You have to big of a prop with a 12x8 LOL try the 12.5x3.75 wide prop but is a heavy prop. also to hover a plane or do 3D stuff the plane needs to be light and have a light wing loading. get rid of that 14 ouncs tank for starters.
Do you have a big exit hole for the air to leave the cowl? i also bet that since you are over proped you are trying to get every bit of rpm out of the engine and it goes lean during your hover and loses power.
also if havent yet remove the baffle in the muffler.

try a 12x4 or 13x4 prop also.

for most planes in this size range a four stroke engine is best.

I will weigh the airplane and report. Dont have a weighing scale myself, I will need to borrow someone's.

When I was flying inverted, I had to give a touch oof elevator to hold level. But it was no so much that I noticed while flying, it was more of a bit of reflex, if at all. I know because I was rolling, bunting, split-S-ing etc from inverted.

With regards to the weight of the airplane with the 91, it will gain 100 odd grams in the nose 5.68 oz (161g) in the nose. Moving the battery back was making the airplane tail heavy with the 55ax but it should help with the 91. I am also considering lightweight faom wheels (2 3/4" Dubros) and a CF wing tube to replace the aluminium one if I can find it in the require dia 15mm x 47.5mm size

Using a #8 plug, already tried a Ftype, there is a lot of preignition at WOT

Airraptor,

you have covered all the bases

I put in the 14oz fuel tank to resolve the engine issues earlier. Now with a 91 I will need the additional capacity

With a 13x4, the engine sound was much harsher than a 13x6. Some at the field remarked that it may be over-revving and the soft compression may have confirmed that. After my final flight with a 12x6 when I was cleaning up, I noticed a lot of black residue on the ground and on the tail of the airplane, if that is some indicator. Though I didnt get it again when I was finishing of the fuel at home

I am not running it lean, I set the needle with someone holding the thing vertical. Looked for max rpm, then turned it back quarter turn or so towards rich side.

Ameyam

What's your current setup? Servos, Rx pack size, etc. I'm asking because you're talking about cutting weight, and several have given tips that will help. You will not need a 14 oz tank for a .91 4-stroke. I put the .82 Saito that was in my Reactor in a Yak 55 profile, and it has a 6oz tank. I still get 8 minute flights! Less fuel weight, less tank weight with a smaller tank. The Reactor was designed for mini servos: I used Hitec 225MG's, though they've fallen into disfavor with me, as several have died on me. I just bought two Spektrum A5040 mini digitals and put them in my Reactor Bipe. Flew it two times yesterday; I like them better for their accuracy: my 225's had different travel/endpoints, even after setting the mix and endpoints on my Futaba 10C. They didn't seem to "travel together" accurately; the Spektrums eliminated that problem. I also used a micro servo on the throttle of my Reactor and also in my Yak55. If you're using full size servos, changing out the servos as I've recommended will save a minimum of 5oz, more than a carbon tube. While on that subject, I believe a carbon tube is available from Graphtech...

55AX, original tank was 10oz (240cc, not stock), Futaba 3010 servos all round except throttle (3004 for that), 6008HS RX with both evevators and ailerons on different channels. I tried botha 5c Hobbico battery and then a 2c LiFe Battery to reduce weight on the weekend. GP nylon spinner with aluminium backplate I think 2.75" dia.

That tank was put in to eliminate tank issuse earlier. I started this thread coz the engine wouldnt remain running and I was getting blcak oil in the exhaust. After tightening the head bolts, it now keeps running, even when the compression goes soft. Due to the reincorcement, I doubt the stock tank will go in. I have to either put this one in or a 240cc 10oz one. Lets see

I had ordered 225MGs for my Reactor. But we chickened out when one of then jammed even before we had put the model together. Thats when we put the 3010s in. Though I have burned-in the servos and they are now more reliable, I dont want to replace the servos. Not only because my model is already drilled for the servos but also, the larger engine will need more torque and relaibility (I should have asked Tower to replace the one 225 that failed, considering what else they have replaced subsequently). I am holding back the 225MGs for my Reactor Bipe. They are the only minis I have

I need to source the CF tube locally, getting from abroad is just too expensive. What I wanted to know was the characteristics of the material. If it shatters or cracks easily when loaded, I am better off with the aluminium one

I am currently using GP 2.75" rubber wheels but have 2.75" foam wheels from Dubro in stock and they are much lighter. I also wanted to know whether I should put the foam ones in.

