Dumas Dragon Rapide

[Chris Walby]

My better half took note that I had a few days this week with some spare time and to be honest the kitchen table is far more appealing than the colder workshop although that's where the repairs/winter servicing needs to be carried out!

 

It should end up looking something like this, if all goes well.

 

This will be my first "sticks and glue" assembly for the fuselage and helpfully the wings are pre cut so it should be just an assembly job (wrong there for starters!) hence I am finding the old techniques and logic a bit of a challenge.

Having spent quite a lot of time on the web it would appear that the designer built his AUW at 13oz which does not look good as all the bits weigh close to 18oz and appears a massive weight gain even before I get the glue out. Good news is that Bob Benjamin's review of his in 2010 came in at 20oz and it flew....but needed to move the c of g forwards (see questions later!).

 

Its all dry fitting at the moment as I am going brushless as opposed to the original design (brushed with lipo) and the first sticking point is the motor mounting. Note bearing in mind the existing bulkhead is balsa and the brushed motors sat on a beam then the solution needs to be light with strength, but only enough to do the intended job.

 

 

Questions for the collective?

• Would a simple balsa X support from the motor mount to the bulkhead be the best solution (light and reasonably strong)? Or is there a better way?
• Sort of related to this, but more a lightbulb moment with another model I had (Focke Wolf Ta 154 80 inch) which was well over weight and we ended up with the C of G well ahead of the published mark. If the AUW increases significantly why do you move the C of G forwards + what effect does that on the stall air speed as I though the Ta 154 would need to fly fast, but contradicted that assumption?

 

Thanks to George at 4-Max for the electric spec + I am going for HK silver covering as it seems as light as any other film covering, no idea if tissue is lighter.  

 

Please like or chip in with any build advice you see fit

 

PS - going with all CA on this one.

 

 

 

 

 

 

 

 

[Basil]

Not many other halves would agree to that, especially over Christmas. Good luck with the build. I love this plane.

Bas

[David Holland 2]

Hi Chris, apologies for the slow reply but I had to dig my Rapide out to weigh it. Mine came in at 12.8 oz (365g) without battery. I went for brushless and counter rotating props and use a 600 3s lipo (1.6oz/44g). Covered in Solite and airbrushed with Humbrol. I was careful with weigh control but not obsessive and I think you would struggle to get as high as 20oz. Flies really nicely, not as tip stally as you would think, but needs very calm winds. Lovely kit to build (in fact I am building a Dumas Tiger Moth as a light weight project while recovering from some fairly major surgery) but the 1/16 square stringers are very delicate as you will find!! I rate the Dumas kits very highly and am about to order the Taylorcraft as a follow on from the Tiger.

 

David

[Chris Walby]

Thanks for the reply and very useful information about the model and building challenges. I was going for 2S1300 which is close on weight, but have some 3S800  and smaller if necessary.

Mine will be pusher/tractor props so the same as yours.

 

The thing I can't understand is the kit (just the bits) weigh 327g without the electrics (150g without lipo), I I understand the "add lightness" mantra but I don't know what to leave out! I am not going to get hung up on this as some of the bits were in plastic bags and will just get on and build it.

 

It can join the "dead air" club of models (DR1 etc) that are best to be flown when there is very little wind at the field, so not an issue there.

 

Love the colour scheme you have there, looks brilliant.

[David Holland 2]

Honestly, Chris, you won’t have an issue with the weight, if you were to weigh the individual parts rather than the laser cut sheets I reckon that would reduce your 327g significantly. I tried 2s lipo but found the power dropped off too much when the pack voltage dropped from the freshly charged state (i.e. fine at 4.2v but not at 3.7v) and there is not room between nacelles and fuselage to fit bigger props. Enjoy the build, let’s us know how it’s going.

 

David

[Chris Walby]

Thanks David, 

 

Having made some progress I now the first question of which I think there will be many!

 

 

The plan shows the aileron servos mounted in he nacelles acing via a short and curved snake and my plan was to dispense with this until I realized there is very little depth in the ribs to achieve a good servo location.

 

Should I stick to plan or try and shoehorn the servo in between he ribs nearest the inner end of the aileron (ribs are too shallow nearer the tip)?

 

Or is it worth using some very shallow servos instead?

 

I am going to make a start on the fuselage so I'll see  what advice is given over the next few days before making a decision.

