Gaui engines and DB Hurricane

[Chris Berry]

I'm researching some petrol 4 strokes prior to starting the build of my DB Hurricane. One engine that seems a likely candidate is the Gaui 50R.

Does anyone have any experience of Gaui engines and what engines do you use in your DB Hurricanes?

Thanks

[Former Member]

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[Chris Berry]

Not sure the 180 will have enough power. Likely to be a 22-24lbs model.

Gaui make a lot of UAV helicopters and RC engines. I'd heard of them from years ago but had forgotten about them in recent years.

**LINK**

[Reno Racer]

That Gaui F-50R look like a nice engine, a 50cc four stroke petrol engine, I also note they are about £900. If it was my choice, I’d chose a better known engine.

Edited By Reno Racer on 27/05/2019 09:01:49

[Braddock, VC]

Go for it and let us know how you get on. I would imagine that any engine designed for UAV operation will be 100% bullet proof as the prime mover for a model.

[Former Member]

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[Former Member]

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[Former Member]

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[Chris Berry]

Thanks folks. A Laser 300 or 360 would be lovely and I'd be happily use one. I just have to check the sizes, particularly the width.

I once built a fully built up DB Spitfire (the bandsaw kit version). All up weight with a MOKI 2.10 was 17lbs, I redesigned the firewall to have a step in it to allow for the rear pits silencer. This resulted in the tank bay being smaller than intended and only gave room for a 14oz tank.

Happy with 17lbs, until I came to sort the CG out. Nearly 7lbs nose weight later (and very nearly some tears from me), and it flew, slowly and way under-powered and gave about 6 minutes flight time.

This time I want to get it right, as I was not a happy chicken with the Spitfire, hence a lot of research.

[Jon H]

This is a topic close to my heart as its taken me 10 years to decide which engine to use in my DB Hurricane.

As has been pointed out already, super tigre 2500, 3000 and zenoah 38s are the powerplants it was designed around in the first place so we are essentially looking at 30-40cc 2 stroke or equivalent.

There is a customer of mine in finland flying his 24lb example with our 180. Personally, i dont know how he gets it off the deck but he assures me its just fine and he is very happy. Personally, i wouldnt fly a hurricane on our 180 if it was more than 20lbs. The YT hurricanes were about this weight and the 180 was great, i just think the DB is getting slightly marginal. That said, i flew an 88 inch 20lb pica spit on the equivalent of a laser 155 and it was ok. Lacked vertical, but it flew fine.

My Current fleet of 80 inch warbirds are La7, P39 and sea fury. They are 20, 21 and 23lbs respectively and powered by 310, 300 and 360v engines. The la7 is a monster with the 310 fitted and is brutally over powered, the P39 has a good balance as does the Fury but both are overpowered in level flight with scale high speed passes done at half throttle.

So if we ignore the 180, i could use a 240v or 300v. Both require significant modifications for fuel tank position and cooling. The 240 fits totally within the cowling but the 300 needs a little cut away for the heads. You will also need to do a multi part cowl to get the exhausts in neatly. The 240 will turn a 19x8 menz at 7300 and the 300 a 20x8 at about 7500. APC or other brands will run faster/slower.

All of this is great but to be honest the two real criteria for engine power are the weight of the model and the expectation of the pilot. Do you want to see scale performance (the hurricane was not exactly ripping round the sky like a p51 or sea fury) or toy aeroplane performance? Once you decide on those two things its easier. My Sea Fury is powered to be the ultimate piston fighter and i estimate i can get a good 800-1000ft of vertical out of it with the 360. The P39 can probably do 600-800? hard to measure from the ground, and im supposed to be below 400ft anyway so i dont take the mick. The Hurricane will need nowhere near that level of vertical performance.

My Hurricane airframe (old foam wing version,built, no servos, no paint, retracts installed etc) is 16lbs. That means i have only 4 lbs to keep it to the 20lb 'limit' for the 180. I think this is a stretch, so the 240 is my victim. It offers more power than the 180 and should easily offer me scale performance, which is all i want. I have the sea fury for monstering the sky, the Hurricane can just swoop about.

