Marston Pterodactyl - RC Groups
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Mar 16, 2006, 05:26 AM
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Build Log

Marston 80" Pterodactyl


See the note at the bottom of this post regarding a PDF downloadable copy of this thread.



I ordered my kit many months ago now and I have decided that it is time to clear off the desk and get started.

This kit is a 'short' or 'builders' kit. I am a slow builder anyway and having to locate a number of the bits and pieces as I go will slow it down more. However, I will try and keep posting information here as I go along.

Key Stats

Wing Span: 80 inches
Web Page: http://www.pteroworks.com/pteros.htm
RTF weight: 68 oz (with Li-poly)
Power: twin brushless motors
Controls: full house (Aileron, Flaps, V-tail, Throttle)

What arrived in the box?

The kit arrived well packed with the following:

- instructions, 3 pages
- two (2) copies of the full size plans
- laser cut ply and balsa sheets (all bundled and protected with some spare wood)

The plans are excellent, CAD drawn, full sized sheets.

Suggested Equipment List

Servos: 2 x HS-81 for V-tail, 4 x HS-5125 for wings
Motors: 2 x Mega 16/25/3
Prop: 2 x APC 6x4E
ESC: 2 x CC25
BEC: Ultimate BEC
Battery: 3S2P 2600 (ie. Qty 2 of 3S Polyquest 2600)

Additional Building Material

You will need additional building material:

- spruce sticks
- balsa sticks
- balsa sheet
- brass tubes for wing joiners
- CF rod, tubes and flats
- covering material
- misc. hardware for control surfaces etc.

Important Information - 24 Feb 2009

A great downloadable version of this thread is available as a set of PDF files. These are all downloadable in posts #368 & #369 in the thread on this page https://www.rcgroups.com/forums/show...492408&page=25.

Flight videos of the the end result of this build thread can be found here: https://www.rcgroups.com/forums/showthread.php?t=810466

A few posts with photos of the 'dactyl:
https://www.rcgroups.com/forums/show...&postcount=299
https://www.rcgroups.com/forums/show...&postcount=307
https://www.rcgroups.com/forums/show...&postcount=321
Last edited by TugBoat; Feb 24, 2009 at 06:37 AM. Reason: Added information on the PDF summary
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Mar 16, 2006, 05:28 AM
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Documentation Errors


I will try and update this post with any errors that I find in the documentation as I go along. I am working from the plans of 10/4/2005.

At this stage the errors I am aware of are:

a) The plans show the battery as 2S3P, this is should be 3S2P. Ron Marston says that he actually uses 2 x 3S Polyquest 2600mah - ie. 5200mah 3S2P.

b) The "Setup and flying" section of the instructions mentions a lot of 'differential' for the elevators. This should read exponential.

c) The plans show the wing tips constructed from ply+balsa. This is no longer correct, the Rev. B kit has the wing tips as 2 x 1/16" balsa - construction will be covered later in the thread.

d) The plans show the bottom of the ailerons and flaps as ply. This is no longer correct, the Rev. B kit has both the top and bottom of the ailerons and flaps as 1/16" balsa.

e) The Rev.B kit does not have a doubler for rib 4. This is an unintended omission and will be corrected in later versions of the kit.

f) The precise lengths of the parts of the suggested wing joiner is unclear. The instructions say: qty 2 of 5.5" brass tube with 10.5" of rod, the plans say 10" brass tube and 10" of rod.

g) The plans show the inner spars going onto the top of rib 9. However, the build photos show the spar butting up to rib 9. Also the laser cut parts do not allow for the inner spar to slot onto the top of rib 9.

h) The instructions at wing step 10 instruct you to remove the alignment tabs on ribs 1 to 8. Do not do this, the tabs are removed once the entire wing has been constructed.

i) The instructions at steps 6 and 13 have the construction broken into two parts (listed as ribs 1 to 9 in step 6 and ribs 10 to 19 in step 13). Rib 9 should actually be part of the step 13 ribs. Ie. the ribs are construct 1 to 8 and then 9 to 19.

