Jeffrey Cottrell 2
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Posts posted by Jeffrey Cottrell 2
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Hi Guys, thanks for your thoughts
Andy
Planning on using a spare OS40FP, so it won't be underpowered. If it turns out to be marginal I do have alternatives up to an Irvine 53. That should scare the horses.
Also, I won't be using the build structure as per plan.
Seems over engineered to me so there's plenty of scope for weight reduction.
We'll see.
Pat
Double checked the decalage both on the plan and on the screen, and they both still show some negative. Bit of a puzzle, but doesn't really matter since I will be changing it all anyway.
If you look at the bottom right hand of page 2 of the plan, you will see it titled 'Killer Watt' which is in fact the clone of an AcroWot, not the Wot4.
Also if you read the text on Outerzone, you will see numerous issues, especially with the rib outlines. I am assuming the note on washout only refers to the tapered wing, certainly can't see any purpose on a parallel chord wing.
Page 1 is usable, but I have pretty much discarded page 2.
When I start the build I will be incorporating 1 deg of positive, the reason being if that proves not to be necessary it will be easy to remove it.
Meanwhile, although it will not be a quick build, I will be keeping a running total of costs, to see how it compares with a commercial kit. Should be an interesting comparison.
Cheers
Jeff -
Hi Brian.
Thanks again for your help, much appreciated.
I did the same check as you, putting a ruler across the plan on the screen. Bit difficult to tell on that small scale, but I did find the same down angle on the wing as on the plan.
However, no matter, since I will be re-doing that section anyway.
I think we are both heading towards the same conclusion, from different directions.
Decision has been made to switch to a fully symmetrical section, probably by using the curve of the lower surface on the top as well.
Not sure that qualifies as a recognised section, but it works on the TLAR principal. Only thing I would change is this.
I see your point about setting it up zero-zero to start, but I would be inclined to have a small amount of positive, say a degree or so, at the start, on the basis that it would be easier to remove if necessary.
Other than that, we are on the same page.
Will let you know how it works out.
Jeff -
Hi Brian
Been re-reading your post. Lots of useful info, thanks for that, but it does leave me in a little bit of a quandary as to how to proceed.
First of all, although I have decided to dispense with page 2 altogether and go my own way, I do notice that the rib shape as shown on that page is almost identical to the outline as shown on the fuz side view on page 1.
Also the rib outline as shown is very similar the that on my Limbo Dancer. This has flown very well for some years now, but its flight envelope is different to that I would hope or a Wot4 lookalike.
Rough measure says this is at 1/2 degree positive, which would indicate that a semi-symmetrical aerofoil does in fact still produce lift even at very low values of decalage. However it might also mean that this set up would produce a flight envelope very similar to the LD, which is not what I want.
So, how to progress:
First of all, go with the plan as is. That is with the semi-symmetrical aerofoil at its set negative decalage. Caveman has downloaded the same plan and his shows the decalage as zero-zero.
I believe this might be due to a difference in printer characteristics, but certainly seems a better option to my amateur eye.
So, second go with the section as shown but reduce decalage to zero-zero as above. Not sure this will give the the flight style I want.
Third. switch to a symmetrical aerofoil. The plan states NACA 63018. I have had a look at this one on the computer, but it looks similar to the upper surface of the plan section, albeit with the max thickness a little further back. but also a distinct curve to the rear edges, unlike the flat rear on the plan section. This would make construction more difficult, though not impossible, but I wonder if it would be worth it given the whole plot is experimental anyway. Rough measure from the screen gives 18% thickness
Note being symmetrical this would need a positive decalage to produce lift.
Fourth, use a symmetrical aerofoill, but of my own design (ahem).
Again this would need a positive decalage, possibly about 1 - 1.5 degree, but wouldn't be an issue at this stage. I produced an aerofoil using the lower section of the plan one duplicated for the top.
Sort of TLAR system, but doesn't need too much modification of the fuz outline, and gives a 16% thickness, which looks about right.
So, I guess my question would be 'where can I get a four sided coin' to make the decision.
Anyway, your thoughts?
Jeff -
Hi Guys, thanks
J D 8
Quite right, the correct term would be decalage. My bad.
Not sure what the designer was trying to achieve, but I've found so many issues with the plan I prefer to go my own way.Caveman
Could be due to different printers producing different results, but since I will be working from my plans, will keep your diagram for info only.RottenRow
Poorly drawn hardly describes it.
If you look at the bottom right corner of page 2, it says 'Killer Watt' which is the clone version of the AcroWot not the Wot4.
