working spitfire exhaust & Ally backplates

[colin bassham]

I am upgrading from laser150 to a 50cc Turnigy petrol on my BT 1/5th scale MK8 Spitfire. In 1999 I read an article in model world about Herman Grobler making a working exhaust and having reread it I thought I would give it a try. (Its only taken me 13 years!) Ive Just been reading about spinner backplates in the 1/4 spitfire thread. This model had its laser ripped out at 100 feet by the spinner coming loose. After which I used a nyloc nut on the threaded rod which can be set just right inside the spinner and another outside tightens on to it this has worked up to now. But with a more powerful engine maybe not, I dont have the means to make a stronger backplate though. what if I screwed 6 pieces of 8mm sq ali x20mm long (at 45 degree intervalls) to the backplate each drilled & tapped (In the ends) to take 3mm dome head cap screws. If they are all made same size should balance out ok. (How do you check the balance ? )

[colin bassham]

I have seen a Biela 20x10 four blade Hamilton prop in black and yellow tips , would I be able to fly with it on this engine. It would look fantanstic , but could be too much for a 50cc petrol to cope with.......... any thoughts?

[stewart clifford]

Hi Colin

I think that size 4 blade prop will be too much for that engine, as for a spinner ask David Brown to make one, he does a great job.

[colin bassham]

Thanks Stewart, I agree about the prop, I will stick to two blade for flying and I am making up a four blade static prop at the moment for photos, I will put one on here when finished. I have made a start on the backplate bits , drilled & tapped, but if it doesn't work out I will contact Dave. I would guess with labour/materials they would need to be quite expensive.

[colin bassham]

[colin bassham]

fill & return valves, when the return nozzle is pulled out the vent line is open to the tank. I just fill till I see fuel returning to the field supply. Tried it yesterday it worked well, I also started the engine for the first time, no problems, incredible power. I ran it with the supplied exhaust and got 8600 RPM, then I fitted my scale exhaust and got up to 8400 RPM so well pleased I only lost 200RPM It sounded nicer with my exhaust on probably because it is divided up into 6 outlets
The home made spinner worked well no undue vibration and it stood up to my very large starter

[John Greenfield]

Colin

I have looked back through your thread but cannot see any mention of the actual prop you used for your test run. From the RPM you quote it is clearly not the 4 blade one you mention !!
Actually 8400 rpm is far to high and indicates that the prop you used is too small. Peak torque for the type of motor you are using is around 6000 to 6500 rpm and that is the sort of figure you should prop for static. The motor will unload a bit in flight so much more than 6500 on the ground will lead to the motor unloading to far in flight and with an effective loss in power.

Hope this helps.

John

[colin bassham]

John
Thankyou for your help. I was using a 20x6 (2 blade) as it was lying around. They recomend 20x8 or 10 and 22x8 or10 I have done some looking online and the nicest prop ive found is a 22x10 (2 blade) Biela semi scale black/yellow tips at 47 euros £38 This is from pp-rc. Modellbau in Germany. The nice thing on this site is they give the cc of the engine next to the props, and this prop is for 50cc. .....Colin

[John Greenfield]

Colin

A 20 x 6...that explains the very high RPM. A 22 x 10 is a much better size and personally I like Biela props and I have them on most of my models.

Biela props are sold in the UK by Dave Wilshire (Motors and Rotors) 01923 270405. He usually has a good stock of sizes.
Give him a call.

John

[Phil Clark]

I wouldn't pay any attention to what a prop looks like...............agreed, the yellow/black Beila's look nice, but having run them and switched to other types, my own experience says they aren't up to much (certinly no better than a Menz wood)

I used to run a Beila 20 x 10 on one of my ZG45........I was recommended the Engel 'Super Silence' brand and looking at their site, it's suggest you can increase the pitch a little due to the far more efficient blade shape. I fitted a 20 x 11 Engel Super Silence carbon prop and without touching any mixture settings, I gained 500 rpm on the top end over the Beila prop.........the performance increase in the air was very noticeable as was the drop in noise (Beila's are very noisy)

I have experienced similar performance increases using Mezjlik carbon props as well.

Compare either of these 2 to a Beila and the blades are MUCH slimmer in section but equally as stiff.

