Laser 80. Needs to be used.

[David Barker 2]

Just finished building aDB Sport & Scale Auster. With a Laser 80 engine fitted. Still got a Laser 80 to use any suggestions of something easy to build or kit and easy to fly to use the Laser 80. Thanks Dave B. 

[Matt Carlton]

Masons Models have reintroduced the Skyway range. The Chippahawk or Hawk 70 would be nice with the Laser 80.

 

Skyway plan packs

[Jon H]

if im honest i think the 80 is a bit big for those skyways jobs as i fly a similar model on an enya 53 without any trouble. Im sure it can be fitted, but it might over egg the pudding. 

 

There should be plenty of options though, depends if you are after artf or a full build

[Eric Robson]

My Latest model is an 80" span  Seagull Chipmunk it has a Laser 100 and anything above half throttle is well over scale speed. I recon a Laser 80 would pull it.

[Chris Walby]

Laser 80 in a VQ FW 190

 

 

Tank height easily achieved, a bit of chopping to get it in but well worth a bit of wood work and runs nicely.

 

No added lead at either end, lands slowly with no flap (just as well as it hasn't got any) looks nice and sounds .......well very Laser!

 

A 70 could scream it around, but if you have an 80 why not.

 

PS - I used single servo for the retracts...bit of a pain in the UC department, but once set up no problems

PPS - This model does not have the more demanding traits like other warbirds and I have seen one flown quite un-scale (IMHO) so it will do most things you can throw at it.

 

[Matt Carlton]

8 hours ago, Jon - Laser Engines said:

if im honest i think the 80 is a bit big for those skyways jobs as i fly a similar model on an enya 53 without any trouble. 

 

That does surprise me John, just goes to show how much we tend to overpower our models! 

[Jon H]

8 hours ago, Eric Robson said:

My Latest model is an 80" span  Seagull Chipmunk it has a Laser 100 and anything above half throttle is well over scale speed. I recon a Laser 80 would pull it.

 

And yet i am lambasted for recommending the 100 by some on the internet. They all think it needs a 155 minimum. 

 

 

Matt, yea we do over power most of our models quite substantially and to be clear, the 53 in my 72 inch Airsail Tomahawk does over power it once in the air! I have mentioned this before, but my flying test bench is 86 inch span and around 20lbs. Although a little slow getting off the ground, it is still aerobatic on a 120 4 stroke if you use your momentum well. 

 

Looking at the skyways models, the key is their weight. 5.5lbs? Light as a feather, and although i suspect another pound will probably come from soemwhere, 6.5lbs is still very light for a model with a 70 inch wing. 

[David Barker 2]

Thanks all for your comments, will have to have a big think.

[Piers Bowlan]

Just because the Skyways models are light ( a good thing) and will fly on a 53, it doesn't necessarily mean that a Laser 80 would over-power it if you use the throttle! Bumbling around on half throttle could be very quiet, economical and pleasant.

[Jon H]

3 hours ago, Piers Bowlan said:

Just because the Skyways models are light ( a good thing) and will fly on a 53, it doesn't necessarily mean that a Laser 80 would over-power it if you use the throttle! Bumbling around on half throttle could be very quiet, economical and pleasant.

 

A friend had a 70 inch cub with a laser 70 fitted. It was awful to fly, 2 clicks off idle and the thing was breaking the sound barrier. 

 

There comes a point where you just cant throttle back

[Matt Carlton]

Whilst that is very true John, and you are probably quite right about the skyway models, is there not always the option of reducing prop pitch for an overpowered model? I don't really know how effective that is, but on your cub example, a larger, flatter prop might have helped? 

 

I just wondered why the recommended engine size is a. 61+ or is that a hangover from the low powered 4 strokes on the market when Skyways were around in their first incarnation? 

[Chris Walby]

I guess it depends on where you fly and your social awareness as factors and fitting bigger than needed engines will have detrimental effect regarding noise.

 

The bigger the engine the more noise will be produced at WOT and while I appreciate most of us fly part throttle most of the time although there are those that spend the entire flight wringing the screamer out. As more and more sites become noise sensitive there are those that will spoil it for the rest of us with excessively noisy engines 

 

If you use a bigger engine then the traditional solution is to over prop it to hold the WOT revs down and while if its minor then its not an issue its not ideal as the engine can become unreliable, run over rich and more difficult to fly plus increased engine wear.  I have come across examples where the engine is so overloaded by the prop (to achieve a noise test pass) and the reliability so reduced that flight performance is impaired/enjoyment reduced. The model in question flies nicely at half throttle, sounds/looks the part and I have no intension of WOT flying around the field with it anyway.

 

I have always found a quick chat with knowledgeable people very helpful in selecting the right size engine for a proposed model to get the best fit and don't go with manufactures recommendations.

 

    

[Jon H]

Prop choice is a subject in itself but yea, you can fiddle with pitch vs dia. In the case of my friend and his cub the engine was new and we were using a 13x6. We swapped to a 15x5 wood that i had and there was no major difference as the thrust increased dramatically. Essentially, we just had too much power and swapping to a 13x5 equipped 50 4 stroke turned it into a really lovely model. 

