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Member postings for GrahamWh

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

Thread: Castor oil in 4 stroke engines
15/03/2019 17:04:17

I wonder if we could use a chemical additive like the e-cig people do to get that caster smell back in the modern fuels? Could try raspberry or caramel to confuse the guys on the flight line instead!

 

Edited By GrahamWh on 15/03/2019 17:05:36

15/03/2019 16:53:19

The great thing about castor oil other than the smell is that it puts a lot of 4 stroke engines onto the second hand market due to poor performance, where bods who like to can buy them cheap-ish and clean them up and use them or sell them on!

Thread: How to reduce voltage?
15/03/2019 16:47:07

 

Also if using a diode, consider the heat it will produce.

Test it carefully and use a heat sink for it if need be.

For example, if using one diode with a voltage drop of 0.6v, if the current going through it (and onwards through the charger) is say 5 amps, then the power turned into heat in the diode itself will be (voltage drop across diode) x current =0.6 x 5=3 watts. This could get the thing quite hot. A higher current will produce more heat. You can get heat sinks that will dissipate the heat produced and connect to the diode.

Heat sinks are rated at temperature increase per watt. Aim to stay below a suitable temperature, say 50 degrees centigrate above room temperature, so a heatsink for 3 watts needs to be 16.7 degrees per watt or better. Of course the diode itself will dissipate its heat to the air naturally without a heatsink, but may get to an unacceptably high temperature to do so.

(It''ll get hotter and hotter until the rate of dissipation (which itself increases with temperature) matches the rate of heat production, ie. 3 watts.)

In our example the heat sink rated at 16.7 'c/watt would get rid of 3 watts by the time it got to 50 degrees above room temperature. Without a heat sink, the diode may get so hot it burns out or causes damage to whatever it touches. When people say they use a diode in a model with high power servos to reduce receiver battery voltage for example, I always wonder how hot that diode is getting .

Edited By GrahamWh on 15/03/2019 16:49:10

Edited By GrahamWh on 15/03/2019 17:01:24

Thread: Can a LiPo battery recover some performance?
07/03/2019 21:12:33

It's certainly interesting to see the differences. Please let us know how you get on. I wondered if the nanotech ones might be a bit fragile and therefore susceptible to variance between packs. I used to fly electric and noticed that my nanotech packs soon deformed (puffed up) even if I used the within the current and discharge limits, compared to the cheaper normal Turnigy ones which stayed good for longer.

Thread: Reduction Drive
03/03/2019 13:19:41

Cymaz, your table has load factor as proportional to diameter^3 x pitch, the one I use has it as diameter^4 x pitch. It makes a lot of difference. Does anyone know which is right?

(MIne comes from RC Model World, Sept 2012)

03/03/2019 09:39:08

Hi Cymaz. As I understand it, it would be the load factor you need to multiply by 1.82

The load factor is proportional to the diameter to the power of 4 and to the pitch to the power of 1 so multiplying both diameter and pitch by 1.82 would multiply the load factor by (1.82)^5 - by 19.6!

An 18x8 prop has a load factor of 840 using a table from an old edition of a model flying mag I have, so you need a load factor of 1.82 x 840 = about 1529.

If you want the same pitch speed the 18x8 gave you at 6000 rpm, you need a pitch of 8x6000 / 3296 (or 8*1.82)= 14.56....or 14 to 15 inches.

An 18x15 would do this as its load factor is 1575..

Alternatives with roughly the same load factor would be 19x11-12, 20x9-10, 21x8, 22x6-7 but hese would have a slower pitch speed.

Load factor = pitch x (diameter^4)/1000.

This would be a good discussion to have as an article in the RCMA mag by someone knowledgeable.

Edited By GrahamWh on 03/03/2019 09:42:56

Edited By GrahamWh on 03/03/2019 09:50:15

Thread: Warped wings
26/02/2019 20:19:36

Hi Tim,

If I remember rightly I have held the wing off the desk on balsa blocks and placed suitable weights on top at sensible positions above spars etc while the dope dries. I think I must have stopped the blocks sticking by having sellotape on them and moving them a little half way through. It's been a while though. Still have a lot of dope left in the workshop which I may never use again!

My last tissue covered model was an SE5a at 26" wingspan for electric power, before that an Aerographics Sopwith Camel adapted for RC.

Thread: Preparing Laser Cut wood for Gluing
21/02/2019 18:45:00

I have just received my first laser cut wood pack. It was ordered from the FMS/Doolittle Media site and looks great! It's for a BE2e at 80 inch wingspan.

Some of the edges of the ply parts are a bit sticky - I guess from vapourised glue from the ply condensing on the edges of the wood. There is obviously a burn mark on all the cut edges of the ply and balsa parts too.

