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

[Colin Leighfield]

l need to tidy my shed again. I've got that much stuff in there and it's a mess. It occurred to me that it might be a good idea to reduce my stock of bits by using some of it up in a quick build. Peter's Super Marauder interested me because it looked that I could convert it into a mostly Depron build working straight off the plan. Also by reducing the weight from the 5 1/4 lbs. indicated in the RCME September build feature, I could use my 375W contra-prop twin motor unit from HK. Also, I want to fit electric retracts, I've got those. I think the contra-props will suit it, it could represent a turbo-prop ground attack plane and the retracts will add to that. Also, the elimination of torque reaction means that the plane will fly like a jet. Another benefit is that there is no torsional load on the motor mounting, all of the applied loads are longitudinal, tensile in acceleration and compressive under deceleration. This greatly suits the lightweight construction. However I will cover it with lightweight glass-cloth, that will add considerable toughness and provide a basis for a better finish than I can achieve with the XB42. The finish will be gloss black with yellow flashes. Here is the co-axial motor unit. It is larger than the 221W 1550KV unit in the XB42, which is very successful. I really like these.

 

Edited By Colin Leighfield on 16/09/2016 23:11:06

[Colin Leighfield]

Here is the start of the build. Exactly as the plan, but substituting 6mm Depron for the balsa fuselage sides, using 1/64" ply for the doublers instead of 1/32", 3mm Liteply instead of ply for F3 and F4. F5,6&7 are 6mm Depron instead of 1/8" balsa. I have used balsa for the rudder post. One shock was that some of the Depron appeared to have been attacked by the Uhu Por used to attach it to the ply doublers. I had to cut chunks out and replace them. I can only think that it was because I stuck them together wet rather than as dry contact. I am continuing with Deluxe Foam-free, which is more expensive but very good. I am not blaming the Por, I've used it a lot successfully, but this experience was odd.I promise I will tidy up as I go along, I am ashamed.

Edited By Colin Leighfield on 16/09/2016 23:26:01

[Piers Bowlan]

Another interesting and unusual project Colin, I will be following with interest. I must have a go at building with depron sometime. Your workshop makes me feel better so don't tidy it up!

[Colin Leighfield]

Thanks Piers! I hope that Peter won't mind me doing this, he is a traditional builder, but this design translates very easily for Depron. The only extra former is my "F1A", which is the motor mount. All the others are as the plan, except for material and cut-outs to suit the different internal arrangements.

I'm not looking for ultra light weight, but a plane that when covered with light glass cloth is a robust flyer and significantly lighter without being featherweight. Ideally a weight below 4lbs.and as close to 3 as I can get it will make the 375W power unit suitable. Appearance will be identical to plan except for around the air intake. I don't need that much air up front, so I will profile the lower front nose section slightly differently. Fingers crossed.

[Peter Miller]

Hi Colin.

I don't mind what you do with the design.

This one looks really interesting. and I shall be following the build with great interest

I did consider retracts on the original but ddn't have a good set to hand. Also a lot of builders might not have wanted to go that route.

[Tony Bennett]

Colin i have had the same issue with the por eating the grey depron, as you said it is because you used it wet and not as a contact adhesive.

though i do think that they have changed the formula for depron slightly as the new stuff is slightly different from the older type.

looks to be another interesting project from you.

[Colin Leighfield]

Hi Peter. Thank you. I've always followed your designs and keep thinking that I must do one, but continue to take on too many ideas without enough time to do them. This is different because it fits in with ideas in my head about contra-props and composite builds, while remaining your design aerodynamically and in most construction detail, except for material substitution and conversion to electric. Apart from whatever weight reduction I get, it will be set up exactly to your advice with c of g position and control throws. One thing about Depron is that it is easier and quicker to work with than wood and you can afford to waste a bit. The need to use glass-cloth and paint rather than film at the end will add some time, but overall I want to get it done quickly, as I did with the XB42.

Tony, thank you also. I'm sure that using the Por wet on a large area where there was no air present was the factor. I'll bear it in mind for the future and only use the dry contact method for joining large surfaces. The Depron is from the large stock I bought a few years ago, so I don't think it's that on this occasion. I'm glad you find it interesting, coming from you that's a compliment. It should be a safe bet, I think.

[Colin Leighfield]

Today I put in the tailplane platform using blue foam instead of 1/2" balsa. Fitted the 1/8" ply plate for the tail skid, with a bit of balsa inside the Depron sides to give a bit more reinforcement to it. For the fuselage underside behind the wing I used 1/8" aero quality Depron. I used 6mm Deoron for the fuselage top, starting short at F2 because forward of there, the cockpit area is going to be a hatch for battery access. I made the fuselage spine, again using 6mm Depron instead of balsa. Also I've fitted the motors to work around as I create the nose area. At the moment it's all square boxes, but it will all sand to shape. Sorry the photos are in reverse order!

[Tony Bennett]

nice work colin.

[Colin Leighfield]

Thanks Tony, although as usual a bit tatty at this stage.

