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Corsair Black Devil Power Problems


terry999
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Hi all, I am new to the Paramotor Forum so please forgive me if my problem has been discussed before, ( I am sure this is not a new problem).

I fly a Dudek Reaction TST with a Fly Kompress (black devl engine). I have recently had problems getting full power with my max revs being 6500 rpm. I have changed the reduction belt and bearings after a prop strike but I'm still having problems getting full power.

On several occaions when my engine is cold it will reach 7600 rpm but after a few mins when I am ready to fly my power is reduced to 6200 - 6500 rpm. I have flown today reaching 6500 rpm but when getting back home and the engine is cold again its going to 7100 rpm. I have tried altering the belt tension.

Has anyone got any suggestions as this engine has only done 50 hrs.

:dive: Terry.

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Hi Terry,

Hmmmmmmm, lack of revs when hot? likely that the coil is breaking down....

Also tried changing the plug or Cap?

I cant understand when hot that the prop is restricting the amount of revs your engine can produce, however if someone can explain that to me that'll be great.

just my 2p worth.

Woody

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The smart Money is to try and ask, very Nicely if Pete B when next at lambourn can take a look at it for you.

My thoughts are that your engine has been tuned whilst cold.

it needs to be tuned whilst hot as that is how it will fly.

it is common for revs to be higher on a cold machine, lower when the same unit is warm.

The fact that the revs change between hot and cold should discount the prop as the problem

Cold air in a cold engine runs leaner, than the same settings when warm.

If I had to guess its worth checking if the top end is too rich, Pete may well say this is Baldwindash

Pete is to tuning what Christine Keeler is to high class hooking :D

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Terry, these guys above are just speculating... go to the Black Devil group and find yourself surrounded by many people who have had exactly the same problem. The Black Devil is renowned for suffering a power loss at around the 50 hour mark and then becomes unable to retain the power to swing the prop it was originally supplied with. This problem is further exacerbated by one current dealer in the UK and one former large scale supplier in the US who constantly recommended props that are now widely understood to be overpitched for this exceedingly pitch sensitive motor. Ask yourself why so many of these motors are flown with ground adjustable propellers. The problem is usually even worse when people break a prop and then try to source aftermarket ones.

Did your prop strike require any repairs to be made to the prop? Can you tell us the manufacturer, diameter and pitch of the prop as well please.

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Terry

I tend to think that Fanman is correct on this matter.

I have a Black Devil and after a ground strike I replaced the prop and it runs up to nearly 8000rpm on the ground but 6700/6800 when flying!

The significance is that I have a variable pitch prop and I am having to test fly (when I can) to try and get the pitch correct.

I would appreciate any help on what pitch to try next, I am at 14.5 degrees at the moment!

Eddie

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Hi Eddie,

Have you tried flying for a 5 minutes or more landing keeping the engine hot and seeing what the revs are on the ground again, to see if the are 8000 or 6500.

when you hold the machine on the ground at full revs keep it there for 40 seconds, kill it with the throttle pinned and check the plug.

At least you can confirm that the engine is running correctly.

cheers Simon

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Hi Simon

When the weather allows I will be at the field to sort this out. I don't believe there is anything wrong with the motor and the only change has been to replace the prop so tend to think that Fanman has a good point!

I can only find out by test flying so I hope to sort this problem out when I get back in the air.

Hope to see you at the field soon and we can try a few things.

See you soon

Eddie

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Hi Terry,

I`m watching this post very carefully :D

As same same issue with my motor :shock:

I have noticed that if I let the motor idle for a few Min's and then nail the throttle, I have full power again for a while before the revs start to drop off again.

Out of interest what plug are you using? I have a NGK BR9ES currently filling the hole, which is possibly a little cold.

The US corsair site recommended Spark plug types: NGK B8ES (for normal or hot climate) and NGK B7ES for cold climate, might just make a difference :?: .

Colin B

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Terry, I am now trying to pick info out of your last post. Are you saying you now having problems since running a replacement prop supplied by Paul Kilburn having destroyed your original prop? As requested earlier, please give us info as to the make and model of props giving the original performance and now the make and model of prop that you are having trouble with.

Just to give you a heads up, I am currently helping someone else resolve prop issues who was originally running a Helix but then broke it and replaced it with one from the same source you mention. He is showing the same problems (different motor though) so we removed the replacement prop and carefully measured it. The stats we found were not consistent with any prop manufactured for aviation use so bearing in mind the factory in Thailand that 'copies' props for dispatch to the UK are actually furniture manufacturers we are wondering if it was copied from an ornamental prop designed purely for hanging on a wall with a clock mounted in the center! Many people try to cut costs when replacing props but it is too much of an important part to do this. You wouldn't drive your car at full pelt down the motorway in 3rd gear but this is often what people are doing when trying to fly with the wrong pitch prop.

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Hi Fanman, my original prop was from Airways where I bought my motor and this was factory fitted by Fly Products. This was destroyed after around 1 year and a replacement purchased from Paul Kilburn. This was a 122cm Power prop which seemed to work fine with no power problems. Three weeks ago I had set up for a foreward launch, I revved up to provide some air movement, stepped back one step ready to run but somehow one line was drawn into the prop pulling most of the left hand lines into and around my prop. Thankfully I was only at tickover but it still threw my back onto the floor, destroying my prop and most of the left hand lines were wound around the reduction wheel causing a slight tear in the belt and lines cut and damaged.

I have had my wing repaired at The Loft, replaced the belt, which seemed to be very tight and overtensioned. I purchased a replacement prop, the same type as before, 122cm power. I fitted this and flew in Wales but had next to no thrust gaining only 400ft above groundat full revs. I then purchased a tiny tach to enable me to accurately measure the revs, 5900rpm at this stage.

