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Super Marauder, Depron/ wood composite with contra-props and retracts.


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Hi Graeme. It's taken about three months from start to finish, but there are many weeks in which nothing got done, so an uninterrupted build would probably have been no more than four weeks. I had always wanted to do one of Peter's designs, had a lot of Depron I wanted to use and I'm fascinated by contra-props, so everything came together! I just need to sort out the Rx issue, but should be able to do the maiden in the next few days. With a bit of luck I'll be able to do a video for the first time.

Cheers,

Colin.

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Thank you Ron and Andrew, here's hoping!

I promise to finish the Chipmunk before I do anything else, then I need to put the Warbirds Spitfire together, looks like a straightforward build, then get to grips with the Supermarine 317. These are the tasks for 2017, combined with improving my flying and getting some good aerial photos of the Seafang!

Happy New Year to all those who've followed this, I hope it's been of some value. Compared to some of the amazing projects other forumites post on here, it isn't anything very significant, but it reflects my fairly basic level of competence and shows that if I can do it, so can anyone else and probably better. (Let's see how well it flies though).

Edited By Colin Leighfield on 02/01/2017 11:21:14

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The Spektrum AR6600T rx is in place, everything set up and working, throws as recommended by Peter in the build article. I have set low rates for 70%.

I can confirm that the design c of g can be achieved with a 3S2200, 3300 or 3700 simply by positioning the battery, no ballast needed. Finished weight without battery is 1.456kgs, 3lbs. 3ozs. With a 3S 3300 Lipo, my intended starting point for test flying, it weighs 1.719 kgs, 3lbs. 12.5 ozs. That's a full 1 1/2 lbs less than for the balsa build with .52 fs motor, I'm chuffed to bits with that. The wing loading will be 15 ozs./sq. ft instead of 21, about 30% less.

We have visitors today so sadly can't do the maiden, but hopefully can do it in the next seven days, work permitting. I will use the video camera, so that's tempting fate, isn't it?

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  • 2 weeks later...

The maiden hasn't been possible yet, the only chance I might have will be Friday, I'm at work the next three days and we leave for Spain on Saturday, but there might be a window of opportunity then.

I ran the motors up with the 9x6 three blade props and was astonished to see only 265 Watts, even though thrust felt pretty reasonable. The motor combination is 375W and a pair of 10x5 two bladers are fitted as bought (impossibly out of balance)! With a bit of fettling I managed to get a pair of 10x6 three bladers fitted. At start there was a reading of 400W, falling back fairly quickly within the 375 range, so I reckon that's ok. It's around the 100W per lb. mark, so although not enough to take it vertically out of my hand, it should be enough.

There's clearly scope for experimentation with the props and the best thrust figure will probably with be with a pair of APC two bladers, but if the plane survives the first couple of flight attempts I can experiment later to establish the best option. That will be the time to look at spinners, although it doesn't look too bad without at the moment.

 

Edited By Colin Leighfield on 16/01/2017 21:53:17

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Have a go Cliff. The easiest way to try it is to do a simple substitution in a standard balsa design, just identify particular stress points where some wood reinforcement is advisable. The ultimate is to follow Simon Chaddock's route of engineering standard monococque designs that are incredibly light and need very little power to fly well. It's cheap enough and dead easy to cut and work. Plenty of scope there.

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iframe width="450" height="253" src="https://www.youtube.com/embed/stycGKkIlUo?rel=0&controls=0&showinfo=0" frameborder="0" allowfullscreen>

It's flown. The video is lousy, it's at an angle because I fitted the camera to a cycle helmet and it's wonky. Also for some reason the video is playing back slowly, the sound is distorted badly. Don't know why, it was ok last time so I need to sort that out. Also it's too far away most of the time.

Although I've got 375/400 watts, performance is very sluggish, clearly the three blade props don't work well, so I need to do something about that. I also found that the ailerons were very sensitive at the recommended throws, so reduced them by 25%. The trimming is sorted for the next time when I have resolved the prop issue.

Bringing it into land I realised at the last second that I hadn't lowered the wheels! In a panic grab for the switch I knocked the plane off-line and landed it on the grass. It promptly nosed over, but no damage. One of the u/c legs had rotated sidewards, clearly I didn't do a good enough job of filing the flat on the leg.

At least I know it flies and all the key characteristics are good. Stall recovery is instant and you can slow it down to nothing. Sort the props out to get some more thrust, do a proper job on the U/c leg and we'll be in business.

Thank you Peter, sorry it isn't a better show but it will be next time. Great design, no vices at all.

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Bob, thank you for doing that. I don't understand why the Tomtom Bandit did that. It appears to be about half-speed, it must have been something that I have done.I'll find out.

It's got to wait for now. The answer to the thrust issue is most likely with a pair of APC two bladers, 9x6, 10x5 or 10x6. I've got all of those, it won't take me long. If there isn't enough poke in the motors, I'll convert it to a single brushless, again easy to do.

At least we know 1. It flies. 2. It handles well, no vices. 3. At this light weight, the stalling speed is very low. 4. With the right thrust, it's going to be suitably lively. Bearing in mind that I'd had the throttle pretty much wide open for most of the flight, I was surprised that the esc's and lipo weren't even warm at the end of the flight. There's plenty of cooling. But they clearly weren't working very hard!

Peter, hopefully next time we'll do a better job and get it closer in. The object was to get it in the air before we go away and we've done it.

Edited By Colin Leighfield on 20/01/2017 22:45:49

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