New Laser engines. What do you want?

[Jon H]

Just a quick one today.

I was able to get out and fly yesterday and did a very brief noise test on my Laser 155. I recorded approx. 78db at 7m with the model tethered to the ground (no one was there to hold it). I did only record from the left side of the model and the recording using the sound meter app on my phone so I cannot say it is 100% accurate but even if it was out by 3db we are still in the ballpark for getting under the normal noise test limit. I will see if I can get a better noise box and have another go.

In other news, work has started on some prototype parts for the new carb I intend to use on our petrol engine. Testing with other parts I got together and a new spray bar I designed has been very promising and so we are making our own design pump/regulator based on this experience.

[Bob Cotsford]

Jon, I don't suppose you have a 160V set up in anything that you could do a parallel test on? I'd be interested to see how the double exhausts add up against a single.

[Jon H]

my 160 is currently resting in a box under my bed. I can do a test on my 300v as that is more or less twice a 155? The only snag is my 300v runs about 600rpm faster on its current prop so it will not be totally fair as a comparison

Edited By Jon Harper - Laser Engines on 17/01/2016 15:03:14

[Bob Cotsford]

I thought the 160 would give a comparison between similar capacities with the same meter, as has been mentioned meters can vary more than you would think. Still, the 300 result would be interesting as to how much noise emissions increase with two cylinders each of the same capacity (as the 150) and two silencers but only one prop generating noise.I seem to remember from last year my 160 was registering 83 or 84 dBa average on a 16*8 3 blade using my cheapo ebay meter, about the same as I got from an ASP 180Fs on an 18*8.

[Jon H]

The 3 blade prop was likely part responsible for the noise, but still that seems awfully high. for a ww2 model I would use a 17x8 2 blader on the 160v. But what I will do when the weather warms up is see if I can get up the field one evening a run a few engines to get a feel for the noise level on the bench. I will use a few different sound meters and take an average reading

[Martin McIntosh]

Further to my post above I am surprised that a three blader was not much quieter since the tips, where most of the noise is generated, would be traveling much slower.

In early F3A we progressed from 11x7 two blade wood to 9 3/8x7 three blade glass which only gave about 2/3 power but were very quiet indeed.

One strange point noted was that if the tips were sanded to an airfoil shape then the noise increased by 3 dBa (double) over fully squared ones. This was presumably because the air increased in speed when flowing over the airfoil, much as wing.

[Jon H]

The issue with 3 blade props is that you have 3 blades thrashing about making a noise not just two. While tip speed is a consideration it is not as important as tip shape as you mention.

The common 3 blade props available as master airscrew and these are not efficient at all. They also have very square tips that do make alot of noise. I ran one of their 12x6 3 bladers on my Laser 70 for an experiment and it did howl at full power even though the rpm was not excessive.

I have used 17x8 2 bladers on my 160v and it was quite quiet, in fact at low rpm the straight cut cam gears in the crankcase could be heard ringing over the exhaust note! I will try and get some numbers

[Bob Cotsford]

Master Airscrews - guilty! What I will say in my defence is that on an OS1.20 surpass III I got quite a good noise reduction by going to a 3 blade prop, but the large 16" props haven't worked out so well.

The Master props are still head and shoulders above the grey Graupner 3 bladers though. I now have a Biela (sp?) 17*8 to try when the ground solidifies again.

[Jon H]

I know the type you mean Bob. White/red, wooden, propeller shaped? I believe they work well but have never tested on myself. They are similar to menz though i think and i have had good experiences with those. I used an apc on my 160 if that is any help.

In general we dont like Master K or classic series props but the scimitar series are ok. I am also not keen on the grey grauper G sonic series as they tend to be very noisy although i believe the pro series are better. Other things to avoid are Duraglo fuel or any fuel where the type and quantity of oil are not given.

[Bob Cotsford]

and to think the Graupner 'blunt force trauma' props were once ('80s?) considered a class above the rest! The appearance of APC on the scene really moved things a long way forward.

[David P Williams]

Jon - what prop would you recommend then for a Laser 150 that looks scale-ish if the Master Classics are no good?

[Jon H]

It all depends on the type of model. A tiger moth or a cub will be ok with the classic series but my 80 inch La7 with tis 300v was just naff with the classic 20x8. The prop went very fast and made lots of noise but the model didn't really move. The menz 20x8 was quieter and gave more thrust at a lower engine rpm.

In general, I have given up with the notion of scale props as you cant tell what it is when its running and the flying performance is far more important than how it looks sat in the pits.

[David P Williams]

Well - You might as well not bother with any scale detail I suppose as you can't see it when it's flying - it's a Chipmunk as it happens.

On any flying day, the model will spend much more time on the ground being examined (and hopefully admired) than it does in the air, and it just doesn't look right with a grey scimitar shaped APC type prop.

Anyway, this is seriously OT - sorry.

[kevin b]

How about making some "falsies" to slip over the blades whilst it is posing in the pits ?

(Was going to add something else, but realised it would incur the wrath of the mods)

Edited By kevin b on 18/01/2016 22:51:23

[ASH.]

David, I agree with what Jon says. The APC prop is very efficient compared to MA or Graupner, which flex badly and make a terrible racket. You can actually see the tips of these props flex back and forth when revving up and down. You can try the APC wide blade 15x4W or 16x4W etc. They are known as fun fly but will have tonnes of thrust to put all that torque to good use and fly the Chipmunk in a scale like manner. Also, you could paint the tips white for aesthetics. Wooden props are a another alternative but again not as efficient.