So, what does one do about the sticky bits - wipe with alcohol perhaps? - and is it best to gently sand off some of the carbonised wood too to help with adhesion before applying PVA?

Thanks for your thoughts.

Thread: Roy Scott's BE2e. Have you ever seen the film," A Very Long Engagement?" This is "A Very Long Build Blog!" a very long build log.
10/02/2019 16:21:36

David I was at the Sywell Rally a couple of years back and got this shot of the cockpit of a BE2c there - might be useful.  (Better resolution available if you pm me so I can email you). I didn't realise I had this until looking through old photos today. It is actually the replica built by C. Boddington - as a small brass plaque inside the cockpit states.

(Still waiting for my plan and parts to arrive!)

 

be2c cockpit.jpg

 

Edited By GrahamWh on 10/02/2019 16:33:05

Thread: De Havilland Airco DH2 scratch build
10/02/2019 12:53:14

Fantastic subject.I have long been put off building one of these not being sure about starting an ic engine in one and not wanting to do an electric version.

Would it be an idea to have the tank on a bit of a tilt (if the bung end was at the engine end) so the clunk is at the bottom of the tank able to sip more fuel? When landing the aircraft it will have a nose up attitude and probably will in flight too, and any remaining fuel in a level-fixed tank will be up against the bung and the clunk left dry at the other end if fuel is low.

Sorry I'm wrong too - the article above seems right - in an steep upward climb the clunk would be out of the fuel if the bung is toward the engine!

Edited By GrahamWh on 10/02/2019 12:57:40

Thread: Show us your workshop!
10/02/2019 07:54:27

Some marvelous examples in this thread guys. Mine is pretty small and simple. I was making a lot of mess around the house with bits of balsa etc. when building an Aerographics Sopwith Camel for RC some years ago, so my Mrs suggested I turn the spare room into a workshop - great!

I started with a 2m x 1m ply table I built using parts from a bed frame then added one shelf, then another when space ran out, and now a sliding door cabinet on the back of the table for still more space. I still use the dining table sometimes though!

.

workshop.jpg

Thread: DH84 Dragon
09/02/2019 21:07:35

Thank you very much Chris - I have been puzzling about some sort of connection to use for some time.

09/02/2019 13:08:09

Lovely build Chris and a clever way of dealing with the wings. Is there any chance you could show a close up of the staple method you describes that holds the wing sections together?

Thread: Servos
03/02/2019 15:45:08

What dimensions will fit Heinkel? Does it have to be that thin? Some may be able to make a recommendation with dimensions.

Thread: Spektrum AR620 receiver problem
02/02/2019 21:09:31

Peter could it be that the Battery port has no signal connection on the PCB - just -ve and +ve, and the ESC of course needs signal connection too?

Thread: Forum members' new models: Let's see them.
02/02/2019 16:16:37

Second hand Flair Fokker D7 bought with a Laser 80 which I removed for another project and replaced with an old OS 70FS with new bearings.

fokker 1.jpg

fokker 2.jpg

...and an RX battery meter so Hans knows if there's enough charge to risk another flight -

fokker 3.jpg

Engine running fine in the garden this afternoon, C of G right, failsafe checked, waiting for the right weather.

Thread: New Sopwith Pup from DBSportandScale
01/02/2019 22:18:47

There is an update now on the DBSportandScale website -

https://www.dbsportandscale.com/sopwith-pup-60-coming-soon-8530-p.asp

Will be released shortly!

Thread: Max revs on SC120FS
01/02/2019 21:48:46

Ronos with the tacho make sure there's plenty of light. Mine will only read up to a certain rpm if it is too dark. I sometimes put a white plastic garden chair a couple of yards in front of the prop and point the tacho at that through the prop arc (always working behind the engine). Sometimes I even sit a torch on the chair pointing back at the tacho and then I get a full reading. Sometimes it will only show up to say 6500 rpm, then when I do the above I get the full reading up to 9000 or 9500 whatever it actually is.

 

Playing with a Laser 80 a few years back - white chair to get the tacho to work to full revs reading:

chair.jpg

Edited By GrahamWh on 01/02/2019 21:55:05

01/02/2019 17:11:08

Ronos I use an MA 14x6 on an ASP 70FS and get over 9000 rpm with it - probably too light for the 120. In fact I get 9000 rpm with my ASP 60FS on that prop!

Edited By GrahamWh on 01/02/2019 17:12:07

Thread: Catastrophe!
01/02/2019 16:59:07

The slide switches look big but inside the plastic case the actual metal switch is small. Open that and the contacts are tiny! I wonder what current they are actually rated at. Good high current toggle switches are easy to get and may be more reliable. Thanks for the video Peter.

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