stuntflyr

Is there a huge benefit to using a 91 four stroke compared to a 61 2 stroke for the World Models Intruder ARF? I have either one. Just bought one to base in FL for southern contests, need to know what you experienced guys think.
Thanks,
Chris...

dhal22

watched a very good pilot fly an OS .91 powered Intruder around at our field once. plenty of power, even at low rpms, add in a smooth pilot and we all watched him fly. it was almost enough to make me run out and buy the combo.

John Hancock

I fly an Intruder with a Magnum .91 and like it. Don't think I have ever seen a .61 in one. May be bad tail heavy with the lighter motor.

stuntflyr

Thanks guys.
I watched Austin Wingo fly his 91 powered Intruder at Chicago and it was pretty impressive, think I'll go that direction.
Chris...

BERUSTY

My Feedback: (3)

Engine choice for the Intruder...

Chris,

I flew my Intruder with the OS .61 FX and the stock muffler. The APC was the best prop based on a half a dozen different props Dave Guerin and I tried. The model was adequately powered to fly but did not have a vry impressive vertical. I did not have a tail heavy situation and actually added 1 ounce of lead stick-on to the tail.

I added a Mac's pipe and well...much better! The airplane came to life and could do really big stuff like my Calypso and the Blue Angel.

The .90 has a very different power curve and is easier to fly than the narrow band offered by a piped .60/.61. Photo is of young master Wingo landing.

Rusty Dose
Team Futaba

stuntflyr

Thanks Rusty.
Point well taken. It's a big model, I was a little surprised when I saw it first hand, so I can see where it would respond as you've indicated with the 61. If I hit a SPA contest I've gotta' be legal too, so the 91 for me. I have three new Magnum 91's (The sale prices are too much for me), no problem on the source.
Chris...

crankpin

My Feedback: (15)

Chris - You coming to FL ? Which area ?

Vince

stuntflyr

Hi Vince,
My parents live in Punta Gorda and Dad is into R/C sport flying. He has a nice shop at the house and he and his buddy even built me a nice high winger to fly there. It'd be neat to be able to hit a contest or two from there through the year. Maybe not this year, but we can plan!
Chris...

NM2K

My Feedback: (14)

The true answer to the question is: It depends upon the engine likes/dislikes of the judges judging you on any given day.


Ed Cregger

crankpin

My Feedback: (15)

[quote]ORIGINAL: NM2K

The true answer to the question is: It depends upon the engine likes/dislikes of the judges judging you on any given day.

Hey ............ Ed, could you please clarify that statement ?

Crank

stuntflyr

Hi Ed and Vince,
I promised myself I'm not going to do this event as a "do or die" thing; fun only. Every judged event has controversy. I've done CLPA so am well versed, not interested in that conversation.
Chris...

NM2K

My Feedback: (14)

I can't blame you for keeping your SPA competition in proper perspective. If you don't have fun, how enjoyable could winning be anyway?

I wonder how much the WM Intruder 90 ARF weighs, and how closely it follows the original Kirkland Intruder's dimensions, when compared to one of Kirkland's contest models? What say ye that the ARF is a pound or two heavier and possibly larger? Try to pull that around with an engine even slightly more powerful than the engine(s) Kirkland used and you might just wish that you had a .91 four-stroke burning 30% nitro fuel. (smile)

I have a Magnum .91, a Thunder Tiger .91 and a Saito .91, all NIB, to try in my WM Intruder 90 (latest edition). By using an Edson Universal Adjustable Engine Mount, as sold by RJL/MECOA these days, I'll be able to switch around the .91 four-strokes and see how they compare with each other. In fact, using that engine mount, I could very well begin the testing with a good two-stroke engine and then proceed to using the four-strokes.

I'd rather talk pattern strategy any day (these days) than actually try to compete in pattern. Ah, time for my afternoon nap!


Ed Cregger

dhal22

ed, i think a lot of us talk more than we compete. i mean that in a good way, it's not sarcasm. it's almost 9 pm, time for bed.

stuntflyr

Hi Ed,
We all "talk" on the internet about what we would like to do, I know. I have great intentions and get about 1/2 of them done.

I know the ARF WM Intruder is longer, bigger, heavier, the wing is higher, etc than the old '70 Nats model, but it's available, legal and mine now. I just asked the question because I wanted to have the best available set-up for a good chance at reasonable success flying the model past Novice. I have to actually get it flying, too. I have to be able to do it in 5 to 7 days total. Hence; the ARF.
I have plenty of both types of engines, I'm just short on time and contests. We don't have any here in the West, so a turn-key, easy model is what I need for a remote location contest model. (At my parents house. They're old, don't tolerate me for too long. See a pattern here?) Most contests in the SE are SPA and the said ARF is legal, so it's a muffled .61 or an OS or Magnum, etc, .91 4 stroke.

I'll make some other model my "Classic Pattern Scale Ship". I saw just such a model at the AMA Convention in Ontario, CA last January. It was a Bridi Kaos with a Clarence Lee K&B .61 with one of those cool, old flow-through mufflers, a Rev-Up prop, Veco spinner, Kraft wheels, a Sig canopy, Williams Bros pilot and it was in clear dope and silk with colored trim and autographed under the clear by Joe Bridi and Clarence Lee. That was cool, but I didn't have a camera unfortunately.

Hope you get yours flying and post some info about the comparison between the engines. Sounds like a great idea.

Chris...

skybolt58

Hi, I see this is a pretty old thread, but I have a Intruder 90. I have a OS .61 VF. just wondering what size prop I should use?

Thanks for any info...

Roguedog

11 x 7 APC should get you in the high 13,000's

If you use a tuned pipe easily in the 14,000 range with that prop.

With a tuned pipe you can also go with 12-8 and tune the pipe length so that it lowers the RPM down to the 11 -12,000 range as if it were a long stroke 61.

Your choice.

Here's an article from Don Lowes RCM Magazine column were he discusses tests he did comparing a 61FSR (61VF has same specs) vs a long stroke OS 61 SF.

The OS 90 carb he is talking about in the article is the 7D carb with the larger diameter insert. You could chose three different throttle bore sizes on the 7D carb. There where 2 brass inserts that could be installed in the carb's rotor.

The large insert 8.5mm bore was designed for the 61FSR engine so that you would get enough vacuum to draw fuel with out a punp or pressure system installed.

The smaller insert 9.5mm and the no insert 10.5mm options were to get better top end out of the engine but required pump to get the engine to idle as the larger bore didn't provide enough vacuum draw for fuel at ldle. By the time Don Lowes article appeared in RCM mag OS had introduced the 90 FSR which include the 7D carb but with minis the brass insert. See the last 2 pics of the 7D/7DV card manual for the specifics of the carb inserts.