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TOPIC: Profile Kits from TSP

Profile Kits from TSP 1 year 9 months ago #1770

  • rogersimmonds
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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!!" :dry:

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.:S
.
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.!B)
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Profile Kits from TSP 1 year 9 months ago #1771

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Still on the subject of the idiosyncratic begaviour of the Gripen, I had an interesting, and most apposite email from Howard Metcalfe, who is a self confessed lover of the black art of trimming and has sorted out many a recalcitrant model.

Howard writes:

"It’s a very nice shape; why haven't I built one yet? I would not hesitate to build from the plan as is, with everything straight and no dihedral and little or no reflex.Which is how I built the small all-Depron test model below:



In test glides, I added a tiny bit of weight to the tail to stop it diving slightly so that the cg was slightly rearward (by 1.5mm on my 11cm span model).
Even without dihedral it snaps back immediately to straight level flight when launched in a very steep bank either to the right or left and it climbed straight and true if thrown hard.
I added a small weight to simulate the weight of a motor and the model flew exactly the same.:)
I suppose I could crank in the dihedral as per Piotr's plan but I don't want to ruin such a fine little model. Perhaps Brian had his CG too as the model definitely gets squirrelly when I moved the CG back to the position you see in the photo. As you can see, the rear of the wing root ties up with the drawing but the pin shows the CG when it was getting squirrelly i.e. Dutch Rolling.



Above: Howard's small all Depron test model, showing the CG at the recommended position. This resulted in the sort of behaviour Brian was was struggling with.

Howard ends his most encouraging email: " What a star design Piotr Tendera has here, it is magic I would not hesitate to build from the plan as is, with everything straight and no dihedral and little or no reflex".

According to the instructions included in the Gripen kit, the CG is 49 mm back fronm the front of the wing, which is (49/132) about 37% root cord:



Above: detail from the Gripen instructions. To my eyes, and according to Howard's experiments, the CG should come forward quite a bit (see arrow)!
The CG of my original (and slightly larger) Gripen prototype (which though I say it myself, fles very nicely indeed) is around 28% of the root cord. This translates to 36-37 mm for the TSP kit model:



Above: corrected CG. In this position it is also in the right place with respect to the TSP L-1 motor!

I did add just a tad of 'up' aileron (no more than 1-1.5 mm) to my prototype, but this, as brian says, is more in the nature of 'washout' rather than 'reflex'.

To sum up: The TSP Gripen should be built WITHOUT the dihedral on the wing. The slight dihedral on the canard can of course be retained for scale purposes. :cheer: The CG dfinitely needs to come forward to around 28% of the root cord, i.e. 36-37 mm back from the leading edge.
As I said in a previous posting, I will now build my own TSP Gripen and, hopefully, confirm these ideas by getting the Gripen to beat up the airfield at Old Warden! :woohoo:



Above: my original profile Gripen for L-2 power. Soon, I hope, to be joined by its small L-1 powered TSP stablemate. B)
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Profile Kits from TSP 1 year 8 months ago #1772

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I built my Gripen, not quite according to the plan, starting Friday afternoon and finishing Monday evening. Luke I know, would have polished it off in under three hours, so my rate of building is equivelent to 0.1-0.2 Goymours. :lol:

I did take photos of the build, which I can put on a separate thread on the forum should anyone be interested. To cut a longish story short, I made it without dihedral and took a lot of care over detailing and painting.



Above: I was quite pleased with my Gripen. Note the addition of the radar pod on the fin, the 'shark's fin' radiator behind the cockpit and the soft rubber missile rails on the wing tips. I painted in areas of a different grey to relieve the monochrome and touched up the jet pipe. None of these refinements is suggested in Piotr's instructions, but they do add a lot to a model's appearance! ;)

One wrinkle I would recommend is rubbing down all the balsa surfaces with 1200 grade 'wet 7 dry' and giving the parts a coat of 50/50 Eze dope before assembly. The surfaces were quite rough straight out of the box' and this may explain why some builders have had problems with the decals not sticking in place very well. Mine did!



Above: motor mount, foil and thrust tab. The foil is included in the kit, but not thr thrust tab, which is a pity. Note the shaped motor mount and the motor retaining wire (22 SWG wire for this is not included).

It weighs a very creditable 14.3 grams with a used motor. This includes 1g lead nose weight. I did not use the horrible green modelling clay included in the kit for this purpose. The CG is 37 mm back from the wing leading edge.





So it's ready to go, but trimming/flight trials will have to await the next calm day. B)
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Profile Kits from TSP 1 year 8 months ago #1773

  • LukeGoymour
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0.1-0.2 Goymours...hahaha I love it!

Looks very smart Roger, look forward to its flight report..:)

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"You make the clouds your chariot, you walk on the wings of the wind" Ps 103 (HB 104):3

Profile Kits from TSP 1 year 8 months ago #1775

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As it calmed off this evening I took the Gripen down to my local (smallish) recreation ground for glide tests. I elected to do this with hand chucks rather than catapult.:unsure:
It needed a firm steady throw, but, given that, it glided perfectly, fast and straight, with the CG just as it was and just a tad of 'up' elevon (1mm or so, with slight differential to correct a tendency to bear right). It corrected itself from a banked launch. :)

This was, as they say in test pilot circles, 'nominal' and most pleasing.

Next stop, flight trials with an L-1. B)
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Profile Kits from TSP 1 year 8 months ago #1782

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Fingers crossed :) If it glides... It flies :D

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