Tips on slow descents

[DieselFan]

Slight problem 582 pre mix,

Cruise at 4500 rpm EGT at 1100-1150, 5000 egt 1050-1100, 4000 egt 1200, 3500 egt 1050

1. Day flying (not morning or late) means I can't fly at 4500 but instead 4000 as you climb too much
2. Long descents if I drop to 3500 plane drops fast and slows somewhat (I think it's prop drag) I found 4000 to be about the same as other trikes on a slow descent

I'm sure it's cause the motor is running too lean but whats the norm / recommended? Fly same alt and then just circle to lose height?

[Morph]

I had the same problem with my 503 in my old Challenger. 4000 rpm was a hotspot. Now you would not have known this without having EGT gauges. The carbs are such simple devices they cannot be mapped at different rpms. So you have to learn to avoid that rpm, especially on those long decents. If you find that this is a problem then repitch your prop so that your cruising rpm is slightly higher to say 5200. Your descent rpm will now come up to 4200 and out of the hotspot.

Btw take long cruise decents in steps as you are at a risk of carb icing. To check for icing power up to cruise rpm every 5 minutes or so. If there are no problems then keep the frequency at 5 minutes.

If the motor hesitates or coughs, your heart will miss a few beats and it will take a few seconds for the ice to be digested by the motor before revs come back up to normal cruise. This is normal. However if this doesn't happen push all the way to full throttle to try get the slide in the carb moving. If it still hesitates and coughs and does not come up to full power do a precautionary landing and check it out. If it does come right then carb icing is present and increase the frequency of your checks

I have also found after decending from 8500ft down though the Franschoek Valley to 2500ft that my plugs gunged up quite badly. Why, I don't know. I would check them after a long decent and clean/replace them if necessary.

If you are still high then fly s-curves or circle to lose height. Remember the dangers of stalling on a decending turn, don't make the turns too steep and never go cross-control for the 3-axis boys, i.e. if turning left don't try to hold the bank off with a bit of right aileron while using left rudder to tighten the turn. Very high risk of an insipient spin.

[Henni]

Hi Morph,

You never stop to amaze me with all your detailed technical know-how. Did this come with years of experience or how else did you attain this knowledge?

How your brain can remember the detail of all of this is beyond me.

[Everytime I fly the Mizer in strong & gusty winds (like Sunday at JHB) I think again about you putting me in contact with this stunning aircraft!]

Please once again relay my regards to Ron & all the other guys down there.

Keep well,

Henni

[Morph]

Partly experience and partly constant reading and researching. I love everything to do with aviation and am always looking up questions. The internet is also a very good source of information, you must just know how to ask. Everytime I get a question I don't know the answer to I research it and in that way constantly learn.

will pass on regards to the boys

[Nick]

Interesting, to me this carb icing business rather begs the question as to why fuel injection is not standard on Rotax and Jab engines?

Indeed - ruminating 'out loud' - I would have thought that all the imperatives that have made fuel injection almost ubiquitous in automotive petrol engines - efficiency, economy, reliability, repeatability, engine mapping etcetera - would similarly apply to aviation avgas/ mogas power plants.

I notice that fuel injection IS fitted to the new 95 HP UL260i.

[Morph]

Agreed,

Hirth now also bring out a 65HP 2cyl and 100HP 3 cyl 2-stroke that uses fuel injection and it is cheaper than the Rattexes. They have had a bad rap in the past but I believe they are good solid engines now

[Nick]

Agreed,
Hirth now also bring out a 65HP 2cyl and 100HP 3 cyl 2-stroke

I confess to having a lip that curls spontaneously into a sneer upon mention of 2-stroke...too redolent of smelly lawn mowers, objectionably noisy motorcycles and forestry equipment. But admit complete ignorance on the matter with regards to aviation engines.

[ZULU1]

In mid summer January ish we get the most evil carb icing, Uncle HKS has an electric carb heater. Typical when at 22degrees and about 90%rh land and serious frost on the carbies. In cold conditions nothing.

Zulu1

[Nick]

In mid summer January ish we get the most evil carb icing, Uncle HKS has an electric carb heater. Typical when at 22degrees and abou

Shouldn't that be 'mid summer January EISH!'...?
..sorry!

[Morph]

I confess to having a lip that curls spontaneously into a sneer upon mention of 2-stroke.... But admit complete ignorance on the matter with regards to aviation engines.

If you treat them well, run them regularly (the more the better) and never ever forget the 2-stroke oil they are surprisingly reliable. In fact of all the problems I have heard of in the past few years the overriding cause was fuel mismanagement which would effect either 4 or 2 stroke. They need to be serviced much more regularly but are cheaper than te 4-strokes to begin with. Horse for courses

[Morph]

if possible, install a carb ice mod.

Do you have the water heater on the throttle body? How does it work, do you have a lever that actuates it

[Massimo]

Nick wrote:
I confess to having a lip that curls spontaneously into a sneer upon mention of 2-stroke...too redolent of smelly lawn mowers, objectionably noisy motorcycles and forestry equipment.

I actually enjoy these littlke 2 strokes. Reminds me of child hood days of riding bikes, cutting grass etc etc. I love the smell. Not that id say no to a grown up four stroke but 582 it good for now. :D

[DieselFan]

Thanks guys I'm ever aware of carb icing perhaps too aware - if thats possible hence the reason why 4000rpm was preferred over 3500.

As it turns out some of ther ppl I fly with don't have EGT's fitted so I will either repitch a tad which could stuff up my max speed or drop faster and just let the trike behind me know of my planned Sssssing.

Alternatively could I fit an enricher?

[Morph]

Your 'choke' is in fact an enricher, i.e. feeds pure fuel directly from the bowl into the intake. I know lamercyfly has used it a little in the air to cool the EGT's down on a long cross country. Maybe try cracking it open a little bit at 4000rpm on a decent and watch your EGT's. It will drop your rpms by about 400

See here

[DieselFan]

I will give this a shot - at first over the airstrip :D