 

Chris's point about not wanting to be flat out all the time is quite correct, but equally you dont want to be staggering round at a fast idle either. The engines like to be in the 50-70% throttle range most of the time as they stay a good temperature which aids reliability as well as engine life. 

 

You are also spot on with the age of the designs. If the 60 they are talking about was a merco 61 then a modern 30 will give more power. 

 

 

[David Davis]

52 minutes ago, Jon - Laser Engines said:

... You are also spot on with the age of the designs. If the 60 they are talking about was a merco 61 then a modern 30 will give more power. 

 

 

Really?

 

[Eric Robson]

It would be nice to power my Brian Taylor Corsair with a modern 30 that would be lost in the cowl. The original had a a Merco 61. But as it will be powered by an 82 fs when finished I will just have to cut a hole in the cowl for the head to stick through.

[Jon H]

25 minutes ago, David Davis said:

Really?

 

 

I read an article years ago where they put and old 60 against a modern 30-40 and the old motor was thrashed. That said, i just looked up some numbers and i am scratching my head a little to verify their results assuming a merco61 vs a modern 35 2 stroke. 

 

The merco 61 is no power house, but its not looking completely pedestrian 

 

EDIT - Just looked it up and it seems a merco 61 is about a match for an OS 46fx with the 46 slightly ahead. 

 

 

Edited May 17, 2021 by Jon - Laser Engines

[Nigel R]

the old crossflow glows seem roughly equal to a recent four stroke of same displacement

 

as jons post, take a recent two stroke of two-thirds the capacity for equivalence

[David Davis]

Ok, I'll buy an OS 46 producing about the same power than a Merco 61 but a 30? Not with a 14" prop that's for sure!

 

[Jon H]

It was a long time ago i read the article and it seems i didnt remember it as accurately as i thought. 

 

In any case, a modern engine will have more go than an old one and a model designed for 40-60 is probably now best aimed at 30-46. Looking again at the specs for the chippahawk its almost identical to the airsail chippy and they flew really well on 50 4 strokes. 

 

The other side to this argument is models that used to have a 60 recommended because it was the biggest you could get. My 1/4 stampe is an example of that and its much better with a 180 4 stroke! Yes the 180 over powers it in level flight, but i run a big prop at between 1/3 and 2/3 throttle most of the time. Full power is needed for aerobatics though. 

 

This is where its almost impossible to choose a power plant for a model based upon recommendations of these older designs. Even modern artf's often get wrong with the seagull gipsy moth being a prime example. It simply does not need a 120 and 70-80 is still more than adequate. 

[Matt Carlton]

The recommendation for a 61 was for a four stroke.

 

If I remember rightly, the old open rocker FS60 developed about 0.6bhp on a good day, maybe on a 13/14" prop. 

 

Thinking about it, if one of the skyway models weighs 6lbs, aiming for 100W/lb puts us smack on the nose of 0.8bhp which is roughly equivalent to a Saito FA50 or similar. 

So I stand corrected, which is absolutely fine by me, I'm always happy to be educated ?

 

 

[Bob Cotsford]

Many years ago I had a Chippahawk powered by an Enya 60III-BB cross flow motor and that made a lovely combination.  While modern schneurle 40-46 motors might turn out the same BHP I doubt that they will do it at the same rpm, and I seriously would not expect the same performance on a 12 or 13" prop appropriate for a 70" model!  If you don't mind your 2ST screaming then no doubt it would fly ok-ish?.  A 60 or 70 FS would be ok, an 80 would be a bit OTT but not by that much.

Are Skyways part kits actually being made?  I'd swear that link and it's prices haven't changed in the last 5 years.

Edited May 17, 2021 by Bob Cotsford

[Jon H]

according to the reviews i found both the merco 61 and os 46 do essentially the same revs on a 12x6 so the performance in flight should be the same. I do understand your point though. HP is easy to match but the rpm is not always the same. 

 

Although they have long wingspans they are not exactly large models. A wot trainer is 67inch ir i recall and they fly on 50 4 strokes at under half throttle. Its not like a 70 inch spitfire or thunderbolt which has far more bulk for a given span

[Chris Walby]

DB2, VQ P39 Aircobra

 

Another home for the Laser 80, no mod to the bulkhead, but a bit of a challenge to get it in the cowl, although no problem with cooling!

 

Decals and maiden next on the agenda and hope it flies as well as the VQ FW190 with a laser 80 in that.

 

 

Oh you want the business side shot as well ?

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Edited June 29, 2021 by Chris Walby

[Peter Philp]

Sorry if I have recorded this in the wrong place. Have read many of these threads but never posted. My question is would a Laser 70 have enough power for a Wot wot kit built plane? I have read people putting 70’s in acrowots and 80’s in wots wots but wonder whether a 70 in a wots wot will be under powered? Thanks Pete

[Jon H]

Nah it will be fine Pete. 12x7 or 13x6 prop will give plenty of performance. An 80 will give more, but a 70 will be plenty for all the normal sport aerobatics.