I have a GP Reactor 46 with a OS FS55AX engine flying a 13x6 prop. Last week I tried (to correct engine problems I had) witha a 12x8 prop. It was good but couldnt hold the hover.

This week with a 13x6 prop the airplane hovers for a second and then drops the nose even on application of power and full elevator. I am already at the full 3D throws. I dont apply full throttle, just about 80% in the hover. I figure that the engine should have some left to pullout if I get into trouble. Another issue is that in high-alpha nearing the hover, the airplane seems to have a lot of wing rock.

When I checked the CG, the thing is just a bit tail heavy at the recommended CG. Problem is even with a CG machine, it drops the tail if the tail is lower and the nose if the nose is lower at the recommended CG, so I guess I am somewhere close to recommended. I have a larger than stock 320cc (14oz) Sullivian flexitank in the airplane, most of the time when I hover, I have a good amount of fuel (I usually land with 1/8 tank of fuel after a 10 minute flight), so in that configuration it should be nose-heavy.

I tried a 13x4 prop also, the engine overheats and there is really no airspeed in that prop.

Please suggest what I should do in this case?

Ameyam

ameyam,

Are you new to 3D are is it just this plane? Are you sure you have your engine tuned properly and you have enough power to hover your plane? I'm running a Saito .82 with an APC 14X4W prop and it does fine. Try using more than 80% of power while your hovering. How much expo are you running?

I am not new to 3D, I have been 3ding a Twist for a couple of years now. Engine issues on the twist earlier and even ths Reactor has prevented me from trying the other 3D moves, mainly hovering, flat spin and high alpha is what I do. Harriers were possible on my Twist but not on this Reactor.

My engine is tuned ok. Initially I did it and when in my second flight I heard the engine struggling in mid air, I had one of the experienced members tune it. Set it 1/8 turn back from max RPM with the nose held vertical.

Thats the point I am asking. Everyone had recommended that 81 size 4c is the right engine for this airplane. But 4c engines are not too popular at my field and 75ax is too big so my mentor suggested a 55ax. What I do want to know is whether the 55ax is powerful enough for this airplane. At that time the 61FX was not available and it is too heavy for its power. Now the 65ax is available and I am told its quite strong. The 81A is just too expensive. After haveing the LG break of recently in a hard landing, I reinforced everything, so it has gained a bit of weight from stock, may be 150-200 grams or so.


None, I am ok with the response curve being straight

Ameyam

I would try a larger dia prop with less pitch. It sounds like you need to get more prop wash over the tail. I am a little concerened about your fuel as well. What are you using and how old is it? What I mean by fuel age is how long ago did you open the bottle and when in storage is it 100% sealed so no air can get to it.

I have worked through all those variables. Remember, I said I had engine problems? I did check just about everything to get them resolved.

I dont think I should put a 14x4 on this engine. Witha 13x4 I noticed that after running for sometime, the compression gets very soft as the engine overheats (compression comes back when engine cools for a few seconds). A 14x4 is likely to make it worse

The fuel I am using is klotz100 based with 10% nitro and 20% lube in the mix. Its only a couple of weeks old and the main can has been mostly sealed. I carry around a litre of fuel, thats all I need for one day's flying

Ameyam

A prop does not provide cooling. Airflow during flight and fuel is what provides the cooling. When swithching to a prop that will rev a bit higher, you need to needle the engine accordingly.

Done that. Also, I am flying without cowl

Ameyam

Ok, had 4 flights on the Reactor yesterday and 2 today. In all of them I had only one goal- to make the thing hover. Started with a 13x4 which I could hear was over-revving and gave me the soft compression problem again when hot though it didnt cut. Then used a 13x6 which was much better but still couldnt hover. Today, I tried a 12x6. Also Last week I already tried out a 12x8. In the hover, even at 100% throttle and full rudder and elevator throws, the plane could hover for a second or so before falling nose down. It fell nose down everytime, did not slide backward or left or right. Today I even got a buddy to make sure I was at full throws and full throtthe when that happened and he confirmed it. And it happened with every prop

I have already checked the CG and its ok if not a bit tail heavy. I flew today with a much lighter 1300mah LiFe battery under the tank to make it tail heavy.

That settles it. The 55ax with whatever prop doesnt have the power to 3D the Reactor, atleast not with my reinforcements. It just lacks the last 10% of power. So while I resolved the engine issue with a 12x8, the engine just doesnt have enough grunt, even with 10% nitro. It is great for pattern flying but not for 3D

I am contemplaing which engine to put in

1) FS91SII- I have this engine in good condition on another airplane. Rather than keeping it unused, I would like to use it on the Reactor. Total weight is 24.2oz (686g) with muffler and that is comparable to a 65ax and is lighter by 2.26oz or 64g than the 75ax. This would be the economic way to go

2) 75AX- had issues on another airplane but those may be due to tank height problems. Has a lot of power by is heavier

3)65AX- has only marginally more power than the 55ax. Is a bit heavier too. I dont have this engine though

Please Suggest

Ameyam

ameyam, what kind of rpm reading are you getting, 13x4 prop should not be puilling to many rpms. What is AUW of your plane?