So, thats it really..not that it helps as i cant build any v twins at the moment. Im working on it.

Oh i forgot, i made the nose longer on my model by about 3/4 inch to turn it into a MkII. It will also help with balance and frankly you could add another 3/4 and i doubt anyone will notice. 

Edited By Jon - Laser Engines on 27/05/2019 23:27:50

[Chris Berry]

Thanks Jon. I've had the kit (an early laser version) for about 6 years and from the start I've been thinking about the engine and still haven't opened the box (other than checking the contents).

I would have liked a valach but its way to big and I'm not sure the Saito and OS 40's would be sufficient....or would they?

That said, the 240v would be ideal, especially if it'll fit inside the cowl. I have a 300 in a Flair Stearman, 24lbs and loops from level, so more than enough power but having measured it, it will be way too wide. The Stearman used to have a 200 and would only just loop from a dive and would be no good for the Hurricane.

You mention split cowl for the 240, is that a top and bottom split, a bit like you see some CARF and big aerobatic aircraft? Presumably lowering the tank will also be needed? Have planned on a MKII possibly with a filter for the same reason.

[Jon H]

Hi Chris

My model arrived built with two cowls. One was new, the other mutilated to accept a petrol. I used the mutilated one for all of my engine fitment testing and the heads dont stick out as far as you might think. When i get a chance i will find it and get a few photos with both a 240 and 300 installed. In terms of power required, the stearman has a huge amount of drag on it and is quite slow. Being slow it lacks momentum into a vertical so its all about power to overcome the weight and the drag. The Hurricane will be less draggy and should be faster so you can use momentum to help round a loop etc and so you can be just fine with a smaller engine. When testing the 180 petrol in my test model i had a much greater performance from it than i now do in my stampe biplane even though the test model has about 3lbs heavier. i had better vertical due to the lower drag and higher momentum of the 'aerobatic' sport model i was testing it with.

I dont have any direct experience with the OS GF40 so cant really comment on it. A customer has a saito FG 40 and its cost him two models now i think as it has stopped on him a few times. Once was a conrod failure, the others..who knows? it just got bored and stopped. That is the only experience i have of it so it may not be representative of others.

Another customer has a valach 60 and while reliable he says its no power house and physically very large. If you want some direct info from him i can ask him if its ok for me to give you his contact details so you can get it from the horses mouth.

You are right about the fuel tank bay needing mods and i was also looking at the cooling situation. I plan to run a duct made of a plastic drain pipe (or similar) to get the hot air out of the belly scoop in the wing. I also plan to split the cowl to give a top/bottom at the very least and perhaps split it in to 4 as the full size. I have recently started splitting my cowls and it makes life so much easier when it comes to installing the engine and getting it all neat and tidy.

As a note, should you use the 240v you need to put significant effort into the cooling as its a hot running engine due to its small size. Even with the best cooling in the world it wont wear it if you fly flat out all the time. I am more than happy with that situation, but if you arent then the 300 is the better choice and it absolutely guarantees the performance of the model.

[Chris Berry]

Thanks Jon. I've heard similar stories about the Saito and OS engines which does concern me. I was just thinking that the 240 would be ideal, as it is mid-way between my 200 and 300, both of which have been in my Stearman, which, as you say, will glide like a brick for obvious reasons.

The Valach is way too big, so ruled out, but would like one some day.

Cooling and tank location will be key. The tank can't drop far due to the wing being in the way, so that would be interesting. I acquired an old fuz and cowl, so I'll also be experimenting with engine dimensions and layouts.

I think I'm going to build the wing and tail feathers first. that will give me a finished weight and then mate to the existing fuz and see what the CG and weight are. Ideally by extending the nose, I won't have to add as much weight. The 300 would be ideal, but unless I can get away with hiding the heads and giving them sufficient air, its not a route I want to go down. Unlike many, I like to use my throttle when it should be used, as opposed to using it like an on-off switch.

