Challenger/Rotax 503 advice please.

[Luan]

Hi fellow aviators!

I am in need of some help with my Challenger and its 503.

I recently bought a clipped wing Challenger,it had been standing a few years, only occasionally started.

I drained the old fuel, replaced the fuel lines and prop started her as the electric start did not work, it was flown from Next door to Bapsfontein.

This fairy flight revealed that the engine only ran up to 5800 rpm. After inspection I found that the mag-end starter ring-gear was broken and off balance after fixing this it got up to 6100 on the ground. Great problem solved right? A big disappointment when the plane could not take off 2up, for my instruction . It now gets 6380 1UP full throttle in flight.

So I then started to look at all the possibilities, even going so far as to phone Dave the designer of the Challenger in America, who informed me that the challenger was overloaded, and that the he is not surprised that it doesn't jump into the air at our altitude. He gave me some tips on the CoG and so forth. He however said that if I am to have a chance of getting into the air I will need at least 6300RPM static, as we know this is close to the sweet-spot on the 503.

So this is what I know:
1. CoG and weight is correct.
2. Carbs, airfilters, have been cleaned, new plugs with a 0.5mm gap.
3. Carb jetting is correct as per Rotax.
4. Both Ignition Systems are OK.
5. It has a 2.6:1 belt drive with a Tennessee 60x44 prop.
6. By turning the prop I can feel the engine compression is good, the engine has 118 Hours from new.

The previous owner suggest that the prop balancing might be out. Could this be the problem? I however used the Static Thrust Calculator located here: http://personal.osi.hu/fuzesisz/strc_eng/ and punching in my prop numbers at our altitude and air density it seems I need 40.533kW to get the prop to 6400 static. Which I am afraid the 503 simply will not deliver, especially up here.

I then turned my attention to the Propeller, talking to the ever helpful and friendly oom Piet from P-Prop, who also said that I need around 6400 static, and that the easiest thing to do would be to start by removing 10mm each side from the prop until I reach my desired RPM. I am lucky in that I have two Identical props so I have one to play with.

Before I start cutting props, which I suspect I will be doing next week. I am hoping someone here might have some advice or notice something that I have missed?

[falconp1]

Hi Luan.

Have you checked to see if both carb slides open fully (go all the way up). Take off your air filter, open throttle as far as it will go and look into carb intake to see if both slides are all the way up. While you are at it you can synchronies them.

Check your tire pressure and that your brakes aren't binding

The 60x44 Tennessee wood prop is as close to ideal as you will get for your plane


Regards
Freddie

[Luan]

Hi Freddie,

Will have a look at the brakes and tires. While I was sitting in the plane ground running it my instructor and AP pulled both carbs by hand until they could not be pulled anymore, I cannot be sure that both were at max as I did not see it with my own eyes. I did notice a very small difference(about 0.5mm) in the slide heights while re-assembling them after the cleaning. I will do a manometer style carb Sync to be sure and make sure the carbs go all the way up with the throttle cable and report my findings. Thanks for your input!

[Tobie]

Did you replace the jets with new ones....if the plane stood for a long time the residual oil in the jet dries and forms a thin layer on the sides making them smaller....they may look open and clean but are in fact not.

[Luan]

Ok so I had a look at the carb slide position at wide open throttle and noticed about 3mm difference between the two. I ended up having to make new throttle cables as the one cable had too much slack and could not reach top position. I then also replaced the prop with my spare prop of the exact same length and pith, and did a carb sync, with the manometer I can see that with both carbs fully open the one cylinder does produce slightly more vacuum, with no apparent reason. I also had a look at the breaks and tire pressure and found them to be good. The engine now gets ~6300 static and ~6500 flat out flying, which is right on the money. @Tobie: 'I will change the jets and see if there is any difference and post my results here.' The plane rotates at 55MPH IAS 1UP and my instructor feels that we might just just get airborne 2UP on the 1km runway at Bapsfontein but that it is simply too marginal. Which is something I wish the previous owner had told me before I bought the plane. So not only will I not be able to do my CCM on the plane but I will also most likely only be able to fly alone with a reasonable amount of fuel, which is sad as one of the things I love most about the gift of flight is sharing it with others. The only options available is installing a 582 or getting a set of long wings, neither of which is a financially viable option for someone who isn't working/stealing for the ANC/EFF. Thanks for all the help guys, you are truly a great community

[Luan]

So I finally found someone who has flown a few challengers and has done instruction on a clipped wing 503, and was about to start my training, just the fairy flight with my new instructor in the way... and so I present crushed hopes and dreams in visual format:

20140519_160319.jpg (79.66 KiB) Viewed 5551 times

[falconp1]

Hi Luan.