j) A text annotation on the plans show the dihedral as 5 degrees. In fact the total dihedral at the join is 7 (or perhaps 7.1) degrees.

k) The plans show the shear webs on the leading edges of the inner spar sections ending at different ribs. The right wing has the double section all the way to rib 9 (ie. over the overlapped joint) while the left wing has it ending at rib 8. The build photos on the web site show the double section ending at rib 8.

l) The instructions (Body: Step 1) give the V-tail as 100 degrees and the plans show 110. Use the plans value of 110 degrees, the instructions contain a typo.

m) The plans show a side view of the body and also a top view. The position of the body spacers is different in the two drawings. I used the position as shown on the top view because I was using that for construction before I realised there was a difference.

n) On the top view of the body the head is not quite central with respect to the body. The neck pieces are therefore not quite in the correct place w.r.t. the head. The error is only 1mm or so, this is not a serious problem but may confuse you if you start taking measurements from this drawing.

o) The laser cut neck ply pieces are not the same shape as the neck pieces shown on the plans. Again not a serious problem, however I would suggest drawing the actual shape onto the plans for reference purposes.
Last edited by TugBoat; Jan 09, 2007 at 01:09 AM.
Mar 16, 2006, 05:29 AM
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Before I start there are a few things I need to work out.

Wing joiners

The suggested wing joiner is a 3/8 x 10 inch carbon rod in a 13/32 x 10 inch brass tube.

This sounds a bit heavy, I need to go and find out what the rod will weigh.

Servos

The suggested wing servos are the digital HS-5125MG, these are very pricy and I don't know that the cost for 4 of these is justified - perhaps I will just switch to the HS-125MG. Also there may be an issue with my synthesised EVO and digital servos - more research required.

Motor / Prop

The motors need to be built into the wing so I need to sort out before I get too far along exactly what I will use for the motor.

The suggested power plant is Mega 16/25/3 with APC 6x4E in direct drive.

The motor calc. I have says that each motor will draw about 14A (145W), run at 17,500 RPM and give about 26oz static thrust and 15 oz in flight thrust.

I would have thought I should be able to do better than this with some sort of outrunner/geared arrangement - I suppose the problem is that the props can't be too big because it needs to belly land.

Does anyone have any other suggestions for a motor/prop arrangement, or anything else for that matter?

Tim
Mar 16, 2006, 05:38 AM
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vintage1's Avatar
Quote:
Originally Posted by TugBoat

The suggested power plant is Mega 16/25/3 with APC 6x4E in direct drive.

The motor calc. I have says that each motor will draw about 14A (145W), run at 17,500 RPM and give about 26oz static thrust and 15 oz in flight thrust.

I would have thought I should be able to do better than this with some sort of outrunner/geared arrangement - I suppose the problem is that the props can't be too big because it needs to belly land.
What? No retractable claws?
Quote:
Does anyone have any other suggestions for a motor/prop arrangement, or anything else for that matter?

Tim
I'd say that a pair of motors like those running at 14A is a real waste of them.. if you want someting in that power class why not put a pair of gearad long cans on it?

Or if you must, a pair of permax 450T's - they will produce similar on a 6x4,albeit drawing more like 18-20A apiece...

I'd definitely go brushed and geared - if only to save money on speed controllers. Try 2.33:1 gears, long cans and 7x5 APC 'E' props..
Mar 17, 2006, 04:32 AM
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Of course, no claws! Perhaps I should look at a modification...

I understand exactly what you are saying about the speed controllers and using brushed motors. I normally make my own brushed ESCs and that is quite an attraction.

I must admit that I don't really like gearboxes, I have them on a few planes and the cheap gearboxes are noisy and heavy. Also a S400 and gearbox is quite heavy. I have also normally found that a S400 + gearbox costs about the same as a brushless motor.

I was thinking that perhaps a pair of RCer WARP 4 5-turn motors could be quite good. Will drive a 7x5 if I want, only weigh 73gms (one ounce less than the 16/25/3).

