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Wots Wot XL

Two wings are better than one

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Timothy Harris 111/10/2017 10:24:26
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538 forum posts
81 photos

No problem Gordon. I had over read the kitchen scales but as you can see it’s quite a hefty plane. I found the 16x8 APC to be more of a max rpm/power prop but did not work nearly as well as the 17x8 APC in my installation. The cowl is quite big on the Wots Wot plus the draggy thick wings favour a prop with more static thrust. I find the 17x8 best. I did try an 18x6 but that was quite slow in the Wots Wot. I have not tried a 17x7 yet as I haven’t found one , but that could be interesting too.

Ron Gray12/10/2017 15:36:28
347 forum posts
111 photos

Just got back from the field, mixed success! Unfortunately didn't get any flying in as I had an elevator servo failure (was working on Monday!) but managed to get that sorted by going home and getting a replacement. Then I spotted a problem with an aileron servo, it appeared to be 'lazy' in that it wasn't responding as quick as the other one. Once again, everything was fine on Monday and I should point out that the servos were all new for the WW.

Discretion told me that today wasn't the day for flying so I concentrated on tuning the 160v in the end getting peak revs at 9150 and steady tick over at about 1500. Did have some problems with one or other cylinder dropping out when slow running but I think that fine tuning of the slow running needles has fixed it. I did find it difficult to detect any rev change at low throttle even turning the adjusters through 180 degrees didn't seem to change things! Just need to get it up in the air now but need to swap out both aileron servos first!

Edited By Ron Gray on 12/10/2017 15:37:30

Timothy Harris 112/10/2017 15:59:58
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538 forum posts
81 photos

Good to hear engine tuned now Ron. I look forward to hearing how it flies once run in.

Ron Gray12/10/2017 16:21:30
347 forum posts
111 photos

Not convinced that I made the right decision with the on board glow drivers (not on board glow!) as I don't think they get the plugs as hot as a glow stick. May well change to a remote connection for the plugs, run in series so that if only 1 plug is working the engine won't start (the same way that Jon has his setup). I did have 3 or 4 occasions when it started on 1 cylinder, the problem is that I didn't realise it as the engine is so smooth even just on 1, I only realised it when I went to full throttle and found it lacking which is exactly what happened on Monday when I had the lack of power, it was running on 1.

Jon Harper - Laser Engines12/10/2017 16:37:06
3180 forum posts
131 photos

9150? thats more like it 1500 is very slow for idle though and i aim for about 1800 just for the reliability factor as idle that low is really only for bragging rights. In all honesty anything at or below 2000rpm is pretty much a win as the model is not likely to move at that. If you reset your idle to about 1800 you may find it easier to set the needles as the engine wont cool down as much.

Also dont start chasing a problem that dosent exist. By that i mean we have had customers in the past who noticed that a cylinder would drop out after about a minute or so at a very slow idle. They then became fixated with getting it to idle for all eternity at the lowest rpm possible. I am not sure how your field is set up, but for me the engine rarely idles for longer than about 10 seconds as i start it, warm it up for about half a minute at 1/3 throttle, give it the big one to test top end (again, 15 seconds at least flat out to check the tune and make sure its warm), then idle just long enough for me to pick it up and take it 'air side'. Once there i put it down and taxi out so it is not at its lowest idle for more than 10 seconds. if i am waiting for the runway to clear i probably have the throttle open a crack and about 2200 on it. In the end, i have never tested how long the engines will idle for as its not really important if it idles for 1 minute or 10 minutes if you only need 30 seconds in normal use.

Ron Gray12/10/2017 16:55:45
347 forum posts
111 photos

Thanks Jon, I will probably set the idle slightly higher than I had it today, bit unfair really as there was a >15mph wind behind the model so out of the restraints it would move along quite a bit (lots of airframe drag!) downwind! Plus we do have a tarmac runway to fly off so there is no real physical rolling restraint as there is with grass. When I taxi out to the runway I always blip the throttle on my other ICs just to keep the engine warm and try and keep low running at a minimum and as you say, there is never a long wait to get airborne as the taxi out means there's a free slot. The trouble with the engine is that its sounds so nice just ticking over!