Sorry about your oops. Dont let this small event kill your dreams. From here the Challenger looks very fixable. Were are you situated. Lets see if we can help.

Freddie

[Loco]

Baie jammer Luan, eks net bly niemand het seergekry nie (ek hoop?)

Wat het gebeur dat ons kan leer asb?

Jy is 'n regte aviator, jy het al meer ondervinding as ouens wat dubbel jou ure het, byt vas en kry haar weer in die lug

Thanks Falcon for offering to help Luan, very admirable

[Luan]

Thanks guys you are a real great bunch of guys! No one was hurt, and that is the most important. I was not on-board, I was half way to Rhino for my first flip! What happened was: The plane was flown solo by 3 other pilots in the last month or so, other than not climbing to well with the 503 they all experienced a buffet/oscillation at around 70mph. Neither under nor above. When my new instructor felt this he thought the tail and/or elevators were coming off and made for the nearest mielie field.

Now why the buffet, having never been able to fly the thing I have no idea how to describe it, but talking to Pieter De Necker about the belt drive and its ratio he remarked that a drive and gearbox should never be exact numbers, such as 2.0 or 2.6, otherwise at a certain speed and rpm there exists a resonant frequency which would cause all sorts of vibrations, but only at a certain speed/rpm. After sending some pictures to the Challenger factory they asked where my trim tabs on the elevator are, there must be one each elevator one trimmed up and one trimmed down, the person I spoke to simply builds them, and cannot tell me why they must be there. Perhaps someone a little more knowledgeable could comment?

I thought it was going to be millions and billions to fix, as I was towing the last pieces of her out of the mielie field with a flatbed trailor at 11pm, stopping at a robot they smashed my window and also damaged my car a bit, I was ready to call it quits. I woke up, saw the wreck in my yard and before I could help myself I was emailing Challenger in America. The good news is its a kit aircraft and the parts are all still for sale, I will have to learn a lot, for instance how to patch that Ceconite stuff its covered with, I will need to find a building area close to my house other than the garden, dismantle large parts of the fuselage to replace the broken brackets and so on... it will be a slow process...

Thanks for all the support guys!!!

[falconp1]

Hi Luan.

If you live in the Gauteng area I have a friend that can repair the fabric for you. He is an aircraft rebuilder / builder. He has just repaired a damaged Challenger for us.

The only thing I can think of that would cause an oscillation at that speed is that the elevator cables are to slack.
Check the tension before anything else. There must be no play at all. Do not over tension them as well. Just enough that all the play has been removed.

There is quite a big Challenger following is South Africa. Most of the metal tubing to repair you plane can be purchased locally.

PS. You do not need trim tabs if your plane has flaperon adjustment. My Challenger flies straight and level hands off no trim tabs.

Regards

[Luan]

Thanks falcon. I stay in Pretoria, I would love to have his number and get a rough idea of what I'm dealing with, covering wise. I was also wondering if I remove my fiberglass wing droops and add the standard standard bow, therefore trading off some speed an roll rate for more lift, is it worth it? I am trying to estimate costs and building a timeline for repairs. I started with the landing gear the 38mm Chromoly tubes, Non-Ferrous Metal Works in pta don't do chromoly, they referred me to a place in JHB that does chrome alloys but they do not have nor do they know of anyone who has chromoly tubes. I will need most of the ribs for the bottom right stringer and the stringer itself, is there a place to find this locally? I will also need a new main gear weldment, don't know if I will ever have peace of mind if I dont replace both, they look slightly flimsy... was wondering if couldnt just cnc cut it from aluminum, as I have access to a 4axis cnc machine?

[falconp1]

Hi Luan.

Ken at rand airport has recently help me with all my chromoly tubing. He also remanufactured all the stainless steel and aluminum brackets. If you supply him with all the damaged goods he will remanufacture new for you. He will also do the welding for you. The company is called Aircraft Rebuilders. 082....921.....0779.