Ash

 

Edited By ASH. on 18/01/2016 23:05:14

[Jon H]

Normally most scale details are visible when the model is flying. Clearly rivets are not going to show but details like weathering will show nicely so i always make an effort there. At 8k rpm though i would challenge almost anyone to tell the difference between prop brands! But, if you wish you can use the classic master on the chippy. For that type of model it will be ok but you will be giving away some performance. You could try one of the xoar WWII style props as they look ace, but they too are not as efficient as other props. They are better than the classic master however. Other alternatives would be the menz series. For the chipmunk i would suggest 17 or 18x6 for nice scale performance. The menz props are wooden and thus are wood coloured, but 10 seconds with some halfords black spray paint sorts that out. Add some yellow tips and tada!

[David P Williams]

Thanks Jon, I'll look into those. It'll be sprayed black and white striped whatever it is, so maybe the shape will be less obvious. I have an APC that size I think so I'll paint it and see what it looks like.

The 150 is a lovely engine by the way - bought it second hand, bench run only, from a bereavement sale, and I'll definitely be buying new engines from you for future projects. Not bothered about smelly petrol, happy to stick with glow (I know I could use Aspen). Thinking of the Jerry Bates/Sweitzer 96inch Dragon Rapide, so probably a pair of 70s.

[Jon H]

Hi David

I hope you have some luck with the props. I was not trying to be dismissive about scale props, its just that often we are asked about 3 blade this and scale diameter that. The problem is torque, model engines have not got the torque for a scale 3 blade prop and a large 2 blade might look nice when running but overloads the engine and costs performance. There is a balance to be had for sure, like on the rapide...

That rapide will be a lovely model and you have a choice of powerplants. You could use 2 70's, 80's, or even 100's.

The 70's would fly it just fine i have no doubt, but 13x6 is likely to be the best prop for it and might look small, so, the 80 would turn a 15x6 for closer to scale looks and the 100 upto 16x6. I would expect them all to fit within the cowlings.

The 70's would be the lightest combo but clearly you might then need lead for balance. The 100's might be an issue if tank space is limited or something prevents you dropping the tank into the correct place.

One last thing to consider is the possibility of engine failure. While uncommon it can happen if a pipe comes off or plug lets go. In that instance, i doubt that a single 70 could keep a 20lb 96inch biplane aloft for very long so a slight excess of power might be better. With the info i have available to me at the moment (no plan in front of me etc) my feeling is that the 80 would be the best compromise of performance, weight, cost etc

[David P Williams]

Thanks very much Jon, I'll get in touch directly when I make a start on this project. I'll stop hijacking your thread now!

[Jon H]

Its no problem, although all the various off thread wanderings have left me thinking about starting a dedicated advice thread.

Another few questions for the masses here about changes you might like to see. I often get asked about dimensions drawings, how important are these and do you want to see them (i know the answer, i just need proof to show the boss!).

No one has so far mentioned availability, is a 2-8 week lead time acceptable? I would like to see things in stock ready to go, but do you guys mind waiting for your engines? Let me know.

Some customers have also reported that glow fuel is getting hard to get and have asked if we will ship it. At the moment we cant, but if we did would anyone buy it and pay the shipping charge? I estimate that 4 gallons of fuel would be about £75-80 which ends up at about £19-20 a gallon. Still cheaper than sport 5 from a shop, but would the demand be enough for us to warrant building a fuel store and holding stock? Again, let me know what you think

Thanks

[David P Williams]

I think overall dimension drawings would be very useful - I have often sought out the old website that has the main sizes to see what would fit potential projects.

I haven't bought new from you yet, but I would be a bit disappointed by a lead time of more than 2-3 weeks.

I live in the middle of nowhere so getting fuel is a headache. I'm a good three hour round trip from any model shop, so get almost all my stuff mail order. Availability of fuel by mail would be a great help to me.

Thanks,

David

[Denis Watkins]

Hi Jon

Surely it is no secret that you can buy 4 gallon of 5% synthetic from the internet, delivered to your door by carrier next day for £52.50, and less for straight fuel. Maybe I have missed the post where this fuel is deemed inadequate, but after 5 years using it, I detect no anomolies with it. Again, I cannot claim it is " the best " , but it does suit me not carrying fuel in this quantity from the shows, and it is found to be far superior in some respects to some brews on the market. I would pay £70 - £80 for 4 gallon if it was a no choice situation as I love flying

[Jon H]

Hi Denis

If you are referring to weston uk i am aware that they ship fuel, but their fuel does not comply with our warranty spec so we do not normally recommend it.

[Bob Cotsford]

Dimensioned drawings - yes please, they're always useful for planning an installation. Apart from the usual beam mount dimensions the installed length from the prop driver and height from the mounting to the top of the rocker box are the really usefull ones.

edit - how about carb height from the mounting/centreline?

Lead time - I would have thought anything over 4 weeks excessive. Ideally I'd be looking around the 14 day mark ie the time to order and assemble a decent size ARTF, though at this time of year 3 months would be perfectly acceptable (waiting for the )

Edited By Bob Cotsford on 20/01/2016 10:39:02

[Jon H]

Regarding dimension drawings, if you guys can check out the dimensions tab on this page http://www.laserengines.com/product/laser-70/ and let me know if they are acceptable and give enough info.

Edited By Jon Harper - Laser Engines on 20/01/2016 12:02:40