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Member postings for Jon - Laser Engines

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

Thread: Exess fuel
17/07/2018 16:40:29

I have an old duvet cover and some cheap towels all over the back of the car. Seems to do the job.

Steve, pour fuel all over the rest of the carpet so it matches and just claim you cleaned up the spot

My next stupid idea is to pour something absorbent over it. I had an oily/cracked cowling in the corner of my building shed and after a while it became covered in balsa dust. I then noticed that the balsa dust had drawn the oil out of most of the cracks as well as off the surface. I was able to wipe it clean without resorting to major solvent abuse. Perhaps careful application of talc would help? If nothing else it will smell clean

Thread: Holding Your Nose
16/07/2018 12:40:56

For the most part, thats all well and good and i agree, but it wont happen in the air. The leaning of the mix due to gravity is offset by the engine unloading and going rich in the air. Assuming RPM does not rise massively and there are no pipes etc involved they cancel out almost perfectly. Which is dead handy.

As for tank positions, i would never trust kit makers to get that right every time.

Anyway i think im done with this discussion. Its pretty obvious its not getting us anywhere and, to be honest, i dont really care any more. we are also way off the op.

The fact of the matter is that the nose up test is not an accurate way to check the tuning of an engine. It is simply not representative of the conditions an engine will see in flight and so will not accurately reflect how the engine will behave.

Anyone who still maintains that the nose up test is good for testing tuning is wrong. I say that as both a modeller and an engine manufacturer and nothing will change that.

Thread: What setting for charging NiMH batteries
16/07/2018 08:34:27

500mah for 1200+mah packs. If i am in a massive rush i will use 1amp but thats not very common.

New batteries get cycled up/down at 10% of their capacity a few times to make sure i dont kill them straight off.

Thread: Holding Your Nose
16/07/2018 00:09:40
Posted by Gary Manuel on 15/07/2018 10:18:14:
Posted by Jon - Laser Engines on 15/07/2018 09:28:00:

If it quits half way through the flight, then will not run up to full power again at that tuning without refuelling then the tank is too high and the mixture has gone lean as the tank level dropped and fuel head changed. Lower the tank, retune the engine for the new tank height and try again.

Can't you see the contradiction here John?

In one breath you are saying that the relative position of the carburettor and tank make no difference once the engine is tuned for maximum revs - hence why the nose up test is pointless. In this paragraph you are saying that the tank position is critical to good running. Which is it to be?

You also say that the tank should be lowered before re-tuning. Are you serious? How does one go about lowering the tank of a model that is already built with it's tank position dictated by the position of the inbuilt tank shelf?

One other observation comes to mind here. Most glow engines are designed with the carb fuel intake close to the centre line of the engine to allow the engine to be mounted in any orientation. I note that the carb fuel intake on laser engines is at the top of the cylinder head. Does this mean that the fuel tank needs to be positioned at a different height depending on how the Laser engine is mounted?

There is no contradiction. You confusing two different issues. Change in fuel head from gravity assist to gravity resist is the normal issue with a tank mounted too high. This causes significant mixture changes as the needle is set with gravity helping the fuel on its trip to the carb causing a lean cut once gravity is against it. If the tank is lowered, the fuel is always resisted by gravity and so the needle is opened further during the initial tune preventing the issue in the air. The point is, the fuel tank position is wrong. Making the needle richer to cover this off is not the fix, the tank must be moved. While an engine set with its tank too high may cut on a nose up test it will not be apparent why and it is highly unlikely the tank position would be considered. Most will incorrectly open the main needle to mask the problem. This increases fuel consumption, decreases reliability, and increases both mess on the model and the chance of corrosion due to unburnt methanol in the crankcase.

So yes im quite serious about moving the tank. It needs to be where it needs to be, anything in the way needs to be cut out or modified to make that happen. There is no way around it and all engines are the same unless pumped.

In the case of Laser with the carb at the top of the cylinder this usually means the tank needs to be significantly lowered when the engine is run inverted. As Ron with attest, this is something I go into in great detail before selling anyone an engine as it can catch people out. I also try to look up the instructions/photos of the model in question and recommend a tank placement and how to make the modifications so people are not lost and confused trying to fit it all together.

