New Prop

[Admin]

Just bought a new 2 bladed prop for my Gazelle $1,320 Ouch but it will be interesting to see what a difference a new prop will make. The current one has had a good life and reco'd several times so I thought hang the expense and get a new one.

 

What is going to be interesting is the old one is a fine pitch one and the new one is inbetween so I am guessing I will lose a little bit of climb performance but will get a better cruise - is that right from you other Gazelle owners or isn't there that much difference?

 

Because my Gazelle is used for training I wasn't able to go for the "non-approved" 3 blader

 

 

[barandbrew]

Hi Ian

 

The only experience I have had with woodern props on my Gazelle were all bad. Poor climb always getting chipped and splits. My Gazelle is not on line now and sports a two bladed Bolly prop which gives 600 fpm climb with two up and 70 knt at 4800 rpm and runs smoothly

 

I am very happy with it

 

Regards

 

John

 

 

[Admin]

Thanks John - yeah the wooden prop that the Gazelle was certified with is one of the few drawbacks of the magnificent Gazelle.

 

Offering my gazelle for training means that I have to use the wooden prop which arrived today and is being fitted tomorrow so it will be interesting to see what difference the new prop makes.

 

 

[PaulN]

Ian,

 

Make sure to fit leading edge tape to help protect it from stone, bug and rain damage. I guess this can be sourced from various locations. The last lot I used was a clear tape and sourced from Bert Flood's ... you can buy it buy req'd length.

 

Paul

 

 

[barandbrew]

Ian

 

How did the new prop go ?

 

I have three wood props in various stages of repair how do you tell what pitch they are

 

Regards

 

John

 

 

[Admin]

Don't know yet John, will get her up in the morning and try it out.

 

Re the prop pitch I don't actually know - I didn't pay much attention but I wonder if the markings in the center state what it is although the Gympie guys said that if I wasn't happy with the pitch then I can take it back to them and they can change it - not for another prop but change the actual one I got. If they did this I wonder if they would mark it as being changed.

 

One thing is that the guy who put it on today has asked me for the certificate of it - all I received from Gympie was an invoice that just says...wait for it....1 x propellar - that is all the invoice says

 

I have to chase them up so I will ask them how to tell what pitch a prop is and let you know.

 

 

[Admin]

Had a call from the mechanic yesterday who said that the new prop was on my Gazelle but two of the plugs were gunked up and the carbies are out of whack so he is going to go over the carbies next week but suggested I give her a go with the new prop to see how she goes. So I went out in her this morning and I must say a bit nervous when I started her up.

 

Full fuel, I weigh 105kg, 0.8hr, 7 landings and an about 3-5 knot wind straight down runway 03 here at Port Macquarie.

 

On first start up there was a vibration - a good vibration as it felt like the prop was really cutting through the air and the sound was a real grunty sound instead of the old wish washy sound.

 

Did my runups at 3,800rpm and the prop sounded so good I thought I had a huge lycoming under the hood.

 

Full throttle down the runway, hand on the throttle ready to stop it if one or both blades decided to suddenly start using the cross strip whilst the Gazelle stayed on the main strip. Now I am noticing the difference - she got to 60 knots in a great hurry - thought to myself hey, I've got a real STOL aircraft now .

 

It was then I noticed the only problem of the entire flight - I was only getting 5,000 rpm out of her at full throttle down the strip. I pulled back on the stick just slightly and continued down the strip at about 5ft off the bitumen, everything seemed ok, so pull right back on the stick and I was getting 700 to 750 feet a minute at 60 knots (indicated) and she was flying smooth.

 

Going downwind I suddenly found that my good old Gazelle was no longer a training circuit only machine but now had grown up and finally was now a real cruiser hitting 75 to 80 knots and that is only at 5,000 rpm. After about the 3rd very tight circuit the nerves began to settle and I started taking her out a bit further and was very pleased how much of a difference the new prop was making compared to the old very fine pitched one.

 

I think (and please correct me if I am wrong) when the carbies are done I should get my 5.500 revs back so I should still get the same climb figures with 2 POB at full weight.

 

The CT is a fantastic machine but gee I love that Gazelle.