As such neither the span or the wing chord match with the fuselage on page 1. Also, as you say, 63018 is a symmetrical section, but the section shown on the plan definitely is not.
All in all, page 2 is useless.
I am using the wing section taken from the fuz side view on page 1, and designing my own structure.That is definitely semi-symmetrical so I wonder where the chord line should be, if not where I have it.
All in all, confusion relgns.Jeff
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Hi Guys, quick question.
Just about to start a build of a Watt Four (Wot4 clone) from the Colin Usher plan on Outerzone.
As downloaded, the plan does have a number of discrepancies, most of which are described in the accompanying text.
However I have come across a very basic oddity which I would like to resolve before cutting wood.
So:
Given this is a high wing sports model, I would expect the wing to be at a slight positive incidence compared with the tailplane. The wing incidence on my plan is in fact negative.
Being a semi-symmetrical aerofoil, I have drawn a line from le centre to te centre and treated this a chord line for incidence purposes. On the plan, the tailplane is level with the fuz top, so using this line as a reference, the wing chord at the le is some 3mm lower than the te, i.e.negative incidence.
First things first, am I measuring this correctly?
Obviously easily corrected before I start, not so much half way through the build !Could use some advice, thanks
Jeff
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Hi Guys
Apologies, I haven't posted for a while. Believe it or not, I've been thinking.
When I first questioned the tank height I was measuring it from the carb to the centre line of the tank.
The diagram Jon posted shows the carb level with the top of the tank, when full. Logical, I suppose, but in this case makes things even worse.
So, I've come to the conclusion that this motor and model do not go together.
Much appreciate all the ideas you guys have come up with, especially the chicken hopper tank and the carb tube extension, but I freely admit I have neither the expertise or the facilities to make these work.
Couple of other things influenced the decision. First of all, although I did run the engine in the model, it never seemed very happy. Not surprised considering the tank issue. However, pulled the motor and run it on my test stand, and it ran so much better. Not familiar with 4 strokes, but 9,800 rpm on a 13 x 6 sounded pretty good. I mount my stand on a Workmate and the motor was trying to tow this across the field, so thrust is not a problem.
Also, in my kit mountain I have a Dave Smith Models Smart Move. Perfect size for the ASP, and being a kit I can choose my own tank location. Sounds ideal, and means the motor won't go to waste.
Win win.
Meanwhile what to do with the current model.
53 mounted sidewinder is very much an option, but a root through my box of junk (er, useful spares) revealed an electric motor, esc and battery just made for the job.
Decision made.
Thanks again for all your help
Jeff -
Hi Guys
leccyflyer
Thanks for that, good advice, but I would suggest probably only for parallel chord or slight taper. Think the steep taper on mine has more effect than you might think.
My root chord is 340mm, so 28% would be 98mm. Even the manual, which generally errs on the safe side, suggests 105mm as start point.
Going even further forward seems like a step back.
Anyway, starting to get a clear idea of what I have to do.
Thanks to everyone who contributed
Jeff
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Hi Matty
Good point, well taken.
Thanks for explaining. Obvious really, when someone else points it out.
Jeff
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Hi Guys, thanks
Paul
Not quite clear what you are suggesting here. What does 'work out the surface' mean? If you're suggesting 25% of the root chord, this comes out to 85mm. Maybe ok for straight wings but these are very sharply tapered, see photo.
Even the manual suggests 105mm and this is probably conservative.
Mike
This is the one I use. Found it very handy over the years, but concerned that is has no provision for wings that have a sharp taper on the trailing edge. Can't be sure whether this is significant or not, but looking at the wing planform, that's a recipe for tip stall if I get it wrong.
Matty
That's the same as the one Mike suggested, albeit with a more complex interface. Can you point out where the provision is for TE taper?
Thanks anyway for your thoughts, most welcome
Jeff
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Hi Guys
Do you have a favourite way to calculate c/g of a model?
Reason I ask is I have bought a second hand model with sharply tapered wings on both LE and TE. I do have a program which will calculate c/g, but it seems to take little account of the TE taper when filing in the dimensions.
I did manage to find part of the manual for the model, which shows a c/g position of 105mm from root LE. The model does have some marks on it which look like c/g position, but they are some 135mm back, quite a difference.
So, I need to calculate a c/g position for myself.
How would you do it?
Thanks
Jeff
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Ok, Brian, I'll give that a try
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Hi Nigel
Good thought, thanks, but I don't know how much it will help. The tank floor is only some 10mm above the u/c mounting plate, and also the captive nuts sit on top of the plate so it would need some sponge packing below the tank to prevent the nuts chafing on it.