 

Thanks for reading 

 

[Paul De Tourtoulon]

Flat  at the Root of the wing with a carbon torque rod  ?.

[David Holland 2]

Hi Chris,

 

I mounted 2.5g servos in the nacelles and made little 1/16 ply bellcranks, holes toughened with cyano, connecting to the inboard end of each aileron and interconnected upper and lower with plastic and tube and heatshrink. Worked a treat.

 

David

[Simon Chaddock]

My own view on such a scale light weight is that any benefit gained from wing mounting the servos close to the ailerons is only worth the effort if you can truly bury the servo inside the wing otherwise it makes sense to use the 'free' nacelle space.

[Chris Walby]

Progress is slow due to nice flying weather and getting stuck on some fundamental points. Stupid question time, but I'll ask it anyway.

 

 

Ok I get the bit of gluing a load of matchsticks together but is it intended that I cut the cross bracing where it meets the main bracing (for example at the red arrows) or should the cross bracing go behind (can't see how that will work).

 

So is it all butt joints and is that ok or should I put a little balsa block in, bearing I mind weight is a major factor and to be kept to a minimum.

 

The other assumption (dangerous I know!) is that I build the fuselage side first and then bow them on the plan view to achieve the correct shape?

 

PS. starting to think the flying bit is easier !

 

 

 

[Ian Lauder]

If you can read this it is thanks to the RCM&E Magazine editor who found a forum person who could save me from 2 days of grief trying to log in to this Forum. The reason is that I found this thread by accident after days of trying to find out which motors / ESCs are suitable for the Dumas DH Rapide kit because - as you have found out - the recommended motor is no longer available. I had a wonderful exchange of emails with Pat Tritle who designed the kit but his suggestions are not available in the UK. I did receive an expensive box of electronics from the shop that sold me the model but that only proved they had no clue about the kit. (motors too fat and powerful, props so long they would have ripped out the fuselage sides etc. 

So whinge over, please tell me what motors and matching ESCs you used or would suggest. 

By the way - my good lady wife bought this wonderful kit for me to build over Christmas because it was the first aircraft I ever flew in aged 8. Bea service to the Isle of Wight with a female pilot accompanied by my sister and ex WWII RAF pilot Dad.

[john stones 1 - Moderator]

Hi Ian.

Welcome to the forum, can't help re the electronics question, but someone will I am sure.

[Chris Walby]

4 hours ago, Ian Lauder said:

If you can read this it is thanks to the RCM&E Magazine editor who found a forum person who could save me from 2 days of grief trying to log in to this Forum. The reason is that I found this thread by accident after days of trying to find out which motors / ESCs are suitable for the Dumas DH Rapide kit because - as you have found out - the recommended motor is no longer available. I had a wonderful exchange of emails with Pat Tritle who designed the kit but his suggestions are not available in the UK. I did receive an expensive box of electronics from the shop that sold me the model but that only proved they had no clue about the kit. (motors too fat and powerful, props so long they would have ripped out the fuselage sides etc. 

So whinge over, please tell me what motors and matching ESCs you used or would suggest. 

By the way - my good lady wife bought this wonderful kit for me to build over Christmas because it was the first aircraft I ever flew in aged 8. Bea service to the Isle of Wight with a female pilot accompanied by my sister and ex WWII RAF pilot Dad.

 Hi Ian, welcome aboard the build,

 

Please note David's previous comment about 2S vs 3S lipo, I have gone for 2S, but will see how the build goes. As for motors and ESC's needless to say I contacted George at 4-Max for advice. 

 

We recommend the following

 

2x Motor         PPOM-2314-2400    £14.99 each www.4-max.co.uk/ppom-2314-2400.html

2x ESC           4M-ESC12A            £13.95 each www.4-max.co.uk/4m-esc12a.html

2x Prop Driver  PP-PDRV30-50        £ 2.75 each www.4-max.co.uk/propdrivers.htm

1x Prop          APCE 6x4 Standard  £ 2.55 each www.4-max.co.uk/apc-props.htm

1x Prop          APCE 6x4 Pusher     £ 2.80 each www.4-max.co.uk/apc-props.htm

1x Battery      PPL-60C2S-1300      £11.00 each www.4-max.co.uk/lipos.htm

2x Aileron Servo    ES9051             £ 6.99 each https://www.4-max.co.uk/servo-emax-ES9051.html

2x Ele Rud Servo   ES08A II           £ 4.99 each https://www.4-max.co.uk/servo-emax-ES08AII.html

 

Please have a look through our “Miscellaneous Accessories section to see if you need any of these items

https://www.4-max.co.uk/accessories.html

  

This Setup will give loads of power and you should be able to cruise around at ½ - 2/3 rds throttle

 

You may even get away with a 2S 1000mAh battery

 

 

Now as you said I will just need to check the 6x4's do fit, unless you can confirm either way? 

