Jump to content

Funfighter belly landing - prop breakage!


Recommended Posts

Your expertise, if you please...

 

Back in the day, I flew lots of 'fling and flop' models. There's something about a 25 screaming at full chat near your right ear that focusses the mind! I must have flown hundreds of flights with hand launched IC models.

 

The standard set up was to set the prop at 'quarter to 3' when the motor is at compression. That way, you can cut the motor just as you commit, and the propeller blades are nicely out of the way. I hardly ever broke propellers.

 

So fast forward, I have a recently completed Cambrian spitfire with an electric set up. Flies great, if a tiny bit porky. 

 

The problem is, I'm getting through a propeller every other flight! I've stopped landing it on our mown strip and am landing in the crops, which is better, but still breaks a prop every 3 or 4 flights. The landings are not particularly heavy, by the way. Certainly not hard enough to expect breakage. I think the issue is just luck; if the first contact is when the blade is pointing straight down, it snaps.

 

Any ideas? Can the motor be reliably braked at a known position? Is there a nice flexible 10x6 out there? How about a folding prop? Does one exist with a 57mm spinner?

 

Thank you all

 

Graham

Link to comment
Share on other sites

I had the same problem with my Skynetic Havok and changed to a folding prop in the end, but you have to check the folding props for max revs tolerance. I know that Gliders UK and Hyperflight list 55mm spinners for folding props not too sure about larger ones though.

Link to comment
Share on other sites

OK, I have ordered an Aeronaut yoke and some 10x6 blades. My motor is a bit, er, committed to duty so I can't use collets. I reckon that I should be able to use the yokes with a more conventional spinner on my prop adapter. May need a bit of fettling, but worth a go. It will soon pay for itself the rate I'm getting through standard props!

Link to comment
Share on other sites

Maybe I'm just lucky but my prop-break ratio is much better than one every four flights, even with APC-E props - I do try to belly land a little tail down, which might help. There is still the occasional prop break. If it's really becoming a problem if you can get hold of the bright orange bendy JPerkins props they are literally indestructible. That's what I have fitted to my Balsacraft Bearcat. Thinking further I only recall breaking a single prop on my Parkzone foamies and that was in a proper crash, never on a normal belly landing, so their props are pretty flexible too.

Link to comment
Share on other sites

Thanks for your comments everyone; much appreciated.

 

A few points;

The spitfire is a little heavy and as such has a fairly fast approach. The stall is also reasonably 'abrupt' and drops a wing, so I don't want to try to slow it too much. That said, the landings would not have caused me any undue concern had they been onto wheels. They were hardly 'slam downs', just slightly fast. Dropping the tail may help, but at some point the prop still has to touch. 

 

As it is a spitfire, the whole point was to evoke the appearance and feel of a spitfire. It has some degree of detailing and looks great in the air. I can't say I'm overly happy about a folding prop, but it's possibly better than other options such as those bright bendy propellers, or skids (I had considered such a thing already Andy).

 

I may have just been very unlucky and might not break another prop all season. As I said, if the prop touches first when it is directly down, it will not tend to 'flatten' around the prop axis, but will bend, and likely snap. It's possible that this has been the case.

 

I have a 4250 motor in a 46" biplane I built and when I cut the throttle on that, the prop stops like an IC engine. I can't find out any settings in the ESC that cause that though! In any case, I have no control of the position of the prop when it stops so short of lots of little throttle blips in the last 1ft of flight, that won't help!

 

I've got more props now, and a folder on order; I shall report back...

 

Graham

 

Spit 120421.JPG

  • Like 1
Link to comment
Share on other sites

H,i I had a FF ME 109 that would break the odd prop or rip the motor off the fire wall depending on its mood.

 

How about a smaller diameter prop? might need to go up on the pitch so not ideal but reduces the chance of catching the tip

 

I tried a folder, not as efficient and effective....if it does not hit anything when it folds back....don't forget if you chop the throttle in flight it will fold back, but has to be able to unfold without removing the cowl/exhaust stacks! so not an option on the wife's Ripmax Spit (hand launch).

 

On the ESC/motor front you can set up a brake to stop the prop, down side is it does it in any point in 360 degrees, I have some motors that have very strong magnets and the prop will stop at almost any speed if the throttle is cut and I have some that windmill in a breeze.

 

The really clever guys with fully programable TX's and electronic skills could I dare say make something that monitors the prop position using an encoder and attempt to stop/hold the prop in the 3 and 9 clock position when landing. but its a lot of effort if you ask me!