In all, I figure I could only lower it about 5mm, which wouldn't be much use.
Haven't done much with the motor, apart from give it a good clean. Will be putting it on the test bench soon, give it a good wringing out.
Have to decide on the way forward with the model first.
Jeff
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Hi Guys
Jon
Thanks for your interest. Unfortunately, can't show the engine install. Last time out I had a mishap (not engine related) but broke the engine mount into several pieces. Have done a lash up with an old mount I had, but I had the cowl front as a guide, so I think it's pretty close.
The outside view can be deceptive. Above the moulded section is a piece of 1/4 ply which the u/c bolts to, and then the tank floor is a framework some 10mm above that.
The red line on the fuz is the tank floor. I have a 10oz one, some 50mm deep, so even without any foam padding under the tank, the centre line is some 25mm above the red line. With the tank full that puts the fuel level at some 45mm above carb centre.
Clue for me was on one occasion, trying to start it, I got a jet of pure fuel upwards out of the carb. Sure indication something's wrong.
Nigel
That is interesting. Would have thought an 80 4stroke would be more powerful that a 53. Did find a sales picture here which suggests a 54 4 stroke. That would have been underpowered. Wonder if they meant 54 2 stroke. Either way, should be good if I decide to fit my Irvine instead.
Thanks for that
Appreciate all your help
Jeff
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Hi Guys
Hope you don't mind me joining the party, but I noticed a couple of posts which might help with an issue I have.
I have started a thread here but long story short I have bought a second hand model with an ASP80 mounted inverted in it.
The engine position is determined by the moulded cowl, and the tank position by the bottom of the g/f fuz.
Trouble is, as installed the centre of the tank is some 25-30mm ABOVE the c/l of the carb, not helpful.
Can't raise the engine enough without half the crankcase being above the fuz top, and can't lower the tank except by cutting away the lower fuz floor which would compromise the strength and also the u/c mount which bolts to it.
Wondering whether a chicken hopper tank might be a solution.
Your thoughts?
Jeff -
Hi Denis
Always amazes me how much expertise is available on this forum, but even more so how quick members are to share it.
Yours is pretty much the fastest reply, many thanks for that.
So, to horse
Can't really lower the tank floor. The fuselage is fiberglass and the lower section of the nose is moulded higher than the rest. Also this section includes the u/c mount, so that would also have to be moved to somewhere with the same strength.
Attached is a photo to show the layout.
Similarly, can't raise the motor, It would have to go up so much half the crankcase would be above the fuz top.
Couple of thoughts spring to mind.
I think the 80 size motor might be overkill. the model is only 55" span after all. I do have a spare Irvine 53 which I think might be a better match. Mounted inverted, this has the same carb position issue, but I'm wondering about mounting it sidewinder.
Puts the carb at the right height, but means cutting more chunks out of the painted cowl.
Otherwise, I have enough spare gear to go electric with it, but that seems like a cop-out.
Looking for a bit of inspiration for other than these two ideas.
Changing the subject slightly.
Seems to me the model must have been designed this way. With all the outlay in moulds and production processes wonder why no-one questioned tank position.
Still work in progress
Jeff
P.S. Been doing a little research on the forum, and I came across a system called a 'chicken hopper' tank. Don't know too much about this, anyone enlighten me?
J -
Hi Guys
Been all electric for years, so here's a question I have not had to deal with for some time.
Bought a second hand model, a Freestyle Iconic XL. Not much about it on t'internet, but what I found seems to suggest a 54 size 4 stroke.
Mine came with an ASP80, ho hum.
Anyway, the motor is mounted inverted and its position fixed by the cut outs in the cowl. Similarly, the tank position is fixed by the internal structure.
Way back when, I understood the tank centre line needed to be level, or perhaps a little below the carb centre line. With the layout of this model, the tank centre is some 25-30mm ABOVE the carb.
With a full tank, that puts the fuel level some 20mm or so higher still.
Seems to start and run ok, but not really cleanly. Could be due to my lack of experience with 4 strokes, but once, when trying to start it, I got a fountain of neat fuel upwards through the carb.
Not good, says I!
So, first of all, am I right in being suspicious of tank level?
Your thoughts
Jeff -
51 minutes ago, RottenRow said:
I can't really see a useful purpose for that switch, except perhaps to switch on the receiver is a model that doesn't use a receiver battery (an electric model with a BEC for example).
