By continuing to use this site, you agree to our use of cookies. Find out more
Forum sponsored by:
Forum sponsored by CML

DG 1000 trouble

It dropped it's wing at quite high speed and crashed on it's maiden flight. I need help!

All Topics | Latest Posts

Search for:  in Thread Title in  
Ian Jones16/04/2011 14:09:33
avatar
3218 forum posts
1397 photos
This is my FlyFly DG1000. Sadly the image is a cheat - I have removed the person that was holding it up before it's maiden flight.
 
One very short flight only! It was hand launched and immediately it dropped the left wing. After something of a fight against gravity I got it to a safe height under full power, at that time my thoughts were that the launch could have been better. With the benefit of hindsight it probably wasn’t the launch that caused the problem.

I didn’t have any problems with the elevator response and under full power it was going at quite some speed so I turned into the gentle breeze started to reduce power. A soon as I did that the left wing dropped and it went into an earthward spiral. By the time I had stopped the roll I could already picture the bits the spread all over the field – all the same I pulled back on the elevator and at first not a lot happened then eventually it started to level out.

Too late though. Not wreckage spread over a wide area as I had at first imagined and the underneath of the fuselage just forward of the cockpit took the full impact.

There’s a fair amount of damage and there will be a lot of work involved in fixing it, however it’s clearly possible.

So why did this happen? Well my belief at the time was that it must have a heavy left wing and that I must check the balance properly after I’ve fixed it. It would be nice if that fixed it but I’m not convinced. That element of doubt is really putting me of fixing it.

Other thoughts I have:

  • The wing chord is very narrow – does that make the CG tolerance narrow too?
  • The dropping of the wing was very sudden – was it a stall, if so why?
There’s lots of glider & slope pilots out there and I’d welcome any suggestion that might help me get a successful flight next time.
 
Thanks, Ian
ken anderson.16/04/2011 16:36:38
avatar
8432 forum posts
772 photos
hello ian....sounds like the wing 'stalled'....flying it too slow/in a turn......pulling up on the elevator......
 
ken anderson ne..1.
Ian Jones16/04/2011 18:02:14
avatar
3218 forum posts
1397 photos
Yes Ken it seems like a stall but when I turned into the wind it was straight and level, no elevator input - all I did was start to throttle back, it was still fair moving when it tipped.
 
I'm not saying it wasn't a stall I just wouldn't expect this model at a relatively high speed, head on into the wind to fall out of the sky like that. I've seen these just not want to come down rather than rush into it like this one did.
 
So if we presume that it was a stall - what could have induced it I wonder?
 
What if, for example, it was nose heavy and due to the narrow chord the wing just won't tolerate anything other than just right on the CG... and even though I've said there was no elevator input... I wonder if I may have automatically been holding the elevator up without realising it. Could these circumstances induce a high speed stall with this type of aircraft?
Stefan Hafner16/04/2011 18:25:38
avatar
382 forum posts
15 photos
HI Ian
 
From what you say about there being plety of elevator respense in your OP I don't think the CG was in the wrong place.
 
Going along the lines of a stall, and the very short chord of gliders, if there were slight problems with the build and the wing wasn't quite rigid enough at high speed it may have been the wing twisting under high load, either the right twisting to increase the angle of attack, or the left twisting to reduce the AoA. May be worth checking how much the wing twist.
 
The other possibility that I can see is that there may have been a problem with a servo in the wing glitching?
 
 
Tom Wright 216/04/2011 18:38:55
avatar
3908 forum posts
297 photos
Seen a couple of these go the same way ,they are C/G critical and require speed at all times, a bit of a "brick" and cant be treated as a thermal soarer ,better chucked off a hill into a good blow.
 
TW2

Edited By tom wright 2 on 16/04/2011 18:39:51

Tom Wright 217/04/2011 01:35:16
avatar
3908 forum posts
297 photos
Ian.
To be slightly more constructive than my post above, when you reduced the power the speed reduction could have easily resulted in a stall ,and this type of model often drops a wing and enters the incipient spin which usually continues on to a fully developed spin with a high rate of rotation .The degree off susceptibility depends on the build accuracy of the wings ,C/G position,and wing loading, the later of course effects the stall speed.
Do you know the wing loading? if it does fall into the high category i think my previous comments are possibly appropriate.
Did your DG come as an EP or did you convert it ? the examples i have seen come to grief were conversions .Did you intend the model to perform as an EP flat field thermal soar-er ? if so you may have taken on a significant challenge.Sorry about all the questions but the answers may have a bearing on what you do next with the model.And as an afterthought did the test glide incident possibly damage a aileron servo that went unnoticed?
 