 

My money is on smaller diameter prop, possibly an IC version or springy pop material.

 

Good luck with whatever and please keep us posted...you are not alone with this problem

 

Link to comment
Share on other sites

Thanks Chris, that's a great answer.

 

I'd forgotten about the exhaust stacks and the likely folding prop restart. Doh. That may be an issue. Fine if I stop it just once... Mind you, that's what I used to do with IC. You can't go around again with a dead engine!

 

So, maybe I set up throttle cut and set my minimum speed to be a slow tickover? That way a stall turn or similar won't cause restart issues, and I can hit the cut when I commit to the last foot of flight?

 

I do have some smaller higher pitch props I can try. I'll do some power tests over the weekend and see if 9x7 or 8 or even 8x8 will work.

 

Club day on Sunday so I'll let you know how many paint stirrers I end up with!

 

Graham

Link to comment
Share on other sites

Here's a though that I've had on this issue. Not sure whether there's anything in it but it's worth considering.

 

I've noticed that some electric motors with no power applied feel very smooth when turned by hand. Others feel very "notchy" as though the rotor is being held between each magnet in the stator. I'm wondering whether this makes a difference to the ability of the motor / prop to "windmill" as it's gliding. Maybe windmilling allows the prop to be thrown to one side when it contacts the grass? Conversely, the "notchy" motor may resist the prop being thrown to one side leaving with nowhere to go but into the bin?

Link to comment
Share on other sites

  This idea may be getting a bit silly but hey ho. On some motor gliders with a fold away power pod on the top of the fuzz when power is taken off a pin pops out from the works to stop the prop in the vertical position so the unit can fold into the fuselage. I think some full size do the same.

Link to comment
Share on other sites

Graham, if you can get a Top flite 10x6 prop they are ideal they are flexy plastic I used the same prop over a period of 10 yr on 4 different models first with a 600 brushed motor then with an Axi 2820/10 then with a MVVS similar to the Axi . 3 were hand launch warbirds the 4th a Miles Magister with fixed u/c it finally broke when  the Seafury went in from a great height nose first.

Link to comment
Share on other sites

Back to original post.
So how expensive are multi buys of efficient (electric) props at this size. I’ve always got the impression of cheap as chips.

Alternative, balance carefully, fit a IC prop. 
But an electric motor is not as tough as a glow motor.
Something is always going to break if it hits the ground. 
Long grass looks good. 
 

ps, lovely looking model


 

Edited by Don Fry
Link to comment
Share on other sites

3 hours ago, Graham Davies 3 said:

JD8, not a daft idea at all. It wouldn't take too much to mix a channel to zero throttle with a delay and raise a pin into the prop path. The tricky bit would be making it robust enough...

Or indeed, not break the prop. A suggestion, the stuff used in a hot glue gun might work. Lot of work mind.

Link to comment
Share on other sites

Further update:

 

3 flights yesterday and no breakages! 10x6 as supplied by HK, and very little wind to assist slowing the bu66er down. All three were flat and into the crops.

 

A nice 10x6 folding prop arrived from Gliders UK. I didn't use it yesterday as a power check revealed that it loads the ESC considerably more to the point where it was a risk. It certainly provides some welly, and may be a solution. I will either need to buy a beefier ESC, or some smaller or shallower blades. Having not used one before I was unsure how it would work without stops to prevent the blades pulling forward. This doesn't seem to be an issue as the naturally swing to the widest arc and still provide huge forward thrust. The blades are quite stiff in the hub, so I don't think it's an issue that they will collapse against the fus if the motor is stopped in flight, but I may put some stops in place to limit this. As it stands, tightening the blade screws so they grip quite tightly will be ideal as it will still allow th eblades to be pushed back on landing.

 

Graham

Link to comment
Share on other sites

Yes Chris, I am a bit concerned about this. However, even with the nuts as tight as I can do them with my fingers (which is not particularly tight!), I don't think the blades will fully fold on wind pressure alone, if at all. The grip of the blades is really  quite high. However, as soon as you touch the throttle they seem to pop open nicely. If I go with them, I may just make a disc to fit behind the hub and prevent the blades folding fully flat.

 

As you say though, I may just carry on and only revisit this if I run out of standard props!

Link to comment
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.
Note: Your post will require moderator approval before it will be visible.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

 Share

×
×
  • Create New...