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Member postings for Evan Pimm

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

Thread: aileron throws, dual rates and end points
02/06/2012 04:56:03

Simple answers to your questions, yes, you have a mechanical problem with aileron, assuming the servo arm is 'centred' and the throw has no mixing, and is set at 100% each way.

The tailplane being not square to the wing will make little difference, unless you have set it up that way for a bit of glide circle trim...

Evan.

Thread: Why? Do you know?
06/11/2011 01:02:49
It could be, Erflog, the wing loading has as much to do with it as the leading edge and aspect ratio. If you take it to the extreme, and assume that the wing loading is '0' then you can't stall it, no matter what AOA you have...Then again it it is so heavy that you can't get it off the ground, again you can't stall it...Joking aside, the low A/R/delta models do seem to be able to operate at apparent wing angles in excess of 'normal' angles, but they also usually have considerably lower loadings too, simply because of the layout.
Evan.
Thread: Angle of incidence
06/11/2011 00:48:56
Again, for Simon, once the balance is set, you must not move it. This model seems to have excessive 'Longitudinal Dihedral', modelspeak for too much difference between the wing and tailplane. Check your ailerons, they should, more or less, line up with the wing chord line. Now check the difference between the wing chord line and the tailplane chord line. They should be more or less the same, with the wing a degree or two more (positive) to the tailplane. Balance per instructions. Then fly. Now you can do the 'dive test' to fine tune the balance. Most rearward is when the model will just slowly pull out from a 30 deg dive. The elevator trim at this point will not necessarily be in line with the tailplane, but will be at a position (trim) for the model at its 'S&L' cruise. Changing the elevator angle with the 'TRIM' lever on the tranny will allow the model to fly slightly faster, or slower, on command. You will probably have to do several flights to sort out a comfortable trim, but do not be confused with those who tell you you can adjust the elevator trim (speed trim) by adding or removing noseweight. As stated, balance is pitch stability. Wing to tail angle is speed trim. the two are quite different, but one can affect the other, which is where the confusion arises.
Evan.
03/11/2011 08:41:25
Seems you are a little confused Steve, yes the dive test will indicate a stable balance position, and this can be adjusted by adding weight fore or aft to produce a gentle pull-out from a dive. But this has nothing to do with the model climbing from 'S&L'. Balance only affects pitch stability. The climbing issue you have is a result of the 'trimmed speed' being lower than the speed you are trying to fly it at. So, of course, the model tries to return to 'trimmed speed' (the speed at which it will fly S&L at the angle of attack the tailplane is trying to hold the main wing at) by climbing. You have two choices, fly it slower so it maintains 'trimmed speed' and 'S&L', or re-trim by reducing the angular difference between the wing and tailplane, and fly faster to maintain 'S&L'. The consequence of changing the wing to fuselage angle, as you are doing, is that you also change the apparent angle of the fuselage to the line of flight, so long as you do not change the weight of the model, the wing will always fly at the same AOA so that, at whatever speed it is flying, Lift equals Weight, in S&L flight. Align the fuselage at the nicest looking angle to flight, set the main wing at 1/2 degree? positive to the line of flight, then shim the tailplane to set a comfortable cruise S&L speed (trimmed airspeed). Most likely this will be a degree or two less than the main wing angle. You won't need to change the balance once it is set per the dive test.
Evan.
Thread: Why the saddening blow to my fms mustang?
18/07/2011 05:56:37
I remember this sort of thing being a problem with soarers...If you got the balance a bit far back, and the speed a bit too high the tail would 'take over' and unless you could get the speed down the model would try to bunt no matter what you did with the elevator. If you weren't high enough then it was time to dig it out of the ground. This looks just the same, slow speed nose high, then at high speed the rapid nose down. Unless you get the power back really quick, and hang on to full up elevator, assuming you have enough movement, then there really is nothing you can do. I think that this one was lost to a rearward balance, not a radio failure at all. I assume that it is a foamy? The flexible nature of the airframe probably didn't help either, the deflection of the control surfaces at high speed (above VMax) may have simply bent the fixed bit, and added zero control effect.
Evan.
Thread: Spitfire's do they use washout?
07/04/2011 21:02:24
Actually, the full size uses 2.5 degrees washout built progressivly into the wing, root to tip. If you are considering a serious scale job, then leaving it out, or using less, would be non-scale, wouldn't it?
Evan.
Thread: Fw 190 D
15/10/2010 23:03:15
