load testing

[aerialfoto]

Can anyone tell me how to load test a canard (dragonfly MKIII)? I had to make a repair to the bottum side of my canard and am not sure how to testing should be done and since i would rather it break on the ground than in the air.......... At 4.4 Gs it comes to a bit over 5000 pounds but since the canard is only supporting a little over 50% of the load does it need to take 5000 pounds? And how should the weight be spread out from root to tip? Thanks SAmuel Miller

[Marc Zeitlin]

Can anyone tell me how to load test a canard (dragonfly MKIII)?

You need something more than advice from people you don't know on the internet in a clear safety related case such as this. I suggest that you hire a structural/aeronautical engineer to advise you on the repairs that you made as well as the testing methodology for ensuring that your repairs are sufficient, if such testing is required based on the evaluation of the repairs.

 

Basically, you'll need to explain the damage, explain the repairs (and the materials used). If testing is deemed necessary, you'll need to supply information about the relative sizes of the main wing/canard on the Dfly, as well as the dimensions of the canard. You'll then need to determine what stress level you want to test to (sounds like you want Utility category), and what safety factor you want applied (usually 1.5). The consultant would then need to determine the lift distribution on the canard from tip to root and advise on a weight distribution (with the aircraft upside down, to mimic positive lift loads).

 

I would estimate that all of this work should be on the order of 2 to 5 hours for someone, so that would give you some idea of the cost involved.

 

There are many folks that advertise engineering services in the back of Sport Aviation and/or Kitplanes magazines - I don't know any of them, but they've all been in business for a long time. I also do similar engineering consulting for homebuilders.

[Steve Innova]

For a flight critical item like the canard, I'd probably rather just re-build it if the damage was anything more than superficial.

 

It'll take about 100 hrs or so, maybe more if you haven't worked with composites before. But you can probably re-use the elevators and all the metal parts from your current canard, which will save lots of time.

[Lynn Erickson]

Can anyone tell me how to load test a canard (dragonfly MKIII)? I had to make a repair to the bottum side of my canard and am not sure how to testing should be done and since i would rather it break on the ground than in the air.......... At 4.4 Gs it comes to a bit over 5000 pounds but since the canard is only supporting a little over 50% of the load does it need to take 5000 pounds? And how should the weight be spread out from root to tip? Thanks SAmuel Miller

to what extent is the repair? where did you get the information used to do the repair? are we talking skin repair or spar repair?

[aerialfoto]

Repair info i got on the dragonfly list and various other sources. Its a spar repair that is why i want to load test it. Carbon spar with damage to the trailing edge in about 1.5 in. or i could do a full span spar replacenent. As for building another canard that is also why i want to load test the one i have if it breaks then i will build a new one if it doesnt ill fly. P.S. it has been flown somewhere around 90 hours by the origanal builder with no repair, i dont think he even knew the spar was damaged. Yes yes i know that does not make it any safer but i know my repair has made a lot stronger therfore the load testing. Thanks SAmuel Miller

[Lynn Erickson]

Repair info i got on the dragonfly list and various other sources. Its a spar repair that is why i want to load test it. Carbon spar with damage to the trailing edge in about 1.5 in. or i could do a full span spar replacenent. As for building another canard that is also why i want to load test the one i have if it breaks then i will build a new one if it doesnt ill fly. P.S. it has been flown somewhere around 90 hours by the origanal builder with no repair, i dont think he even knew the spar was damaged. Yes yes i know that does not make it any safer but i know my repair has made a lot stronger therfore the load testing. Thanks SAmuel Miller

one of the problems with load testing is it may damage the wing in a way that you can not see. most of this type of testing is done on a wing that will never fly, tested to failure. lets say you do a load test and the spar does not fail, how do you know that it did not do some unseen damage to the other parts of the structure. what if it crushes the foam beyond repair and it is not detected. what if the attach points are affected in some way that shows up latter on a flight. what if the test causes a crack or delam to start but you don't hear or see it.