15/07/2018 09:28:00

Gary my comments relate to all glow engine operation. In 3d flying you are never flat out while not moving, the engines in those models have sufficient power to prop hang the model at a considerably lower power setting than full throttle and the moment the throttle is raised the model begins to move. As soon as its moving, everything changes. Many 3d models also have mini pipes or other exhaust tuning and as Bob pointed out some time ago they change things considerably as well.

in contrast, scale can in fact put greater load on the engine as loops (for example) need to be large and sweeping. That requires power and given that most warbirds are very heavy full power is often needed for a long period. I don't know if you have ever seen me fly, but those that have will tell you I don't spent much time straight and level.

My big fat Sea Fury for example could climb vertically from ground level to around 800ft if I asked it too, my La7 could as well, both at full power. The engines in these dont stop, I would have to bring to model to a complete halt and stall it out before the engine would start to suffer from the mixture change. And even then, reducing the throttle by 20% would keep the engine running. It would sound that the engine was slowing down through the climb, and it would be as the airspeed bled off, but the effect would be made worse by the doppler component of the sound. This would lead you to believe that the darn thing was on the verge of throwing in the towel when in fact it is quite happy. I would try a nose up test with it to see if it would fall over on the ground, but there is no way im waving a 23 lb 58cc model around with its nose in the air.

I am not for a moment suggesting that the effect of gravity on fuel flow make no difference, clearly it does, im simply saying that the test will not reveal how this will effect the engine in flight as the unloading of the engine in the air will more than cancel out the gravity effect. An airspeed of only 5mph can increase rpm buy as much as 500 depending on the prop. This is a significant load off the engine, more or less equal to an inch of pitch or dia depending on prop brand.

As for being an expert, well, i would like to think i am better educated in glow engine operation than most given my current occupation.

Given that fact, instead of giving me both barrels and accusing me of spreading false information, even though this is the same information i provide as a manufacturer to my customers, why not listen to me? give my method a go?  forget the anecdotes, why not give it a try? Especially when Ron, who has followed my advice, tells you that it worked. I know that we modellers are often stubborn so n so's stuck in our ways but we all have to accept change some time.

Start the engine, run it up to half throttle for about 20 seconds. run up to full power and tune for max rpm. The best way to do this is lean the needle until rpm drops (too lean), then open the needle until rpm drops (too rich). Anything in the middle of that arc can be considered optimum tuning so i set the needle in the middle of that optimum range. Hold this needle setting at full power for at least 10 seconds. By now, the engine has been flat out for a little while and is likely nice and toasty. If it made it through the 10 second power test without significant loss of power (more than about 50-100 revs) get it out on the runway and stick it in the air. Don't nose up test it, just fly it. If you are worried about the climb out, take off at 70-80% power as most models are plenty powerful and this will be more than enough. If you have done this correctly, and there is no other external influence screwing things up the engine will not stop.

If it quits half way through the flight, then will not run up to full power again at that tuning without refuelling then the tank is too high and the mixture has gone lean as the tank level dropped and fuel head changed. Lower the tank, retune the engine for the new tank height and try again.

If it stops after a while but will restart and hold full power at the original tuning then it overheated and the cowling design is poor and baffles need to be installed. Most engines will not deliver peak power indefinitely without overheating even with good cooling.

Engine cuts in flight are always blamed on being lean and i suspect this is the root of this nose up nonsense. In reality, this is rarely the case and there are plenty of other explanations for engine flame out.

 

 

 

Edited By Jon - Laser Engines on 15/07/2018 09:31:59

Thread: Laser Engines - Technical questions
14/07/2018 21:13:19

Trebor, im not sure of the size. I was only 10 when laser stopped using them! Im sure M+R can help you.

Rocker, the 100 would be plenty. As Percy says the 100 is a long stroke motor with plenty of grunt. The spacewalker is not a high performance model, a 15x8 would be my choice of prop and im sure it would putter around quite happily.

