I have had an interesting email from Brian Lever, whose building of the Gripen is featured earlier in this thread.
Above: Brian's Gripen before flight tests. Looks good!
Brian is an experienced rocketeer, so I was looking forward to hearing about his flight tests. Brian writes:
"The model initially wallowed from left to right on test glides [this from a hand launch]. I introduced some small washout by cutting out and elevating the ailerons. This can be seen in the attached photos. This made some improvement but did not eliminate this characteristic altogether.
Nevertheless, I decided to make some power on tests using old green case Rapier L1 motors as they do not have excessive fizz for test flights.
The model did make some reasonable flights (of sorts), but wallowing was still present and although I made adjustments to the GG, ailerons, and motor thrust line I could not obtain any consistency".
This afternoon I have spent a good amount of time trying to achieve a fast, flat straight glide in my garden, and after half an hour or so of experiments I achieved this rather difficult objective.
Above: Brian's Gripen showing the very enlarged fin and extra dihedral the main plane required for a decent glide. Brian comments, "Not very Scale!!"
Brian continues: "Whilst the additional fin area helped the glide, it was only when I increased the main plane dihedral that I obtain any glide consistency. The model also required a very good launch (directly into wind, everything level at the moment of release and just the right amount of speed to consistently glide well. It certainly isn't a beginner’s model!
Perhaps youngsters will not mind the model jagging around and think this part of the fun? Hmmm ... not for me.
I shall take the model to Buckminster this weekend and if time allows try once more under L1 Rapier power. I will report back on results.".
Thank you Brian.
The TSP Gripen should fly as well as my original prototype, so Brian's findings are a bit of a puzzle. I will obviously have to buy my own kit and see if I find it any easier to trim.!