My thoughts, definitely before considering a new engine:

The .55AX should be more than enough power for the .46 Reactor. The .55 was designed to fit in .46 planes to give them more power. As others have mentioned, 2-strokes need more throttle (rpm) to hover a plane than 4-strokes with their increased throttle response and torque.
-I think 13x5 would give good vertical performance on that engine in that plane. I have a 12x8 in mine for aerobatics.
-I did notice in the GP video they are flying the 4-stroke .70, but the .55 should give you more power, just with more RPM.

I would try more nitro (15-20%) and less oil (18%).
-2% more oil means 2% less fuel.

I wonder if the problem lies in the engine tune. Hovering is probably the hardest thing on an engine - high power, no air flow, and demanding fuel vertically against gravity.
-Check the tuning of the idle valve; most people seem to try to attack tuning with only the HSN, but it is a 2-part system. You're getting hot and lacking power, sounds like fuel draw is an issue in vertical attitude.
-Run the engine on the ground. Advance to full power, drop to idle, and watch your RPM. They should stay constant for a good 20 seconds. If you see a gain in RPM, your idle valve is lean. If you see a decrease, your idle valve is rich. Adjusting one means you have to go and check the other; it is an iterative process.
-Check your fuel system for leaks. Close off the vent, disconnect the engine, and pressurize it over night (by mouth). Or if you want to do a more thorough check, pull the system from the plane, pressurize it, and dunk it in water to check for bubbles.

Check the balance of the plane in the air, not on the stand. The stand gets you close, all adjustments to be made by flying. Fly straight and level at 3/4 throttle, pull to 45 degrees, roll inverted and let off elevator. What happens? If you are concerned mostly with 3D, the plane should continue straight, or even gain a touch of altitude. "Neutral" will have a very slight decrease in altitude.
-Don't forget that balancing on the machine is without fuel, and if you're flying 10 min and landing with fuel in reserve, that's a bunch of extra weight in the nose.

Hope this helps. Good luck!

Though it was designed for a 46 engine, that would only give sufficient power for sports flying. The FS72A wont be any better, it would give the power of a 46 size 2C (2/3 SIZE)

I noticed with the 12x8 that aerobatics were quite good and the engine was running well. With a 13x4, the engine did not have compression after running a few minutes. It did not have the airspeed for any pattern flying either. When I landed I found that the engine could turn over without any perceptible compression. After it had cooled a bit compression was back. This happened repeatedly even with the 12x6. I presume engine is overheating. I have the engine tuned ok, half turn rich from max rpm. I didnt however tach or check the temperature


It it overheats at 10%, it will have more problems at 15-20. I dont want to put that much nitro in it anyway



My LSN is a bit rich but not by much, may be by 1/8th or 1/16th turn. In any case, I dont think that will affect the hover. If I need to put in 100% power just to hover, where is the spare for pullout?


Already done that


Didnt do the in air test. I did balance without fuel. I dont think the reserve fuel is that critical to balance In any case, that reserve was for when I start getting more comfortable with the setup, I had two timers one set for 10 and the other for 12 minutes. So if I do a lot of hovering, I will fly for 10 and if I do more pattern, I will fly for 12mins.

Some weeks back, I had a hard landing after the engine quit in flight and broke the LG. When I repaired, I added more ply and tristock everywhere. I also added 1" wide birch wood to the LG Block so that it would take harder landings. Consequently, the airplane has become slightly heavier. Note that I do have a FS72A. I just dont want to open it as if it doesnt have sufficient power either (which is likely), I will have another unused engine. I have already run in the 91 and it would be better to keep it operating instead of idle

Ameyam

You keep saying the engine is "overrevving" with a 13x4 prop.Then you want to switch to a smaller prop??
Put a 14x4 prop on it!! If that don't work try a 15x3!

Just a minute, KB9STD. I put in a lower size prop with a higher pitch. I went from 13x4 to 12x8 to 12x6. I had similar problems with the 12x6 and 13x4 but the engine was quite happy with 12x8. However, I couldnt 3D that prop

Ameyam

RICHEN it up off of the high RPM the AX likes a little rich mixture .Get a good stream of smoke and it will be a happyer eng. Use 15% for more power.

I think he is leaning out and has weak fuel..
if not the OS` 91 should give the punch and torque he is looking for

Here's the plane hovering just fine on an OS .70 four stroke:
http://video1.hobbico.com/gallery/gp...021-deluxe.mpg

All this stuff you're talking about with the engine sounds like you're missing something with the tuning and setup (temperature, compression, lack of power). I don't think the problem is the plane or motor.

