Engine selection (Rotax)

[dlegg]

17 minutes ago, sfGnome said:

Skip. I’ve said that I can stretch to a 914, that I’m not a STOL jockey, I like to fly high (high in this instance is <10k ft) and that the airframe in question can take to full range of Rotax engines (and only those engines). All I’m asking is, in the opinion of all our friends here, is it better to go for more power with the downsides of ice/blockages/tuning (914), or no carbie and better fuel figures with the downside of less power (912is). Also, are there other pros and cons that I haven’t listed? That’s all.

Biggest issue you have there is choice between electrically dependant aircraft or not. Fuel injected engine shuts down pretty quick with no electrons flowing, and you pay a huge premium for the pleasure. Airframe and fuel system also has to take into account likely fuel return lines to tank, duplex fuel valves, high pressure fuel pumps operating continuously, associated high pressure lines and filters. Having said that, there is certainly a good case for using the iS. I have attached a good article about changing to the iS and associated issues and benefits.

TheMagicofElectronicFuelInjection.pdf

[skippydiesel]

1 minute ago, dlegg said:

Biggest issue you have there is choice between electrically dependant aircraft or not. Fuel injected engine shuts down pretty quick with no electrons flowing, and you pay a huge premium for the pleasure. Airframe and fuel system also has to take into account likely fuel return lines to tank, duplex fuel valves, high pressure fuel pumps operating continuously, associated high pressure lines and filters. Having said that, there is certainly a good case for using the iS. I have attached a good article about changing to the iS and associated issues and benefits.

TheMagicofElectronicFuelInjection.pdf 817.15 kB · 0 downloads

There is no doubt that fuel injection offers the potential for greater fuel econamy and may also improve engine performance (slightly) in other ways BUT the cost of an iS, compared with the very similar ULS, must surely beg the question - are the benefit cost effective for most private owners doing well under 100 hrs/annum??

[facthunter]

Some engine safety issues can be solved by injection but some electronic ones have their own problems. A float carburetter on a modern engjne is an anachronism and a flooding risk. 

    As a rough rule of thumb up to say 120 kts cruise you won't get a lot of benefit from a C/S prop compared to a well matched fixed pitch one.   Most GA planes like a piper or Cessna basic models will make FL 140  (Just)  Some days a Gazelle would be lucky to make 5.000 ft. Nev

[sfGnome]

2 hours ago, facthunter said:

It won't hurt you to go to the Vans Aircraft site.  Nev

Spent a lot of time there. The RV9 with the 160hp Lycoming (the only one that they support directly for that model) has an empty weight of 490kg. Add in 160kg for my beloved and me, then 50kg luggage (her requirement - she was sick of only being able to take 10kg in a 600kg plane when we went to visit the kids), and you’re left with only 60kg of fuel, or about 2.5 hours with reserves. 
 

Damn! Drifted my own thread… 🙄

[facthunter]

They do handle a lot of the motors you might be considering so might fill you in on performance.  If I read you correctly I wouldn't stray from the standard  engines.  That's from a person who would fly an Anzani  engined plane If it was offered and the aerodrome was suitable or in an extreme case, build my own. crude engine.  Nev 

[BurnieM]

Not saying 'electrically dependant' is not an issue to be remediated but is it actually a bigger risk than carbs/magnetos ?

 

The 912IS requires battery power to start but not to run.

The IS has two alternators with the first being 10?amps for engine (ecu/fuel pumps/spark). If this fails the ecu can switch everything automatically to the second 30?amp alternator (normally used for avionics/battery charging only). If the second alternator fails then the engine will stop.

Reconnecting the start power will allow you to restart the engine but it is recommended to reduce the avionics load and land with 30 minutes.

This seems like a pretty fair level of redundancy to me.

 

You can also fit a third external 30amp alternator but this can only be used for avionics/main battery charging.

Edited October 27, 2023 by BurnieM

[RFguy]

I would not buy a fuel injected Rotax product. I'll leave it at that.

 

[facthunter]

You don't need electronic fuel injection on an aero engine. Mechanical, calibrated well is fine with a simple single point at throttle body backup.   Nev

[RFguy]

yes.... An IO-360 is pretty simple and reliable...

[facthunter]

Helped a bit if you know how to operate and treat it. It's NOT difficult and one of the worst things to do is not use it enough and get it thoroughly HOT each time it is run.  IF it's left idle it must have some minimum inhibitor process and  the longer the period idle, the more involved the  teatment needed. Protect your investment and your safety. Nev

[skippydiesel]

40 minutes ago, facthunter said:

You don't need electronic fuel injection on an aero engine. Mechanical, calibrated well is fine with a simple single point at throttle body backup.   Nev

True  BUT it does seem to be a backward step, away from all the potential benefits of computer controlled electronic fuel injection (I am happy with my ULS)

[skippydiesel]

7 hours ago, facthunter said:

Some engine safety issues can be solved by injection but some electronic ones have their own problems. A float carburetter on a modern engjne is an anachronism and a flooding risk. 

