Tequesta

I am about to start building a Sig King Kobra, and need some advice about the engine. Is it best to stay with a 2s rather than a 4s do to prop clearance? What size would be the best? Does anyone have advice on retracts (never dealt with them my self, this would be the first.) I am also contemplating making it a tail dragger. How far forward should I move the main gear.

Any help will be greatly appreciated.


John

gyrocptr

Could you explain what you mean by "2s" and "4s"?

gyrocptr

http://www.rcuniverse.com/forum/m_64...tm.htm#6496478

Here's a thread regarding the building of a King Kobra.

Tequesta

I am sorry 4 stroke, 2 stroke

John

R8893

My Feedback: (20)

John,
On a taildragger the main gear axles ought to be on a line 15 degrees forward of the CG (rule of thumb). This usually puts the axle at about the leading edge.

I have used Robart, Rhom, Century Jet and some cheap mechanical retracts. I would suggest the Robart based on price and reliability.

Chuck

Tequesta

I like the OS FS-91 II Surpass http://www3.towerhobbies.com/cgi-bin...?&I=LXSY82&P=0 or perhaps the Magnum XL-91 RFS http://www3.towerhobbies.com/cgi-bin...?&I=LXAN96&P=0 , for 50$ more why take the chance with the Magnum. OS has a great reputation. My third choice is the OS 75 AX, 2 oz heavier, but not as tall .8" shorter.

dhal22

any high performance .61 would be a good engine for this plane. i am using spring air retracts on my build. they are very high quality and their customer service is outstanding. in fact i am about to order another set from spring air. you can do a search here for king kobra's, there you will find my incomplete king kobra build and a couple of other excellent build threads.

david

bigedmustafa

My Feedback: (2)

I'd read that the King Kobra wasn't a good match for four strokes before selected the engine for mine. Some folks had reported that torque roll was an issue when a four stroke was used. Prop clearance would be another issue as the nose gear isn't particularly tall, either.

I ended up selecting a Super Tigre G-61 ringed 2-stroke for it because I wanted an "old school" engine design that I thought would match well with the airframe's classic characteristics. My King Kobra turned out nice and lightweight and the G-61 is a good match. If you really want to go fast, however, a 2-stroke .75 or .90 and a high pitched prop should do the trick.

Good luck and good shopping!

Tequesta

Ok
I am 86ing the 4 stroke. I can put the money saved to good use. Spring Air retracts. The new questions is 61 GMS, Magnum or OS. I have 2 magnum .15 and several OS .45 and under. all great engines. Absolutely no experience with GMC. If I spent the extra 100 bucks for the OS 75 would it be worth it. I know it's nice to have power if you need it. but the question is do you really need it. I am looking for a realistic plane with great flying characteristics and good vertical.

John

WMB

My Feedback: (1)

I have this one to build as well. I am thinking of the Magnum 90 2 stroke. Have heard this is a great engine. Also no weight penalty going from 60 up to 90 size.
For me, the only time it is too much power is when the added power comes with more weight. Lighter always flies better.
MikeB

dhal22

the king kobra would really benefit from a high performance 61. a gms is not a high performance 61, neither is a magnum for that matter. although the magnum 91 might be a good fit.

david

Tequesta

Now this is confusing, the Magnum and OS .91's are 2oz lighter then the OS .75, and only 1.2-.7 oz's more than the OS .61. I agree with Mike lighter is better. The heavy OS .75 is out. I'll save 70$ with the Magnum but gain an once or so over the .61. Not a bad trade. What do you think?

John

iflyg450

I had great results with a evolution .61

WMB

My Feedback: (1)

Tequesta, How is the build going? Have you deciced on an engine yet?? I see you are in the state of hanging chads, must be building season now. Hope all is well, MikeB

Tequesta

WMB,

I ordered a Tower .75 in May and I am still waiting. Although this is upsetting me, I was ask (ordered) by my wife to "remodel the bathroom before starting any airplane stuff". This project has turned out to be much bigger and more expensive than I was expecting. When the bathroom is done I will get started on the KK.

Summer is the best time of year here. The heat scares away the snow birds and the field is less congested.

John

XTOL

Im afraid you may be waiting a LONG time. I was wanting a
TH 75 for my King Kobra back LAST OCTOBER. They were
out of stock then.

They have begun to push the out of stock Super Tiger and GMS
engines back to August and the TH 75 is listed as September.
That makes it almost one full year for the TH 75s.

If you ever want to put your plane in the air my advice would be
to cancel the TH 75 and look at other options. By the looks of
things the TH 75 may never be available again.

Someone at Tower should step up and come clean with
the real story here and quit playing this stupid month by
month game.

Tequesta

I wont give them a year but until the bathroom is done I can wait. I heard the delay was due to the Olympics.

Who knows?

John

Beowolf

Hi Tequesta.

I did a fast check on both .61 and .91 engines made by Thunder Tiger and OS Max. It seems that for the money, the Thunder Tiger Pro .91 really fits the bill best. It's lighter and stronger than the Pro .61 and is cheaper than the OS .91 and has nearly the same perfomace. I guess it would depend on your budget. lol

I ran these two brands because you can find parts for them in any hobby shop! And both companies are reputed as having great customer support. If they don't have the parts in stock they can usualy get them in by the next day. And even better, most hobby shops have them in stock!


OS Max:
.61FX: Wieght: 19.4 oz Power: 1.90hp @ 16,000rpm Price: $179.99

.91FX: Weight: 19.3oz Power:2.80hp @ 15,000rpm Price: $229.98

Thunder Tiger:
Pro .61: Weight: 26.75oz Power: 1.85hp @ 16,000rpm Price: $109.95 to $129.99

Pro .91: Weight: 19.83oz Power: 2.75hp @ 15,000rpm Price: $189.95

I hope this helps you!