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Member postings for PatMc

Here is a list of all the postings PatMc has made in our forums. Click on a thread name to jump to the thread.

Thread: Keil Kraft Caprice CoG
13/07/2019 23:19:00
Posted by John Roberts 9 on 13/07/2019 18:50:21:

The wing chord is 16cm and the recommended balance point is 9cm behind the leading edge. That seemed a long way back but I assumed it was required due to the lifting tailplane.

 

It's actually the other way round. The rearward cg was meant to take advantage of a "lifting" tailplane. In fact it's a concept that doesn't really add up, at least for rc flight.

Edited By PatMc on 13/07/2019 23:20:34

Thread: Electric conversion Bowman's Sunduster
11/07/2019 21:52:31

A couple of years ago I built an Amigo 2 (about the same span as the Sunduster) modified to take this 1050kv motor. Lipo used for first flights was a 3s 1400, lately I've been using a 3s 700 for flat field & the 1400 when slope soaring in light wind conditions.
I decided to limit the current & power by using a 9x5 folder. Current 14A, power 165W, which gives a good climb to thermal hunting altitude in about 25 - 30 secs.

There's also an 860kv version of the same motor which should enable a faster climb rate, if desired, using a bigger prop at the same current & power.

Edited By PatMc on 11/07/2019 21:54:49

Thread: What to use on a Cub
10/07/2019 10:04:46
Posted by Martin Harris on 10/07/2019 00:09:44:

Isn't it a ASK14 single seater Pat? The ASW15 was a pure glider - or it could be a K16 side by side 2 seater but I think the tail is wrong for that.

You're right, Martin.
Slip of the keyboard here, I meant ASK14. embarrassed

09/07/2019 23:48:12

Martin, you can scale the weight & power pretty accurately around this size model of a light full size aircraft. Also the power to weight ratio should be the same for all scales regardless of prototype's weight.
As an example, my 1/5 scale ASK15 (see my Avatar) is almost exactly the scale weight & power of the full size, it weighs 5.5 lb & flies nicely using a 1956 vintage Fox 19 - aprox power 0.3 bhp. Though it will be getting electrified with a similar power when I get around to refurbing it.

09/07/2019 23:08:33

According to the specs for the original Great Planes Electri-Cub the RTF weight should be 3.3 - 3.5 lb. Note that's with a brushed motor & 7 - 8 cell 1700 - 2000mAH nicads. The nicad battery would be more than double the weight of a typical 3s 2000 lipo. It would seem reasonable to expect a brushless + lipo or an OS15 powered version to weigh around 3 - 3.3 lb.

Dunno which OS 15 Denis is referring to that can produce 500W.
If the OP's engine is an OS15 LA this was rated by the manufacturer at 0.41 bhp (300W) @ 17,000 rpm. As tested by Brian Winch with an APC 8x4 15000 rpm & APC 9x5 11,000 rpm - with a practical size prop around 220W seems more realistic.
OTOH if the engine's an older OS Max 15 the max power was recorded by Peter Chinn at 0.31 bhp (230W) @ 16,000 rpm. The power is probably little different from the LA 15 when using a suitable size prop for this model.

The model to be aprox 1/7 scale Piper Cub. The full size nearly max loaded take off weight is around 1200lb & max power is 65 bhp (48.5kW) At 1/7 scale this equates to 3.5lb & 0.19 bhp (140W)

IMO the model should cruise around nicely in a livelier than scale fashion with the OS15 at 1/2 throttle, whichever version it is.

Thread: The demise of. ASP/SC
05/07/2019 17:16:37
Posted by kc on 05/07/2019 15:21:40:

Can someone explain why there are lots of i.c engine collectors but nobody collects old electric motors?

Because electric motors are always capable of doing they were designed to do. wink 2

Thread: Prop selection for glow to electric conversion
29/06/2019 22:41:52

If the 10x6 draws 27A on 7.4v then that limits the power to 200W. A smaller prop that draws the same current on 11,1V will increase the power by 50%. Even though the smaller prop is less efficient at converting this power into thrust it will not be 50% less efficient so you could reasonably expect a significantly better performance by using 3s rather than 2s.

