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I need help to identify a T-tail fiberglass sailplanene

Old 07-28-2020, 12:26 PM
  #1  
jb48
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Default I need help to identify a T-tail fiberglass sailplanene

Last week I received a gift from a friend who himself received it from the widow of a rc flyer: a big (at least for me) pure sailplane. He gave it to me after years of sitting in an attic. Since he has no idea (nor me) of the make of this rc bird, I hope that somebody in the Wattflyer community could help me.
It is a rudder/elevator only T-tail where the elevator part consist in a full flying stabilator. Fuselage, except moving parts of the tail is all fiberglass. Wingspan (including width of fuselage) is 112 inch/2.85 meter. Total lenght is 49.5 inch. Wing root chord is 7.875 inch and tip chord is 5.875 inch. Each wing panel is 54.25 inch, excluding the 2 round protruding metal spars. I calculated wing area to be around 775 sq in. Width of fuselage at wings joigning area is 3.675 inch. The plane was complete, including ballast in nose, old Futaba 4 AA cells power pack, 3 Futaba FP s148 servos (one is dedicated to release tow string and/or catapult line). Flying weight appears to be 64 oz / 4 lbs. I have no clue of the age of this aircraft.
I took pictures after cleaning it from accumulated dust. Thanks
.
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Old 07-28-2020, 03:01 PM
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solentlife
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Cannot help with identifying ... but very nice ....
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Old 07-28-2020, 03:28 PM
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Might be a Kestral. The stab differs but the rest, and the wingspan, seem to match.

Outerzone has the plan.

https://outerzone.co.uk/plan_details.asp?ID=11675

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Old 07-28-2020, 05:00 PM
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No ailerons on such a glider seems a bit optimistic unless the wing has significant dihedral and/or washout to give adequate aerodynamic roll stability.
No full size glider with such shape would ever consider it safe to fly without ailerons.
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Old 07-29-2020, 12:04 PM
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Having no aileron makes me perplex too! But after viewing many many videos from John Woodfield slope flying his numerous big sailplanes, most of them without ailerons and/or flaps, I am not so sure. After taking care of small minor repairs I intent to do some handthrown testing for control and cg. Speaking about cg, there is a small metal eye screw imbedded in middle of fuselage top that I mesured carefullly to be at 33%-34% from leading edge at root chord. (Albeit this detail is not pertinent to the no-aileron situation, it's maybe another information that can help to identify this mysterious bog sailplane). I will do some checking for washout.
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Old 07-29-2020, 12:43 PM
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That sailplane at rear of the shot was without ailerons and flew perfect ... had similar dihedral to the OP's unidentified model. Of course the amount was not sufficient to ROLL the model ... but it produced smooth controlled turns suitable for a thermal flat field soarer.

The OP's model is in my opinion - NOT slope suitable as you need a tighter turning machine to stay in the uplift ... but is a flat field thermal soarer.

Today so many have evolved to using powered soarers with the advent of BL motors and LiPo's ... that the older unpowered soarers have basically disappeared from the flight sites ...

This is from when I was living in UK ... 80's .. early 90's ..... all these were Rud / Elev only.


I know the quality of video is terrible .. it was made with a Cine camera - then to VHS - then to DV !! But at least you see the dihedral of a non-aileron thermal soarer.
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Old 07-29-2020, 01:19 PM
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Solentlife, thanks for your observations and old film which reminds me the flying style of my beloved Gentle Lady: mainly the small delay between rudder input and reaction! Per Abuelo suggestion, I carefully studied many versions of the suggested Kestrel sailplane(s) and I don't think that my unidentified sailplane is a Kestrel. I am still looking for what is it.
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Old 07-29-2020, 03:06 PM
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jb48
I would still suggest that it is the dihedral angle of the outer wing panels that is important for good RET control along with some washout to reduce the tendency for the inner wing tip to stall as the rudder induced yaw takes effect. A single dihedral wing is much more likely to 'bite' if the rudder input takes place close to the stall speed.
With ailerons the rudder is reduced to providing a 'yaw correction' function which can be reduced even further if differential action ailerons are used.

