Free air 503

[The Baron]

What is the best application,free air or fan cooled for my thruster where would i get a air scoop if free air is the way to go, cheers, Steve.

 

 

[fly_tornado]

fan cooling. the fan slows the air at high speeds and speeds it up on the ground

 

 

[The Baron]

fan cooling. the fan slows the air at high speeds and speeds it up on the ground

Thanks FT

 

 

[Deskpilot]

fan cooling. the fan slows the air at high speeds and speeds it up on the ground

Makes sense but how much drag does the assembly create?

 

 

[fly_tornado]

can't be much.

 

 

[M61A1]

Makes sense but how much drag does the assembly create?

I'd be more concerned with how much power it robs from the engine, if I was going to worry at all. In a Thruster you're unlikely to make noticeable drag with a cooling fan.

 

 

[JG3]

Nearly everyone I know who has tried free-air cooling has had issues with overheating, particularly while maneuvering on the ground and often in climb as well. That fan is great for keeping a 503 at a steady temp.

 

 

[Deskpilot]

Thanks for your info JG. Now I've got to find a fan and cowl.

 

 

[farri]

Thanks for your info JG. Now I've got to find a fan and cowl.

Hi DP! Doesn`t your 503 have a cooling fan, driven by a V belt at the Mag end of the engine?

 

Frank.

 

 

[Deskpilot]

No Farri, just a scoop for rear cylinder cooling. As received, last run 3 years ago. Said to be in good condition and should only need a clean!!

 

 

 

 

 

[farri]

No Farri,

Well there you go! Havn`t seen one like that before!

 

As the last run was three years ago, if it`s just been sitting there, without proper internal lubrication, it could have some rust on the wall of the cylinders, piston pin bearings, crankshaft bearings and the crankshaft itself and then there`s the gearbox!

 

I wouldn`t even start the engine, without dismantling it, and the gearbox, to inspect everything.

 

Frank.

 

 

[kasper]

Ummm you are in for a bit of a parts search - its not a simple conversion of a free air 503 or 447 to fan cooling - you have to buy/find/scrounge a new rear casting with the fan in it and the lower end belt drive plates and belt.

 

Hopefully there is a time expired 503 sitting out there in an L2 workshop with the bits you need.

 

And if it is going onto your T300/Gemini/TST Thruster ... you will have to consider that the 95.25 registration on those means you have to leave it as a free air 503 unless you have an engineering signoff - or maybe MARAP can help. If its for a T85 then you can do whatever you like.

 

And I agree with others - free air with the scoop means you have to watch your CHT on the ground and in the descent

 

 

[farri]

And I agree with others - free air with the scoop means you have to watch your CHT on the ground and in the descent

Hi Casper! I`ve copied and pasted, from this web site!..What are your thoughts on this?

 

EGT, Exhaust gas temperature, CHT, cylinder head temperature gauges, tachometers, and hobbs hour meters.

 

 

 

Cylinder Head Temperature Gauges

 

Experience has shown that CHT's on two stroke engines are a waste of money. By the time a gauge reacts through the head to tell you, you have a problem your prop has stopped and you already know it.

 

Frank.

 

 

[kasper]

Hi Casper! I`ve copied and pasted, from this web site!..What are your thoughts on this?EGT, Exhaust gas temperature, CHT, cylinder head temperature gauges, tachometers, and hobbs hour meters.

 

 

 

Cylinder Head Temperature Gauges

 

Experience has shown that CHT's on two stroke engines are a waste of money. By the time a gauge reacts through the head to tell you, you have a problem your prop has stopped and you already know it.

 

Frank.

Yes and no.

On a 503 T300 thruster you are needing SO much power to pull the beastie around on the ground at taxi speed - esp with two up - that you have a distinct mismatch between cooling ability and heat generated. If you are taxiing around you watch the CHT not for actual number but direction of movement ... its where its going and when it starts climbing that you pull power, pull over and face into wind to give the engine a break ... before it breaks.

 

On EGT I would disagree entirely that its a waste of money ... if i was going to have only 1 engine instrument on a 2 stroke its the EGT ... even more important than tacho.

 

Why?

 

1. I can hear the engine - I know what full power sounds like and I can tell its making it and on the ground idle with a rotax box its just keep it above the tin-of-bolts rattling sound that you get with too low an idlel - so tacho not critical.

 

2. CHT - not critical if the overall set up is optimized for the engine - that's why a fan cooled engine is SO much better than free air - it pretty much manages and matches cooling flows to heating load

 

3. EGT I cannot see or hear and it's for engine/prop unloaded situation that EGT tells you to stop doing something you can't see or hear in enough time to stop you doing something that you really do not like ... hole in piston if its a Robin or burnt crown and heat seized for a Rotax ... never had a Hirth go and I hope not to.

 

Basically once you take the load off the two strokes prop the throttle position to maintain the unloaded condition leads to a very lean mix which has the double whammy of under lube and over heat of exhaust gas ... never underestimate the 'value' of the unburned petrol in an aircooled two stroke that is passing through the engine as part of the cooling of the engine.