OTOH the motor you have has a weedy 3.17mm shaft which means that it will be prone to bending or breaking easily in any sort of prop strike [such as a nose over on landing].
Also IMO it's too light to convert the battery power to thrust at the power level that would do a 1.4 Kg model justice.

The motor needs to be about 30% - 40% heavier, have a 4mm (min) or 5mm (preferred) shaft & preferably lower KV (900kv - 1100kv) for instance this Turnigy from HK. There are plenty of other similar specified & reasonably priced motors out there.

28/06/2019 23:48:49

I think it's this 1500 kv motor 7738 is the Graupner part number.

It seems to be rated at a max of 30A but it's not stated if this is continuous running. OTOH max output at nominal voltage (7.4v) is 148W, which suggests that the max continuous current is actually 20A .
I think an 8x4 on 3s would probably take it to around 20A giving about 220W which is about the same power as a ST20-23 with silencer, albeit on a smaller prop at higher revs.

Thread: Dismantling and cleaning
28/06/2019 11:35:12
Posted by playtime222 on 27/06/2019 14:35:15:

Watched a youtube vid on dismantling engines and they just pop the casing off, no drama. So I obviously had something physical stopping it.

The next attempt, mine just popped off too. And I found a staple and one of the grub screws that secures the shaft I lost the first time I tried to dismantle it. You couldn't make it up. Everything fine, no sign of oxidation, bad scratches or anything.

So a bit of good luck this time around.

Good result thumbs up glad it wasn't my doomsday scenario.

Thread: Mercury Aeronca Sedan
27/06/2019 23:36:33
Posted by Chris Freeman 3 on 27/06/2019 06:40:34:

I have started building a enlarged Aeronca as I need to play with some balsa after the composite Mustang and the Cub rebuild as they were not much building as such. I am not sure about the incidences on the plan as the wing is about Zero and the stab is very negative and lots of downthrust. Does this not result in the aircraft flying very tail low which makes it look about to stall most of the time. I prefer a tail high look in flight.

Any ideas?

The rigging angles of the full size Sedan WRT the datum are : wings +1⁰ (note that's through LE to TE, not the section's flat bottom), the tailplane : -3⁰ , thrust line zero.

IMO the full size angles with a flat section tailplane would make a better RC model than the Mercury plan especially when it's being built to a substantially bigger scale.
It would also look so much better if the fin was covered to fair into the fuselage instead of as a discrete unit.

27/06/2019 23:07:00
Posted by brokenenglish on 27/06/2019 18:28:19:
Posted by colin wray 2 on 27/06/2019 13:28:55:

i have the Phil Smith plan of the aeronca sedan ive put off building it because of the wing mounting Have any of the more expreienced builders got any ideas Any sugestions would be most welcome

Colin, my only remark would be that you're being put off by something that's been working perfectly well for sixty-odd years...
Seems like an excellent opportunity to learn new techniques to me.
Of course, the model has to be built more or less like the original, not heavily modified and tons overweight...

This article from Flying Scale Models suggests that the working strut fixings are fine for FF but it's necessary to modify them if converting to RC.

Thread: Windmill
24/06/2019 17:59:48
Posted by John Tee on 24/06/2019 16:06:05:

I first flew this one on a OS15 and it was way overpowered using the built in downthrust of the engine bearers. Now using an Eflite Power10 electric motor with an extra 3 degrees of downthrust and still need to put in more, so power is no issue. Did think of putting a folding prop on. It may work I will have to try but the nose is a three inch square (approx) so would need reshaping. Glides nicely without power , just had the problem with prop breaking on landing.