    As a rough rule of thumb up to say 120 kts cruise you won't get a lot of benefit from a C/S prop compared to a well matched fixed pitch one.   Most GA planes like a piper or Cessna basic models will make FL 140  (Just)  Some days a Gazelle would be lucky to make 5.000 ft. Nev

Nev! Nev! - flying is a falling risk - does that stop us from doing it?

 

Carburettors have now been around for about 200 years - while they are no where near as efficient as a modern fuel injection system, they are relativly simple, robust, cheap and minimal risk (if maintained correctly).

 

Ref. The desirability of CS prop for high (?) flying aircraft  - I bow to your superior knowledge but find it hard to believe that your justification for not equipping a turbo (normalised) engage, specifically selected to facility high altitude flight, is that a Cessna ,with a fixed pitch prop, may just make it to 14Kft. The question actually relates to optimising the altitude ability of the Rotax 914 which is "16000 ft is the critical altitude, max continuous performance is available to that altitude at standard ISA conditions.". - I don't have the answer(s) but speculate that the ability to adjust the blade pitch, in flight, may compensate (in part) for the diminishing air density.

[facthunter]

Take a sip of the cool aid .. I said as a "rough rule of thumb" What U/L's are going to operate above 10,000 feet,? A fixed pitch prop will be "Perfect" at one spot if it's chosen well.  C/S is also blade shape (twist) compromised. Costly, Heavier and can FAIL in a control fail way. Go to a fine pitch stop. If that's not set properly it may overspeed at a forward speed too low to be any use to you. The tend is always to go to a finer pitch and more forcibly at higher RPM.  Geoffrey DeHavilland got a  MOTH type plane to 23,000 feet in the 20s with a wooden prop.  Mixture leaning is more of a must than anything else in getting there.   As you get older the Hypoxia  effect may start a lot lower than 10,000ft  and you aren't aware of it's effect  either. as it overcomes you..  You are also getting to a higher angle of attack on the wings as you get near it's service ceiling. Nev

[danny_galaga]

Sorry to be a Bernard (Yes Minister) but the euphemism of Kool Aid refers to crazy cult members killing themselves. This is the opposite, I assume of what you actually intended to imply with "take a sip of the Kool Aid"

 

😇

[skippydiesel]

On 28/10/2023 at 11:03 AM, facthunter said:

Take a sip of the cool aid .. I said as a "rough rule of thumb" What U/L's are going to operate above 10,000 feet,? A fixed pitch prop will be "Perfect" at one spot if it's chosen well.  C/S is also blade shape (twist) compromised. Costly, Heavier and can FAIL in a control fail way. Go to a fine pitch stop. If that's not set properly it may overspeed at a forward speed too low to be any use to you. The tend is always to go to a finer pitch and more forcibly at higher RPM.  Geoffrey DeHavilland got a  MOTH type plane to 23,000 feet in the 20s with a wooden prop.  Mixture leaning is more of a must than anything else in getting there.   As you get older the Hypoxia  effect may start a lot lower than 10,000ft  and you aren't aware of it's effect  either. as it overcomes you..  You are also getting to a higher angle of attack on the wings as you get near it's service ceiling. Nev

My guess - you don't have the answer, so are "blinding" us with random tangential thoughts on dimly related topics -  a classic "muddying the waters" tactic.

[facthunter]

  It's all facts that you might consider if you wish to deal in facts. How is that "muddying the waters? I don't DO tactics.  Relate to the facts I bring to the discussion and keep your personal insults out of this exchange of ideas and we'll all be better off. Nev

[skippydiesel]

There were no insults intended (unless you decide to take it that way).

 

Tangential muddying of the water - the question/topic ( as I understand it ) has to do with engine selection for high altitude performance/capacity. The topic initiator's choices are between, carburetted, fuel injected and turbo charged variants of the Rotax 9 series engine. Interesting "stuff" about  Geoffrey DH Moths/prop composition, age related hypoxia and even wing angle of attack are, I suggest, not addressing the question and at at best distantly related to the same. Sure I understand that your "stuff" illustrates the achievement of others and associated risk but how does this directly relate to engine choice?

 

I confess to being prone to drifting off topic, in that I  speculated on the potential for a CS prop to mitigate the effect of thinning atmosphere, thereby helping the engine/aircraft to achieve its best high altitude performance - in this I suggested you might have the answers.

[facthunter]

There's a lot of "context" in my posts. which you have failed to appreciate. If a crude underpowered plane can make 23,000 feet with a wooden prop, how is an in flight variable pitch with it's inherent losses going to be the silver bullet answer? Prop blade angle of attack works like a wing's angle of attack. It has ONE best angle. You need bigger wings to go high not a higher angle of attack for them or the lift/drag bit  comes in.  Enabling the engine to rev higher will help reduce the blade AoA so that would be a plus but a bit hard to quantify. My view is the "order of magnitude" is not a deal breaker or maker. DC-3's in PNG had special prop blades fitted to assist at higher altitudes. The SAME engines but with turbochargers fitted in lieu of the mechanical ones  powered the Liberators that flew at 30,000 feet.   Nev