Edited By Ron Gray on 12/10/2017 16:57:12

Rich too13/10/2017 07:26:56
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2475 forum posts
940 photos

Bad news on the servos, good job you spotted it though. What servos are you using?

Ron Gray13/10/2017 07:55:43
347 forum posts
111 photos

Hitec 4245 on the elevators and New Power 45HMD on the ailerons. I know that I’ve had problems with some New Power servos before, stripping gears, but thought that as these were brand New I’d use them. Obviously a bad decision and reinforces what I’ve said on another thread that I won’t be using them again. Now replaced with McGregor cordless hi voltage, hi torque ones, overkill, I know, but what price peace of mind?

Rich too13/10/2017 08:13:11
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2475 forum posts
940 photos

Agreed, I’ve recently changed to Hitec for peace of mind.

Jon Harper - Laser Engines13/10/2017 08:45:44
3180 forum posts
131 photos

I wouldnt touch new power servos with a barge pole. We got some in for our wot4 xl test model and i rejected 3 of the 5 the moment i powered them up. TThey went into oscillations and got really hot if you let the stick spring back to centre. I know you shouldnt do that, but still. A clubmate also uses them alot and failures are not unknown.

TartanMac13/10/2017 15:11:21
144 forum posts
104 photos

Yeah I can say New Power is to be avoided also. I got 2 new power XLD-25HB BB servos I was drawn in by the specs 0.045 sec/60 deg 2.5KG. Put them in a Kyosho mini ST with an .09 engine 1 tank on idle to start running in the engine the throttle servo packed in went really slow and then stopped. They cannot handle vibration at all or maybe the circuitry is rubbish I don't know but won't buy cheap brands ever again I usually never do. Savox is my go to brand these days.

Ron Gray13/10/2017 15:38:33
347 forum posts
111 photos

It’s quite strange, before this year I haven’t had any problems with them, in fact my Giant Revolver has them throughout and, touch wood, hasn’t misbehaved. It seems to be the problems have been with ones bought this year.

Timothy Harris 113/10/2017 16:58:39
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538 forum posts
81 photos

This Wotty certainly needs strong servos in its wings though as there can be a lot of “stiction” a good term for the sticky friction from the double set of ailerons. My first set of servos died too as the hinges were to tight and servos too weak. All was sorted soon though.

Ron Gray13/10/2017 17:31:33
347 forum posts
111 photos

These are the new ones now fitted

http://macgregor.co.uk/macservo/mac5921hv.htm

Edited By Ron Gray on 13/10/2017 17:32:27

Timothy Harris 114/10/2017 08:52:18
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538 forum posts
81 photos

Blimey Ron they are monsters !😊 will be fine . Mine are Hi-tech HS5685 which are also a good strong servo. 

Edited By Timothy Harris 1 on 14/10/2017 08:57:57

Chris Channon14/10/2017 13:24:13
500 forum posts
Hi all, how do you wire glow plugs in series on a twin ?
I have a Saito 120 dual plug and this sounds like a good idea.
Thank you
Chris C.
Ron Gray14/10/2017 19:16:41
347 forum posts
111 photos

+ive to the top of one plug then -ive from the top of the other. Current will go from top of first plug through element to the engine then through the other plug returning on the other cable.

Jon Harper - Laser Engines14/10/2017 19:59:12
3180 forum posts
131 photos
Posted by Chris Channon on 14/10/2017 13:24:13:
Hi all, how do you wire glow plugs in series on a twin ?
I have a Saito 120 dual plug and this sounds like a good idea.
Thank you
Chris C.

If there are 2 plugs in one cylinder you only need to power one of them. The other will light when the engine fires

Ron Gray14/10/2017 20:33:56
347 forum posts
111 photos

Sorry, I didn’t thorough read the post as I thought that it referred to a twin, not a twin plug, my bad.

Itisme15/10/2017 08:32:16
24 forum posts
16 photos

My Wotswot. XL joined its older brother today, these two are a pleasure to fly, even the pilot enjoyed himselfaf1f6cb9-f1ae-4b69-964b-c0df3532517d.jpeg1cafb3c0-eff3-42fb-8c0b-0e2223440c24.jpeg

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