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Posts posted by Jon H
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that prop is a little feeble and may have been part of your problem. I would have run a 14x7 at lower rpm for more bite.
That said, you are in a bit of a pickle anyway as an 80 size 4 stroke of almost any brand will take a 14x6 to low 9000's. I expected about 9200 from a laser 80 when i tested them on 14x6 apc's.
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I have a bunch of the asp/JEN exhausts. Work well, no complaints.
I certainly wasnt prepared to pay OS prices
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Most unfortunate Martin but sadly, not entirely unexpected.
The little radials are really cool but do not have much muscle. What sort of performance were you getting from it in the end? As in what rpm and prop did you see?
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I think you were a little unlucky with the 'arrival' in the wind. It looks like the wind, and maybe a little PIO while distracted slightly by the engine cut was the likely cause. As i have already mentioned, I had a situation with my little hurricane where the wind lifted it slightly and then slammed it into the runway. There was nothing i could do about it, but as with yours damage was minor.
Looking at the video thought your rates seem really high across the board. I would have to reset all of my rates to get the roll rate and elevator response your model demonstrates. I have not measured the travel on mine, but its really low.
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1 hour ago, PatMc said:
Really ?
Surely the airflow over the top surface of the wing will have become detached & turbulent well before reaching the ailerons.
AS the ailerons work with whatever airflow they get as it is, setting them up a tiny bit will help as relative aoa will reduce. But its sub optimal.
1 hour ago, Piers Bowlan said:Whilst it is true there is not much that can be done about the washout, wing section or a warp Jon, having a knowledge of why the model behaves this way might help us not to build, or buy one, like it again!
If Maurice has not already done so he could try adjusting the C of G to see if there is any improvement? Alternatively he could try increasing the aileron differential incase adverse yaw is precipitating a wing drop or even adding a tad of coupled aileron and rudder ☠️.
I tend not to take the view, you are stuck with it, just trim for speed and all will be well. If the C of G is out then the model can be speed unstable. If a model is well designed, built and set up correctly, as I have no doubt yours are, the model will behave itself if trimmed for a stable approach.
This isnt personal, but having left the modelling industry i find myself with a complete disinterest in explaining myself 500 times in order to get a point across. I have made my recommendation, and we are rapidly approaching take it or leave it territory as i no longer have the desire to chew the fat ad infinitum.
I am not saying your points are wrong, although aileron rudder mixing on the tx is the devils work (2 hands, 2 sticks. Do it yourself), but as some point you just have to fly what you have warts n all. Without input from Maurice on the specifics, we are just talking ourselves in circles and these days i just lack the enthusiasm for that sort of thing.
All i can say is that using the technique i described i was able to take someone who's flying would not get them through an A cert, and within a day get them to a point where they could safely fly their 80 inch Spitfire. Arguments about the merits of that can wait for another day, but the point is someone with limited ability can fly a model like that purely by following procedures like the one i posted earlier. Its not ideal, but better than them having a crash. Even if our troublesome chipmunk can be tweaked, i would still land it with a flap mix if i felt it needed it as it takes the thinking out of itand allows brain power to to be allocated to other things.
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17 minutes ago, Piers Bowlan said:
Unlike a full size aircraft we have no idea how near the critical pitch attitude the aircraft is to the stall
Very true, which is exactly why you trim it for a speed just shy of the stalling angle. The model will then naturally fly at this speed no matter what you do with it and you do not have to judge the speed as its locked in by the trim.
Of course extreme gusts of wind etc can rock our applecart, but its by far the easiest and most unstallable a model is going to get.
When i flew my sea fury the other weekend i had 3 great flights with easy landings, but the 3rd was a real challenge with 2 go arounds due to a shift in the wind causing turbulence over the patch. Could it all have gone wrong? yes, would have been a tip stall in the usual sense? no. The wind will always ruin our day by micro bursting us into the floor or similar, but most models are stall/spun on base entry or halfway down the approach and the method i describe will get most through that phase.
19 minutes ago, Piers Bowlan said:This doesn’t help Maurice with his Chipmunk ‘that stalls at the merest suggestion of landing’.
The question is why is his aircraft so unforgiving? As I said before (now deleted!) there are questions?
1. Is it overweight (high wing loading)
2) is there any inbuilt washout.
3) is it always one wing that drops (warp?)
4) differential ailerons would be helpful.
5) is the aerofoil ‘thin’ and unforgiving which won’t help matters.
6) C of G position?
Well it does help. While i agree in principal the issues you raise are important, and covered rates and cg in my post, he has the model he has at this point and there is likely not much that can be done about the washout or wing section. So its a matter of dealing with what is i front of him and flying approaches in the way i describe will help as it takes the airspeed judgement call out of the equation.
All that said, more details on its bad habits would be helpful.