 

Comparisons:

 

Old Prop - very fine pitched one that had seen a good life but had rough edges

 

New Prop - medium pitch in between fine and course

 

Item Old prop New Prop

 

Revs 5,500 5,000

 

Climb 650 750

 

Cruise 65-70 75-80

 

 

[Admin]

It's a bit of both Chris - in my humble opinion (IMHO)

 

The engine is working harder with the new prop which means that is there is anything wrong i.e. the carbies, then you will know about it wheras with the old prop you wouldn't know there was something wrong - this is a good thing...isn't it :;)5:

 

 

[PaulN]

Onya Ian, sounds like fun.

 

I'm sure you're going to find that with the new prop having a more coarse pitch your RPM will remain lower than with the finer pitch prop, even after the service.

 

Paul

 

 

[Admin]

IanHow did the new prop go ?

I have three wood props in various stages of repair how do you tell what pitch they are

 

Regards

 

John

- Hi John, just spoke to Tony Kerr, Gympie Aviation who holds the certificate for the Allsize Props that are the only ones Certified for the Gazelle (07 5483 5170 - [email protected]) and he said that all the props are suppose to be the same but their not as they tweek them to be between fine and course. he says that they are not stamped with any indicator and that the only way to tell is to measure the angle at the tip.

My new one he says and all he will commit to is that it is "about" medium but all I know is that it is bloody good :big_grin:

 

 

[Guest brentc]

How many revs Ian is it pulling at full throttle now? If it's 5,000 at full power you will probably need to pull back to 4,700 to get the manifold pressure down and fuel consumption back to normal again. When the Gazelle's all had a standard prop a manifold pressure guage was never required as they were all the same. 5,500 is where the engine is doing good things so I personally would send it back for some modifications. You might find that no matter what the prop / pitch combination you will never get a Gazelle at over much more than 73 knots in the cruise. I applaud your decision to fit a certified propellor and I applaud the ability of the supplier to raise the price from $750 to $1,300+ in 3 years.

 

 

[barandbrew]

Thanks Ian

 

I will be interested to see what the perfomance is with full fuel and MTOW.

 

It sounds like its performing as good as my Bolly Prop. How many Hrs does your Gazelle have on the airswitch?

 

Regards

 

John

 

 

[Admin]

Hi John

 

I am not sure of the time but I think about 2200hrs.

 

Just spoke to one of the instructors who flew it up here to Port Mac from Tyabb and took it up yesterday with the new prop and he says it is just a completely different aircraft - he is about 80kg and went solo in her and also confirmed 700-800ft climb and 80 knots downwind.

 

Mick poole was up here the other day (he looked after her at Tyabb) and commented that the old prop was just way to fine.

 

So I will go up tomorrow 2 up and see how she goes - the Gazelle, you just can't beat them for general flying ;)

 

 

[barandbrew]

Ian

 

You hear plenty of people knocking the Gazelle however there is not many other types in the RAA that do any where near the hrs the Gazelle does.

 

Only time will tell if the more popular trainers can hack the treatment and deliver such SAFE enjoyable flying

 

Kind Regards

 

John

 

 

[Guest pelorus32]

Ian,

 

just a note about 5000rpm. That's all the Rotax engines in the 2 Tecnams at Shep do. Both of them the same. They have GT Tognini props. In Italy recently I was told that they reckon that "GT" means "no two props the same pitch".

 

Whatever the Tecnams do not top 5000 revs but they still perform well.

 

Regards

 

Mike

 

 

[Guest brentc]

Mike, do the tecnams at Shep have manifold pressure guages? I'd be interested to know what the reading is at 5,000rpm (full power) plus the fuel economy at that RPM. I know of a Kitfox 912 that revs at 4,000 rpm max and is the fastest Kitfox around, however he has to be careful not to apply full power as the engine is still working hard even though it's at those low revs.

 

When Gazelle's came out of the factory they revved to 5,500 - 5,600 rpm because that's max power and the props were designed for that RPM setting. It is interesting to see that over time they have definitely coarsened up.

 

 

[Admin]

Beautiful morning flying in the Gazelle today - went two up and she performed fantastic. I was getting the same performance figures so I am amazed how much difference the new prop had made in her.

 

Still getting 5,000rpm on take off and climb at full throttle but getting about 5,200 on cruise.

 

I have asked the level 2 to check the tacho and make sure that it is reading correctly just for a check anyway - doesn't hurt.