Call Peter Magnus on 073……515…..6269 for your fabric repairs. If you don’t want to go to the effort of sourcing the metal bits yourself Pete can do that for you.

Just remember that your aircraft has been built using aircraft grade material . Don’t change it for anything else.

One of the reasons I fly a Challenger is that out of the more than 4500 sold there hasn't been one in-flight breakup reported.
This is very well build aircraft. We have one at Klip that has done 1167 hours. All student hours.

Johan at Bara will be able to tell you more about the clip wind mod as he owns one. He might be able to tell you if there is a difference in lift with or without the wing vortex gates. Contact him on 082....822....3179.

Hope this helps
Regards

[Luan]

Awesome, thanks will call all these people systematically. Here is an e-mail from Dave at the Challenger factory regarding the wing mod and flutter, I will however still call Johan and hear of his first hand experience.

"Luan,

It's okay to remove drooped tips and install standard tip bows but the drooped tips give almost the same lift but much faster roll rate.

Some older planes get elevator flutter at certain speeds. Installing elevator trim tabs with one up and one down seems to eliminate flutter at all speeds up to VNE.

Dave at the Challenger factory "

[johnythelaw]

Hi Luan en al die challenger manne

Ek praat maar afrikaans - ons Namibiers kan engels praat maar doen dit net uit self verdediging
My seun het ook n kortvlerk 503 en ons vlieg hom hier op Swakopmund.
Het dit in Saldanha gekoop , uitmekaar gehaal en weer hier aanmekaar gesit.
Die vliegtuig het slegs 45 uur van nuut en het ook lank gestaan maar ons vlieg hom nou gereeld.
By die kus vlieg ons hom vol brandstof 10 gallon = 40 liter en met ons twee op is nog 180 kg.
Kry so op cruise maklik 75 mph teen 5600 rpm . teen vol krag gelyk klim die spoed maklik na 85 tot 90 mph
wat sy VNE is so ons bly maar rondom 75 mph.
Wat ek gevind het is ook die buffet so teen ongeveer 80 mph maar sodra jy n myl of 2 per uur afhaal is dit weg.
Het ook nie enige trim tab nie.
Opstyg kan jy hom afterk teen 55 en klim teen 65 dan klim dit lekker.
Nadering vlieg ons op 65 en oor die draad af na 60 - dan rond jy hom uit so 2-3 m bo baan en maak die krag stadig toe.
Die aerie land hom regtig self en die hantering is regtig fantasties.
Ons het al n "fuel starvation" gehad en ek moes dit in die swakop rivier land. Dit op sigself was ook nie n groot skrik nie.
Die naderingshoek is net baie styl afdraand om die spoed op 60 te hou- uitrond en land sonder enige skade.
Ek vind net dat as die spoed afkom nader aan 50 mph dan word dinge ongemaklik - sy stall op 43 mph.
So die kort vlerk soek beslis spoed en as die enjin krag min is sal dit knater - Ek het self al gewonder wat sy sal doen
in die binneland op n redelik warm dag- Ek persoonlik dink die 503 is te lig in die broek. Daar is natuurlik geen vergelyking met my aviatika met 582
enjin in klim en opstyg nie en ek dink vir binneland het die chally tenminste 65 pk nodig vir 2 man.
Luan moenie moed opgee, maak hom rustig reg en as iemand vir n trike die 503 soek verkoop hom.
Kyk dan uit vir n 582 en glo my jy het n lekker glibberige aerie.
Hier by die kus vlieg die chally met vol vrag en klein enjin kringe om n gyro met 100 pk en baie ander microlights perform nie so goed soos
die challenger nie

groete
Johan de Wet
Swakopmund

[falconp1]

Hi Luan


'Quote'
The only thing I can think of that would cause an oscillation at that speed is that the elevator cables are to slack.
Check the tension before anything else. There must be no play at all. Do not over tension them as well. Just enough that all the play has been removed.

Bit of a brain fart. That happened to my Condor. As soon as I removed all play from the cables the problem was solved.
The Challenger has a pushrod and linage system.

I still think you should check for play on all the linkages and push rods first. The elevator hinges should also have minimal play.

Regards