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Laser Engines - Technical questions

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Jon - Laser Engines14/01/2020 13:34:22
5063 forum posts
217 photos
Posted by Martin Harris on 14/01/2020 13:19:23:

It's certainly a video to show to the electrofanatic ICphobics...

Dare I mention the practicality of on-board glows in such an installation?

Only in the interest of getting them started

Nigel, in other videos i have seen the chap starts each engine in turn and gives it a quick tune/power test. Once satisfied he turns it off and moves down the line. That way, when he comes to his display slot all of the engines are ready to go having been set earlier on.

SR 7114/01/2020 14:24:48
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335 forum posts
84 photos

REF, the Laser exhaust, that was one of the reasons i wanted to fit Lasers, so small neat and tidy, really dont want big lumps of exhaust sticking out

Martin Harris16/01/2020 13:24:54
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9071 forum posts
224 photos

Earlier in the thread there was considerable discussion of the chicken hopper fuel system. I took my plans for my Tempest to Jon while deciding on the purchase of a 200v a few years ago and he thought I'd get away with the fuel tanks which, due to structural considerations and the very short nose, are not practical to lower. Now that things are progressing again and reading informed comment on other installations from Jon, I'm reconsidering the wisdom of "getting away with it".

Installing a chicken hopper system on a twin seems horrendously complex and I'm wondering whether the system illustrated below would work so perhaps anyone seeing a problem with it could comment?

20200116_125630.jpg

My initial concern would be that maybe one of the red tanks would not fill properly - and am I right in assuming that the suction involved in pulling fuel up from the lower tank should lower the fuel head seen by the engines?

It seems a much simpler solution if it will work...I have some T pieces on order so that I can do some practical testing.

20200115_195440.jpg 20200115_195428.jpg

Ron Gray16/01/2020 14:03:37
1604 forum posts
394 photos

I can't really see the logic of the design as shown in the sketch. If the 2 tanks shown at the top are feeding the engine then it will cut out as there is no vent to those tanks. Plus when you fill the top 2 they will overflow into the bottom one which will fill but it will not be able to supply fuel to the top 2. If you invert the tanks, so 2 at the bottom and fit them as per the chicken hopper plumbing then it will work and TBH the work involved is not that much.

Can't you just put the engine in upright? or isn't there cowl room to do that? I was lucky with my Bearcat installation that allowed me to do just that.

86c72b29-a14b-42dc-8dfd-2607839cbafc.jpeg

Jon - Laser Engines16/01/2020 15:00:08
5063 forum posts
217 photos

Having slept since we spoke Martin i have zero recollection of our discussion! In any case, it looks like you might just about get away with it but i would suggest a tank change you can squeeze a little more capacity out of this **LINK** in more or less the same space.

That said, the plate the tanks currently sit on looks pretty easy to remove. You could then lower the tank, notch the leading edge of the wing slightly and it would be all good. You might even get away with slinging the tank/s under that plate and then you only have to notch the wing.

I did the exact same on my hurricane recently and its worked out nicely as it also means i can run the cooling tunnel under the tanks. Not that cooling air exit will be a problem for a tempest. As long as you can replace the moved structure with a ply box it will be plenty strong enough.

hurri 7.jpg

hurri 9.jpg

Martin Harris16/01/2020 16:01:19
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9071 forum posts
224 photos

The problem with removing the floor is that the tank bay overlaps the wing fixing plate for the front wing pegs.

The logic is that you fill the top tanks which, once they Ooverflow, spill into the lower tank. All venting is through the vent from the bottom tank which would be arranged to provide the "Laser" forward facing vent. As the top tanks supply the carbs, fuel is drawn from the bottom tank as the fuel is pulled while the tank vents.

Nigel R16/01/2020 16:13:13
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3391 forum posts
524 photos

"perhaps anyone seeing a problem with it could comment"

I presume the carbs are level with the centre of the lower tank?

If so, it will be exactly like having one tank a long way up - you simply have two tanks linked by a thin pipe, the fluid head hasn't been altered.

The chicken hopper setup provides a pressure neutral lower tank. For a V twin, surely the only added complexity is that you need two clunk lines in the small tank?

Steve Dunne16/01/2020 16:21:09
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125 forum posts
56 photos

For what it's worth...

1 I don't think that the fuel head problem would be resolved at all - the syphoning and leaking issues will remain.
You still need to have the feed tank on the same level as the carburetter.