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One thing i forgot.
Aborted landing/go-around procedure.
With your elevator flap mix enabled if you need to go around do not under any circumstances firewall the throttle. If you do, especially on a 50cc class model, you will have a massive shot of torque rolling you left and because of your low speed your ailerons will not cope and may in fact induce a stall. The rise in speed will also cause an almost uncontrollable pitch up if you just boot it.
If you need to go around rapidly advance the throttle to about half, hold the model level (forward elevator pressure), flaps up to half, gear up, increase to 75% throttle, flaps up, climb away.
I use a variation of this technique and just go to flaps half and cruise round the circuit at half throttle holding the model down, but i am very used to this type of flying so for the newcomer to this style its best to just tidy the model up and go again.
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Without knowing the exact model being discussed i cant say if the following will apply directly. For very light foamy models will will not be applicable, but for everything else it should apply.
Flaps tend to be a little misunderstood in modelling circles with a great focus on the increase in lift they provide. This is true of course, but the big thing they add is drag.
This is important as it completely changes the way you fly the approach.
Many modellers fly long an fairly flat approaches with the nose high in an effort to bleed speed off. This is not at all uncommon and i do it myself with some of my more slippery sport models.
However, this is not ideal from a tip stalling point of view as you already have the wing near its critical angle of attack, and as we know stalling is all about angle of attack and not airspeed.
If you add flaps to a model, and give them a fairly healthy deflection the added drag means you can fly a steeper nose down approach with power off and not accelerate to warp speed in the process. The added lift will also mean a lower angle of attack is needed on the wing as a whole, further improving tip stall margins. As your efforts in this configuration are mostly aimed at shoving the nose down, rather than holding it up, you cannot stall the model.
21 hours ago, Maurice Dyer said:Question for the experts. Got a Chipmunk 68 inch span that tip stalls at the merest suggestion of landing. Would flaps help ??
Maurice
Yes
As i have said many times before, one great help is an elevator flap mix. I use these all the time on my warbirds to re trim the model for landing as lowering the gear and flaps along with reduced airspeed usually causes a significant nose down trim change. Set up correctly this will make your model 'stall proof' if the correct technique is used. It should also help in your case with the chipmunk.
First, make sure your c/g and elevator rates are half decent. IF the model has massive elevator rate and/or is out of balance your are on a looser from the get go.
With that covered, set your flaps to the desired deflection. Dont be shy, get them down a good 40 degrees or more (89 degrees for a spitfire!) and enable the elevator flap mix on your tx. It should be set up so that as the flaps are lowered elevator position changes to deal with the trim change. The flaps are the master channel, moving the elevator should not move the flaps. Generally, models will need up trim with flaps deployed if they have retracts as well. The added drag of the gear below the model causes a nose down pitch, so i always start with about 5% up on the mix just to make sure its working as intended.
With that done leave the mix menu open on the radio and go flying. Get the model into the landing configuration and observe the response. Adjust the mix while in the air until you get to a point where the flap mix is set to hold the model in level flight at just over idle power without stalling. The way i set this is to increase the up elevator on the mix until the model stalls, note the value, and then knock a bit off. Sometimes i will get to a comfortable feeling setting before a stall, and in those cases i give the elevator a few tugs to see how close i am to provoking a stall, then make adjustments as needed. If you are not confident beeping your tx buttons without taking your eye off the model employ an assistant to beep for you. if it all goes wrong be on a hair trigger to get the flaps up so the mix is disabled. If you have to look at your radio to find your switches, spend a little time before flying finding them on the radio by feel until you can do it with your eyes shut. Having a standard switch layout for all models is also very handy. I cant believe the number of people i have flown with who have a different layout of switches for every model. Its like they loaded a shot gun with switch assignments and just fired it at the radio each time.
With your mix set up nicely its time to land and you need to fly a more formal landing circuit than most are used to and at a higher altitude. If you whizz downwind and just dump full flap the model will damn near do a backflip as the model will be way too fast for your flap mix trimmed speed. A 3 position switch is needed as a minimum, a slider or servo slow on the radio is ideal. Either way, the general idea is to slowly add flaps as you slow down on your downwind leg so that when you turn base they are full down and you are holding a small amount of forward elevator pressure on the stick. You can then bin your forward elevator pressure as you roll into your base turn using the slight up trim condition to float you round. Once lined up leave the elevator alone. If the model is falling too fast add power, if its going long pull some power off. Use the throttle to control the rate of descent and dont touch the elevator. We know the model is trimmed for a just above idle level flight airspeed/aoa which is below the stall so it will naturally fly to that trimmed speed and so cannot stall. The energy to maintain that speed can come from the engine, or from gravity. More more engine you use the less gravity, so a lower rate of descent. The less engine and more gravity...you get the idea. The point is if you just leave it alone it cannot be stalled like this as its just parachuting down with those big draggy flaps keeping it all under control. All you have to do is decide when you level off, and use just a tiny squeeze of elevator with a little added power to achieve this. Ideally you are now about an inch off the floor in level flight. Chop the power and slowly tug on the elevator until you either stall or mush onto the runway.