I think I also need to use Motocalc as well to cross check the numbers that I got for the Mega to make sure the Web system I used is in the ball park.

Tim
Last edited by TugBoat; Mar 17, 2006 at 05:05 AM.
Mar 17, 2006, 05:08 AM
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Ok, so I have unpacked all the laser cut parts. Everything looks fine, note that the ribs all have alignment tabs to get the washout correct as you build!

A word of warning: there are a number of small wedge shaped bits that you need to build the ailerons and flaps. These tend to drop out of the sheets - I appear to have lost one already. I have used a bit of sticky tape to hold the others in so that I know which ribs they correspond to.

I am going to start by extracting ribs 1 - 9 and the doublers. This will give me enough parts to get the central wing section completed. I can't find the doublers for rib 4 so I will make them out of scrap material.

As these ribs come on two identical sheets I am going to use ribs from alternating sheets to try and keep the balance as even as possible. So I am going to put the ribs into two boxes, take out all the lightening holes and give each side of the ribs a fine sand.
Mar 17, 2006, 05:37 AM
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I put a couple of strips of double sided tape on the bench and use these to hold the ribs a few at a time and I sand one side, vacuum the dust up, sand the other side and then vacuum again.

If you do this be carefull - some of the ribs get thin at the trailing edge. It would be easy to break bits off.

I also run the sanding block over the edge to remove any of the little bits that are left to hold the part in the sheet.

I suppose you could call this the boring bit!
Mar 17, 2006, 06:24 AM
Registered User
Just about it for tonight.

(Wing: step 4 )

I am going to laminate the doublers to ribs 1-4 using PU glue and a lot of pressure. The doublers go on the outside of the ribs so at this stage you need to decide which box of bits is the left and which is the right. Also the doublers for ribs 1 & 2 are 1/8 ply and the others are 1/16 so I will laminate them in two lots so I get the clamps down hard.

Note: the Rev. B kit is missing the doublers for rib 4. You can make a template for these doublers by drawing around rib 4 onto a sheet of paper - also mark the large hole. Then put a rib 3 doubler on the paper so that the hole overlaps and draw around the doubler. Now you cut the paper around the rib 3 doubler line, trim the top and bottom to the rib 4 outline and that's it. Use the paper to mark the shape onto some spare 1/16 ply, cut out two doublers, sand them.

- Locate the position of the doubler on the rib and mark around the outside so that you know where to apply the glue. Note that the doublers need to go the 'right way up' otherwise the spar and tube holes will not line up.

- My ribs also appear to have a hole that is slightly too small for the 13/32 wing joiner tube. The doublers are correct! I think I will enlarge the holes in the ribs later after laminating.

- Apply a very thin layer of PU to the parts. Spread in out with an old credit card and try and remove as much of the glue as possible.

- Put between two sheets of waxed paper, check alignment and then clamp between two sheets of wood.

- Leave for at least 24 hours, the longer the better.
Last edited by TugBoat; Mar 26, 2006 at 03:27 AM.
Mar 18, 2006, 11:41 PM
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(Wing: Step 3)

The next thing to do is to joint the wing leading edge pieces together using the doubler at the motor mount position to strengthen the whole thing.

Because of the way the sheets of material are arranged there are actually twice as many doublers as you need. At this stage I am going to just use one doubler on the top of the join - I will work out the motor mount details once I get a bit further along.

Again I am going to laminate these with PU, and use the plans to get the alignment correct.

- Remove the parts from the sheet, sand both sides and also the edges to get rid of the the little rough bits.

- Position on the plans, place a small piece of grease proof paper under the join to protect the plans, mark the area you want to glue.

- Again apply a very thin layer of PU, spread very thin, align parts and put as much weight as you can on top.

Repeat for the other wing (my work table isn't large enough to do both sides at the same time).
Last edited by TugBoat; Mar 19, 2006 at 12:48 AM.
Mar 19, 2006, 01:24 AM
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Tail: step 1 - sorry, we are jumping around a bit, but while one thing is drying it is nice to have something else on the go.