Thread: Holding Your Nose
13/07/2018 16:59:51
Posted by David Davis on 13/07/2018 16:57:34:
Posted by Jon - Laser Engines on 12/07/2018 16:21:03:

Its a pointless test that dates back to the early days. With modern engines that have considerably better fuel draw and/or are pressurised its really redundant....

What about us cheapskates who use old engines to power our models, e.g, the Meteor 60 I have in the Boomerang trainer? wink

As pointed out on the other thread, they should stop burning their money on a stash of kits and buy some new engines

13/07/2018 16:59:07
Posted by The Wright Stuff on 13/07/2018 14:35:31:
Posted by Jon - Laser Engines on 12/07/2018 16:21:03:

Its a pointless test that dates back to the early days. With modern engines that have considerably better fuel draw and/or are pressurised its really redundant.

Jon, what do you mean specifically by 'early days'. All the OS manuals appear to recommend pointing the nose 15 degrees up (as opposed to vertical).

I always like to try to reconcile difference of experience - it's the scientist in me, I guess, but is it possible that (due to your experience) your engine tuning is generally pretty good to start with, whereas there may be some benefit to the 'nose up' practice if it is grotesquely out of tune (or badly plumbed)...

Early days being the un silenced days with things like the original os max engines. You remember the type with a plate over the exhaust to alter the backpressure with the throttle.

Also I accept that I am probably better at tuning engines than many, but part of the reason for that is by ignoring the test as there are many other factors that cause issues for the tuning.

In the case of Extra Slims example, which is a common one, the issue is likely to be heat and not the original tuning of the engine. This is because the required tuning changes with engine temperature and the long run at full power on the climbout heats the engine up to a point where the tuning it held on the ground is no longer viable and she goes out. To be clear, the engine has not overheated at this point, its just too hot for that tuning. If the engine was run for a longer period of time before tuning it on the ground then it would be hot and any adjustments would be appropriate for the engine at its operating temperature. Equally, upon the restart the engine will not return to full power, because its hot...its retuned and off it goes. in this case, the nose up test is again not proving anything, retuning the engine at its higher temperature was the thing that actually fixed it.

Its very important to run engines up to full temperature before tuning them.

13/07/2018 14:03:35
Posted by Gary Manuel on 13/07/2018 13:00:56:

No offence taken Jon. You are entitled to your opinion even if it goes against what I've seen with my own eyes.

Pleased to hear it Gary but please dont mistake the facts i present here as opinion.

All you guys still claiming it will give indications of XYZ im telling you it simply will not do that.

13/07/2018 12:39:58
Posted by Gary Manuel on 12/07/2018 17:08:33:

As I said earlier, "I've heard it said that it makes no difference". I suspected that someone would come along and say it again.

How do you explain that I've seen it many times with my own eyes Jon? The last time I saw it was last weekend.

With regard to unloading in flight, there are plenty of aerobatic manoeuvres that require nose up, plenty of throttle and low airspeed - including climbing from take off. I've seen plenty of dead-sticks right after take off too.

Edited By Gary Manuel on 12/07/2018 17:10:57

Im not getting drawn into another long debate about it as i have explained it many times in the past. The test is pointless, it does not show if the tuning of the engine is incorrect and there is no changing that fact. Sure the engine you saw at the weekend stopped, why wouldnt it? the conditions it saw were beyond what it could cope with and certainly beyond what it would see in flight. Not many models sit stationary with their nose held high while screaming flat out. I am sure that most of my engines would stop if i did a nose up test with them, but in flight they are no problem and im sure that if your example took flight it would not stop.

Simply put, anyone who thinks this test will prove incorrect tuning is wrong, irrespective of how many anecdotes are thrown around, the fact remains it will not show poor tuning. If you are lucky it will give an indication of poor tank position, but even then there are better ways to find that out.

Gary, apologies if you take offence to this post. it is not my intention to offend anyone, but at the same time i work with glow engines every day and am quite well versed in their operation. If i had any doubts about this topic i wouldnt say a word.