John

John, I built my Robot for ic using a paxolin plate to mount the motor to the wood bearers. I tried several different glow & diesel engines including a PAW19, Yin Yan 2.5cc, Fox 15 & Enya 09 III. The Fox & Enya were best power/weight match with the Enya slightly less powerful but better throttling.
Photo is after converting to electric using an inrunner on 2200 3s lipo. A whoopsy caused damage to the nose & the inrunner got replaced by a Turnigy 3536/1000 on 1800 3s lipo.

e-robot_inrunner.jpg

As you will see it has ailerons as well as elevator & rudder. Never broken a prop yet even when I damaged the nose area.
If you do use a folder there is no need to alter the nose profile as the folding action will bring the bottom blade back against the underside avoiding damage if the prop stops in a vertical position & if it stops horizontally it's not going to hit the ground anyway even though it will be prevented from folding.

BTW mine originally had the downthrust as per plan but I found the nose lifted when power was reduced, when I repaired the nose I zeroed the thrustline & it's fine. Can you not just use throttle control as a substitute for elevator when under power ?

Edited By PatMc on 24/06/2019 18:01:38

Thread: Dismantling and cleaning
24/06/2019 11:26:53

Have a look at this thread posted by Gordon Whitehead last year.
I think my post in it referring to a Wiki article explains the problem. But your motor is probably scrap, I'm afraid.sad

Thread: Spinners for brushless.
22/06/2019 23:45:34

The prop saver linked fits straight onto the 3mm shaft it would be instead of the adaptor. I don't think you'd be able to use a spinner with the prop saver. Perhaps a folding prop would suit you better, spinners for them here. There may be more spinners on the Robot birds site [The owners of BRC].

Thread: Ben Buckle Junior 60 build
22/06/2019 23:22:36

Andy, I wonder if by "wallowing" you're referring to a "dutch roll" - this is the model repeatably rolling about 20⁰ - 40⁰ one way then the other ?
It's quite a common phenomena with the Junior 60 in some circumstances if it's pushed too fast or encountering turbulence. It's largely due to the excessive dihedral balanced against a moderate fin area. Many free flight models display the same characteristic when converted to RC because they were designed to be very stable with generous dihedral & fly at a single (slow) speed. If the fin area was increased or dihedral reduced to obviate the dutch rolling they would then be prone to entering a spiral dive if displaced from normal stable flight due to turbulence. Although it looks untidy, dutch rolling is harmless to a FF model which is more than can be said for a spiral dive.

I can understand needing more elevator authority with the BB version, mine is probably more powerful than the normal Flair ones because of the rearward cg but still not oversensitive by any means.
OTOH, as it is, the rudder control on mine is a bit OTT - when I used to fly it with my old 35 meg Futaba FF7 Tx I sometimes flew it around only using the rudder trim from take off to landing. wink 2
I would have thought that the BB size of rudder with the Flair size elevators would give better balanced control.

BTW if you normally fly aileron & rudder equipped models you will no doubt be using the "aileron" stick for rudder on the Junior but be used to normally steering with the other stick on rudder control during take off.
Tip I picked up is to mix 50% or so "aileron" control from the normal rudder stick in the Tx - saves you inadvertently & vainly trying to steer a REM model with the wrong stick during take off.

Edited By PatMc on 22/06/2019 23:29:25

Thread: Transmitter / receiver issues, help needed pls
22/06/2019 21:57:57

Daire, the problem is probably because the ESC has a linear mode BEC.
Linear BEC's reduce the input voltage down to the output voltage level by absorbing and dissipating the difference in the form of heat. This means that the higher the I/P voltage the fewer servos they can run without overheating & also reducing the O/P voltage.
For example if you were to use a 2s lipo the BEC would probably run 4 servos with no problem but of course your model would then be underpowered.
Not all ESCs with linear BECs are restricted to the same balance of I/P voltage against servo count but they are all restricted by the heat they can absorb or dissipate. Also some servos take more current than others so the actual servo count can differ but is always restricted with any linear BEC.

Some ESC's have switching mode BEC's. SBEC's reduce the voltage in, as you might guess, a switching process that I'm not going to explain further other than to say it's much more efficient, produces less heat & is much less restricted in servo current against I/P voltage.

AFAIK most ESC's below about 40A rating only have linear BEC's. However I received an email the other day from Hobbyking advertising the launch of a new range of their Turnigy Plush brand ESC's that all claim to have SBEC's fitted. As yet I've not bought one from this new range so can't recommend them on experience but I have used Turnigy Plush ESC's from their previous range with no issues.