Go to the RCU Ratings page:
http://www.rcuniverse.com/product_gu...fm?kit_id=4630

Everyone else is happy with the 55AX. Some people are using a smaller prop (12.5x5 or something like that).

So what changed?? The work on the landing gear? Is it balanced different? Different throws? Change radio settings?

My persistance in hovering, thats what changed. At the time I wrote that, I was not much used to the airplane so I would hover only for a few seconds and the 55AX was able to hover that time. I still does hover for a few seconds, but when I persist, it stalls out. Further, I landed hard and broke my LG sometime back. When I reinforced it, I added additional ply above the LG Block and 10mmx25mm birch wood below the LG in two rows along the fuse width with the 25mm pointing towards the LG. I also added a lot of ply and tristock along the side walls of the fue to make it stiffer so that it could take harder landings.

It worked- in the week after the repair I had a deadstick and with no where to go and no air speed and pointing downwind, I landed in area with a lot of rubble. It threw up so much dust, the others thought I had totalled it. But there was no damage whatsoever, just a very dusty airplane. A slower landing in the same gravel broke the MUCH stronged LG Block on my colleague's Phoenix Yak 60" (with a 120ax, so it was heavier, it stalled at head height with no engine)

Probably I have added some weight or may be I am having engine problems. Engine problems cant be diagnosed on the net, my mentor and some other members at my club seem to have given up. So I am better of installing an engine that I know works well instead of extending the 2 month long trial-&-error session. Will replace the piston and liner in that engine later

I have the following lightening plans to help reduce the weight and hence wing loading.

1) Since the 91 4c is a big engine, I will be using Dubro antivive beam mounts to lessen the wear on the airframe. I will be using the 50-75 2c variety as that is the lighter (and I have it at hand). I wont use the GP adjustable mount unless you guys suggest otherwise.
2) The LiFe battery will go into the tail to balance the airplane.
3) I will also be putting in 2 3/4" foam wheels from Dubro
4) I am considering replacing the stock aluminium 15mm dia wing tube with a CF tube if I can find it.

There is little more in the airplane to lighten

Ameyam

As I've pointed out repeatedly.... means the engine is lacking sufficient cooling airflow...

Remove the cowl, then try the same thing again with the wider prop... even try the 13x6 prop too.

As said, this engine is more than enough for that plane.... so something is very wrong with the setup.

Opjose,

the only thing I didnt try is 14x4. Otherwise 12x6, 12x8, 13x4, 13x6- tried them all. I accept the 55ax is good enough for this airplane- for pattern. With a 12x8 the airplane flew with authority. I did all the pattern moves I am familiar with and very well. Evn with the 12x6 (on Sunday) and 13x6 (on saturday), when I had concluded it couldnt 3d, I had the confidence to demonstrate the rest of the flying at high throws (triple rates were set in my TX) to some aerobatic beginners. In fact I was confident enough to fly upside down, do the slow roll, knife-edge- usually moves I dont even contemplate on my airplanes on a Saturday when I am lacking practice. But it couldnt hover, harrier, flat spin, waterfall etc even at 3D throws.

Like you said, there is something wrong with the 3D setup... or this specific engine doesnt have the power for 3D

Ameyam

Perhaps it will help if I post pics of my airplane. It is now sitting on my loft without the prop. As you can see, I have already opened up the cowl all I can.

Now please dont say that irrespective of how open it is, it required more cooling. Remember, I have tried it out without the cowl.

Ameyam

Great now we can see what you've done.

Some would argue that there is not a cooling hole, but there is enough of a cutout over the head that you should not be having problems.

So it's back to what is causing all of the heat issues...?


What is the ready to fly weight of the plane?

You may have posted it before... but if you would please post it again.

What are you using for a glow plug??

Weigh the plane and let us know. My Reactor originally had an older OS50FSR with a Mac's tuned pipe. It weighed approx 5lb 10 oz with that setup. Best prop was a 12x4 Xoar, but even then, it wouldn't hold a hover for long. From all accounts, the 55AX is a fair bit stronger.

I switched to a Saito 82 with a 14x4W and had plenty of power for hover. All up weight was almost identicial, as I lost the weight of the tuned pipe setup. If your plane is over 6lbs, you're asking too much of the 55AX. A 4 stroke .91 would be good; you're going to have to juggle setup (battery location, etc) to keep if from being too nose heavy.

As far as your CG is concerned.... you're probably nose heavy. The only TRUE indication of nose/tail heavy I have found is to fly the plane inverted, hands off - in my experience. The plane should be able to fly level, or VERY near it without losing altitude when upside down at normal cruising speed. The CG tools have only gotten me in the ballpark so it isnt a disaster at takeoff.

Once I started flying 3D, no matter how perfectly I might have set everything up, the true tests and adjustments come after flying.