582 in a KB2

[dabkb2]

I have a 582 with a B box that I want to put into a standard KB2 frame. I have all the parts, but I need to know what prop to go with. 52" is all the frame will hold. Has anyone done this before. Do I want a 3 blade or a 4 blade? any info would be great.
__________________

 

[All_In]

Hi Dave are you changing the mac out or is this another gyro?
Waiting to learn the answer to your questions too?

PS:
We like pictures Dave.

 

[scottessex]

Try a 4 blade IVO, or a 4 blade warpdrive.

 

[Brent_Brown]

I made longer plates for the head and push rods to fit a 60" prop. Not hard and worked fine would do again if I had a KB2. In the end I had a 72" mast FYI just like the KB3.

 

[Doug Riley]

This is precisely the process that started us down the road to the PPO nightmare in the early 80's. The redrive Rotaxes just beg for props that are 60" or more in diameter. When you take a KB-2 frame and add a 60" prop, you have to jack the engine up six inches, creating a 6" HTL.

Of course, that's essentially what a KB-3 is: a KB-2 with raised engine and longer mast. The KB-3 is a PPO-prone deathtrap in its stock form.

Raise the seat to a "drop keel" setup if you're going to switch to a 60" prop. Then measure your CG location to make sure you have CLT, as the stock KB-2 has.

 

[dabkb2]

I already have a KB3, but I like the way a KB2 handles better, so I was thinking of putting my 582 into a standard KB2. I know that putting a 52" prop will be less power than a 60", but I think it will still be stronger than a 72 Mac.

I'm thinking a Warp drive prop will flex less than an Ivo, but do I want less flex? I could put more pitch and get more bottom end thrust, or is my thinking off here?

Here is a video of me flying my KB3 http://www.youtube.com/watch?v=JBVhq5udUm4

 

[Doug Riley]

Dave, if you keep the prop that short and mount the engine with the plugs up and the redrive down, you probably won't have a CG/thrustline problem. It would pay to measure the CG height when you're done, though.

OTOH, you may find that you need so much pitch (to load the engine) that the gyro is really sluggish at low airspeeds. What can happen is that the high pitch (maybe 16 degrees) results in a partly-stalled prop blade until the gyro is moving. The prop may un-stall at 30 or it may un-stall at 60; if the latter, you'll have a machine that's a doggy climber but seems to have a turbo kick in when you hammer it and go flat out. In extreme cases, the engine can't get itself over some mid-range RPM value (some number below the RPM where the tuned pipe kicks in) unless the gyro is moving briskly. Such a gyro may not even get off the ground.

The folks who've tried short props on 582's may be able to give you specifics. I had a gyro with excess prop pitch years ago (though it wasn't a 582) and that is certainly the way it behaved. It wouldn't climb worth a damn but it was frisky over 70 mph. Others have reported similar experiences with Rotax 912's having short props and big pitch.

 

[Friendly]

This is precisely the process that started us down the road to the PPO nightmare in the early 80's. The redrive Rotaxes just beg for props that are 60" or more in diameter. When you take a KB-2 frame and add a 60" prop, you have to jack the engine up six inches, creating a 6" HTL.

Of course, that's essentially what a KB-3 is: a KB-2 with raised engine and longer mast. The KB-3 is a PPO-prone deathtrap in its stock form.

Raise the seat to a "drop keel" setup if you're going to switch to a 60" prop. Then measure your CG location to make sure you have CLT, as the stock KB-2 has.

Dave, this is easier than you might think. Just change the cluster plates and braces. cut the keel in 1/2 for upper and lower keel. add some pulley guides for the rudder cables and extend the nose wheel. You don't have to drill new holes in the keel or mast.
Here is my conversion with Ernies Tail.
http://www.youtube.com/watch?v=3N6KKDGnfaY

 

[dabkb2]

Dave, this is easier than you might think. Just change the cluster plates and braces. cut the keel in 1/2 for upper and lower keel. add some pulley guides for the rudder cables and extend the nose wheel. You don't have to drill new holes in the keel or mast.
Here is my conversion with Ernies Tail.
http://www.youtube.com/watch?v=3N6KKDGnfaY

Can you swing a 68" prop with that conversion?

 

[bpearson]

It'll fly OK with 52" prop but will need 2.24 box not 2.58 to spin it fast.

 

[dabkb2]

Doug- it sounds like a short prop might not be the answer.

My KB3 flys well but the taller mast makes it slower in responding to stick inputs than I am used to in my KB2. I like the quick hard turns. It might be the horizontal stab that is slowing it down also, ether way it doesn't fly as sharp as a KB2.

I guess the trade off for more reliability is worth it, and after all it is still a blast to fly.

 

[dabkb2]

bpearson- how will it act at slower speeds? It sounds like you have a good idea, have you every tried it?

 

[Friendly]

David, I can swing a 62 with no problem. If I switch to a 68 then, I would have to move the seat as Doug mentioned in order to keep it CLT. that would mean drilling more holes in the mast. This conversion keeps the same hole pattern as as KB 2 or 3. Guys gyro has a higher arch in the rudder down tubes than mine. He can run a 64 in prop if he chooses, but he is currently running a 60in Ivo. His has a taller mast than mine. I have flown both and I like the smaller mast for ground stability.* He is running a 503. There are videos of it on you tube under my other videos. It is sorta Green & Black in Color. Mine is not quite as agile as the Bensen with the 72 but, I will give up some performance for the ease of starting and the comfort of leaving the pattern for an hour and half flight.

 

[scottessex]

Tim chick just put a 503 with 2.0 gearbox on his KB2 with a short prop, he would be the one to ask.

 

[Timchick]

Dave,
Try it first with a 52" prop and 2:1 gears. My 52" Warp Drive prop is pitched at 8* and I'm getting 500-600 fpm climb rate on a 90*+ day. I don't have much experience with Rotax engines and the different props so I can't really say which prop would work best. I wonder what a 2 blade Tennessee prop with a wider cord than the 3 blade WD would do. Sure you can get more thrust with a 60" + prop but you lose some of the benefits of the short KB-2. I can roll my gyro into my garage like it is now. If I went to a taller mast I couldn't do that.

 

[bpearson]

bpearson- how will it act at slower speeds? It sounds like you have a good idea, have you every tried it?

Yes. Me and dozens of others. It won't set your world on fire but like Doug said, the problems started when people just bolted big props onto Bensons without any other mods.

We have been flying Benson clones with 532/582's and 52" props over here for years (replacing VW) without problems. Tests show the T/L a bit more than 2" high but not much and a seat tank would probably sort it out.

We found you need to spin it fast though so the box ratio needs altering.

Heres mine. Don't laugh, they don't let us do a lot over here and this dates back to the sixties! If I wanted to use a big prop and was allowed to fly it I'd do it right and build a Dominator.

 

[All_In]

Laugh, are you kidding? You are flying a gyro, man! How cool is that!!!

 

[dabkb2]

bpearson- sounds good, I noticed you have a 3 blade prop, is that beter than a 4 blade? I think you gyro is great.

 

[dabkb2]

Thanks for all the good ideas, I guess all I need know is a 52" prop.

 

[bpearson]

We almost all use three blade Dave. I've now got a W/Drive (expensive Arplast started to crack) and although I havent flown it yet with that prop on due to paperwork issues my inspector says it seems to go fine.