I have also recently helped a mate set up a pair of ZG62's in a large twin......originally on Menz 22 x 10's, we've fitted Engel 22 x 10's and have seen top end rpm increased of around 800 rpm.......

Phil

[Simon Willey]

Are those Engel props 3 blade ones Phil
I was looking for a prop for my 62 powered tug with a Tuned pipe on which is quieter in the air than a stock exhaust, now I am looking to reduce prop noise.

Si

[Phil Clark]

Hi Simon

No, these are 2 blade props and the mufflers are the standard ZG twin outlet black boxes........................he's after better performance rather than low noise output.

If you have a pipe on there already, then a 3 blade Engel will really quieten it down. I have a 22 x 10 on the 62 in my 190D with one of the kit built 80mm diameter Toni Clark canister type mufflers. Also a carb bend & intake trumpet drawing air from inside the fuz.........it's pretty quiet anyway, but flying downwind at full throttle I can barely hear it if there are other models in the air.....................

I've got a handful of 2 blade sizes in stock, but the only 3 bladers I have in I think are 19 x 10's for 45's.

Phil

[Simon Willey]

Thanks for the Reply Phil.

I will look for a 22x10 3 blade in the new year, sounds like that will help. This set up also has the carb bend ,and drawing air from the Fuz,so hopefully it will be nice a quite.

Thanks and have a happy Xmas.

Simon

[colin bassham]

Thanks for the input Phil. I have seen a Zoar carbon 22x10 for £49 on Kings Lynn Models do you know anything about these? What would an Engle cost and who sells them?

[John Greenfield]

Interesting thread and just goes to show what works for one person /model set up does not necessarily work on another. I have tried the Mezjlik and Engel props and whilst I agree the RPM's are higher I can't agree that the model pulls better. Probably ok in level flight but pull the nose up and the thin prop blades cant get hold of the air to keep pulling the model up.

I guess you pays your money and makes your choice.

Interesting point is that I do not sell props !!!"!!

Happy Christmas

John

[Phil Clark]

Thanks for the input Phil. I have seen a Zoar carbon 22x10 for £49 on Kings Lynn Models do you know anything about these? What would an Engle cost and who sells them?

Never used Zoar props so cannot comment.........

As mentioned above I (Fighteraces) carry a small quantity of Engel props.......not on the website though at the moment, so if I can be of assistance, just give me a call. Engel props are a comparable price (maybe a fraction more) to Zoar's

I don't make a point of blatantly plugging products I sell here......I was just commenting on various prop makes I'd tried and had the best success with.

As John says....each to their own and you spend your money & takes your chances.

In my experience, Beila are no better than Menz (apart from lasting longer being carbon not wood).......they do have a broader blade than an Engel or Mezjlik which keeps rpm's down.......in my experience, i've find performance bleeds off as soon as you stick the nose up with a Beila (engine loading up and can't keep pulling). With a higher initial rpm, they just seem to pull better. A lot of this will be airframe/engine combination related as well........one make of prop will suit one airframe/engine whereas another won't.

Phil

[colin bassham]

Shame I cant use this one!! I have a 20x12 wood prop (puntillio) I might give that a try to see what revs I get, befor I decide which carbon prop to get for flying. John does that 6500rpm apply to all petrol engines , because i have a rcgf 26 in my T240 and that is turning at over 7000........Merry Christmas. Ps I would love to see your big Tiger Moth fly would you be bringing it up north next year? I love my 1/4 scale Tiger.

[John Greenfield]

Colin

My comment about 6500 rpm was in relation to motors in the 40 to 150cc range. Much smaller than this and they need to turn faster so 7000 on your 26 is about right. Much bigger than 150cc and the max torque is at a lower RPM. Mt Tiger Moth motor at 380cc turns at 4200 max.

Happy Christmas whatever prop you decide upon.

John

[colin bassham]

http://youtu.be/C5mO-oP7nNg
Just put this on You tube, hope you like it, if you do please leave a comment. I fitted a small smoke system to highlight the working exhaust system. Just the smallest trickle of smoke oil gives a good effect it is switched on with a rotary switch which also controls the flow rate. When I turned it up it must have looked like my garage was on fire

[Cary Bailey]

Fantastic, well done! I've always wanted to see a true exhaust system.
Cary