Any pics you have of engine and cowl combo would be great.

cheers

[Jon H]

Looking at my plans a few weeks back i think the tanks can go low enough without touching the wing. If twin tanks are used (recommended) then a pair of 14 oz slec tanks fit nicely. These will give more than enough duration and i might use a pair of slec 11oz tanks as they should still be enough for a 10 minute flight with fuel to spare as they will take up less room. The tank bay floor will have to go however and will be modified to become the top of the cooling channel i suspect.

This cooling channel will then be routed somehow to get the air into the radiator on the wing. This will provide a nice suction to help get the hot air out of the cowling. I have plans for cooling inside the cowl as well, its quite involved but not difficult.

[Jon H]

had a forage after work and found the cowling. still need to find my plans though.

Anyway this shows the 240 installed...an no, you cant have a black one :P

 

I dont have a 300 spare but the heads are 10mm taller than on the 240 so im sure you can imagine how it would look. 

I intend to remove the firewall below the mount and do something clever with the tank bay. I have to get my cooling duct in there somewhere as well. Im sure i will come up with something. 

Edited By Jon - Laser Engines on 29/05/2019 23:07:40

[Braddock, VC]

If you want to use a laser inverted with the tank on the prop centre line with no problems, modify an old strimmer carb or similar e, buy a set of gaskets for it so you have a repair kit if it becomes necessary.

The modification is straightforward, first I will explain the reasoning and then general guidance which any modeller worthy of the name can follow.

The carb as fitted to a petrol two stroke is pumped by crankcase pressure, this oscillates the diaphragm until the pressure on the fuel side equals the pressure on the pump side and the situation will stay like this until the engine is running with no fuel leaking through the carb. When the engine starts running, the vacuum on the upstroke of the piston causes fuel to be drawn through the jets and the pressure on the fuel side of the carb drops, the diaphragm valve is pushed over to allow more fuel into the carb and thence to the engine.

To modify it, we no longer have the crankcase pressure to operate the pump side of the carb, so a nipple must be installed (if the carb is bolted direct to the block with a passageway through to the crankcase) you can install the nipple by tapping that hole, some carbs, like on the range of engines made by evolution, have an adaptor fitted so you won't have to do that.

You no longer need the jets so these can be shut off completely by screwing the H & L needles closed (I prefer to dremel the heads off once this is done to prevent fiddling but it isn't necessary - I also remove the throttle and choke assemblies too).

You now need to fit a nipple into the carb casing on the pressurised fuel side, a 3mm hole and epoxy in a 3mm alloy tube and the most of the work is done.

The old mounting holes can be used to fasten the carb any where convenient, connect up the fuel outlet to your carb and the nipple for the crankcase pressure to preferably your exhaust pressure nipple on the engine or to the crankcase vent on a laser via a T piece, the open end of which you reduce in size, if it's plastic, with a hot soldering iron, if it's metal by crimping.

Choking the engine will draw fuel through and when it's started the pressure pulses from the engine will pump the fuel, the little flap valves in the element will prevent fuel flow when the engine is stopped.

I can assure you it will pull fuel from about 8" away from the engine, I fitted one inverted in a WM midget mustang with a laser 80, that's where I learned to crimp the open end of the T piece.

I also used it on an OS 160 Fx on crankcase pressure at first then on silencer pressure as I was plagued with leaks from the crankcase, using a drilled bolt via one of the backplate mounting screws on through a 1.5 mm hole into the crankcase.

I gave one to my pal at the flying field who had a super tigre 20/23 that was plagued with dead sticks, his tank was about a foot away from the engine and he took the pulses from the silencer, the dead sticks stopped.

You can pick the old carbs up for free if you know the proprietor of a lawnmower repair place, couple of quid if he's tight.

I forgot to say that you leave the fuel inlet nipple where it is, but you knew that anyway, didn't you.