I then changed the reduction bearings and tested the revs reaching 7500rpm at cold, I thought my problems had ended. I flew the next day but the power was down when the engine was warm reaching 6500 max in flight. I have cleaned and changed my carb gaskets again with no effect. I tried the engine with no prop ( I know this should not be done but I needed to know if the engine would rev freely) 11500 rpm reached immediately. The engine was tuned when warm and the plug is coffee colour.

Yesterday I tried the same type prop but 115cn and it reached 7500rpm.

I have sent the prop back to Paul along with my original Fly prop which has one edge damaged for him to check and compare the pitch.

If I have left any info you need please let me know and thanks for your help in this matter.

Terry

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Terry, thanks for taking the time to write all that, it really helps with diagnosis. You're right, you shouldn't have taken it up to full revs with no prop on it! With no forced air cooling system (fan and shroud) the BD is totally dependent on the air drawn by the prop for cooling. It also needs the prop for its flywheel effect (especially important for the pull start version). The BD was originally designed to run at much higher than its current max 7500rpm so hopefully everything should be fine. There are some guys that deliberately run fine pitch to obtain over 8000rpm regularly.

The best way to get the right belt tension is to warm the engine (and belt) up by running it. Then switch off and put a torque wrench (preferably the old type with the bar indicator) on the nut that holds the small pulley on and turn the prop by hand. if the tension is correct the warm belt will slip at somewhere between 15-18 foot lbs. More than this and the belt is too tight which will damage the bearings, less than this and the belt will 'chirrup', slip and wear quickly.

The annoying thing about this pitch issue is that it will send you looking at every other component of your machine before realising that it was the prop all along. Ask DanTheMan, he went through exactly the same issues with his HE R120 last winter until we convinced him it was prop related (his prop was 6 inches overpitched!). My personal recommendation would be to bite the bullet and go to Fly Products and get another original Kompress prop or failing that go to a guy called Mike Hay in the States who knows BD props inside out (he makes beautiful wooden ones) or GSC for either their fixed pitch or ground adjustable. Avoid the Woodcomp sold by the UK BD agents as you will have the same problem you are having now. PK is a nice guy but almost every problem prop I have come accross has originated from this source.

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The annoying thing about this pitch issue is that it will send you looking at every other component of your machine before realising that it was the prop all along. Ask DanTheMan, he went through exactly the same issues with his HE R120 last winter until we convinced him it was prop related (his prop was 6 inches overpitched!).

Aye I remember that very well. PK's props are nice though, I think I had the wrong one delivered (P11/P12 mix up) hence the overpitch issue and by the time I got a genuine H&E Aerobat prop and got my repaired one back I did not need PK's prop so sent it back and did not ask him for the correct prop - so I can't offer a true comparison.

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I have exactly the same problem, but mine was with the standard prop on the av8er black devil. I have rebuilt the engine and replaced every single bearing, seal and carb gasket etc.

If you have had the belt too tight just once you would have cooked the bearings in the reduction pulley.

I now run C4' instead of C3 bearings in the reduction pulley. Feel the belt tension and temperature of the belt when warmed up correctly and see how warm it is?

Louis

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How many hours has your motor done and what are the details of your prop (manufacturer, diameter and pitch)?

As mentioned earlier in this thread a lot of dealers send out the machines with props that are right at the top end of what the motor can sustain which allows it to keep its reputation for being a powerful motor however a few hours into its life and it struggles to be able to continue swinging this pitch so after a few minutes of running it gets bogged down. But "hey, it's still the original prop" so it can't be that that's wrong, so then starts the process of rebuilding the carburettor, the ignition system, the redrive, the crankcase seals, etc, etc until someone who has been there before tells you that you've just lost the last seasons flying chasing an apparantly unresolvable problem because of something you swore couldn't possibly be wrong because it is original!

When this motor is on song it is a really good motor. The trouble is it takes a bit of understanding and pooling of knowledge to keep it there.

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My motor has done 65 hours. They recommend you change the redrive bearings at 60 hours which is when mine went.

I changed my prop off Paul Kilburn lately and mine works fine with that on full throttle.

Mine was defitnaly the redrive bearings and belt tension.

When mine was loosing power the drive belt and pulley were red hot that you couldn't touvh it.

Do a search on yahoo groups for black devil ppg and the forum on there is really useful. It has Alex Varr, the guy who designed the motor.

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  • 2 weeks later...

My new original Fly prop arrived yesterday and was fitted today. Unfortunately there is no change to the revvs :evil: which was a great dissapointment. I took the head off and de-coked it today but still no change. As soon as the weather picks up I will see if the power is any better in flight.

I am now running out of ideas to solve the power problem.

:explode:

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Hi all, latest update. I have taken my motor to Airways Airsports today to let them look at it. After a short time we decided to try one of their props. Hoorah!!!! 7900rpm, the prop from USA (supposedly an original Ply Products prop has an incorrect pitch). I nave now bought a 3rd prop, sent the one back to the USA, which will cost me £90 in postage and taxes and am hoping to get a refund from PK for the first prop off him. This is one big lesson learnt.

Hopefully the weather will pick up and I'll be in the sky soon.

Thanks for all the help and most people were correct with their diagnosis that the prop was the problem.

Safe landings,

Terry :acro:

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Making assumptions on the span of your prop based on your cage diameter I would imagine that 13.5 to 14 degrees when using a GSC pitch guage. IIRC the GSC pitch guage doesn't sit at 75% span as the same guage is used whatever the prop diameter it is measuring and relies on sliding on until the profile of the tool matches the profile of the prop. GSC adjustables on a BD in a 1400 cage probably need about 1 degree less. These figures are an approximate starter for ten from which you can then fine tune to suit your particular motor. Hope that helps.

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