TW2.
 

Edited By tom wright 2 on 17/04/2011 01:40:41

Ian Jones17/04/2011 01:38:57
avatar
3218 forum posts
1397 photos
Stefan,
 
Thanks you have pointed a couple out of possibilies I hadn't considered and will look into
 
Tom (TW2),
 
C/G critcal eh? Hmm you're tending to confirm my worst fear; that I just hadn't been able to balance it properly, would mind telling me what method you would use?
 
Thanks both, Ian
 

Edited By Ian Jones on 17/04/2011 01:39:53

Tom Wright 217/04/2011 01:44:38
avatar
3908 forum posts
297 photos
HI Ian.
Or should i say fellow night owl,would need some more info as requested to make further comment.
TOM.
 
PS for test flights i would go for c/g a bit forward of the indicated position,

Edited By tom wright 2 on 17/04/2011 01:50:37

Ian Jones17/04/2011 01:53:46
avatar
3218 forum posts
1397 photos
Posted by tom wright 2 on 17/04/2011 01:35:16:
Ian.
To be slightly more constructive than my post above, when you reduced the power the speed reduction could have easily resulted in a stall ,and this type of model often drops a wing and enters the incipient spin which usually continues on to a fully developed spin with a high rate of rotation .The degree off susceptibility depends on the build accuracy of the wings ,C/G position,and wing loading, the later of course effects the stall speed.
Do you know the wing loading? if it does fall into the high category i think my previous comments are possibly appropriate.
Did your DG come as an EP or did you convert it ? the examples i have seen come to grief were conversions .Did you intend the model to perform as an EP flat field thermal soar-er ? if so you may have taken on a significant challenge.Sorry about all the questions but the answers may have a bearing on what you do next with the model.And as an afterthought did the test glide incident possibly damage a aileron servo that went unnoticed?
 
TW2.
 

Edited By tom wright 2 on 17/04/2011 01:40:41

Posts crossed a little Tom,
 
Now you are really getting to to the nuts and bolts of it. The model was available as either a soarer or EP - I bought the EP versiojn version but it appears to me that this just means the nose was cut off and motor mounts provided.
 
My intentions had been to use the motor to gain altitude them thermal soar from there.
 
I'm happy to accept whatever questions you throw at me, even if the answers indicate that I've bitten off a big chunk of something unchewable.
 
I'll look up the wing loading and post again and I'm very interested in your comments re C/G as I suspect that it may be a contributory factor.
 
As far as I can tell all servos were in good in working order before & after the flight to disaster.
 
Very much appreciate your help,
 
Ian

 P.S. Yep a bit of night owl and it does me no good at all it just seem to happen this way.

 

Edited By Ian Jones on 17/04/2011 01:55:12

Edited By Ian Jones on 17/04/2011 02:07:06

Ian Jones17/04/2011 02:01:28
avatar
3218 forum posts
1397 photos
The wing loading is stated as 33-35g/dm2 (sq) the aerofoil (translated into English) is HQ 3012
 
Ian
Tom Wright 217/04/2011 02:39:18
avatar
3908 forum posts
297 photos
OK thanks for that Ian,
Would i be right in thinking that when you bought the model you were seduced by the elegant scale appearance? if so your not alone ,i had similar experience with a Discus ,and eventually did get a decent performance but the modifications i carried out were a bit drastic ,the main objectives were to reduce weight ,find a c/g that suited me ,and adding some dihedral, i then reduced the aileron throws to minimum and coupled the rudder to the ailerons ,the latter illuminated adverse yaw that on its own can initiate a tip stall and develop into a spin ,so in effect i made the model more inherently stable and simpler to fly,but these high aspect ratio models operating at low Reynolds numbers can more often than not represent a bit of a challenge ,part of the price we pay for scale appearance.As i am sure you know if the model was not a hand full in pitch it is unlikely that the C/G was to far out ,but of course with such a narrow chord a bit is a lot !
.
 
