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Member postings for Mike Rolls

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

Thread: A pitch too far
10/03/2013 22:34:18
Posted by Frank Skilbeck on 10/03/2013 18:56:14:
Posted by Mike Rolls on 10/03/2013 11:25:09:

But with IC the revs will increase in partial compensation not sotrue for electric, of course..

Mike

Actually if you fit a smaller prop on an electric motor it will turn at a higher speed, just not by very much. With an IC engine you should prop it so it's working below it's max power on the ground and it can then unload in the air, if you put too small a prop on the engine you'll go over peak power and hence you won't get much of a speed increase. On a four stroke i the revs go too high you may also start to get valve float, it's when the valves springs can't keep up with the valve train inertia so the valves don't close exactly when the cams tell them too, result is reduced power or worse valves meeting the piston.

Frank

That's why I said 'not so true'. The effect of changing prop sizes on RPM is far less marked with electric than with IC - what changes greatly is the current draw. On the question of peak power on IC my experience is with 2 stroks only - never owned a four stroke - but very, very few IC engines in run of the mill models (excepting the like of C/L speed and team race and R/C pylon) are being run at peak power - if they were the noise complaints would be never-ending!

Mike

10/03/2013 11:25:09
Posted by Ruprect Spode on 10/03/2013 10:45:09:

Basically a propellor with a 6 inch pitch means that 'theoretically', for every revolution the propellor will 'screw' through 6 inches of air, therefore by fitting your 4 inch pitch propellor for every revolution it will screw through 4 inches of air. This obviously equates to a 'theoretical' 33.3 percent reduction in amount of air screwed through per revolution. Thats a big drop.

Ruprectface 23

But with IC the revs will increase in partial compensation not sotrue for electric, of course..

Mike

Thread: What is a typical sink rate for a 2M glider?
28/02/2013 12:02:23

We always used to trim by reducing tailplane incidence until just at the stall - packing up the tail TE, then removing the last piece of packing or possible and/or tightening the glide circle.

Mike

27/02/2013 12:46:32

Oh - I should have mentioned - wing loading for these models is 4.5 to 4.7 ozs per square foot.

Mike

27/02/2013 11:24:03

Very interesting thread - I was intrigued by some of the sink rates quoted as an illustration - perhaps - of piloting techniques? The lowest sink rates I have come across are in the F/F F1A class (a/2 to we old fogies) where good models achieve around 1 foot per second in dead air.

Mike

Thread: Keil Craft Ajax
13/02/2013 12:39:00

The KK beginners' kits showed the cg at 1/3 back, but could, in fact, be trimmed out with it further back - my Cadet flew much better balanced at the rear spar (about 2/3) rather than the 1/3 shown

HTH

Mike

Thread: Charging lipos in advance or not.
21/11/2012 08:30:50

I'm another who 'charges and leaves'. To be fair, I have had some protest - one pack by puffing up (this was before cell balancing leads came along) and 3 or 4 who have had a cell die, but as I can only fly infrequently, the convenience of being able to go flying at a moment's notice far outweighs the downside. The batteries are kept in a fireproof safe, so I'm not worried about them getting more aggressive!

Mike

Thread: BMFA - Is the 'A' for apathy?
21/11/2012 08:24:14

Well my excuse is that it is 386 miles away.

Mike

Thread: Acro Wot side thrust
10/11/2012 09:17:12

The amount of sidethrust you need can also be affected by the engine/prop combination. With my AW I found that the design sidethrust was fine with an 11x6 (ST51 and quiet silencer) but the combination was too noisy for our site so had to try alternative props. I found that an 11x9 and a 12x6 (my eventual choice) both needed a little more right thrust than the design figure.

The best check, of course, is to pull a truly vertical upline and see what the model does. As speed decays it will start to yaw - obvioulsy if it yaws left, more right thrust is needed and vice versa. However, if it climbs straight up long enough to meet what you want, no need to fiddle!

Mike

Thread: Plan Drawing Meanings
30/09/2012 09:56:29

Just one ppoint - grain direction in ply can sometimes be important - for eaxample dihedral braces which tend tobe long and narrow. With 3-ply being the domnant material we use, such braces are noticeably stonger if the grain on tho outer two ply laminations runs lengthwise.

Mike

Thread: Backburn Beverley
10/06/2012 07:51:03

Just looked it up via Google maps - brings back memories. We had occasional visits from Beverleys at Marham (this was '56-58) which we christened 'heavily beverly' - even made the Valiants look slim!

Mike

Thread: Lipo connections
18/05/2012 16:11:05

3.5 on motor/ESC interface, 4 on ESC/Battery, except for the tiddlers which have 2mm all round

Mike

Thread: So you think you are a good modeller.
15/05/2012 17:41:35

Absolutely incredible!!

Mike

Thread: P-40 found in desert.
11/05/2012 19:30:51

Actually, Peter, it wasn't the journalist who said that:

"Andy Saunders, a military aviation historian" was the one.

Mike

Edited By David Ashby on 12/05/2012 09:22:08

Thread: Bomber
10/05/2012 08:30:34

Oh, and in Goodbye Micky Mouse he inferred that the USAAF preferred the P-51 to the P-47because it was cheaper.

Mike

10/05/2012 08:29:20

Bomber and Goodbye Micky Mouse I thoroughly enjoyed. Fighter was a decent historical analysis, but one thing I found odd - he claimed that the turning radiius of the Bf109 was superior to that of the Hurricane and Spitfire because of its smaller wingspan. Not so..

Mike

Thread: Brushless motors - reliability survey
09/05/2012 09:03:46

I have a wide variety of motors from Jeti Phasor 30/3 to cheapest possible bell motors. Never had any problems other than one ham-fisted damage to a small shockie motor - entirley my fault, not that of the motor.

Mike

Thread: A note to the mods
29/04/2012 19:16:49

@Mike - no I mean what I say - constructive criticism that indicates pratical ways forward or makes positive suggestions - not just negative, in some cases ill-informed, comment.

Sorry - but that just smacks of a totally closed mind. What have I typed that is ill-informed?

Mike

29/04/2012 16:19:02

BEB

From the tone of your posting I take it that by constructuve criticism , you mean only criticism which refuses to recognise that there are a good few other fora on a vareity of subjects, not just modelling, which work far more easily than does this one.

Sorry if that upsets you - but this forum is far from being as easy to use and navigate around than others that I use.

Mike

29/04/2012 07:44:31

I must agree that this site is not very easy on the mouse wielder. Why does it not have the facility to check postings since one's last visit as so many sites do?

Mike

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