Forum sponsored by:

Avro Vulcan

Graham Dorschell 68" 4*EDF

Search for: in Thread Title in

<< First < Prev 1 2 3 4 5 6 7 Next > Last >>

andy watson	09/02/2011 21:28:48
1931 forum posts 20 photos	Well it looks like this build might be stop start from the very beginning! Finding the time is proving tough, but as always I am in no hurry. Also the plans are taking quite a lot of head scratching to decipher in places! To be fair to Graham he has said as much, and has always said they are for experienced builders. I seem to have got myself lumped into this category with only 2 builds behind me! The plans I have are "preproduction", so I guess they will get cleaned up. As a very definate plus point though, the CD of build photos I was also sent is invaluable at helping pick my way through. Anyway, I normally start on the wings for some reason- so I have started on the fuselage. The front of the fuselage is very straightforwards. The only thing of any note at all is I have bought a 2nd hand balsa stripper- excellent piece of kit for saving money. All joints are glued with thin cyano. The main fuselage section is then built onto this using the (quite thick) stringers as joiners. It's quite a clever system, and should be plenty strong enough as the front will be under very little stress. One of the formers needed making up and cutting for the new design. The formers have flat sides and bottom- the underside will be made up as a seperate hatch, and the sides are covered with what look like giant sized wing ribs. The wood pack has been a real benefit to speed. In fact with the plans being a bit tricky in places it's been useful to be able to look at the precut pieces, match them to the old pusher plan and then see how they match up to the new plan! Having said that, I think I am coming to the conclusion I won't buy a wood pack again. Little things annoy me- where wood is warped, however slighly; or where plywood has that filler/glue patches. I know my own wood selection would be better- albeit I am probably just being over selective. Another little thing that annoyed me is the joining of the ribs. I have accepted some of the ribs needed producing in 2 parts (the big fus side ribs were in 4!), but if you look at the next photo: I'm not sure if it's clear, but the fus side is made up of the 2 "ribs" that are made from a ply/balsa laminate. Fair enough, but the joins in the ply/balsa ribs match perfectly. I would have thought offsetting that join by an inch would have prevented a join running the full thickness of the rib, and made it much stronger. If I had cut my own ribs this is how I would have done it. Anyway, that's where I'm up to. I have been having some interesting email chats with some guys selling electronic retracts. Hopefully we have a little progress there, but it's been interupted by Chinese new year. Oh, and for those that have built the previous version- how did you work out where the intake sheeting goes to set the next rib? I can't seem to get a measurement point!
andy watson	16/02/2011 22:26:25
1931 forum posts 20 photos	There has been a little progress- though it's not through a lack of time/effort. Just frustratingly little to show for it. Worse there is no one else to blame than myself. I am adding the intakes and next ribs out on the fuselage, but for some reason I keep making a compete pigs ear of it. I will detail it later with a photo or 2. But I really need some help from some people with EDF experience here, so I hope someone is reading! #1) Graham secured his fans with glass tape. I think they were then also supported by the thrust tubes which were also taped in place. I don't like this method. Bearing in mind there is very little extra room around the outside of the fans, and each wing will have 2 fans next to each other with nothing directly between them, does anyone have any suggestions (including the fact that I am worrying about nothing). #2) The thrust tubes Graham used are made from cardboard postage tubes that he has cut down and glass taped (I think he has shares in the company!). What alternatives are there to cardboard for this (which seem potentially heavy). #3) The plans have the fans at the front of the tubes. In effect there is no inlet pipe, and a 50cm exhaust pipe. I have read that you get better thrust having a longer inlet and the exhaust limited to maybe 15cm. The plans don't seem to have any major reason not to move the fans (except possible C of G). Is it worth pushing the fans back? How much difference will it make? The pipe is straight (obviously tapered though) #4) The fans have a removeable inlet lip. I have read this makes a massive difference to thrust. Fitting them will be a pain. Again- how big is the effect compared to a straight tube inlet? For the record I have 4*750W of power on a model with a target weight of 14lbs (214W/lb) Thanks in advance for the help
Tim Mackey	16/02/2011 23:29:21