 

 

[rick-p]

Ian I hate to be a killjoy but a word of advice, watch your top cruise speed in a Skyfox whether it has a tail wheel or training wheel it dosn't matter they are really only designed to cruise at a speed of less than 80 knots, more in the order of 73 knots.

 

I have addressed this issue in these forums previously.

 

I can assure you that my statements are based on fact not fiction.

 

The fox is a wonderful light aircraft if flown within it's design envelope but go outside it and it will one day bite you and 80knots cruise is not good as it is borderline as to the Fox's design limits.

 

As for the cost of the prop it would help if there was a little competition but unfortunately it would appear, probably because of the cost in doing so, that IVO or BOLLY props are not interested in obtaining certification.

 

rick-p

 

 

[Guest brentc]

I beg to differ!

 

In my hot little hands I have a brochure titled 'Skyfox CA-25n Gazelle'

 

The performance section states:

 

Top Speed TAS 5,000ft 90 knots

 

Cruise 75% at 5,000 rpm 85 knots

 

Cruise 70% at 4,800 rpm 80 knots

 

Loiter 50% at 4,000 rpm 50 knots

 

Best rate of climb speed 55 knots

 

Best angle of climb 52 knots

 

Stall speed 42 knots

 

Takeoff 110m

 

Landing roll 90m

 

Rate of climb @ sealevel 800ft pm

 

Fuel flow at 75% power 13.5 lph

 

Demonstrated crosswind 20 knots

 

It seems that the designers intented high speeds. In reality these speeds were near impossible, especially with the very low quoted fuel flow. I'm not sure how they got away with this creative marketing. Nowdays u/l importers get hounded when they make up dodgey cruise figures.

 

PS: Barandbrew, your copy went into Aussie post yesterday.

 

 

[rick-p]

Brentc,

 

It's not my allegation it is in fact the experts from whom I have obtained my facts.

 

If I get a chance I will send a private message to you with the relevant info and if you feel so minded to do so you can call some people and find out for yourself.

 

I still own and fly my CA21 Skyfox but I know it's limitations and I fly it within them.

 

As a point of interest I understood that the cross wind rating on a Skyfox was only 14 knots not 20.

 

Regards,

 

rick-p

 

 

[Guest brentc]

Perhaps the CA21/22 have different limitations to the 25? As I said in another thread the CA25N is built from stronger materials so that may explain the difference.

 

I was merely reading off the original factory brochure for the Gazelle.

 

 

[barandbrew]

The Gazelle flight manual also states a cross wind component of 20 knts.

 

From personal experience x/wind gusts of 20 knts are handeled reasonable well in the Gazelle

 

 

[Guest Crash Lander]

Full fuel, I weigh 105kg, 0.8hr, 7 landings and an about 3-5 knot wind straight down runway 03 here at Port Macquarie.I think (and please correct me if I am wrong) when the carbies are done I should get my 5.500 revs back so I should still get the same climb figures with 2 POB at full weight.

This has always had me worried. You weigh 105kg, with full fuel, and a second person, say 90kg, doesn't this put you over the 544kg weight limit?

 

I mentioned it to someone and they said that yes it's over the weight but the a/c handles it fine. How far over the 544 can you actually go? I mean, it's a 2 seater, but it seems if you want to go anywhere that requires a reasonable amount of fuel, you need to leave one person behind. Comments?

 

 

[rick-p]

Simple, you can't legally exceed your maximum takeoff weight thats what what "maximum" means dosn't it? (tongue in cheek).

 

If you read Ian's post carefully no where in it did he say that he exceeded maximum takeoff weight or will exceed maximum takeoff weight.

 

I'm sure Ian's passenger if 90kg then he will reduce his fuel load or take his passenger to the steam room first.

 

When we crunch numbers to achieve our figures for weight and balance we shed something somewhere if over elsewhere it's the PIC obligation and legal resposibility to do so.

 

Assumptions drawn from text can be very dangerous so one has to be carefullnot to make the wrong assumption because of a lack of facts which could thereafter put all concerned in the gun.

 

I hope that you are not offended by my comments but I have notice some dangerous assumptions drawn on innocent statements made in certain of these forums.

 

Always remember that someone maybe watching who could make life very difficult for us all if predisposed to do so.

 

Just a word of advice from the intiated.

 

Kindest regards,

 

too all.

 

 

[Guest brentc]

All good except that the Gazelle MTOW is not 544 kg's!