The "two tails (or feet)" - so that's where the claws are - are constructed out of two pieces of 1/4" balsa each, and the control surface is a 3rd piece of 1/4" balsa. They need to be glued and then sanded to an "aerodynamic profile".

- Again these are on two sheets so select parts from each sheet to try and even out any weight variation. Put the parts into the 'left' and 'right' boxes.

- At this stage just a light sand around the inside of the lightening holes and also to knock of the rough bits.

And these are the parts you have. The square shows the line that is at right angles to the CF tubes that are used as longerons.

(Raw weight of these 3 parts: 25gms)
Last edited by TugBoat; Mar 19, 2006 at 02:26 AM.
Mar 19, 2006, 01:26 AM
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Tail: step 1 - question

I think I will use some plastic pinned hinges for the tail. I have never used these before, so we will see how it goes...

I think for the "aerodynamic profile" I will sand the profile as follows:

- along the line 'L1' I will make the material 1mm thick
- along the line 'L2' (hinge line) I will make it 4mm thick
- along the line 'L3' I will get to the original 1/4" thickness
- I will just round off the leading edge so it 'looks OK'
- the hinges are mounted as shown

Any comments?
Can I use the Dubro small nylon hinges in 4mm of material?
Have I got enough hinges - 4 over a distance of 10.75 inches?
Mar 19, 2006, 02:00 AM
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Quote:
Originally Posted by TugBoat
I am going to laminate the doublers to ribs 1-4 using PU glue and a lot of pressure.
Now, that's an awesome looking model. Just what I need to get revenge on the magpies - and empty my bank account.

Just one question - what's PU glue?

Quote:
I think I will use some plastic pinned hinges for the tail. I have never used these before, so we will see how it goes...
I used those nylon pin hinges all the time back in my sailplane days - they work pretty well, as long as you take time installing them. Make (or buy) a jig to cut the slots down the center line of the surfaces. Use plastic cling wrap to stop glue getting into the joints. Can be reinforced with pins, but usually not necessary.
Mar 19, 2006, 02:19 AM
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dangitman:

Thanks for the info - I did wonder if 'anyone was out there'...

Sorry, PU is short for Polyurethane - "Gorilla glue" I think from memory. I try not to use much because it is heavy - but it is good for laminating and you don't use much in this application.

I must admit I was attracted to this model on the basis of looks - only time will tell if mine looks as good.

I have a jig for the slot cutting. I was going to cut the slots and get the hinge installation correct before I sand the shape. I think that this should make it as easy as possible.

Thanks for the cling wrap idea, I will keep that in mind. I was sort of wondering how to keep the epoxy out of the hinge itself.

Tim
Mar 19, 2006, 02:34 AM
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Quote:
Originally Posted by TugBoat
Sorry, PU is short for Polyurethane - "Gorilla glue" I think from memory. I try not to use much because it is heavy - but it is good for laminating and you don't use much in this application.
Hmmm, I think I have an ancient tube of Gorilla Glue around. Not sure if it is the same thing. I usually use white glue - or PVA as we call it here (Poly Vinyl Acrylic?)

Quote:
I have a jig for the slot cutting. I was going to cut the slots and get the hinge installation correct before I sand the shape. I think that this should make it as easy as possible.
Yes, I think that is by far the best idea. It's nearly impossible to do once you have sanded tapers on the edge.

Quote:
Thanks for the cling wrap idea, I will keep that in mind. I was sort of wondering how to keep the epoxy out of the hinge itself.
Slow-drying thick CA might be just as good for this purpose. Epoxy may be difficult to penetrate the hinge, and may ooze out more. It's been a while since I made a full-sized hinge, so I'lll defer to others on this point.

Another idea might be vaseline on the hinge to keep the glue out.
Mar 20, 2006, 04:03 AM
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Tail: step 1 - continued

I sanded along the join in the tail piece to get the join nice and flush and then use 'yellow' glue to join them together.

Line the hinge line up with a straight edge, weigh the whole thing down to keep it flat and to clamp the join.

(Meanwhile I have the other wing leading edge glueing, and also a few more ribs)


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