I have spent so much time getting the setup right on this airplane without much joy, sometimes I feel I should give up on it and open up my Phoenix Extra 330 60" with the 120ax reserved for it

Ameyam

Well, I did weigh it. The scale I am using isint very accurate (it doesent have markings between 2 & 3 kgs) but the weight minus fuel and prop is 2.6-2.8 kgs which is 5.7-5.9 lb. So I guess it a bit heavier than stock.

I am posting pics of my repair (it has the effect of birch beams or I beams under the LG. Yes, I am a mechanical engineer). I am proceeding with taking off the engine though. Havent installed the wing bolts when taking this pic

Ameyam

A .46AX may not be enough for a 6lb plane to hover it as you want.

4-5lbs is OK, but that extra pound makes all the difference.

Well, I took out the FS91SII from the donor (sad time. That engine made that airplane so happy, especially after I had the time with the 75ax) and was somehow able to open up the muffler. I couldnt get the nut on the extension to rotate, however, it will take more trained hands than mine. I also took the 55ax aoff the Reactor.

Big cricket match tomorrow, no one will want to help put the airplane together. I will take her to the mentor's workshop on Thurday evening and finish the setup on Friday. Then Sunday is test flight day

One doubt- the original FRP mount (GP's adjustable mount) weighs only 120gms. Whereas the one I am considering (Dubro's 75-1.08 2c antivibe aluminium beam mount) weighs 195grm and the actual one that should be used (80-91 4c antivibe aluminium beam mount) weighs 215 gms. I am still not sure whether I should use the 2c one or get a 50-75 one and use it. In either case, it will be a (161+125) 286 gms gain in nose weight. That is why I was pushing for a weight reduction elsewhere

Ameyam

I don't think there's anything wrong with using the nylon mounts like the Great Planes or Dave Brown ones for 4-strokes. I also have a Kyosho Flip with a Saito 100 and a Dave Brown nylon mount; it is plenty sturdy. I would not use the anti-vibe mounts precisely because of the weight gain. As mentioned by myself and others, to fly 3D as you seem to be wanting to do, you can't necessarily built for durability or toughness. You are looking for as light a wing loading as you can get. If you use full size servos, over-size tank, heavier engine mount, etc, it all adds up, and you are thus fighting a losing battle of bigger engine to hover, heavier servos, heavier mount, etc, and end up on the heavy end of the scale. It will be a fine sport/pattern flying plane, but not a 3D one...

It certainly seems you have tried everything without success. Conclusion: engine worn out. My Reactor is one of my favorites and hovers great. Howsever, I have a Saito 82 in it and it's a perfect fit.

The GRP mount I have is a GP 40-70 mount. Can it take the 91? I think I will take both mounts to my mentor's workshop and we will see then & there if the GRP one is OK. If so, I will use it

Another question would be, should I open up the 72A, will that engine be able to pull 5.8-5.9lb into a hover with pullout to spare?

Ameyam

At the weight your at (almost 6lb), I think the .91 would be the better choice. Another club member here had a Showtime 50 with a similar OS91, and it flew quite nicely on that...

Gave my Reactor for fitting the 91 yesterday. Wanted to do it myself under my mentor's guidance but they were more interested in the cricket yesterday

Ameyam

You've got to got to got to go large diameter and low pitch for 3d'in. Your trying to hover in 5th gear instead of 1st gear. Higher pitch doesn't not have the throttle response needed to control the plane in the hover.

Well, turns out the 91 is too long to install the cowl. That leaves me with the 72A and the 75ax. Either way, looks like sunday flying seems difficult[][][]

Anyway, do you thing the 72A will have sufficient muscle to hover the 5.8lb airplane?

Ameyam