[Ian Lauder]

Thankyou so much Chris. It is so good to be in touch with a fellow UK Dumas DH Rapide builder - at last.

Pat Tritle suggested linking the two aileron servos and the two ESCs with 'Y' cables or were you planning to synchronise them by adjusting the transmitter controls?

It is many decades since I built a balsa and tissue model or flown RC and never electric so this is all new to me.

Sorry, can't help with the 6x4s but can you explain the use of a standard and a pusher prop - is it the same as contra-rotating props? 

I am certain will have many more naive questions but I will go through all you suggest and let you know how I get on.

Cheers

Ian 

[Chris Walby]

On holiday at the moment, so if you can wait I'll measure the props when I get back and confirm the 6x4's are ok. As for standard/pusher or normal/contra-rotating its the same thing. As you appreciate its not easy with model IC to achieve counter rotating engines so its a case on make do. The problem is most noticed when taking off (P effect) by a swing on the the model to the left and worse but rapid opening of the throttle. The motor/engine thrust line can be adjusted to counter this and other in flight issues although I agree with Peter Miller...swing can be countered with the rudder for most occasions. This brings us to electric power and with the limited selection of standard/counter rotating props, there might be a pair that match you application then why not use them. 

 

 

 

 

 

 

 

[Ian Lauder]

On 29/01/2022 at 20:33, Chris Walby said:

On holiday at the moment, so if you can wait I'll measure the props when I get back and confirm the 6x4's are ok. As for standard/pusher or normal/contra-rotating its the same thing. As you appreciate its not easy with model IC to achieve counter rotating engines so its a case on make do. The problem is most noticed when taking off (P effect) by a swing on the the model to the left and worse but rapid opening of the throttle. The motor/engine thrust line can be adjusted to counter this and other in flight issues although I agree with Peter Miller...swing can be countered with the rudder for most occasions. This brings us to electric power and with the limited selection of standard/counter rotating props, there might be a pair that match you application then why not use them. 

 

 

 

 

 

 

 

Another naive question for when you are back off holiday - Do you just revers the wiring on one motor to get one prop clockwise and the other clockwise? An if so I assume the motors are happy to turn in either direction?

[David Holland 2]

If you are using brushless motors you just connect the three wires to the ESC and test (without props if you value your fingers!). If the direction of rotation is wrong, swap two of the wires.

David

[Ian Lauder]

On 28/01/2022 at 22:00, Chris Walby said:

 Hi Ian, welcome aboard the build,

 

Please note David's previous comment about 2S vs 3S lipo, I have gone for 2S, but will see how the build goes. As for motors and ESC's needless to say I contacted George at 4-Max for advice. 

 

We recommend the following

 

2x Motor         PPOM-2314-2400    £14.99 each www.4-max.co.uk/ppom-2314-2400.html

2x ESC           4M-ESC12A            £13.95 each www.4-max.co.uk/4m-esc12a.html

2x Prop Driver  PP-PDRV30-50        £ 2.75 each www.4-max.co.uk/propdrivers.htm

1x Prop          APCE 6x4 Standard  £ 2.55 each www.4-max.co.uk/apc-props.htm

1x Prop          APCE 6x4 Pusher     £ 2.80 each www.4-max.co.uk/apc-props.htm

1x Battery      PPL-60C2S-1300      £11.00 each www.4-max.co.uk/lipos.htm

2x Aileron Servo    ES9051             £ 6.99 each https://www.4-max.co.uk/servo-emax-ES9051.html

2x Ele Rud Servo   ES08A II           £ 4.99 each https://www.4-max.co.uk/servo-emax-ES08AII.html

 

Please have a look through our “Miscellaneous Accessories section to see if you need any of these items

https://www.4-max.co.uk/accessories.html

  

This Setup will give loads of power and you should be able to cruise around at ½ - 2/3 rds throttle

 

You may even get away with a 2S 1000mAh battery

 

 

Now as you said I will just need to check the 6x4's do fit, unless you can confirm either way? 