The tail of your plane looks very similar to the Schempp-Hirth Standard Cirrus but the wings have a slightly broader chord. Not usual when converting from full size to a model.
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Old 07-29-2020, 05:25 PM
  #9  
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Solentlife, I agree with you that the overall shape of both sailplane are very similar. Now, is (was) there a rc plane kit and/or arf maker for the S-H S Cirrus?
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Old 07-30-2020, 08:12 AM
  #10  
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Nowadays we are spoiled for gear ... but back in the 80's etc. - even the 5001 JR servos were larger / heavier than the ones we can use today. It was common those days to have only rudder / elevator a) because of servo size, b) the factor of where to fit them .....
With low aspect ratio wings - it was common for a central servo and torque rods ... not so common for separate wing mounted. Today we have powerful servos that we can even modify old models to have servos out in those high aspect ratio wings ...

I agree that ailerons make for a more responsive model ... but as with the Gentle Lady .... (my 2m Thermal job back then - was a derivative of the GL) ... what we wanted was gentle but responsive turn to maintain a thermal climb ... R/E was more than enough ..

Sometimes - with greatest respect ... I feel some of the old tricks / abilities have been lost with todays all singing dancing models / gear.
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Old 07-30-2020, 09:21 AM
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I was thinking it was a Graupner ASW 17 or similar but that swept tailplane is no match for any of them.
Still think is is a Graupner kit.
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Old 07-30-2020, 11:43 AM
  #12  
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The thing is - a GRP fuselage ... this IMHO makes the identification harder .... because its unlikely to be from a plan ...
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Old 07-30-2020, 12:56 PM
  #13  
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I also think that the flawless fiberglass fuselage cannot comes from a kit. Also, the wings appear to be balsa full covered wood under the Monokote style skin: perfectly smooth and impossible to see through in full sun facing or powerfull light. Yesterday I tried my first handthrow with big deception: at 4 pounds, it is on the heavy side for a non athletic 72 years old man! The plane glided for about 10 to 15 feet before hitting long grass covered field, tip of a wing first. No damage but it showed that I don't understand the button in a keyhole locking mecanism, since a wing slided back from fuselage root about 3/16 of an inch.
I filmed this aborted launch with a small camera velcroed on a cap. I tried to upload it in the present text but a notice appeared saying it was over maximum file size. The video duration is about 20 seconds from start to finish but in high resolution and full screen presentation. If I am lucky enough to be able to reduce size (I am not good at all at computer and programs fiddling), I'll try to post it later on.
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Old 07-30-2020, 03:52 PM
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Upload to Youtube and link from there ............ videos direct from your PC are not good idea.

Looking again at last photo ... the red line is hand painted as the masking has failed in places ... so that's owner added I reckon (previous of course).

The Keyhole ... only one like that I've seen with alloy rods as well fixed - the button is inserted from inside fuselage ... button goes fwd and is tightened to lock wing ... not so sure about yours ...
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Old 07-30-2020, 05:39 PM
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Solentlife, after maybe one hour of fiddling, I succeeded to upload the video on Youtube at
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Old 07-30-2020, 07:35 PM
  #16  
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Well first thing ... she appears to be balanced ok as she did not pitch up or down ... BUT she's either heavy one side or rudder is trimmed left.

I would suggest hanging it by the CoG and then seeing if one wing drops ... if it does ... see if gear is sitting to one side ... if not then old practice is to use tin tacks or small nail in the light wing tip to get her to hang level.
If she hangs level without correction - then check angle of each wing by sighting from front and slowly pitching nose up / down and watching the Leading edge against trailing edge and see that both wings occlude at same time.
While looking from ahead .. move rudder left - right - left and see that rudder blade appears to side at same amount of stick each side ... and then from underneath check rudder is straight to fin ...

I would choose a softer area to hand check .. one with long grass to save damaging the model.
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Old 07-30-2020, 08:37 PM
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JB48, those wings are more than likely sheeted with Obecchi veneer rather than balsa. It was quite common years ago. You need to throw it harder and straight out, not down. (nor up)
Incidentally, I have seen a 16 Ft glider, rudder only and it performed real nice and could turn quite tight. I have a 2.3 meter with rudder only and it can turn tighter than an aileron one.
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Old 07-30-2020, 08:54 PM
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Panther has a point about the veneer ... but usually Obechi was kept for sheeting over foam core as it has a tendency to split if not supported. Balsa is much better over open structures as it is softer and less liable to split.
You can tell which it is often by seeing if the wood 'dents' ... Balsa will and Obechi being harder shouldn't.