20206 forum posts 244 photos 16 articles	1) Silicon sealant? 2) Acetate, laminating film etc.... 3) Could muck up your COG? - not sure if it will make a huge difference in power 4) Inlet lips make a big difference if the fan is not fed by an inlet tube as such. 5) Plenty powerful enough - in theory - assuming that power converts to proper thrust
andy watson	17/02/2011 08:56:42
1931 forum posts 20 photos	Cheers Tim, re. #2, those materials seem awfully thin (and hence weak). How strong does the tube need to be? This was one of the things I was worried about really- the balance of over engineering and adding unecessary weight. re. #4. I guess I better try fit those lips then, or push the fans back and use tubes.
Tim Mackey	17/02/2011 10:46:14
20206 forum posts 244 photos 16 articles	Laminating film is available in different thickness, but TBH, even the thinner acetate sheet should be OK if supported in various places with a ring of ply, or maybe you could sleeve it, or add depron ribs to the outside of it ? I think the lips would probably be best - if you can get the front of the shroud in the right spot, then the lips could blend in nicely with the surroundings. I did some practical testing of the effect of the lips some time ago, Ill see if I can find them.
Tim Mackey	17/02/2011 10:49:36
20206 forum posts 244 photos 16 articles	Try THIS Andy.
Tim Mackey	17/02/2011 12:18:25
20206 forum posts 244 photos 16 articles	Seems a lot of the original videos, and pictures have been lost after the platform changes a while back. However the pertinent info in this case is that in identical static test conditions, the 90mm midifan with no lip or spinner produced 1444 grams of thrust, and with the spinner and intake lip fitted this increased to 1817 ( over 25% increase ) The smoke pellet testing videos also clearly showed the smoothing effect on the intakes.
andy watson	17/02/2011 15:04:30
1931 forum posts 20 photos	Cheers for that Tim- well worth making the effort to fit the lips then. I am still a bit unsure about the tubes though. The method you describe seems perfect where the tube runs inside a [bigger] fuselage. I am trying to squeeze them into the wing, so size is an issue. This is probably why Graham went for cardboard as a fully self supporting structure.
Tim Mackey	17/02/2011 16:55:11
20206 forum posts 244 photos 16 articles	How about some light paper rolled into the tube shape you need, then covered with lightweight tissue and a few coats of Poly-C
BizJet Tech	17/02/2011 17:51:46
10 forum posts 16 photos	Hi. I bought just about all the plans available for the Vulcan and settled on Graham’s. But as I’ve just returned to modelling after over 20 years, I’m fascinated by the explosion in electric power. I remember having an Electric Islander which did a great job of converting volts to noise (just like the real one) it certainly didn’t fly!! I decided to scale down Gordon’s model to 45” approx and build it mainly from Depron. I kept the fuselage sides and the wing root ply. But I only used 1/32” (1mm) ply. The fuselage and wing ribs are 6mm laser cut depron. The stringers are all 1/8 square balsa. Skin is 3mm depron. The nose went together beautifully. I was concerned about the joining so I made it so the skin fitted between the fuselage sides by flattening the sides of F5 and an extra frame which butts onto F6. Looks scale too with the splitter plates like the real thing. Like Andy, I’m concerned by the lack of any structure between the fuselage and wing. I’ve put in 2 sub ribs which are a 1/32 & 1/8 balsa sandwich to support the motors. I’ll use a couple of spots of silicone to secure them. I tried to make ducts from 3mm depron but kept cracking it, so I’m trying to see if 160 grm postcard paper wrapped around 41mm waste pipe and soaked with Eze-Kote to stiffen them. Funnily, the card is heavier than depron. I’ll put a support and another ply sub rib in the rear area. I’ll then paint it all with fibreglass resin which hopefully will strengthen the structure. I’ll try to make a mould of the underwing jetpipe fairings and press out 3mm depron for the undersurface to protect the ducts. I’ll cover the lower surface with light glass fibre/resin for ding protection.
TonyS	17/02/2011 19:02:11
1141 forum posts 323 photos	Have you considered cartridge paper for the tubes - covered with lightweight glass cloth coated in Poly-C? This is what I'd use. You can leave some untreated glass cloth protruding to make the right intake lip. Just a thought......
Graham Dorschell	22/02/2011 03:13:14
77 forum posts 40 photos	Posted by jez on 24/01/2011 21:58:09: hi andy nice to see the build comming on , i have been building the same kit for 12 months on and off but mine is a pusher prop one , greham is very helpfull , just got to take the plunge and fly her now , have put lots of pics on my album of the build cheers jez Have you flown it yet ?
andy watson	25/02/2011 11:16:01