Here's a couple of links to the Turnigy 20A ESC & to the 30A ESC . If you do decide to get one of these my advice would be the 30A if the model can accommodate the greater bulk.

PS other than being a customer I have no connection with HK.

Edited By PatMc on 22/06/2019 22:10:04

Thread: Ben Buckle Junior 60 build
21/06/2019 23:27:13

Cymaz, raising the wing LE would raise the motor thrustline by the same angle exacerbating any pitching up with power tendency.

Andy, to cut the 0 - 4mm wedge shape - cut a piece of balsa (1/4" ?) the desired length by about 8cm - 10cm. Split down the length near the centre angled at the 0 - 4mm. Now cut straight down the grain of each piece to give 2 of the desired wedges. Best done using a small table saw or bandsaw.

Sounds like your first flight antics could have been caused overcontrol due to too much control movement being available, especially the elevator throw.

For comparison I've measured the elevator chord & rudder bottom chord on my Jnr 60 also the control throws & permanent down trim setting of the elevators.

Elevator chord = 35mm, permanent downtrim = 5mm [8⁰] , full up from perm trim = 10mm [17⁰] , full down from perm trim = 7mm [11.5⁰]

Rudder chord = 98mm, throws EW = 43mm [26⁰] .

The rudder is more powerful than necessary because I like to do a few uncharacteristic Jnr 60 aerobatics when I get bored with the normal sedate pattern. Elevator is less powerful but still enough for loops & to hold inverted.
Halving the rudder throws would be more than adequate for normal flying.

Edited By PatMc on 21/06/2019 23:29:55

20/06/2019 22:30:08
Posted by Andy Hat on 20/06/2019 20:56:22:

It's finished!

I had to add 220g of lead to the front to get it anywhere near balancing.

Looking forward to flying it soon. Slightly worried about it climbing too fast and needing permanent downtrim. Also worried about the small rudder - will it be enough to control it?

Looks great, Andy thumbs up

Once you've flown it a few times & are happy with the trim you could try removing the lead incrementally, adjusting the elevator trim as you do. My Junior has the cg 1.3 inches rearwards to that shown on the plan & has been flying without problems since 1986. The rearward cg improves the glide & widens the speed range.

Control the rate of climb with the throttle & the speed with elevator trim. Don't worry if you end up with some permanent down elevator when you've established a comfortable cruise setting, it will have no ill effect. With the tx trim at neutral mine has 1/4" permanent down elevator which gives a nice cruise setting at about 1/4 - 1/3 throttle.

The Junior is quite responsive to rudder & even though the BB version rudder is much smaller than the Flair the rudder control should be more than adequate.

Thread: Confirmation - The World Really Has Gone Mad......
20/06/2019 19:54:37

The lady who collided with the cyclist is a 28 year old Yoga teacher called Gemma Brushett. The papers have got hold of 2 pin up type photos of her posing as she performs stretching exercises whilst dressed in a bikini.
Without these photos I doubt if the story would have made more than a few lines in any, other than her local, newspaper.

Thread: Futaba 6EX 35 MHZ not transmitting
18/06/2019 23:32:34
Posted by Percy Verance on 17/06/2019 06:35:16:

Well it's good you found great humour in my trying to help someone.............

Sarcsasm and misplaced wit is of great benefit to us all. There is of course the fact that my post may still be valid or helpful if someone needs a radio repair doing? Another post suggests that was indeed the case. Perhaps you didn't consider that? Like certain others on here, point scoring jibes seems to be a little side hobby of yours........

Edited By Percy Verance on 17/06/2019 06:51:03

You are the only one who has descended to using sarcasm, Percy.
There is none in my post, why on earth do you think I would ever want to ?
You've overreacted to a gentle leg pull with a pompous attempt to justify a mistake that many of us have made at some time when replying to resurrected old posts.
When the mistake is realised after a leg pull most of us respond with - "Doh !! blush" or similar.

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