Can I ask please about your selection -

why you chose two types of servos ? Why not have all lightest weight ones and why mix digital with analog?

Will you have "Y" splitter cables connecting the ESCs and the aileron servos?

[Chris Walby]

On 02/02/2022 at 09:16, Ian Lauder said:

Can I ask please about your selection -

why you chose two types of servos ? Why not have all lightest weight ones and why mix digital with analog?

Will you have "Y" splitter cables connecting the ESCs and the aileron servos?

Hi,

 

Apologies for my tardy reply and regarding props

this is 6x4 overlay and looks good to me.

 

As for the servos, its what George at 4_max suggested

and yes ESC's will be Y leaded for control....no need for differential thrust and it has a working rudder so I'll us that! Tried differential thrust on a model that had a fixed rudder and it produced a very horrible un-scale yaw in flight so won't be doing that again (it doe have its uses, but not here IMO).

 

And a bit more progress!

Sort of finished one side and started on the other! Ian how are you getting on?

 

 

[Chris Walby]

A bit more progress due to weather!

 

Both fuselage sides glued (not complete), which still leaves bowing them, nacelles and tail surfaces next, then it might look like some real progress!

 

I'll have another weigh in after dog walking,,,Collies away 

 

 

 

 

 

[Ian Lauder]

Welcome back.  I hope I have uploaded my Rapide pic.  I haven't worked on it much reently due to house hunting and selling our 2 historic canal boats. I am thinking of installing the aileron servos in the tip end of each wing if I can find servos small enough and matched with the lipo.  I need to order the hardware now and tried to email 4Max through their website but clicking on their email tab does not work. I will try telephoning them tomorrow. (if we don't get blown away).

Cheers, Ian

[Chris Walby]

Hi Ian,

Well ahead of me then ?

 

I had a quick look at in wing servo direct to aileron and it seemed to be a lot of modifications for little gain so put it on the back burner. Don't know why the servo needs to match the lipo? The lipo be it 2S or 3S is connected to the ESC's which as long as they are rated for 3S and you use only one of the ESC BEC's will provide the right voltage for the RX (That's what supplies the servos). My 12A ESC is rated at 2A for the BEC and as its only got to supply 4 servos then that will be more than enough).

 

For bigger models some advocate using both ESC UBEC's via diodes, but I prefer George's approach of a separate high power UBEC. 

 

Any tips for the UC, joining the two fuselage half's  or the back end?

 

Good news, after a weigh in of all the bits glued and not fitted it looks like the AUW is getting closer to 500g ?

 

PS George can be a bit tricky to get hold of, but has a wealth of knowledge and advice + service is normally very prompt.

 

 

[Ian Lauder]

I was looking for micro servos to put in the wingtips and in an ad for a Ripmax type it said "Described as the world's most power-saving micro servo, it draws only 310mA at stall. Suitable for high voltage applications such as 2S Li-Po." Which made me wonder if other types burn out?

 

As for the undercarriage. I just followed the instructions being very careful to make sure I chose the correct gauge of wire.

 

The method I devised to keep the fuselage square whilst gluing the sides together might look crude but it worked. I photocopied the plan and glued it to a board. Then I sawed up the blocks from a length with good square edges and stuck them along the plan. By the time I saw your last message, I had knocked off the board to use elsewhere and have just placed them back for the photo, so it looks a bit inaccurate. I glued in the crosspieces to push the sides firmly against the blocks and used a combination of balsa shims and a couple of temporary solid sheet formers to maintain shape where the top side is narrower than the bottom.  I left it fir two days to set hard and it worked well.  

 

Hope that helps

Ian   

[michael harper 2]

I've just bought the two motors from 4-max. The only problem I see is the x frame mount for the motor is too big. It will stick out of the cowling if the motor is mounted forward for prop position. I also managed to buy years ago the motors specified on plans but with a different gear ratio and got a replacement kit with correct ratio. 

[Shaun Walsh]

18 minutes ago, michael harper 2 said:

I've just bought the two motors from 4-max. The only problem I see is the x frame mount for the motor is too big. It will stick out of the cowling if the motor is mounted forward for prop position. I also managed to buy years ago the motors specified on plans but with a different gear ratio and got a replacement kit with correct ratio. 

Would a couple of Hacker 10-7L motors fit if they were front mounted rather than rear mounted, 21mm diameter?

Hacker motor