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Member postings for Toni Reynaud

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

Thread: Prop size and efficiency
20/08/2019 13:29:47

" Off the top of my head, the simple formula used takes no account of inefficiency around centre of prop, inefficiency around tip of prop, speed differential between static body of air and the air moved by the prop, drag of power train components in the airflow... among what are probably many other real world effects "

Absolutely right, BUT if all calculations are made on the same basis and contain the same errors, then the comparitive results are acceptable. It all started ages ago because I wanted some idea of the different size of prop I would need when changing from a direct drive Speed 400 to a 2.5:1 geared Speed 400 - about 40% less rpm, approximately the same power, so what size prop would work?

 

Edited By Toni Reynaud on 20/08/2019 13:42:10

19/08/2019 15:05:47

I suppose the bottom line is that it's always worth trying different props, sometimes at odds with what we might expact to work. As long as the plane gets off the ground and can fly safely enough to check the characteristics with the new prop, all should be well. LiPo duration also comes into play. I will go away and try a 3S and bigger prop instead of a 4S in my Travelair at some stage.

19/08/2019 14:49:14

The test system was fairly basic - a 90 degree rig with one arm vertical with the motor mounted on it, and the other horizontal reaching out to an electroni kitchen scale for thrust measurments. We were using a Medusa Research Power Analyser Pro connected to a PC, and a selection of battery packs and props. Sanyo SCR 2400 NiCd cells and a Castle Creations 25A ESC were used for all tests.

fig 1 test stand overview.jpg

This graph is representative of the results we obtained.

graph.jpg

19/08/2019 14:26:31

Thanks for all the replies, gents

I'm curious as to what formula you used for the "Volume of air per rev (cubic inches)" value.

This is why I posted - it made me go back and re -examine the formulae I used - I had the square in the wrong place!! Amended figures below. However, the general principle and the question is still valid.prop size vs eff 04.jpg

19/08/2019 09:21:29

It is evident from the figures that a big prop turning more slowly moves more air for less power. Should I therefore go to 2s LiPos or lower Kv motors with bigger props, or am I missing something?

Over to those who know about these things for discussion.

Edited By Toni Reynaud on 19/08/2019 09:26:05

19/08/2019 09:19:03

prop size vs eff 01.jpg

19/08/2019 09:04:38

Disconnected jottings - I have seen one or two comments on this forum that a bigger prop spinning more slowly is more efficient. A good few years ago I was involved in testing some brushless motors and producing performance graphs for them. At one time or another I have wondered about just how much air a prop actually moves and made up an Excel spreadsheet to help the thought process.

Add that lot together, and in a moment of boredom (or maybe curiosity) I took some information from three of the said performance graphs, put it into the air moved spreadsheet, and came up with some interesting figures. See the next post.

 

 

Edited By Toni Reynaud on 19/08/2019 09:26:42

Thread: Electric Cars.
14/08/2019 15:26:56

Gross overpopulation is the elephant in the room unfortunately

Not necessarily. Selfishness and poor distribution of assets count for a lot.

Other than that, nigel r's post 12/08/2019 15:23:38 presents a sensible picture that I have seen previously - as child deaths decrease in a society and culture, the birth rate follows.

21/07/2019 16:04:25

Just for interest................

https://www.wired.co.uk/article/lithium-batteries-environment-impact?fbclid=IwAR0hvO_49eGkcpTeasvDfSZY70N4urjuF2zgWsew25Swug1LmmTQrOFgVyk

Thread: AND finally.....the 'Mini Jet' TSR2
20/07/2019 10:48:18

I like that Warthog!!

Thread: New EDF Mini Jets- Jet Provost & Folland Gnat
09/05/2019 17:13:51

They're all so good. I like the Provost and I'm looking forward to the Lightning - I was a radio man on 5 Sqn for five years - love them!

Thread: Electric Cars.
29/04/2019 18:21:45

As an aside, this website provides a look at how power is generated in the UK. Gridwatch

Edited By Toni Reynaud on 29/04/2019 18:22:01

Thread: Canopy/Hatch magnets
21/02/2019 14:26:48

I like the idea of the thin ply. Actually getting magnets to permanently stay somewhere, even using epoxy, is not always successful. A thin ply cover will work wonders. Also plus one for the use of magnets removed from old motors.

Edited By Toni Reynaud on 21/02/2019 14:27:29

21/02/2019 08:44:30

Try these people for the magnets. https://e-magnetsuk.com 8mm ones are good with tinplate (or a flat headed nail trimmed for length), 6mm ones are useable in pairs.

Other than that, what PatMcC says is good. However, I tend to use the magnets in pairs when I want a stronger hold. Take a pair of magnets with at least two layers of THIN polythene between them and epoxy into place in previously prepared rebates on the airframe and hatch.

Thread: Antonov AN2
11/02/2019 14:59:19

Beautiful scale speed flying. Wonderful model too.

Thread: Retractable tailwheel
10/02/2019 16:04:25

Yes, Martin, there is a collet, and when I get round to doing the installation properly, things will end up in the right place. I just have to work out how to organise the rudder and tailwheel linkage without ading too much weight to the back of the plane. Room is a bit tight, and access is by cutting lumps out of the bottom of the fus!

10/02/2019 12:18:15

Thank you all for the replies. Time to go and finish the installation and linkages.

10/02/2019 09:55:56

Can't sort the pictures while working on the phone. Had to come back indoors to the PC!

15497916404467011870814883720967.jpg

10/02/2019 09:49:51
I have a Flair Beaufighter, beautifully built by someone else. I have replaced the brushed 600 motors with ex foa.y Wot brushless and it flies nicely, but hand launching g and landing on the grass is a pail. I have fitted electric retracts in the wi gs and bought a retractable tailwheel unit. Question - what is the purpose of the cat's whisker type wire poking upon the pivot area of the u it? Any thoughts gratefully received.
Thread: Film covering to repair "alumium" Mustang wing
06/02/2019 15:05:05

I have heard of the "silver" being used then flatted down with wire wool to give a better mstch to aluminium. Just a thought.

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