Indeed, you illuminate the biggest problem we ground based operators have. Typically, our stereo vision 'depth perception' only works out to 30 feet or so, after that we are relying on visual silhouette clues for orientation. Accepted wisdom says light colours on top and dark colours on the bottom, for just this reason, whereas these aircraft have got it all wrong. Not only are they light on the bottom and dark on the top, but the shades used tend to blend with the background (waddaya mean, it's supposed to?). I well remember flying my 152 round the circuit, with an observer, and as it turned away, and we are talking a fully equipped 100" scale model with flaps/retracts etc and big glow engine, it just shimmered, then disappeared. I think we both yelped at the same time, looked at each other in disbelief, then it just as quickly reappeared as the top of the model came into view. I have great respect for the German late war camo choices. There is one thing that might help, all the operational 152's were assigned to JG 301, and had those nice bright red and yellow tail bands so that will at least help with 'which way is front'. Obviously, the smaller the model, the bigger this problem becomes, hence my preference for the larger size when the colour choices are limited to schemes designed to hide the aircraft in the air. As I said, I have no experience with small likrice models.
Evan.
15/10/2010 11:34:35
I no longer have the 152, I am currently flying a near 1/4 scale A-8 with my old D-13 waiting for an overhaul and repaint. All FW's seem to fly well, although I can only comment from my own models, all over 70" span. The Anton is the most neutral, the 152 was the most 'trainer' like and the D fits somewhere between. Experience has led me, and several other scale modellers, to believe that models of this type are best around 70 to 80" span, at that size they fly well, and you can still transport them in normal cars without too much of a problem. I have no experience of models as small as yours, nor any with electric propulsion so your comments about the flight characteristics will be waited with interest. Let us hear all about it!
Evan.
15/10/2010 05:43:27
Erflog, don't sweat the cockpit position, FW did not move it from the A-8, D-9 position. What they did do was bolt an extension plug 772 mm long onto the original fuselage engine mounts, which moved the wing forward 420 mm, thus giving the visual illusion that the cockpit was moved back. They also added a 500mm spar extension to the centre of the wing, moving each u/c leg out 250mm from the A/D position. They also list the overall a/c dimensions of the H series as: Span, 14.4 metres, length, 10.7 m. They list the armament as 2x MG 151/20 in the wings and 1x MK 108 engine mounted. So no cowl guns to worry about. Your models look good and we will be looking forward to a flight report soon.
 Evan.
13/10/2010 08:27:52
Erflog, my documentation indicates 17 D-11 delivered, 4 with a gyro gunsight. I was wrong, it seems about red 13, it was red 4 that was the -11. I have photos of another D-11 captured after the surrender, white 61. Like a lot of the late war 190's this one has natural metal wing undersurfaces and extension plug so there are lots of variations of colour you can choose. Very interesting study, the last months of the Luftwaffe. So far as the plug and tail, the D-9 parts catalogue lists the standard fin and the 152 fin as interchangeable as early as October 1944. Dunno where the idea that 152's and D's were different came from, all were based on the A-8 fuselage, and if FW reckon you can fit 152 tails to 190's, well, who are we to argue? I used to fly a 152 'some time ago' 100" long wing version, was a glider and quite difficult to land, took a long time to dump the wing lift after touch-down and I had to 'fly' it until the tail dropped, and the wing basically stalled. Land into wind in any breeze, much like a WW1 machine.
Evan.
13/10/2010 06:24:17
Hmm, all my documentation shows at lest 68 152H built, photos of at least 3 lined up on an operational airfield, and one a Farnborough after the end, and flown at last twice by Eric Brown, and at least one in the US, and still at Silver Hill awaiting restoration. So far as the fuselage plug is concerned, it is the same as the D version, the 152 and 190 tail and plug being interchangeable. There is at least one photo of a D sporting the 152 tail... perhaps the reason for suspecting that the plug was longer is because the wing on the 152 is some 6" forward of the D position.
There are good drawings of all these versions available if you look around. Yes, the long and short winged 152's use a new wing, the long one is washed out to the aileron inner, then straight from there, the shorter one is more like the standard D wing, but both use hydraulic retraction, not electric. As for the later D's, only one survives in the US, recently restored is a D-13 ex JG 26. You should be able to find lots about that one.
Evan.
12/10/2010 09:05:53
