By continuing to use this site, you agree to our use of cookies. Find out more
Forum sponsored by:
Forum sponsored by CML

ESM Tigercat - powered by Laser engines

Not a build blog, more of an insight

All Topics | Latest Posts

Search for:  in Thread Title in  
Tim Flyer04/01/2020 10:02:06
avatar
1326 forum posts
239 photos

The idea of proportion of outlet to inlet sizes is only a very rough guide. The most important factor is how both the inlet an outlet sit in the air stream . On my Chipmunk the inlet is smallish but at 90degrees to the airflow so will receive high pressure, and has been well baffled . The outlet was also at 90 degrees to airflow but needed a spoiler to create a reduction in pressure near the outlet ... that dramatically increases extraction flow . The area of inlet and outlet are quite similar. A small spoiler near the outlet guides air away from the exit and really helps . 

Edited By Tim Flyer on 04/01/2020 10:04:34

Jon - Laser Engines04/01/2020 11:07:08
5621 forum posts
271 photos
Posted by Peter Jenkins on 04/01/2020 09:32:37:

Jon, I rather think you may the only proponent of equal entry and exit areas. I agree with Ron that exit area needs to be 2-3x intake area, plus any necessary baffling, to ensure good cooling. I think correct baffling is also vital to getting the cooling air where it's needed. Has worked for me on both IC (glow/petrol) and moderately powerful electric setups (using 3000 watts).

Edited By Peter Jenkins on 04/01/2020 09:33:59

i know its the accepted rule of thumb but its not actually true. Its one of those modelling folk lore jobs that is intended to give a system that more or less cant be screwed up.

On my ESM sea fury i have the exact same setup as Ron. I have an upright V twin with a baffled cowl venting though the scale exhaust outlets exactly as on the tigercat. While i have not measured it, i would estimate that my outlet area is about half that of my inlet area but i have no problems at all with cooling due to the shape of the cowl creating low pressure and effectively sucking the hot air out the back. It works so well that if i have not flown the model for a while and some oil has got onto the exhaust can the smoke from this oil is very obvious venting from the cooling outlet as it burns off. Even at idle it rushes out with great enthusiasm.

Its the shape of the ducting and air outlet that is the most important part of a cooling system and the more i think about it the more models i think i have that are barely 1:1 in/out but cool just fine. My La7 and Acrowot XL certainly dont make it, my Tomahawk and P39 are probably closer to even but to be honest i have never actually measured it

Martian04/01/2020 18:24:49
2579 forum posts
1170 photos
Posted by Ron Gray on 04/01/2020 08:45:11:

Hi Martian, that's very kind of you and that would be great if you could print off a couple for me. The cowl is 190mm diameter.

PS the i3 is the printer that was / is on my short list and the wife still keeps saying I should get one!

@ Jon - I must admit that I always laboured under the impression that it should be 1 in to 3 (ideally 4) out?

Hi Ron a tigercat is on my next build list so I printed a pair and will not be in a position to use them for some time they are 180mm if thats any good message me Martian

Chris Walby04/01/2020 21:22:48
avatar
1323 forum posts
332 photos

Ron,

My calculations could be wrong, but at a typical flying speed without the prop wash effect you'll be pushing 128 litres per second into the cowl (that's a lot or air per second in my book!). Forming a baffle to direct the incoming air over engines would reduce total frontal area, but increase the in/exit area ratio.

As Jon mentions I don't think the total area is important, rather directing the air in the right direction and allowing it to exit the cowl is more important.

PS What fuel are you using and % nitro?

Regards

Ron Gray04/01/2020 22:12:46
2320 forum posts
1000 photos

Chris, I fully agree that it’s directing the air / baffles that is the most important thing, I know that from past experience with my Wots Wot XL when it was powered by a 240v. The engine just wasn’t happy until I had baffled the cowl.

Regarding fuel, I use Model Technics 5% Laser.

Ron Gray18/01/2020 22:15:02
2320 forum posts
1000 photos

I now have 2 of these beauties thanks to Martian. They really are splendid and I'll get to work fitting them as baffles to the cowls.

f8c4390e-c647-49d8-92fe-32bfaf2ffa6d.jpeg

Ron Gray06/08/2020 20:19:34
2320 forum posts
1000 photos

Well 7 months later and I decided to address the problem I had with one of the engines. To cut a long story short I took the problem motor off the 'plane and then it was obvious what was wrong, the carbs on that engine were not mechanically balanced, in other words the barrels were opening at different angles, I don't know when that happened but I adjusted both so that they were in sync, put the engine back on and bingo, it ran perfectly. I then balanced the low and high end of both engines and with no more excuses I took it up to the field today for its maiden flight. the following video shows that flight which didn't end quite the way I was expecting!

cymaz06/08/2020 20:33:05
avatar
9333 forum posts
1211 photos

Well, sometimes the luck of the Gods are with you. Luckily for the plane and the pilot.

surprise

 

 

Edited By cymaz on 06/08/2020 20:33:28

Ron Gray06/08/2020 21:23:17
2320 forum posts
1000 photos

Yep Cymaz. my lucky day, no damage at all to the 'plane.

cymaz06/08/2020 21:58:35
avatar
9333 forum posts
1211 photos

Did you find out why you had an engine quit?

