Development of a composite twin boom pusher airframe.

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Tags: airframe, boom, compsite, pusher, twin

Comment by Richard on November 3, 2012 at 3:22pm

ah haa... yes a nice strip would be beneficial, 100mm wheels huh. i am going to be doing my maiden from similar length grassy field, may need to increase the dia of the current 70mm wheels! 

My plane would be 5kg if I had the two 5000mah 4s batteries in there. that gives me a little confidence, aybe i'll try to fly it at that weight and see what happens! point taken about a few safe flights. 

I have fpv equipment all on 2.4ghz, and only use 35mhz for control. I will be using the 433mhz modems for control through the ardupilot soon.

I've heard mixed reports with 5.8ghz video. You will definitely need a patch, omni, and diversity to get good performance out of it.

I'm considering replacing my alloy 16mm 133g booms with lighter 12mm pultruded c booms as they are only 55g each from smc in the UK. I know you are using 12mm dia c tubes, do you think they are upto the job of being structurally strong enough for a 5kg airplane?

Cheers

 

Comment by Leo Hogg on November 3, 2012 at 5:08pm

I think the 12mm tubes will be up to it but the protruded tubes have vulnerable ends and can split easily. As mine were needed to fit inside a 12.5 hole (the 16mm wrapped tube) I wound some carbon tow (with epoxy)around the ends for protection and then a light sanding to get a good fit. I did NOT do this to the nosewheel strut which failed.

FPV freq – big problem. Of course one should not even consider the other illegal options. ;)

 

 

Comment by Richard on November 4, 2012 at 8:56am

Went for these in the end, mainly because my boom and tail holder should fit them a bit better than 12mm. they should be lighter than the current alloy booms from B & Q at a whopping 133g each. They may be what is making it difficult to balance the plane.  

Yeah i hear 900mhz isn't well received in the UK!

Comment by Leo Hogg on November 4, 2012 at 11:26am

Narrowly avoided a disaster today. After turning on the RX before flying I noticed some servos twitched and the RX LED blinked. I wiggled some wires and the power died. Turned out to be a faulty connection in the switch harness so did away with it and soldered together. Could get paranoid as all the servos use the same type of connectors.

Turning the motor around moved the CG back to 34% so decided to  try it there. Bit less weight on the (new) nosewheel.

Take off much easier today despite a waterlogged field.  Probably a combination of longer nosewheel strut and more aft CG.

Great news. The new motor position is MUCH quieter, quite unbelieveable.

New nosewheel given a test by a non elegant landing and survived.

Have fitted a spinner cap on the front of the motor to improve airflow through the prop (and it looks cool).

 

Comment by Leo Hogg on November 4, 2012 at 11:35am

Richard, those tubes look the business. Much better to have some carbon wound around to keep the whole lot together. If mine show signs of splitting I will replace with those.

 

Comment by Ricardo Affonso on November 5, 2012 at 3:29pm

that's great, Leo! i never thought that the broken nose wheel could rip off the entire servo body, but problem solved, the takeoff on high grass was fine. but if you plan to fly always there, with this new huge motor and that big field, you can do belly takeoffs, if the propeller has enough clearance.

Comment by Richard on November 13, 2012 at 12:59am

Leo, good progress, the cf tubes are the business, super strong, and lighter than the alloy. The plane almost balances at 33% now. Fingers crossed i'll do a flight this weekend!

Comment by Ricardo Affonso on November 13, 2012 at 7:05pm

Leo, do you have any hint, or maybe a source material, for cutting the styrofoam on the hot wire? i never worked with this material (just found it in Brazil about 2 weeks ago), this week i made the molds (clark-y 200mm) and tried cutting it with AWG27 NiCr wire, on 24v AC and 600mm span. the molds were made on aluminium. 

my problem is that the leading edge gets deformed, i'm not sure if i'm going too fast, if the wire is not with strained enough or if it's too cold. i'll try those modifications in the process, and hope to get something better soon.

Comment by Leo Hogg on November 15, 2012 at 1:23pm

Ricardo, did you try to cut around the leading edge? It should be cut in 2 half’s, top and bottom (or visa versa). The wire will drag in the middle which is not a big problem on the flatter bits but will cause distortion around tight curves. Cutting in 2 half’s will leave a step on the L.E which can be cut or sanded off. There is a lot of advice on the net and youtube about cutting and glassing wings. You can get good results using weights to steadily pull the wire. Check out this VID.

I think my gravity wire goes about 15cm a minute but I havent measured it.

Comment by Leo Hogg on November 15, 2012 at 1:29pm

After a few successful flights with the standard RC gear installed it was time to fit the APM. What on earth was I thinking when I thought that little avionics shelf was a good idea?

I did manage to cram it all in but was not happy with the arrangement so ripped it all out before flying.

A new extended shelf was moulded that clips on the old one and extends it. Also I have fitted an elyq regulator so that I can use a 2s lipo that gives 6v to the servos and 5v to the rest. It also incorporates a pocket for the 2s lipo so it is ‘self contained’ and easily removed.

 

First testing flight yesterday was ok in most modes but some of the automatic manoeuvring was more aggressive than I would have liked. I should have read the tuning advice more carefully as I discovered its FBW-B that limits bank angle not stabilize (after rolling inverted). Got good 3dr telemetry with the signal not going below 70%. Not so good today though as it kept dropping out with poor strength and I dont know why. The 3dr radios have locked up a couple of times now and have had to be recovered with a bootloader reset.

 

It is still a little difficult getting airborne off the long grass but I now have permission to cut a strip.

 

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