I can't claim responsibility for this idea, it was published in one of the mags from when we had a choice, modelflyer I think and was passed on by the editor Ken somebody or other I think who used it on a laser 150 iirc, but I can't remember if he used crankcase or exh pressure.

As fuel is only supplied on demand it won't drip when stopped, flood the engine etc.

Going back to the OP, what about the OS 200 Surpass?

[Jon H]

With the greatest respect to Braddock i would strongly advise against any such modification. Many have tried, many have failed. The result is always the same with inconsistent running caused by variations in fuel flow. This leads to lean runs, overheating and damage. One chap melted both pistons on his brand new 240v due to a mod like this causing erratic tuning. The engine just wouldnt peak and in the process of figuring it out, it overheated and the (admittedly rubbish) oil in his fuel burnt off. This did the engine no favours i can assure you.

I do recall the article referenced in the magazine and at the time was unimpressed as it didnt actually fix the problem it claimed to and was extremely misleading with his conclusions being rather wide of the mark.

I always have the same conversation with customers about this and the answer is simple. Move the tank. Dont strap a bunch of junk to the engine, just move the tank. Its the cheapest solution as you dont have to buy anything, and its guaranteed to work. Once you start messing about with the fuel delivery it is impossible for me to diagnose running problems and the only advice i will give you when you have trouble would be...move the tank.

If the engine is installed in accordance with our instructions i can guarantee its performance and advise on running issues. However, if you think you know better and you mess with it you are essentially on your own as its all uncharted territory and i cant help you.

Oh yes, and your warranty goes out the window too.

As the manufacturer of the engine we do not recommend any additions to the fuel system and require the tank to be in line with the tanks. Dont try to argue with me about it, i wont be changing my mind and wont be filling up this thread with something unrelated.

Move your tanks chaps. Address the disease, not the symptoms.

[Braddock, VC]

Posted by Jon - Laser Engines on 30/05/2019 08:46:10:

With the greatest respect to Braddock i would strongly advise against any such modification. Many have tried, many have failed. The result is always the same with inconsistent running caused by variations in fuel flow. This leads to lean runs, overheating and damage. One chap melted both pistons on his brand new 240v due to a mod like this causing erratic tuning. The engine just wouldnt peak and in the process of figuring it out, it overheated and the (admittedly rubbish) oil in his fuel burnt off. This did the engine no favours i can assure you.

I do recall the article referenced in the magazine and at the time was unimpressed as it didnt actually fix the problem it claimed to and was extremely misleading with his conclusions being rather wide of the mark.

I always have the same conversation with customers about this and the answer is simple. Move the tank. Dont strap a bunch of junk to the engine, just move the tank. Its the cheapest solution as you dont have to buy anything, and its guaranteed to work. Once you start messing about with the fuel delivery it is impossible for me to diagnose running problems and the only advice i will give you when you have trouble would be...move the tank.

If the engine is installed in accordance with our instructions i can guarantee its performance and advise on running issues. However, if you think you know better and you mess with it you are essentially on your own as its all uncharted territory and i cant help you.

Oh yes, and your warranty goes out the window too.

As the manufacturer of the engine we do not recommend any additions to the fuel system and require the tank to be in line with the tanks. Dont try to argue with me about it, i wont be changing my mind and wont be filling up this thread with something unrelated.

Move your tanks chaps. Address the disease, not the symptoms.

Remind me when you came to my flying field and observed my engines running, don't seem to be able to recall that.

I can recall your diagnosis of rc plane flyer's irvine 46 which, to be honest, was wide of the mark.

Now how shall I regard your advice? I think I'll pass.

[Martin Harris - Moderator]

In fairness to Jon, his "suggestion" on the Irvine 46 thread was accompanied by a smilie.

[Chris Berry]

Thanks Jon. Looks like a neat install. Would a perry pump help at all, or is it not smooth enough fuel flow?

As you say, tank movement is the best option really.