Jon - Laser Engines06/08/2020 23:22:23
5621 forum posts
271 photos

well then...

First off, you handled the engine out well. Given the lack of stick time on it i think it was wise to straighten it up and put it down where you did given the space was available. I would probably have tried to fly myself out of it on the other engine given how many twins i have flown but i cant fault your choice here. It wasnt worth the risk of throwing it on to final at such a tight angle with the right engine dead. On the bright side it seems quite well behaved with one engine and the rudder is clearly very powerful.

For the engine to stop like that is really unusual. Our twins will run on one cylinder so an instant flame out on both sides is really strange, especially as they have their own tanks and cooling was not a factor. There was no steep climb going on so a lean cut in the normal sense is ruled out. I suspect it was fuel starvation of some sort but im not exactly sure what to suggest as its such a rare occurrence.

Ron Gray07/08/2020 06:36:23
2320 forum posts
1000 photos

Well, the results of the ‘Air Accident Investigation team’ are in. And the findings are...........

cymaz07/08/2020 06:40:52
avatar
9333 forum posts
1211 photos

.......... the suspense is hurting me !

Ron Gray07/08/2020 06:42:38
2320 forum posts
1000 photos

Just as Jon said, fuel starvation, due to a lack of fuel! When I got home I drained the tanks and there was nothing to drain from the right hand tanks. This was strange as I had filled them up at the same time as the left ones, so I think that, for some reason, they did not fill right up. The only explanation I can think of is that I filled through one vent until the fuel spilled from the other whereas I normally fill through the fill with one vent blocked, wait for the spill from the other vent then block that one off and continue to fill until the other vent spills. I know it shouldn’t make any difference but that’s the only explanation I have. At least I have found the cause of the problem and can confidently take the big cat out again.

cymaz07/08/2020 06:51:35
avatar
9333 forum posts
1211 photos

yes. That’s good to find out.

Ron Gray07/08/2020 08:43:37
2320 forum posts
1000 photos

The other thing that didn’t help was that I was held up, with the engines running,before going to the flight line. I thought that it was only for a couple of minutes or so, but having just looked at the telemetry it was in excess of 8. Even on tickover fuel was obviously being consumed. Note to self, if held, top up immediately before going to flight line.

Jon - Laser Engines07/08/2020 10:33:09
5621 forum posts
271 photos

Yea even a laser will dead stick without any go go juice in the tank.

Last week i took my 80 powered hurricane out. Had a flight, no worries, chatted away for a bit while i got the model ready for another flight. Fired up, then as you say i was delayed getting in the air as one of the chaps was having some control problems and needed to get down. He got it down after a few minutes wrestling it, and as i went to taxi onto the runway it stopped...

Guess who forgot to fuel it up embarrassed

Distractions during pre flight or changes to routines can be really dangerous. I think you were pretty lucky!

Chris Walby07/08/2020 12:20:47
avatar
1323 forum posts
332 photos

Ron, Good result following the engine out, well done and ease the bike clips off slowly.wink

Just looking at the video on the phone, was there a big pitch change for some reason?

Its a bit of effort, but I always fill mine with the hand fuel pump and count to fill and refill, handy to know how many revs for each coupled with flight times. IMHO can't see the benefits of electric fuel pumps, but each to their own.

Ron Gray07/08/2020 13:49:40
2320 forum posts
1000 photos

Actually I put it down to the new fuel I'm using, the 'Laser Less', you put 100% in but you only get 90%. I mistook it for the Laser Pro reduced oil version.

Ron Gray07/08/2020 15:14:00
2320 forum posts
1000 photos

@Chris - the big pitch change you can see in the vid is when the engine cut. I was in a banked turn, to the right, so the left wing was higher than the right and as the right engine cut the left one pushed the nose down. I corrected that with big left rudder which then pulled the nose up and the subsequent roller coaster ride was me trying to balance the 2 and turn it into wind, at the same time trying to avoid the big hay stack (I actually flew over the top of it!!). The whole process was complicated by having a cross wind blowing! A change of underwear when I got home, but a good training session in one engine flying.

All Topics | Latest Posts

Please login to post a reply.

Support Our Partners
CML
Slec
electricwingman 2017
Sussex Model Centre
Sarik
Advertise With Us
Latest "For Sale" Ads
NEW POLL - has the pandemic altered your event safety perceptions?
Q: Has the covid pandemic deterred you from attending shows and events in 2021?

 No, I'll be attending just as many as I usually do
 No, but I'll choose my event with greater care
 Yes, I'll attend fewer events going forward
 Yes, I wont attend any where previously I have

Latest Reviews
Digital Back Issues

RCM&E Digital Back Issues

Contact us

Contact us

Magazine Locator

Want the latest issue of RCM&E? Use our magazine locator link to find your nearest stockist!

Find RCM&E!