I didn't mention in the previous post that one other variation from the original is the positioning of the rudder and elevator servos at the tail instead of inside the fuselage further forward. I've used 9g servos with metal gears. I still haven't got used to the range of miniature servos now available. These look inadequate yet have a pull of 2.5 kgs. I used to fly a Giant Zlin 86" span with a single aileron servo. That had a pull of 4lbs, less than 2kgs, yet never gave any trouble. I don't think I need to worry about these.

Peter said in the build feature to use a heavy hard wood for the tail because it might be nose-heavy and need some weight in the back end. The weight distribution in this Depron build will be different, also there is that much scope for battery size and position that I don't see any difficulty in getting the c of g right.

[Peter Miller]

I use the 9 gram MG servos when using one per control surface such as ailerons and flaps.

Only used them on the tail on my Slingsby T31M.

[Simon Chaddock]

Colin

Very neat but the construction still looks pretty massive to me with lots of wood!

I must say I have not come across "POR eating Depron".

I have left "wet" POR on Depron for some time typically when adding a large area of wing skin. The only problem normally results from the POR drying sufficiently that it becomes a contact adhesive when you actually want a bit of adjustment.

I do agree that the avoidance of motor torque does make flying (slowly in particular) much less stressful but I wish I could justify to myself the cost of those lovely contra rotating motor units!

With the aim of "reducing the weight from the 51/4 lbs indicated" yet you are worried about a servo that only has a pull greater than the total weight of the plane!

[Colin Leighfield]

Peter, thank you. I'm seriously thinking of using one of these to drive both ailerons. It doesn't feel instinctively right, but 2.5 kgs say it should be perfectly adequate. We'll see!

Hi Simon. The circumstance with the Por was gluing the fuselage sides to the doublers. The only thing I can think of as a factor is the lack of air in that situation. The Depron was half eaten away and adhesion completely destroyed.Tony mentions that he's experienced it as well.

The construction is chunky, there is a lot of (mostly light) mass in there, but probably half of it will be sanded away as the shape is achieved. I'm not going for minimum weight, for that I'd change the construction completely. In this case I'm looking for a useful weight reduction with a robust weekend sport flyer. That is why I've used a composite Depron/ balsa approach with little deviation from Peter's robust all-wood design.

I think the HK co-axial motors are good value for,what they are, although certainly not in the "throw-away" category that we are so used to these days. Not expensive though in comparison with i/c. I really like them. I'm with you on the servo thinking, one of these should handle strip ailerons on a 58" wing. It just looks too small!

[Peter Miller]

I really am not sure about using just 1 9 gram servo for both ailerons.

The motor and gears might take it but the mountings are a bit on the feeble side.

Super Marauder does not hang about and can really pick up speed in a dive.

I have not really thrashed mine yet. So far maximum G pulled is a mere 3.7 so I must have been messing about with big jet style manoeuvres. Must see what I can pull on it.

[Colin Leighfield]

Peter, I had 't considered the mounting, thank you. You've persuaded me.

[Colin Leighfield]

I had to fly today, too nice to miss. Here are the Fw190D9, XB42 and Cub "Grasshopper" at Fradley. After running perfectly two weeks ago, I couldn't get the Saito FA82 to tune properly today, so didn't fly the Fw, sadly. I must sort it out. I had some great flying with the Mixmaster and the Grasshopper, so it was a good day. Next step in the Super Marauder is the battery box. It has a structural role so the sides will be 1/8" balsa.

[Andrew Price 2]

Lurking!!

[Colin Leighfield]

It has all the makings of a very good lurker!

[Colin Leighfield]

I thought the next thing to do was to solder all the motor connections and work out how it will fit into the plane. I've made the engine cowl. (Sorry about the duplicated upside down photo). I realised that somehow I've got the thrust-line too high, don't know how I did that. I'll need to take the motor mount out and do some re-work on the front end. I'll do that tomorrow evening.

[Stephen Jones]

Have you gone down under Colin

[Colin Leighfield]

Well done Stephen, you noticed that I've moved to Wagga Wagga! Mind you, when I realised last night that I'd messed up on the thrust-line I wondered if I had. It's a stupid mistake on my new former "F1A", which is the motor mounting plate. Won't take long to correct, although it will be a bit brutal.

[Colin Leighfield]

Sorting out the mistake with the engine mounting plate has messed the front end up, but it will be ok when I've finished with it. The duct formed by the large air intake and the floor of the engine bay is the perfect place for the two ESCs, remember this is a twin! There's a lot of air coming in at the front, even though I've reduced the depth of the nose and curved the underside. I will make sure that it can all get out.

[Peter Miller]

I designed in a pretty big air exit

[Colin Leighfield]

Peter, it looks well sorted on the plan. Also the intake looks the part and cools a four stroke engine. It's more than I need for the electric set-up but I like the look of it, so I didn't take too much of a liberty with it when I reduced it. It will still need a good size exit, I'm going to split it between leaving the cowl under the wing and through a vent under the fuselage behind the wing.

[Simon Chaddock]

Colin

That all looks quite impressive.

I think you might be right about the inlet being at over kill as far as cooling the ESC is conce3rned. Air cooling all depends on getting the air where and only where you really need it.