2 I don't think that carburetter suction will provide enough suction power to raise fuel from the lower tank. The carb usually provides only air suction against against a neutral head - i.e. the tank is on the same level.
On my own chicken hopper installation (which works very well on my Spitfire) I cannot empty the lower tank by using the electric pump to suck out fuel via the upper tank. I have to invert the Spitfire to drain the bottom tank via the spill tube..

3 There is nothing to balance the suction fuel head in the two tanks.

I'm sorry to be the gainsayer, but I think your configuration, though ingenious, will not help you at all.

Steve.

Jon - Laser Engines16/01/2020 16:39:09
5063 forum posts
217 photos
Posted by Martin Harris on 16/01/2020 16:01:19:

The problem with removing the floor is that the tank bay overlaps the wing fixing plate for the front wing pegs.

Can the wing dowel former not be tied to the side frames with fishplates on the outside? It could also be braced internally if the tank you choose is narrower than the fuselage. Once the tanks are in you can add another plate above/below them to box them in and this will take the loads the original plate would have seen.

I had to do this on the hurricane as well as i removed more or less all of the wing dowel former as you can see below.

hurri 5.jpg

Martin Harris16/01/2020 16:39:26
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9071 forum posts
224 photos

After some further thought, the effect - if it works - would actually raise the effective fuel head while the bottom tank was emptying and then reduce it as the top tanks empty.

The carbs are at the level of the tank floor.

Edited By Martin Harris on 16/01/2020 16:55:24

Jon - Laser Engines16/01/2020 16:40:13
5063 forum posts
217 photos
Posted by Ron Gray on 16/01/2020 14:03:37:

86c72b29-a14b-42dc-8dfd-2607839cbafc.jpeg

Looking good Ron yes

Martin Harris16/01/2020 16:54:09
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9071 forum posts
224 photos
Posted by Jon - Laser Engines on 16/01/2020 15:00:08:

Having slept since we spoke Martin i have zero recollection of our discussion! In any case, it looks like you might just about get away with it but i would suggest a tank change you can squeeze a little more capacity out of this **LINK** in more or less the same space.

Sorry - missed the link when I read your reply on my mobile at the field. Interesting thought - would 16 oz be sufficient? My original intention was to use 2 11 oz SLEC tanks which you seemed to endorse at the time - although I don't recall specifically discussing duration.

Ron Gray16/01/2020 17:59:51
1604 forum posts
394 photos
Posted by Jon - Laser Engines on 16/01/2020 16:40:13:
Posted by Ron Gray on 16/01/2020 14:03:37:

86c72b29-a14b-42dc-8dfd-2607839cbafc.jpeg

Looking good Ron yes

Thanks Jon, will be putting up a mini thread on the build soon.

Jon - Laser Engines16/01/2020 18:45:44
5063 forum posts
217 photos
Posted by Martin Harris on 16/01/2020 16:54:09:
Posted by Jon - Laser Engines on 16/01/2020 15:00:08:

Having slept since we spoke Martin i have zero recollection of our discussion! In any case, it looks like you might just about get away with it but i would suggest a tank change you can squeeze a little more capacity out of this **LINK** in more or less the same space.

Sorry - missed the link when I read your reply on my mobile at the field. Interesting thought - would 16 oz be sufficient? My original intention was to use 2 11 oz SLEC tanks which you seemed to endorse at the time - although I don't recall specifically discussing duration.

a 240v will run for 10 minutes at 3/4 throttle on 14oz so the 200 should be fine on 16. A 10-12 minute flight should not pose too many problems.

Martin Harris22/01/2020 13:44:06
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9071 forum posts
224 photos

I've got hold of one of the tanks you linked to Jon and it should be just about perfect. I'll install dual clunks and the filler in the bung and add a fitting for the vent in the top.

Just for clarification with the vertical orientation of the carbs, I assume that the centre of the spraybar/inlet tract is the ideal target height for the mid tank position?

Edited By Martin Harris on 22/01/2020 13:45:04

Jon - Laser Engines22/01/2020 13:48:20
5063 forum posts
217 photos
Posted by Martin Harris on 22/01/2020 13:44:06:

I've got hold of one of the tanks you linked to Jon and it should be just about perfect. I'll install dual clunks and the filler in the bung and add a fitting for the vent in the top.

Just for clarification with the vertical orientation of the carbs, I assume that the centre of the spraybar/inlet tract is the ideal target height for the mid tank position?

Edited By Martin Harris on 22/01/2020 13:45:04

I tend to shoot for top of the tank, that way all of the fuel is below the carb all of the time so you dont get a change in fuel head like you would if it crosses the mid point. There is some wiggle room but i always aim for the top if i can

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