Nobler ARF with TT GP .25

I’ve had a few flights on the Nobler ARF and overall I think I’m going to be happy. This is my first flapped craft and things are a bit different. I first flew with a .35 FP S RNV that I’d used in my first Ukey 35. I never could get the thing to run right in the Ukey (hot and fast or blubbering) and it was no different in the Nobler. Switched tanks around, changed props, etc. but just could not get happy with it.

Switched to a .40 LA RC RNV wired open. Gobs of power and way fast. Went all the way down to an APC 10-3 to tame it. Better consistent run that the .35 FP has ever had. Seemed like a lot of weight to carry around and would need another, bigger tank. I might like the extra power someday, but I’m just learning to get inverted and some inside maneuvers.

Next up, a tried and true TT GP .25 RC wired open with MAS Scimitar 10-5. I flew this engine all last summer on a foam wing profile and it was very consistent and thrifty on the fuel. I feel it should have the power to pull the ARF. I think the weight will be a little over 35 ounces with this engine, but I don’t have good scales, so who really knows.

Any thoughts on this combo? My only first flight worry is the CG is now a bit more that 2 ¾ back from the leading edge, at the fuselage. A search of the site showed lots of discussion about modern .25’s and their potential to fly this plane. I could not find any “Wow this worked great” threads. Any direct experience?

Best regards and thanks for you comments,

Clay

Ps Best thing about the ARF is no attachment to it. Fill and drill on the engine mounts to try new power trains, hack open the tail for plus and minus weight, packing tape to keep the canopy on, hammer in little ply wedges to keep the grass field LG from getting too wiggly etc. Worried about the control system? Cut it open, have a look, shore up if necessary, and tape that baby back up. Great learning tool for me. If ARF’s did get appearance points this one would be in the negative digits.

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Any thoughts on this combo? ....... A search of the site showed lots of discussion about modern .25’s and their potential to fly this plane. I could not find any “Wow this worked great” threads. Any direct experience?"

Clay, good luck, we are hoping you will give us this information!

Clay, the FP 2 and 25 are the same except for the bore. The timing on each is identical. To me the 25 is the better engine. Same weight (actually a little lighter) and 25% more power potential.

That said, the Tt GP 25 is identical inside to the FP 25. So, if the FP works (as a few have said it does) you should have no problems with the GP 25. If anything, fit it with a properly sized venturi/prop/muffler combination and have fun.

Note: The more restrictive the muffler, the less prop you will be able to turn or the larger the venturi you will need. The less restrictive the muffler, the more prop you will be able to turn, or the smaller the venturi you will need. (The venturi is a little like a carberator. If you need more power, open it up. If you need less power, close it down.) Speed is controlled by engine rpm and prop pitch. You don't need to go to a smaller engine if you are going too fast. You need to slow down the engine (sometimes put on a bigger prop) or go to a lesser pitch.

Stole the kitchen scales again. Best I can see I’m looking at 41 oz. RTF, my earlier estimate was optimistic to say the least. Searching the board reveals lot’s of opinions and comparisons between Foxes .35 (stock, stuffed, hemi’d, tooled, decked, whispered, etc.) and modern .20’s and .25’s (stock, uiniflowed, tounged, venturied, inboard tanked, boosted and not, etc.) and the weight/size of craft they will fly. Should be interesting to see how she goes. My only tests will be comfortable lap speed and line tension in simple maneuvers. If you return to this thread to glean information about thrust or tension in the squares etc. you will be disappointed. Again, I state the obvious.

Alan

I will report after this evening if the weather holds w/o T-storms and I can get out of work cleanly. I’m going to try the MAS Scimitar 10/5 first and maybe the APC 9/6. I also have a few others in a similar range but think one of these two will be close.

Len

Thanks for the reply. Maybe the idea of slowing down the .40 by going even larger in prop diameter, say up to 11” from the 10” I tried, would have helped. Ground clearance might have been a problem there, and sadly, I don’t happen to own anything larger than a 10”.

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Both of my TF Nobler ARF's have TT 25 Pros in them. I might be tempeted to put an Enya 25 SS in one of them to see how that one does. Incidentally if anyone uses an Enya 25 the Tongue muffler that Len sells for the TT25/36 fits perfectly.
Oh I think that I had reported that one of the club members did fly one with an OS20FP.
Dennis

Well, got out for an hour or so last night before dark. Hot and humid here in Music City, with the temp and the RH racing each other to stay at 90. Just enough wind to keep things cleared out. Using 15% Wildcat with 6oz castor added, so total oil is around 22% and nitro is headed towards 14%, I guess. 60 foot .015 lines. ARF provided “Viper” plastic tank on muffler pressure. Top half of a Scooby Doo toothbrush for a pilot. Hey, I got little kids. Talk about high zoot!

Started with the MAS Scimitar 10/5. Seemed like this was limiting the TT .25 GP’s ability to get the RPM where it wants/needs to be. Flew around level with moderate tension. Semi wingovers lugged out the engine (RPM drop) so I figured the prop was a bit big. I was also getting some fast/slow pulsing, probably from bubbles in the fuel line.

Switched to an APC 9/5. Much better needle control from 4 cycle to fat 2 and above with this prop. Noticed at lower RPM I was getting some vibration that was causing bubbles in the fuel line. Fiddled around the tubing, filter, and tank a bit and got things smoothed out, especially at a flat out 2 cycle. I figured out a while back to start flying this thing without the cowl on so I can see what’s going on inside.

Excellent ROG with plenty of power through the grass. Slight increase in RPM once underway. Good tension level, just falls off slightly at the peak of wingovers and BOL’s (Big Ol’ Loops). I have not put any weight in the wing tip (I think the original instructions called for 1 ounce) so that may help. Seems to fly level now, but I may try weight to improve tension a bit. Leans out for the last 2 or 3 laps and tension is excellent/high, but lap time seems fast for me. I would guestimate that I was about 5 sec/lap for most of the flight, and getting down below that once it went a bit lean. After a couple more flights I got happy with the needle setting and flew some more WO’s, BOL’s and Lazy 8’s. Biggest change seems to be CG and I had to be careful not to get things so tight that I would start losing flying speed. I mounted this engine a the very end of the rails, but the CG is still 1/4 to 1/2 back of where it should be according to Top Filte. Seemed to glide well so I don’t think I’m off by much. Engine temp stayed reasonable according to the smellometer and hot restarts were easy with the judicious use of the electric starter.

Bottom line for me is that this combo is going to work very well for my needs at this time. I have no doubt that this little power plant can haul the mail, at least to the address I am currently at. Wonder what a real flyer would think?

Follow up question:

I have a minor vertical fin/rudder repair to make. Should I remove the rudder offset while I'm at it? I seem to recall that this may/can improve overhead line tension.

Thanks,

If there is any significant offset there, I would. The only problem is, with a fixed leadout position it is hard to trim without shifting the cg.