[Steve Innova]

Spar damage = scrap the part. That'll give you most peace of mind.

 

I've been investigating destructive testing of a new seat-back / shoulder harness set up. It's actually very expensive to get the neccessary amount of lead or iron weights and build a test rig. From a steel supply store, steel costs about $1/lb. If you need 2500 lbs, do the math. You might save money just building a new one, and you can re-use the aelerons and metal components.

 

 

It can actually be a very fun experience, building a canard.

[aerialfoto]

Stress goes to the stiffest part (the spar) so it should fail first right? Also this is the bottum spar (tension load) and in every test report i have read the top (compression) falied first. On the dragonfly the top and bottum spars are the same number of plys so the botttum side is the strongest. Thanks SAmuel Miller

[jpolenek]

On the dragonfly the top and bottum spars are the same number of plys so the botttum side is the strongest.

According to Viking's [revised] spar lay-up schedule, the canard's upper and lower spar caps should have 9 plies and 6 plies respectively, at their thickest points (near the root). They taper down to 2 and 2 near the tips.

 

Joe Polenek

[aerialfoto]

Not sure when that was revised but my building manual must have been before that it shows 6 plys top and bottum the same

[jpolenek]

My plans were purchased circa 1997 and IIRC the revised layup schedule for the wing and canard were already included in the plans. They were prefaced with a letter from Viking stating that althought ther had been no in-flight structural failures, they felt the need to re-engineer those layups because of the growing trend of builders making the Dragonflys heavier than the plane was intended to be.

Although the letter doesn't mention it, part of the reason may have been because a few people broke their canards on hard and/or bouncy landings. This applies to the MK I with the main gear at the ends of the canard, so if you have a MK II or III, the revised layup schedule may not be as important.

 

Joe Polenek

[argoldman]

My plans were purchased circa 1997 and IIRC the revised layup schedule for the wing and canard were already included in the plans. They were prefaced with a letter from Viking stating that althought ther had been no in-flight structural failures, they felt the need to re-engineer those layups because of the growing trend of builders making the Dragonflys heavier than the plane was intended to be.

Although the letter doesn't mention it, part of the reason may have been because a few people broke their canards on hard and/or bouncy landings. This applies to the MK I with the main gear at the ends of the canard, so if you have a MK II or III, the revised layup schedule may not be as important.

 

Joe Polenek

 

Joe,

 

If I am not mistaken, those lay-up schedules were revised with respect to the canard-tip wheels.

 

In the prototype, they found that after a time, the canard sagged giving less prop clearance at takeoff and landing attitude (minimal at best). Additionally, hard landings with the increased spring of the diving board type gear caused the same decrease (although almost instantaneously.) Rex's (Taylor) solution was to heat the canard, bend it to the original anhedral and let it cool.

 

The hoop and inboard mounted main gear do not put nearly as much of a load or bending moment on the tips of the canard spar, and probably the additional sparcap layup was not necessary.

 

When a dragonfly broke a canard it was usually the result of a badly botched landing (I did it on my first-- no dual in a dragonfly--thought my years of experience would suffice). there, if I can remember was a considerable amount of conversation about if various parts are made stronger, the failure mode would be at a different part of the aircraft (bulkheads in the case of the D-fly). One point of notice is that these canards did not break at the outside (only 2 layers of carbon as I remember) but broke close to the fuselage where the carbon layups are max. Additionally there was talk that the breaks happened where the canard emerged from the fuselage and were indeed touching the fuselage at that point (design as opposed to the Q birds specified clearance) which served as a "kink" point. Mine failed about 10-12" outboard of this point. (outboard gear, at that point-- changed to hoop in the new canard)

 

That being said, it probably would be prudent to do the extra layers.

 

I personally would endorse the hoop gear. (x-dragonfly N222TH (MK II-h)

[aerialfoto]

Thanks guys im learning a lot now i better get back to work on my plane.