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David Ovenden

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Posts posted by David Ovenden

    Scale warbird for a .61 fs engine

    in Scale Matters

    Posted · Edited by David Ovenden

    All the points above noted. Maybe the Dauntless would be too much for a 61fs. Its stated AUW is only 3.2k with a 60" wingspan.

    My Brian Taylor Kingfisher had 59" wingspan but turned out very porky at over 8lbs. That flew fine on an Enya 53 four stroke. Not overpowered mind you, but flew well so you could loop from level flight.

    Curtis Condor biplane twin

    in Building from Traditional Kits and Plans

    Posted · Edited by David Ovenden

    I have tweaked the downthrust and adjusted the top wing incidence very slightly as there apeared to be a very small difference between left and right sides. I will test fly again on Tuesday all being well with the heavier lipos which moves the CG forward just a bit. 

     

    I am very pleased with the speed and ease of fitting and removing the outboard wing panels. It is just as quick and easy as I had hoped. It's nice when things work as planned - which isn't always the case.

     

    wing tubes and mountings.jpg

    wing folded top.jpg

    wings folded left.jpg

    wings folded right.jpg

     

    • Like 2

    Curtis Condor biplane twin

    in Building from Traditional Kits and Plans

    Posted

    1 hour ago, Colin Leighfield said:

    That would be my instinct, not that it is necessarily correct! If you moved it forward say 3 mm it would at least be an indicator of what to expect and is unlikely to cause a disaster, I would have thought. I suppose the most important thing if you do move the c of g forward is what the nose does after you reduce throttle.

    Well that's my thinking Colin. A forward move of the CG is the "safer" direction. It is easily achieved with a slightly heavier LiPo pack and involves no permanent changes so easy to undo if it doesn't work.  

    • Like 1

    Dom Smith F7F-3 Tigercat

    in Building from Traditional Kits and Plans

    Posted

    Great effort Martin. It's a shame the nacelles build is a bit  "bogged down" at the movement but it will all come good in the end. Clearing up the workbench often give the new perspective one needs to push on again with a project.

     I find that I am trapped in a repetitive cycle of  clutter /declutter. I work until my workspace becomes unusable and/or I can find any of my tools because they are all buried under the mess. Then I tidy it all up and everything is fine for a bit until the clutter builds up again. Will I ever develop tidier habits.? Seems unlikely at this stage of life.

    Curtis Condor biplane twin

    in Building from Traditional Kits and Plans

    Posted · Edited by David Ovenden
    spelling!

    In a follow up to the last post. I have checked the plan which shows the CG position at 76mm from the leading edge. The wings are parallel chord and there is no stagger or sweepback. 76mm on a 230mm chord wing means the plan cg is at 33% of mean wing chord. This seemed a little far back.  So I've spent 1/2 an hour using the formula in Gordon Whitehead's  book "Scale Aircraft" to calculate the CG. According to that formula it suggests the CG should be even further back at 80mm!  So my question is am I right in trying to move the CG further forward. Any thoughts?

    Whitehead book.jpg

    cg photo.jpg

    Curtis Condor biplane twin

    in Building from Traditional Kits and Plans

    Posted

    Well, yesterday's flight proved that 4S power is enough to fly the plane easily. However, it still climbs steeply under full power. The elevator with reduced throw is still sensitive even with 30% expo added. That might suggest the CG is too far back - though it is spot on where the plan shows it. The Condor does fly but not currently in the relaxed smooth fashion I was hoping for.

    So I will add some more down thrust and move the CG forward a bit (use higher C / heavier LiPo) and see if that improves things.

    • Like 1

    Curtis Condor biplane twin

    in Building from Traditional Kits and Plans

    Posted

    On 31/03/2021 at 00:11, Colin Leighfield said:

    Congratulations David, you must be chuffed with that.

    Thanks Colin. Tomorrow I am taking the model out again for more flights having made a few tweaks. Biggest one is a change from 5s to 4S power as the model really didn't ever need full throttle and climbed strongly at WOT. We will see how it works out in practice tomorrow.