Taxi back looking smug as your club mates look on after your perfect landing.
This is a very different landing technique than most modellers are used to and it demands accurate use of throttle as well as resisting the urge to yank on the elevator. If you can do that, your scale models should be a great deal easier to get down.
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17 hours ago, Alan Gorham_ said:
Didn't Ian say he had an operable sliding canopy on his model? If that's radio operable I'd say that is weight you can well do without for a maiden flight.
Or at all. Every sliding canopy i have ever seen has done one thing, and one thing only. Fall off.
They look cool, but every one i have ever seen has made a bid for freedom in short order!
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On the climbing/diving thing i do not agree that it is related to c/g, at least within the realms i am on about.
Its virtually impossible to get a scale model to be in trim through its entire speed range and certainly the full size is trimmed regularly. Even your basic cessna is constantly in need of trimming so if a model climbs with speed and falls with less speed i would consider this normal.
My sea fury is the most neutral of my warbird fleet and its also the one with the thinnest and most symmetrical wing. My La7 and P39 really need a good shove of forward elevator at high speed. In the case of the P39 i have watched a number of those old WWII training videos for the full size and from many of the shots i can see my model behaving very much like the full size. In practice its not an issue and i just hold the nose down with some forward stick on fast passes.
However, if a model climbs with power, that is another story and engine thrust lines should be investigated. Again i keep things simple these days with 0-0 on my up/side thrust and just fly the thing. I have not come across a warbird yet were this has been any kind of problem.
The only tricky part is working out if the model is climbing with speed or power, but usually this can be tested by just opening and closing the throttle before the speed has a chance to change much.
When it comes to rates, i have high/low set for ailerons and elevator on different switches. Generally i use high elevator low aileron for takeoff, and go to low elevator when in the air with the gear up. Landing is normally the same but i may use high aileron rate if the wind is choppy and i want more authority.
Lowering flaps also enables my elevator flap mix to effectively trim the model for the landing configuration as the slow speed and drag of te gear usually makes the model want to bury its nose in the earth.
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From your description it sounds like there should be more than enough compression to me. I was once distracted by a phone call and forgot to put piston rings in a laser i assembled. On test It started and ran, even tuned up, but idle and acceleration was very poor and compression very low so i took it apart to find out why. Imagine my surprise to find no rings! While i appreciate that glow and diesel are not the same, the basic point is these engines should operate to some degree even when the fit is less than stellar.
Also, if you can get the thing running the heat cycles should grow the piston slightly and you may find it all comes good. The trick is getting the thing going in the first place.
I echo the feeling of others who are cautious about an electric starter, but used correctly it might be the way to go as the dynamic compression will be higher than when hand flipped. If you use an electric starter do not prime the engine at all and just let it draw its own fuel.
I am sure there will be a way to get it going.
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There has been plenty of comment on the compression, the piston nip etc but its very hard to quantify. Are you able to post a video showing the engine being flipped over with a prop on? Might be able to judge better what it happening. Unless the fit is truly awful, which i doubt, a heavy port prime and gradual increase of compression while flicking should at least get a pop out of it even if it wont run right away. I find it strange that it is completely devoid of life.
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11 hours ago, Martin Harris - Moderator said:
Don't forget that these instructions were written before modern synthetics were widely available. Back in the day, Neil Tidey only recommended castor for Lasers...
Yea, and the 20% castor recommendation was binned in favour of 15% synth by the mid 90's, then halved to 7% a few years back. While i dont think 7% synth is a good idea in this case, 15 will be absolutely no problem.
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a gusting wind can wipe out any model under the right (or wrong?) circumstances. My little hurricane got faceplanted into the runway once with a sharp downdraft despite full corrective action. But as you say, these traditional models can usually absorb the abuse and bent undercarriage was the worst of it.
One other thing to consider though is the model is now a half pound lighter and will fly that bit slower. If your flare was at the normal speed you are used to you may have had just enough excess energy for the wind to really pick it up before dropping it back down. That said, it would probably have been a non event had the engine not decided to give up at that exact moment.
In any case, retracts are always more prone to damage and I tend to hangar my warbirds in gusting conditions for that reason. Last weekend i took my sea fury to put some hours on the rebuilt engine. The first 3 flights were perfect with nice smooth landings. The 4th took me 3 approaches with 2 go arounds as i couldnt get it stable as the wind had swung to the north a little and the turbulence off some trees caused real problems. WIth the wind in that direction, 4 flights already and an undamaged model i decided to call it a day.