Many years ago - I had a sideline biz called "Wings and Things' that used to cut cores and sheet wings for people .. Obechi was a real pain as it had to be very carefully handled or it split .. I either had it laid on hardboard or dampened it down to avoid it. Whereas Balsa was much easier ..
The biz never took of as I couldn't compete with commercial ... I did it more for people I flew with and even that fizzled out.
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Old 07-31-2020, 01:19 PM
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Solentlife and Panther, thanks for your observations. The wings are very rigid and super smooth: no dent, no crease, no defect. I weighted them on an electronic postal scale: left wing is 290 gr, right wing is 288 gr. It is very possible that the wings are made from a foam core nicely covered with Obechi (I didn't know this veneer material) and kind of Monokote skin; definitely a high skilled made job. The plane is perfectly balanced when hanged from the cg hook at 33-34% from root leading edge. Wings are level albeit the 2 gr difference. Rudder looks very well centered. At 11.9 oz/sq ft wing loading, I would not be surprised that left wing stalled because lack of airspeed, since it is too large and too heavy for me to throw it much more faster. I have to find a young athletic boy to throw it for me or a sharp cliff. I am not a bungee adept, so I have not the required equipment for that. Another option is begining to germ: motorize it, and once there since it would no longer be original, add ailerons and flaps/spoilers to the wing. A nice winter project with many pros and cons to think about. But I still wish to know identity of this sailplane first.
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Old 07-31-2020, 02:28 PM
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The Bungee is way to go ... see that video I posted ... that's all bungee work.

Obechi : its a veneer that was common in laminating door panels .. hard wearing, easy to form and sand. Some bright spark realised its potential to cover foam panels such as wings and topdecks.

When used on models ... you have to be very careful not to sand through it - as its very thin to save weight.
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Old 07-31-2020, 02:55 PM
  #21  
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At 11.9 oz/sq ft you need to be careful if and when you motorise it to avoid an upward weight spiral given that it is no light weight to start with.
You could easily end up with a 'sport plane' wing loading. It would still fly fine but it would tend limit its soaring ability unless on a ridge.
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Old 07-31-2020, 04:50 PM
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I agree 11.9 is a bit on the steep side and may be better at slope soaring than flat field.

Back when I was heavily into Thermal Soarers ... wing loading we tried to keep well under 9 oz/sgft ... with many actually getting 5 - 6 oz results.
But of course in those days as well we were pushing CoG limits to get the thermal sensitivity ... you could see long moment arm gliders with CoG as far back as 65% of chord ... using the long fuselage, low loading and powerful tail to control it ... but the CoG giving extreme sensitivity to thermal action.

Higher loading of course meant moving CoG fwd to allow person to control it !!
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Old 07-31-2020, 05:26 PM
  #23  
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First thing I did when I got this bird was to remove lead ballast and old 4 x AA power pack and weight them: lead ballast was 193 gr / 6.8 oz; power pack was 92 gr / 3.25 oz; plus I removed a 2 oz / 57 gr servo which was connected to tow hook mecanism, for a total weight 12 oz / 342 gr. This weight being at the very front end means that these 12 oz would help a lot to reduce weight gain. Anyway, I agree with you that odds are that the modified sailplane would become a slow landing power plane with long wings, albeit very far from my newly built BOF 60
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Old 07-31-2020, 05:42 PM
  #24  
solentlife
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We all want to remove weight but we also have to pay regards to CoG etc.

If all that weight was up front ... question is why the lead was added ??
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Old 08-01-2020, 12:23 PM
  #25  
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I am not sure to understand your question. Of course the added lead weight was added to help balancing the plane's designed cg at 33-34%. I removed it just to weight it and put it back for correct cg before my aborted handlaunch test. Now, if you replace the lead weight, at the same spot or near to, with a motor, propeller, esc and battery totaling the same weight than lead ballast, you get a motorized sailplane at the same weight of pure sailplane. But reality is that motorization for an over 4 lbs plane will make it heavier, not only because of motor/batt/esc but also from weight to add to tail to counterbalance the now nose heaviness. That is what happenned when I motorized my Gentle Lady: 3.53 oz / 101 gr heavier than original, including the 1/2 oz / 14 gr tail ballast for keeping the designed cg. But in some aircraft, there is empty space where you can position battery more near cg to correct balance without adding lead in tail, which looks being the case on my still unknown sailplane, thanks to the relatively wide empty fuselage going far under wing position. Since I am not a very skilled pilot, I prefer to keep conservative cg.
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