[Nigel R]

Might well do but Jon won't guarantee it

I've had a VP20 (the 'engine vibration' one) running nicely with an OS70 on the bench. Was tolerant of tank being anywhere within about 10" of the needle, above or below, and ran happily. It needed a fair amount of careful setting up, there was quite a balancing act between the pump adjust and the two needles on the carb.

[Jon H]

Posted by Chris Berry on 30/05/2019 12:33:00:

Thanks Jon. Looks like a neat install. Would a perry pump help at all, or is it not smooth enough fuel flow?

As you say, tank movement is the best option really.

Yep, perry pumps, regulators and on board glow. Its all a bandage on a broken leg. Get the basics right and you dont need any of it. Perry pumps are also better suited to pushing fuel up hill than stopping it falling down hill. Remember too that with the twin you have two tanks, two pumps and 4 needles to match up in a configuration that i wont be able to help you with. As i said before, you would be all on your lonesome sorting it out. 

In the event that it is absolutely impossible for the tanks to go low enough there is a chicken hopper setup that does work but it requires modification of a tank and some pretty complicated plumbing. Its not a simple one tank into the next job, it takes more work than that. There are also issues with filling and draining that come with it so its a last ditch effort that one. The only models that come to mind as being impossible to lower the tank are things like tucano's and PC9's with a nose retract as it gets right in the way. My solution in these cases is to mount the engine sideways.

In the case of the Hurricane i would consider chopping wood about to be far easier as you are building the model from scratch anyway and can do what you like with it.

The OS200 suggested earlier will not need any tank mods but its performance is lower than the 200v you already have so its not likely to be man enough.

I will make another effort to find my plans and double check this is all going to work.

Then i suppose i need to work out how to actually get you an engine should you go for it as the twins are an issue at the moment. Need more parts

 

Edited By Jon - Laser Engines on 30/05/2019 13:20:10

[Nigel R]

Posted by Jon - Laser Engines on 30/05/2019 13:17:37:

Perry pumps are also better suited to pushing fuel up hill than stopping it falling down hill.

Don't want to go too far off thread with this, but, I thought the Perry/Conley units regulated pressure at their output?

Which should (!) mean that it didn't matter if the pressure came from gravity or the pump itself?

Perhaps I misunderstand how they operate, or I'm missing a limitation of their design.

I'm sure you've run into similar issues when sorting the Laser petrol carb?

[Nigel R]

I found this diagram of a chicken hopper if anyone is interested.

The big tank will drain into the small tank, until the small tank vent is covered. That's the vent into the top of the big tank - not the air vent to atmosphere.

Looks quite a neat answer actually. To my mind, easier than trying to hack around to fit a big tank lower down.

Has anyone used this setup?

[Jon H]

You are right Nigel but the problem is complexity. The one liner of 'fit a perry pump' does little to explain what is actually required, what specific pump you need, how to set it up and all the rest of it. Also how much is one of those pumps now? 50 quid? Which is why is easier to just put the tank in the right place and forget all about it.

The chicken hopper setup you have there is the same as the one i touched on before. A customer (steve where are you?) uses it but tells me filling and draining both tanks can be problematic. manufacturing it in the first place can also pose a challenge as you need a very specific setup and most freely available tanks would need modification. Get the mod wrong and you either have too much fuel or not enough. You could make your own, and that would certainly be an option, but how much work is that?

Again, its much easier to just move the tank. Why create all the extra work if you dont have to?

 

The petrol carb was another story all together and it runs with its own pump and pressure regulator. Due to its setup the pump isnt likely to work well on glow fuel but its something i can investigate if asked to. But, again you can pay a bunch more money for a pumped engine or you can just...move the tank. 

I cant help but laugh at those who resist such a simple idea. Many would rather completely re-invent the wheel, buy all manor of bits and pieces, go for a plumbing job that would make Thames water run for cover, or buy an expensive pumped engine rather than cut out a former and lower their tank. It boggles my mind  

Anyway for further discussion on this topic we should probably start a new thread before the mods get us  

Edited By Jon - Laser Engines on 30/05/2019 14:38:58