    • Like 2

    "Hybrid" Cessna T-50 Bobcat twin?

    in Scale Matters

    Posted · Edited by David Ovenden
    photo alteration

    I started drawing up the plan for the  Bobcat wing yesterday. I have settled on 1:6.5 scale which will give 77" wingspan. I will be using my two Enya 53-4C engines but I am hoping to design the model to accept interchangeable electric motor power too. I have two SK3 4250 500KV motors and I am thinking that 13x6 3-blade props with  5S lipos will give equivalent power to the Enya using 12x6 2-blade props. More testing is needed.  Once that is sorted I can look at designing the engine nacelles to accept interchangeable electric or glow  power modules. In the meantime I better press on with drawing up the wing. I am currently planning on using NACA 2414 wing section at the root changing to NACA 2412 at the tip with 2 degrees of washout at the tip.

    I am thinking of modelling one of these aircraft as the colour schemes are not too complicated to do.

     

     

    Bobcat cropped.JPG

     

    blue bobcat.jpg

    • Like 2

    CAD software for beginner

    in Own Design Project Blogs

    Posted

    Hi,

    This question is probably answered somewhere on the forum, but so far a search hasn't led me to it!

    I want to design the  wing for my Cessna Bobcat. I don't need to do a complete detailed plan, but I DO want to be able to plot the wing ribs for the tapered wing with a progressive change of NACA profile from root to tip, and Ideally show spar and LE locations.

    What would be a suitable app/ program to do this?  

    I am capable of doing it by hand, but like the idea of using the PC to make printing out shapes easier. (Maybe even laser cut ribs??)

    Who has experience and what to you suggest?

    Thanks

    CAF flying small.jpg

    Reverse rotation for a twin?

    in IC Engines

    Posted · Edited by David Ovenden

    4 hours ago, Jon - Laser Engines said:

    yep, twins tend to be heavy too. Also David is building a twin, fixed gear biplane so there will be no shortage of drag. Fine pitch props of large dia are called for me thinks. 

    I have managed a first flight with the Curtiss Condor. I used 10x6 3-blade props. Both motors were standard rotation with no sidethrust. There was a small torque pull to the left on take-off but easily manageable with a bit of rudder.  As Chris rightly says "it's what it's there for".

     

    Given the advice here, and my experience with the Condor, I will stick with the same standard rotation and no sidethrust for the new Bobcat project.

    bobcat_1.jpg

    Reverse rotation for a twin?

    in IC Engines

    Posted

    Thanks Jon & Nigel for your very helpful input.,

    That is what I was tempted to do. It means I will set up both electric motors and I/C engines with standard rotation. Then I don't have to find matching opposite rotation props and don't have to re-time the Enya. Whilst I imagine it will work in terms of allowing it to run "backward", I can't believe it will run exactly the same as the standard motor would. As I now have three Enya 53-4C engines to choose from, I will concentrate on finding which 2 run closest to each in terms of max rpm and transition across the mid-range.

     

    Reverse rotation for a twin?

    in IC Engines

    Posted

    Having completed my Curtiss Condor twin project I'm planning my next model. I'm going to do a Cessna T-50 Bobcat twin. My intention is to design it to have interchangeable I/C and electric power modules. With electric its easy to have one motor with standard rotation and the other reversed with a "CCW/pusher" prop to avoid the torque issues. I wondered about doing the same with the I/C powerplants so the flying dynamics of the model would be the same with either electric or I/C module fitted.

    So her is the question. I now have 2 Enya 53-4C engines that I will use in the model. I found online the following diagram for retiming the Enya for reverse rotation. Anyone tried it? Is the re-timed reversed rotation engine likely to run very differently from the standard rotation engine? Would it be better to to have them both on standard rotation and concentrate on reliable engine set-up so neither of them stops?

    There is a video of someone who has done this on YouTube but the engine is only seen running on the bench and is not properly set up in the video so its hard to tell how successful it was in reality.

     

    Enya 53-4C reverse rotation diagram.JPG

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