Tom.
Tom Wright 217/04/2011 02:43:15
avatar
3908 forum posts
297 photos
Ian.
I am old school ,very old school,do you know what that is in old English? like oz per sq ft,
 
TOM.
Doug Ireland17/04/2011 02:51:09
avatar
2088 forum posts
42 photos
I wonder if the wing incidence pin on the left wing was a bit out?
Tom Wright 217/04/2011 02:54:25
avatar
3908 forum posts
297 photos
Now something like this ,really does the job, without any hassle, 8oz per sq ft.
 
Tom Wright 217/04/2011 02:59:55
avatar
3908 forum posts
297 photos
Ian sounds like a an experienced builder Doug i assumed he would have checked vital stuff like that, but of course your right such an error would have a significant effect........like disaster!
 
Tom.

Edited By tom wright 2 on 17/04/2011 03:10:02

Tom Wright 217/04/2011 03:14:47
avatar
3908 forum posts
297 photos
Ian do you have the flying weight and wing span, i was assuming it would be 2.5 M and about 3.5 lbs.but it looks bigger in the photo?
TOM

Edited By tom wright 2 on 17/04/2011 03:17:28

Ian Jones17/04/2011 03:38:09
avatar
3218 forum posts
1397 photos
Hi Tom,
I'm more at home with imperial measures too but here's what's in the instructions which is one sheet of paper with an exploded view for the non powered version ,
wing span 103"
weight 1000g - 1100 g (don't know what that is in lbs)
Wing area 28.5dm2 (ugh)
CG 30mm from leading edge at 200mm from root
 
 
Oh just done a check on 1100g aparantly it's 2.42 lbs, given that I have a motor & battery too then your estimation would be about right. (I've lost the weight I checked it at but my recollection is that it was nearer 3 lbs)
 
Thanks Doug but yes both wings had the same incidence. As I say all suggestions welcome. As Tom suggested it's a good looking scale glider (even if the motor is in the wrong place) and I really would like to able to enjoy flying it. I'm an experienced sport/scale power flyer but gliders are new to me.
 
Ian

Edited By Ian Jones on 17/04/2011 03:42:58

Edited By Ian Jones on 17/04/2011 03:45:50

Ian Jones17/04/2011 12:34:42
avatar
3218 forum posts
1397 photos
Posted by tom wright 2 on 17/04/2011 02:54:25:
Now something like this ,really does the job, without any hassle, 8oz per sq ft.
 

That does look nice Tom, lots of wing to keep it aloft and someone to carry it for you too

Edited By Ian Jones on 17/04/2011 12:35:25

Tom Wright 217/04/2011 20:51:23
avatar
3908 forum posts
297 photos
Hi Ian.
 
Have been out flying all day and out socially this evening hope to get back to the thread later or tomorrow.
 
Tom.
Tom Wright 218/04/2011 00:50:47
avatar
3908 forum posts
297 photos
Hi Ian.
It was been established that aspect ratios of above 12 at reynold numbers calculated for 3m span models ,do not produce any significant improvement in performance, but does result in a higher wing mass for a given area,which is detrimental to the characteristics of a true thermal soaring glider.The DG 1000 has an aspect ratio of about 18 so the structure has to be strong to resist the bending and twisting moments,this results in a heavy wing,which returns a poor weight to area ratio.The wing section is possibly designed for laminar flow which makes it efficient but rather temperamental by comparison to other popular sections ,the air flow breakaway can cause dramatic stall characteristics ,the use of turbulators can reduce the tip stall severity but as this type of wing plan form and section are designed to give good L/D ratios at speed the suitability as a thermal soar-er at model size is in my view limited.What can be done to make the best of your DG ? I will post my ideas below .
 
TOM.
 

All Topics | Latest Posts

Please login to post a reply.

Magazine Locator

Want the latest issue of RCM&E? Use our magazine locator link to find your nearest stockist!

Find RCM&E! 

Support Our Partners
Wings & Wheels 2019
Gliders Distribution
CML
Pepe Aircraft
Cambridge Gliding Club
Slec
electricwingman 2017
Advertise With Us
Sarik
Latest "For Sale" Ads
New Poll - Sticky situations...
Q: How often - when using superglue - do you end up with it on your fingers?

 Every time
 Occasionally
 Sometimes
 Rarely
 Never
 Wear rubber gloves

Latest Reviews
Digital Back Issues

RCM&E Digital Back Issues

Contact us

Contact us