Hi Brian
Can't really understand that. If you have an ic model with a separate pack for the electrics, how would you go about disconnecting after a flight?
On my electric models, it's now second nature to unplug the battery immediately after a flight. This switch gives me the same quick option for my ic models.
Been dealing with Blacksmith Products for years and can recommend their service. Really not to blame for one of their products not doing what it's supposed to, but you have to admire the speed at which they changed the website to show correctly.
Thanks for the link to an alternative switch. That's the one I have on the model now, made by Etronix. Works fine, but a bit big and bulky (much like the pilot, I daresay) for a tight install.
Will be rolling my own as soon as the bits arrive, see how that goes.
Finally, while it would be my preference to switch only the positive leads, doesn't mean Denis's method is not as valid. In fact probably make for a neater soldering job.
Just seems to me if both contacts are used adds a little inbuilt redundancy. Bonus, although not really needed for our purpose, is that the current carrying capacity is doubled as well. Win-win.
Work in progress
Jeff
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Hi Guys
RottenRow
Been a bit reluctant to publish links since both suppliers have been very fair in their dealings with me.
However, since I feel I have found a switch type to be avoided, here we go:Note, after my enquiry, they changed the text to specify that the sockets were NOT there to charge the battery.
Makes sense from a safety point of view, but can't see why fit two sockets for running other items but still having to unplug the battery to charge it.
Having said that, after I asked the question, they did give me a full refund without asking for the switch back. Fair play to them.
Have to agree they all probably come from the same factory, probably in China.Denis
Opening up the switch was easy, but it does look odd. The internals are mounted on a small circuit board, but the switch seems to be a simple single terminal on/off slide switch. Not at all what I was expecting. I have been refunded for the item, so no reason why I should not unsolder the switch, and check separately, but I don't think I'll find anything different.Can't see a way I would be happy to use these, but I still like the idea of switch, led and charge socket in one unit, so I'm thinking of just using the case, and fitting my own internals.
Got some bits on order, will see how that goes.
Meanwhile, thanks for the how-to on wiring up a 6 pin slider. Obviously works fine, but could I suggest a slightly different approach?
I would gang together all the negative wires and only switch the positives. However I would solder the positives to both terminals, so in case one set of contacts should fail, the other would still take the load. Safety first.Thanks for all your thoughts
Jeff
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Hi Ian
Just a quick follow up.
Took a chance, dug out an old surplus receiver, plugged it into the switch, and measured 8v going into the receiver.
Glad I used a surplus one.
Jeff
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Hi Ian
I'll try to be concise, here it is.
I have a wall charger with led indicators for charge flowing. Off load terminal voltage of 9v.
1) Switch to off position, plug in charger. No led on charger, but terminal voltage (9v) at receiver plug. Also led on switch glows brighter than expected.
2) Switch to on position. Led on on charger, led on switch glows less bright. Increase in voltage at battery, but same voltage appears at receiver switch.
So, no charging with switch off. Switch on and charge starts, but also powers up the receiver.
I have only measured off load voltage at receiver plug. Reluctant to try with receiver in case it puts 9v into it, and magic smoke.
I would expect to be able to charge the battery with the switch off and receiver isolated, but what I have is exactly the opposite.
Any thoughts?
Jeff
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Don
Three different units, from two different suppliers, each exhibiting the same fault.
Wouldn't you be curious how that came about?
Expense doesn't enter into it.
Jeff
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Hi David
Was your one the same as mine, two sockets on top, one male, one female? If so, how did you re-arrange the wiring so it worked right.
Thanks
Jeff
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Hi Guys.
Bit of a mundane subject, but it's causing me a bit of head scratching.
Looking for an on/off switch for my latest project. Will be fitting this under the canopy, so wanted one with a built in led for visible check.
Bought one from a well known retailer.
This has two leads coming out the bottom, one to the battery the other to the RX. Also two sockets on the top plate, one male, one female for charging in situ.
Mine is giving very odd results.
Anybody used one of these, had any issues?
Thanks
Jeff -
Hi Guys
Little bit of a find.
Went to a model show today. On the SLEC stand I found they do a conversion kit for a clunk tank for petrol or diesel. Rubber bung not really of use, but a length of the thinnest, most flexible Tygon tubing I have ever come across. Perfect for my needs, and only £2.
Game on!
Jeff
Wing/Tail incidence
in All Things Model Flying
Posted
Hi Guys
Masher
Can't seem to find this post on the forum. can you confirm date?
Brian
If this is right, can you confirm if it was from the Colin Usher plan on Outerzone?
Thanks
jeff