! Whatever happens at the maiden, the catharsis of the build has been worthwhile already. Whether it zooms off to one side to crash sickeningly, or the wings fold in flames on its first high start launch, I've already tucked all that childhood frustration to bed. Basically, I understand what's happening and why at every step. That's such a good feeling.