AK Models Su-27 with push/pull configuration
 

Hello all

This is a re-post, as I had already posted this question in the jet forum, and people out there are strangely quiet about this question. So here I go again.
I'm interested in the big AK Models Su-27, but I can't shell out the big $$$ for a Jett .90 LX... So, my plan is to use a push-pull configuration with one engine in the nose, and another in the tail. These would be .50/.55 class engines. My question is the following one : would it be doable with minor mods ? And would be say two webras 55 equivalent to a jett .90 ?
Any help appreciated :)

http://home.clara.net/acf/scale/scal...essna320-4.jpg

RE: AK Models Su-27 with push/pull configuration
 

I'll take a stab....I'm looking at my AK-27 "half built" plane right now and I think it would really take away the looks to add a prop to the back. Even if you tried to put the motor midway (like the Balsa USA enforcer), it would take away the strength of the body because the wing area is not that large.

I too feel like the Jett engine is a bit much and if you are willing to sacrifice a little power you might want to look at the Evolution 1.00NX or the OS .91.

It sounds like a great project though.

RE: AK Models Su-27 with push/pull configuration
 

No offense, but I think you are wasting your time with that endeavour. CG issues alone would turn that great flying plane into a dog.
Build it as is, put a OS.91 with a Jett pipe on it and enjoy the ride. Read through the build thread on here and heed the tips for a successful build.

Spar

RE: AK Models Su-27 with push/pull configuration
 

OK Spar, do you have any picture of the internals of your Su-27 ? I would like to see how radio gear is installed.. thx !

RE: AK Models Su-27 with push/pull configuration
 

The tail is full of radio gear not much extra room.

RE: AK Models Su-27 with push/pull configuration
 

That's exactly my point. I thought it was like the Cermark F16 where the tail is also full of rc gear. SO, I conclude this is a nose heavy design, thus spreading engine weight at the front and at the rear end could be a way to have good balance, and therefore radio gear could be moved forward. The banck engine would be heavier than rc gear anyway...

RE: AK Models Su-27 with push/pull configuration
 

To get a perspective of the radio installation, 1) downlolad and review the build manual from AK Models, and 2) review the pics from the build thread from other pilots, the one in this Forum.
My build thread can be viewed here: [link=http://www.lobstercove.ca/cgi-bin/yabb/YaBB.cgi?num=1150245080]http://www.lobstercove.ca/cgi-bin/yabb/YaBB.cgi?num=1150245080[/link]

Spar

RE: AK Models Su-27 with push/pull configuration
 

thx [sm=thumbup.gif]

Oh and by any chance do you have any video of yours flying ? It would be very nice to see how it performs compared to the real Jett one...

RE: AK Models Su-27 with push/pull configuration
 

I dont think this whole thing is a matter of will it work because just about anything can be done if you really want to do it but I think it would be more work than it is worth. If you can't afford a Jett then I think the recommendation to get an OS91 or a supertiger with a Jett muffler is about the best way to go. I have personnely never used either engine so I cant give much advice on what would be better but there have been many posts from guys using the ST 90 with very good success on prop jets and it doesn't get any cheaper than that. The flanker is a time consuming build it is not hard just labor intensive so all the mods you would have to do would increase the build time substantially.

RE: AK Models Su-27 with push/pull configuration
 

Yeah the os91 seems more and more like the way to go. There are quite other .90 brands out there.

http://www.der-schweighofer.at/web/p...495&prodID=885
http://www.der-schweighofer.at/web/p...265&prodID=253
http://www.der-schweighofer.at/web/p...10&prodID=1232
http://www.der-schweighofer.at/web/p...303&prodID=252

Is the OS the most powerful ?

RE: AK Models Su-27 with push/pull configuration
 

Well I have just checked the latest OS 120 AX. Same mounting pattern as the 91FX, roughly same weight, but bigger head. Nearly same price ( twice cheaper than a jett 90) .Do YOU think it could be faster with it ?
I am afraid this is design for low rev due to overbored engine and smaller transfer ports. What do you think ? Revver or not ?

RE: AK Models Su-27 with push/pull configuration
 

OK that was right, the 120AX is not at all apropriate. I have a NIB 91vrdf. Would it be better than the Jett 90LX ? Bob ?

RE: AK Models Su-27 with push/pull configuration
 

If you can get the ducted fan engine in there..... go for it. The design is not very compatible with a rear exhaust engine, and might take a bit of work to incorporate a rear intake engine. But with some modeling skill, anything is possible :)

Just out of curiosity... how cost effective are the Weston engines for you? The W-75 and W-90 are real nice powerplants, and I think both are suppied with the weston tuned exhaust system. Defiantely something to consider
http://www.westonuk.co.uk/index_021.htm

Other than that.... the OS91FX and jett-stream combo works very well. Few have been disappointed [&:]

And my guess is the ASP 91x engine might also be a nice surprise on a tuned muffler - but might need a little TLC with the carb.

Bob

RE: AK Models Su-27 with push/pull configuration
 

Thank you Bob for your input [sm=thumbup.gif]
Actually I did not even know that weston was selling big beasts. Talking about price, the BSE Jett .90LX (including VAT) is 20% cheaper than the Jett weston 91 [X(]. I would favor Jett's durability & user feedback, even if I haven't heard any negative durability feedback for these weston beasts (though I have, for the .50).
Dollar is weak these days. The difference between the OS91 + Jett muffler is actually not that big... I'll have to think about it seriously :)
What is the performance difference on this Jett90LX between 0% nitro and 15 % (btw is it the recommended nitro percentage ?) ?
Thx

PS : What is TLC ??

RE: AK Models Su-27 with push/pull configuration
 

that stuff women desire, tender love and care.

kc

RE: AK Models Su-27 with push/pull configuration
 

Yes, I looked up the price conversion chart in Yahoo just for info on the Weston engines - The US dollar is terrible right now.

The 90LX will run fine on zero nitro if you choose. It can run on any fuel you wish. The key is, you will lose a few rpm. With an 11x8 or 11x7.5 you will be fine. Figure you will see a 700-800 rpm drop on the ground.

The engines are specified with 15% fuel, mainly because that is what we run for the racing engines, and we use that fuel in just about everything (except my OS160.... it definately liked 5%).

There are quite a few Jett engines over in Europe running zero and 5% fuel . If possible, try for at least 5% if you can. Helps the idle a bit.

If you know it will only see zero-low nitro, Dub can snug the head down a few mils.

Bob

RE: AK Models Su-27 with push/pull configuration
 

KC, thanks for the tip :D, as a non native english speaker, it is not always that easy lol


Bob, thank you for your answer. OK I think I would go for 5% then, I don't want any high idle [&:]. Have to check my purse now [:@]. The kit price is very low right now too ... so tempting !

RE: AK Models Su-27 with push/pull configuration
 

Sparhwak, is it me or did you use a fancy scheme for your Su-27 ? It appears to me that this scheme belongs to the Mig-29 OVT ... The scheme used by Russian Su-27 demo team is not like this one actually.

RE: AK Models Su-27 with push/pull configuration
 

Yes, it is the Mig-29 OVT scheme. I scaled it exactly from the Mig to the Flanker, and the result can be seen in the other long thread on the AKM Flanker.

Spar