Thread: How many do you have in stock?
13/07/2018 12:04:39

My P51 is the pica 5th scale and to be fair it is surplus to my requirements. I did list it for sale but noone fancied it

Thread: Precedent Stampe 1/4 Scale
13/07/2018 08:29:31

how much wonga is he after?

Thread: How many do you have in stock?
13/07/2018 08:28:45
Posted by SR 71 on 13/07/2018 08:17:24:

The OP seems to have money to burn, cannot understand the need to have so many unstarted kits and projects, I usually have two ongoing scratch builds at one time, no kits, at the moment it's one A10 Thunder Bolt for twin turbines, and a 1/4 scale F104 Starfighter, that will be powered by the same two turbines

Forgive the smirk on my face, but anyone with two turbines really has money to burn! :P

David, you are far from alone. My list is:

Airworthy - Piper Tomahawk, Hurricane, La7, P39, Sea Fury, Pulse 125,1/4 Stampe, Nieuport 17, own design twin.

Kits/projects - DB Spitfire, DB Hurricane, 1/4 La7, 3x 1/4 Pups (dont ask), 1/4 Stampe, bf109, bf109 (smaller one), fw190, a6m zero, p51, p40, Yak3, 1/6 pup, Yak9, 1/6 nueuport 17, 1/6 fokker DR1.

Many of the kits i have are now out of production and/or i have got them at good prices. The stampe was bought to replace the currently airworthy one when it was damaged and i didnt know if i was going to fix it. The DB hurricane i have had for over 10 years im sure of it but its on hold as i dont have the powerplant i want for it just yet. I also dont crash too often so my turnover of models is low.

Thread: Holding Your Nose
12/07/2018 16:21:03

Its a pointless test that dates back to the early days. With modern engines that have considerably better fuel draw and/or are pressurised its really redundant.

Unless prop hanging its totally unrepresentative of conditions the model will see in flight. The engine will naturally go rich in flight due to unloading so its all good.

Just tune the engine for max revs and go fly.

The only time a nose up test is on any use is with a petrol engine as a nose up at idle can reveal an issue with the pump. That said, poor idle/starting and erratic running are symptoms more likely to catch the attention.

Thread: Fed Up!
12/07/2018 09:36:22

im just glad its over at this point. I couldnt take another rendition of the lightning seeds so i gave up on listening to the radio over a week ago and just used my own music collection to keep myself entertained.

Thread: P A W 35
10/07/2018 15:11:00

I was too hasty looking at the recommended props and 11x5 is small. 13x5 or 14x5 would be fine as Alan suggests.

10/07/2018 11:28:24

I would have thought something like an 11x5 prop would be nice. Large diameter for thrust but low pitch for a sedate top speed.

Thread: It's Too Darn Hot
08/07/2018 10:08:58

During the cold of winter we all complain, during the wet of spring we all complain, first decent summer in years and we all complain.

Cool pic though, at least in the shade!

Thread: Who Else Wants a 63" Lavochkin La7 kit?
08/07/2018 10:05:34

10.8lbs is pretty porky so if you can find some way of removing a little beef then that would be good. That said, the 80 with a 14x6 should be doing 9k plus and while you might not have much vertical due to the weight straight line speed should be good. In general our engines tend to give all they are going to more or less from the get go. Just forget the running in, thrash it to within an inch of its life. I promise you, you wont break it.

Flying style may also be a factor. With a heavy model it wont accelerate that quickly so if you are tight on your turns etc it will feel like its dragging its backside around with no real go. See what happens if you make really smooth/sweeping turns sacrificing height for speed and then turning speed into height to repeat the process. You will find that momentum is your friend and its a good thing to practice as the big Hurricane will need to be flown this way as well.

I also agree with Richards comment about the hot weather. My nieuport is like a pig on a skateboard when its really hot. It likes air so thick you can chew it!

07/07/2018 19:50:36

My Hurricane was 10lbs and was an over powered meteor with my laser 80 so im really surprised you are having trouble. Which prop are you swinging?

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