1931 forum posts 20 photos	OK, there has been some progress, but not as much as you might expect from the time I have actually spent. Anyone that reads my blogs knows I will call it as I see it, and if I have issues with the plans/kit/anything then I try make it clear. Well in this case it's all me. The job is simple- I need to fix the next 2 ribs in place, which will include the air intakes at the root of the wing. It is probably easier to show the finished job. From the photo you can see 2 tubes at the bottom. These are stainless steel, and are simply there to make sure the outer rib is aligned properly. They are now removed (as the ducting will fit right in the middle of this space). The permanant fixture is the angled sheets of balsa that joins the rib to the fuselage and acts as the top/bottom of intakes. These were the bits that took a long time for no good reason. The system is simple. 1/16 sheet balsa cut to give a 146mm space between the ribs to allow the motors to fit. They are glued to the fus/rib and strengthed using triangles. Easy. It took ages, and I still don't know why. The cyano refused to grip, I ended up marking it out about 4 times, I had to take them off and on about 3 times because I got them in the wrong place. I just don't know. I do know I ended up using both the new EDF plan and the old pusher prop plan to finally satisfy myself I was in the right place. I ended up having to glue them with aliphatic wood glue one end at a time. So I have done them, but they took ages, and I still don't really know why- but I blame myself! It looks a bit like a rocket!!
Graham Dorschell	25/02/2011 12:25:58
77 forum posts 40 photos	Hi andy , looks like the intakes a bit on the small side on the ends , I would make it larger ?? have a look at the pics on the disc I sent , worth doing it now before you start sheeting over .
Martin Harris	25/02/2011 13:18:32
3798 forum posts 104 photos	Sure you've got the right plan, Andy? Looks more like Thunderbird 1 to me!
andy watson	25/02/2011 19:45:21
1931 forum posts 20 photos	Hmm, Martin, you might be right! Graham, I'm glad your still around! Just goes to show that modellers are interested in modelling, no matter what the distractions! The final positions I decided on were as a result of the new EDF plans, the pusher plans and the photos. For those of you that are wondering what the problem is, I will try explain it (probably a similar issue to the full size plane). Think about the rib rather than the fuselage side- and more specificaly how the intake sheets joins to it. As you move from the tip of the rib the depth of that rib increases. This means the intakes at that point can be either as far forward as possible for a nice neat looking leading edge, or further back but with what looks like a big chuck chopped out of the wing. However, the further forward the intake, the narrower the rib, and therefore the intake. Anyway, some maths. My intake is 146mm wide. At the fuselage it is 69mm high, and at the rib 38mm high. My calculations make this an area of 7789mm2. Each fan has a FSA of 3231mm2. The intake serves 2 fans, therefore the 2 fans have a total FSA of 6462mm2. This means the intake is 121% of the FSA of 2 fans. Is this enough? It should be noted that there is a secondary intake as a gap in the sheeting on the underside of the wing. From memory this is approximately 150mm*40mm, or 6000mm2, or 93% of the fans FSA. Having said that this will allow air in at an oblique angle, so I presume it will be less efficient than the intakes on the front of the wing which has a clean straight run in. So given those numbers, what do people think? Is my intake too small? To increase it will mean bringing the intake sheets back further from the front of the rib and make a bigger gap- which to my mind will look wrong. Comments more than welcome!
BizJet Tech	25/02/2011 22:46:00
10 forum posts 16 photos	I went through something similar regarding the intake. Mine is 100mm wide with inbd 35mm and obd 20mm = 2750sq mm. The EDFs are AEO Tech 40mm with 23mm motors giving an FSA of 1700 sqmm for the pair. Now I've got to tune the jetpipes! Alan
Tony Prince	26/02/2011 05:15:46
725 forum posts 13 photos	I think you're on the right track there Andy, but, your intake must be a pure box, no air masses coming in from the side, top or bottom to interfere with the flow.
andy watson	26/02/2011 08:50:38
1931 forum posts 20 photos	That's interesting Tony, because that's exactly the opposite to the design here. The intake is a straight box, and the top of the wing is sheeted. In fact Bizjets photo shows it nicely- the underside is left open (ignore the big lightening hole on the fuselage). The numbers for the sizes are above- but in your opinion you think the extra (non-scale) underwing intakes will do more harm than good by dirtying the airflow onto the fan?
BizJet Tech	26/02/2011 09:09:25
10 forum posts 16 photos	Actually, I'm going to sheet over top & bottom with 3mm Depron and rely on the intake being big enough. I'll probably leave the lightening holes.

<< First < Prev 1 2 3 4 5 6 7 Next > Last >>

All Topics | Latest Posts

Please login to post a reply.

Shopping Partners

New Poll - Crash Causes

Discuss

Modelflying Offers