You are not wrong, Erflog, those are the known aircraft, I don't have the book to hand, but I think the first 3 were D-9's and red 13 was the D-11 (no Cowl guns and the Jumo 213F engine). While the 152 was designed for high altitude work by the time it was in service there wasn't any high altitude bombing anyway so it was used, according to those that flew it anyway, mostly on low altitude fighter-bomber interception. Mostly used by Jg 301, and with yellow/red RvD bands. Heck, there was only a handful ever built so unless it's scale comp you want, you could even makeup your own 1946 scheme...
Evan.
09/10/2010 22:13:24
No. There were three D-9's and one D-11 found at Ainring airfield after the final whistle, and all were eventually broken up. These aircraft have been subject to pretty heavy investigation, 'Doras of the Galland Circus' is the tome, and airfield defense of JV44's 262's was the aim. Apparently the never flew above a couple of thousand feet, and only as the jets were leaving or arriving, hence the garish markings, black humor of the personal markings, and the very real chance of being shot down by the airfield defenses. Interesting story, but.
Evan.
Thread: c o g
26/08/2010 07:56:13
If you read what I initially wrote Martin, 'With this wing shape...'
Evan.
25/08/2010 04:59:43
It might, Martin, but so long as the taper isn't gross, when you do the drawing, it makes very little difference and with my usual 'slightly forward' balance advice (25~30%) the balance is nicely conservative and unlikely to be a worry during those first trimming flights. Simple too, which was the point of the thing.
Evan. 
23/08/2010 07:30:55
Or, with this wing shape, measure 1/2 way from root to tip and that is the Mean Chord. Place the balance point at the suggested 25 to 30% on this chord. Flavour to taste after flying it there and getting a bit of trimming done. Simple enough, and works for any straight taper (unswept) wing.
Evan.
Thread: Taking Off And Landing
23/08/2010 07:18:06
After 6 pages of differing, and quite dearly held views, a little addition from 'the other side of the world'. Most clubs down here use quite small grass strips, courtesy of some kind landowner. We all stand 1/2 way down the strip in some sort of 'box'. It just makes communication much easier. The other, very good, reason for doing so is simply this...at any sort of competition you might ever enter, Scale, Pattern, whatever needs a 'Takeoff' and 'Landing' you will find that there is only one place you are allowed to stand, 'runway centre'. And the very good reason for that is so you can centre your flight patterns so that the judges can both see, and mark your flight, including take off and landing, which must remain straight. It does not take much practise to learn this, and it very quickly becomes normal. It does not matter which way the wind is blowing, you very quickly learn to compensate for that too, it comes down to 'practise'. It is not ever intended to make flying harder, or the pilot superior, it just makes you disciplined, and therefore safer. Although I know of one club "instructor" who crosses the 'active' if the wind blows the other way 'cause he can only land from one direction...
Evan.
Thread: Phil Smith
30/05/2010 06:07:29
Coming so soon after Boddington's demise, this is really quite distressing. I have some of Phil's typed letters he sent when we were exchanging information on 'Concord' and they will remain treasured reminders of the man, as will the model itself.  Dunno how many cut their teeth on Phils designs, but it was that every 'Aeromodeller', 'Model Aircraft' and early 'RCM&E'  had a page of Veron ads. My thoughts are with the family. We won't see the like again.
Evan. 
Thread: Metal to metal interference
29/05/2010 13:13:48
Well Erflog, I can confirm that the rolling elements most definitely rely on the oil film for survival, part of my job is to provide Root Cause Analysis for gas turbine failures, and you would be surprised how short the life of a bearing is when deprived of oil, how rapidly things get really hot, and the amount of energy stored in a compressor rotor at 10,000 rpm. Even piston scraper and compression rings in IC reciprocating engines have a remarkably short life when the oil film on the cylinder walls disappears. It isn't the running that wears engines, it's the starting, when the oil film is either missing or not completely there that allows the wear to take place.
Evan.
28/05/2010 23:27:43
As you say Erflog, not always an issue, and not ever likely to be with a glider, you need some energy input to the system, via the vibration. If your engine is producing metal to metal noise, then the oil film has failed, and the engine will soon to, or the muffler is loose, and that has caused servo jitters. As an example, I use nylon bolts on a UPF to anchor the flying wires, these are removed for transport. If I forget, and fit even one metal bolt, the throttle will have occasional random operation. Replacing the metal bolt with a nylon one, and everything is solid again. Now, I'm not going to say that it is 'metal to metal' noise, but it only happens when the engine is running, the radio system is on, and a metal bolt has been inserted where a nylon one should be. Pretty solid grounds for the suspicion, but. And you actually need two bits of metal to be in contact, with just enough space between the to allow some relative motion between the two bits.
Evan.
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