 

So I use CHT on the ground in a free air engine to manage what in the air flying around the cooling system can deal with, I know my engine sounds at various power settings so a tacho is not the end of the world but without an EGT we will never see me doing any form of low power descent in a two stroke because I have no cues from the engine that its about to or just started melting until its too late ... been there, done that have the melted pistons to show for it ... so to speak ... generally they are customers engines I rebuilt after they made the mistakes.

 

 

[Geoff_H]

I saw an article on mixture adjustment in flight on a pressure carb. They kept the EHT low by adjusting the idle mixture using a cable. They claimed that the idle mixture gave enough change to keep the EGT from getting too high. I intend to try this on my project.

 

 

[Deskpilot]

Geoff, your comment is noted for future consideration. Cheers.

 

 

[kasper]

... but not on any airframe where there is a production certificate ... CAO 95.25 regn means you must not change configuration of engine/airframe without authorization be it the designer/manufacturer or MARAP thorugh RAAus ... you can't even replace a free air 503 with a fan cooled 503 ... the design is fixed in time

 

 

[Geoff_H]

Very true. And it is not wise unless you take all precautions and testing. My project is in the experimental class. I don't have an RAA license at this stage.

 

 

[Deskpilot]

Can the registration class be changed? just curious.

 

 

[Geoff_H]

I am not entirely sure. But as long as you have made 51% of the aircraft yourself and get an approved person to certify what you are allowed to do with the aircraft (eg fly over built up areas etc) then you can register as VH- Experimental class. SAAA can do the certifications. But there are private certifiers, the one I spoke to some time ago wanted a full load test on the aircraft, I am not objecting to that as I would do it even if he did not demand it.

 

 

[Deskpilot]

Now the real work begins!

 

 

 

[Don Arnold]

What is the best application,free air or fan cooled for my thruster where would i get a air scoop if free air is the way to go, cheers, Steve.

The "Supercowl" from curedcomposites.com These are as supplied to Flightstar here in the states. Very high quality, predrilled, hardware included.

 

 

[The Baron]

Looking at your aircraft DP it is a single seat Thruster which means it is not a 95/25 compliant aircraft it is 95/10 so you can either fan cool it or free air it with no issues. Of all the 503 powered Thrusters i have seen have been free air cooled with the rear cylinder scoop supplied by rotax. Pilots i have been speaking to recently all say they haven't had overheating problems while taxiing as there is ample air coming from the prop, so i will be setting mine up as free air

 

 

[PaulJ]

Hi Baron, I've experience with both free air and fan on a 503 and would not go down the free air path again. The primary reason relates to on ground movement where a long transit from hangar to threshold and the start of my take off role caused over heating and costly engine damage when relying on free air.

 

In my case early in my flying hours, the cylinder head bolts snapped and the piston destroyed the cylinder wall at 1500 feet elevation plus 3 miles after take-off. This was enough prompting to make me seek the advice of Eddie the Expert, Gary at Bert Flood Imports. No matter how cleverly I framed my question to trick him into endorsing Free Air, Gary seemed to frame his response the same (and I'm paraphrasing here), "the fan is of part of the 503 for a reason you idiot". Also he seemed to suggest that fuel mix, fresh fuel, good filters, guages, plugs and all else per Rotax operators manual contributed to good safe performance.

 

Strangely, since operating with the fan and factory cowlings, the overheating issue has resolved.

 

If the relatively minor amount of power expended to drive the fan effects your aircrafts overall performance a motor upgrade may be required.

 

Many pilots operate with free air with no problems. Of course there are generally many solutions to engineering problems, however Rotax built in a solution for temperature issues and trying to reinvent the wheel so to speak is a waste of energy which adds to down time and cost; that's my experience.

 

By the way, it took a couple of rebuilds before the message finally sank in. Cheers, Paul

 

 

[The Baron]

Hi Baron, I've experience with both free air and fan on a 503 and would not go down the free air path again. The primary reason relates to on ground movement where a long transit from hangar to threshold and the start of my take off role caused over heating and costly engine damage when relying on free air.In my case early in my flying hours, the cylinder head bolts snapped and the piston destroyed the cylinder wall at 1500 feet elevation plus 3 miles after take-off. This was enough prompting to make me seek the advice of Eddie the Expert, Gary at Bert Flood Imports. No matter how cleverly I framed my question to trick him into endorsing Free Air, Gary seemed to frame his response the same (and I'm paraphrasing here), "the fan is of part of the 503 for a reason you idiot". Also he seemed to suggest that fuel mix, fresh fuel, good filters, guages, plugs and all else per Rotax operators manual contributed to good safe performance.

Strangely, since operating with the fan and factory cowlings, the overheating issue has resolved.

 

If the relatively minor amount of power expended to drive the fan effects your aircrafts overall performance a motor upgrade may be required.

 

Many pilots operate with free air with no problems. Of course there are generally many solutions to engineering problems, however Rotax built in a solution for temperature issues and trying to reinvent the wheel so to speak is a waste of energy which adds to down time and cost; that's my experience.

 

By the way, it took a couple of rebuilds before the message finally sank in. Cheers, Paul

What sort of aircraft did you have your 503 in Paul, cheers Baron