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I have OS engines of the same vintage running 15% synthetic and 5 nitro with no issues and i cant see any reason why there ever would be.
25% oil will make an utterly horrendous mess and there is just no need for it.
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ill add my 2p as well.
I can see that if you had 2 identical models, but one was a brick, it might be less stable than its lighter mate when flown at the same speed as it would need a greater aoa, but generally weight is not a factor as long as the model is within the range of weights appropriate for its size.
On reynolds and all that...ehhh its pretty much meaningless unless we are building exact scale replicas with identical wing sections etc. As we dont tend to do that, just forget it and move on.
As a side note, most model warbirds tend to have over size tails to 'improve stability'. I have a big problem with this as making the tail bigger also makes the elevator bigger, and thus more effective. This makes an already sensitive model more sensitive leading to excess nose weight to tame the beast.
I believe this larger tail idea is a hangover from the free flight days when the bigger tail would have probably been an asset. However, now we have our dumb thumbs on the controls the static stability of the aircraft is less important as we are able to correct deviations we do not like.
With this in mind i built my little hurricane with a scale (or more scale) tail on it and i have no stability problems with it, and my elevator movements are still very small.
So take that modelling folk lore. I advocate scale tails and rearward c/g in the pursuit of model warbird bliss. Oh and i cant be bothered with side or down thrust either. Mount it straight and use the tall waggly thing on the back.
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15x8 would get my vote in that model. use apc, master are rubbish.
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4 hours ago, martin collins 1 said:
there is a low oil content Laser fuel, would that work on my 1993 100
yep it will be fine
4 hours ago, martin collins 1 said:what advice would laser users give to a glow sceptic like me re operating this engine?
Tank in the right place, OS f plug, correct prop for model (what is it?)
With that sorted, start it, tune it, fly it. Repeat until tired, go home, crack open a beer (or beverage of your choice) and reflect on your day of flying.
Hopefully the engine is in decent mechanical condition. I would recommend you whip the front housing off the engine and take peek inside before you run it. If its rusty or otherwise not nice change the bearings etc and then go from there.
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8 minutes ago, Martin Harris - Moderator said:
Sorry, what I meant Jon, was would there be any possibility of listing identification clues for the whole range.
Ah look see, i try and help one chap id his engine and im back doing a job i no longer have for a company that no longer exists at half 7 on a Monday night. I dont mind helping out here and there but going through the entire range from start to finish would be like writing war and peace. Just the 150 alone has about 6 major versions to cover although many of the versions hardly differ visually.
I have given details for the 100 and 120, the 150 is the same as the 120 just 100mm tall not 90. That's going to have to do for now.
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Martin yours is a 100, Brian's a 120 circa...ehh 96? sure why not. 120 has 45mm case, 90mm tall, bulges for head bolts on crankcase above mount rails, large head, large exhaust etc...and, it just looks like a 120 as that is what 120's look like.
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Well it looks like a 100...they look like that. if it looks like that its a 100 as that is what they look like.
This is also a 100. 100's look like this
https://www.laserengines.com/product/laser-100/
You will note it looks the same as the old one, just not as square.
What else...well 45mm case, 100mm tall...square case with no bulges above the mount rails for head bolts....small head, small carb, small exhaust....and it just looks like a 100.
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18 hours ago, mikem65d said:
Had the opposed twins been Boxer design they would have been in huge demand. Especially at the price they were listed for.
it couldnt have been done for the same price as a common throw crank. A full boxer would have cost a fortune and at maybe twice the cost of a v it wouldnt have sold. Also as vibration with a single throw was not a problem on test, and no owner has ever complained its a moot point anyway. This was discussed to death during the development.
I have seen posts on facebook from people who have not owned one or seen one run claiming excessive vibration, but they simply havent a clue what they are talking about. They run fine, not as smooth as a V but not as 'bad' as a single, and power that thrashes the competition.
Although unrelated, i like the 180 degree firing interval too. Makes a nice sound.
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5 hours ago, RottenRow said:
one wonders why they were left anonymous
Dont look at me. i stamped the size on mine and in 1993 i was only 8 so not my problem.
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19 hours ago, martin collins 1 said:
Its a 100. 1993 manufacture. There is an outside chance its a very late 90, but i doubt it.
Weights are meaningless as carbs changed, early engines had solid cranks, later ones hollow etc.
Seagull PT19
in Scale and Semi-Scale kits
Posted
If you install the screws into the nuts leaving half inch free play you can easily remove them with a hammer and a sharp tap. If you want you can fill the holes by gluing a dowel in there. once dry cut it off, sand it smooth etc front and back, then set about drilling your new holes.
Should not be a big job