Didn't have enough clearance between the top of the carb and the cowling wall for a true velocity stack. Decided to make a "hat" out of foam air filter material from Briggs & Stratton. Made this a three sided hat, with the open face toward the prop. This foam hat captures the bits of fuel that spit back from the carb, yet still gives me good air intake flow.

This has solved the problem of getting raw fuel sprayed down the side of the fuselage.

Thanks for the idea. Didn't use the idea exactly as you stated, but it was enough to get me think of alternatives.

Making slow progress - no time. Ran a 24x10 2-blade and got almost 6K rpm. Dropped a 22x8 and bumped the rpm up to 7K. The thing really screams now. Need to get a different instrument so that I can measure the static thrust better - my arms aren't that well calibrated, but I can really tell there's a big difference in pulling power.

Would like to try a 23x10 and a 23x8, by modifying 24 inch props down to 23. However, I think I've got the one I'll start flying with in the 22x8.

Just using TopFlight wood props - cheaper to test with. Very noisy at the 7K rpm range - I think its mostly due to the higher engine RPM, cold temps and lack of any foliage to dampen the sound. The prop tip speed is higher, but the difference between the 24x10 and 22x8 is only 30 mph - not enough, I don't think, to account for the drastic change in noise volume. Did not notice this much difference between the 3-blade prop and the 24x10. The 22x8 is just louder at all RPM levels.

Just have to balance it and figure out a way to keep the sliding canopy closed and its ready for flight. No way to get anymore weight out of the tail now, so I'm stuck with adding to the nose. Have pushed everything forward that I can move. With the short nose on this bird, the penalty is awful.

Thanks for your suggestions.

Hi Dale,

I just got one of the same kits you did. The Byron Original Hellcat. Same engine too I think. So you may be getting questions from me from time to time. Hope you dont mind! I will probably start working on mine in a few weeks. Do you have the Robart retract system in yours?


Chuck

Hi Chuck,

No, I don't mind if you ask a few questions. I've gotten alot of good advice before and after building my kit. The latest has come from a question regarding balancing the plane. Got some good ideas, and some recommendations about elevator and flap control rods/linkages. If you search RCUniverse for "Hellcat" and "balance," you should find it.

Yes, I have the Robart retracts. I disassembled my set so that I could swing the scissor links so that they are now pointing forward, rather than backward - this is how the original Hellcat was setup. I've also used wheel collets on the airlines as restrictor valves to control the flow rates, both up and down. Do you have a question or problem with yours?

I've not flown mine, yet. I'm working on a means to keep my sliding canopy closed, then I must balance it.

While doing this, I'm working a lot of OT, raising two kids, and working on home improvements - so I'm a bit slow on this one. Built a new fuse for a Super Chipmunk this Fall/Winter - so this is what I'll be flying first.

Feel free to contact me. I check my home email only about 1/week, so please be patient - I will reply.

Dale

Hello Chuck

Checking to see how your Hellcat is coming.

Busted a torque link on my Robart retracts last weekend during taxi tests at our grass field. Could have been caused by one, two or a combination of the two things: A high speed taxi turn on rough ground; a loose torque link mount, which allowed the right main wheel rotate a bit around the strut axis.

Make sure your torque link mounts are tight, and watch the speed of your turns when on rough ground.

If you're finished, I would like to know what RPM you're getting out of your engine and your prop specs. Also, the aircraft's weight is of interest to me. My engine is getting 5000 rpm on a Top Flite 24x10 (a bit shy of the 6K target given in the manual for this prop), and my all up weight, minus fuel is 30 lbs, giving me a wing loading of 56 oz/sqfoot.

I've still not flown it - its heavier than spec and the engine is peforming under spec - not a good combination. Though during taxi tests with 20% flaps, it did seem to want to fly at half throttle, but even at half throttle it was moving a lot faster than I'm comfortable with - one has to land the plane too, not just take off and the stall speed is quite a bit higher than my other planse.

I'm actually considering the option of building new outer wing panels (a one pound/panel savings, possible), a new stab/elevator (4-8 oz savings, possible) - which together might allow me to pull 2 lbs of balance weight out of the nose. 4.5 lbs of savings is significant and I'd be much more comfortable flying this plane then, even with the under performing engine.

I think I can really get the savings by moving from foam core, glassed/painted panels to built-up (ribbed) panels minus the glass.

Dale

Its been awhile, but I'm now trying to answer the last questions about my Hellcat before attempting to fly it. Hoped you might be able to answer these questions or point me to someone that can help.

My Precision Eagle 4.2 with a 24x10 is running at only 5000 rpm - Have had some experienced people look at it, but no ideas as to why its running this slow - spec indicates it should be running at or above 6000 rpm. Using a Top Flite prop now - may try a Zinger - perhaps there's a significant difference between brands.

Have checked to make sure muffler is not restricted, throttle linkages/plates are all moving to full extent, etc. Adjusting the mixtures either direction lowers the max rpm.

Running a 22x10 Top Flite produces about 7000 rpm, and the static thrust is noticiably higher, though I've not measured it. Maybe the specs are wrong and the engine is over propped with a 24x10?

Also, weight may be an issue - specs called for 24 lbs. My aircraft is at 30 lbs (56 oz/sqfoot wing loading). I've not flown it, but it seems to want to take off at half throtttle, 20% flaps - but its moving a lot faster than I'm used to taking off/landing at.

I think a I can get 4-4.5 lbs out of the aircraft by building new wing/stab/elevator panels using a different construction/finishing techniqued, which would also allow me to pull all my added nose weight out.

Any suggestions appreciated.

Dale

Pull off the cylinder and have a look at the piston and ring. Perhaps the ring is stuck with carbon or worn out. While the cylinder is off, turn the crank carefully by hand and see if the bearings are free.

Big Top Flite props really load the engine, and don't do a lot of pulling. Both of my 4.2 Sachs based engines would turn a Zinger 24x10 about 63-6500rpm. The Pro Zinger will pull better yet.

My buddy has a 4.2 Sachs on a Lanier 33% Extra. It built heavy and comes in at 28 lb. It will turn a Menz S 24 x 10 at 6300 with good flight performance. No it's not a 3Der, but he doesn't fly like that. I agree about the bigger TF props loading an engine and not turning it into thrust. They are even worse than the Zingers. My buddy saw a big difference when he switched from the Zinger 24 x 10 to the Menz.

I have a Precision Eagle 4.2 with CH ignition and prop hub adapter that really likes a Menz 22X12. It does spit more fuel out the carb than my other gassers but less than what you describe.

Hi Dale,

My Hellcat project got set aside for the past couple months due to the intense heat over the summer in my garage. Its just unbearable in there when its that hot. Its cooling down now though so I think I will resume. I noticed you found a 2 blade adapter. From CH ignitions. Hope they still have them because I want one. Been told by several people to keep the 3 blade setup for static display and fly with the 2 - blade. I did work on my engine just setting up all the linkages. Im using the mechanical advance system with the CH ignition that came with mine. Got it all set up now and seems to function properly. Of course I havent fired up the engine yet. Still a long way from that event. I still havent glued my fuse halves together. I have to finish my horizontal stab and elevators first.

How did you attach your gear door strut fairings? I finished one of em so far according to plans but it seems rather flimsy. Those spring loaded gear doors though .. they came out pretty trick.

Maybe you have flown yours by now?

Chuck

Regarding the gear doors - I followed the plans, too and have busted them off in taxi tests already on a grass strip. I used epoxy to adhere the glass reinforcement to the doors, but this is peeling off already. The place they broke first was at the top attachment point. For the lower attachment, the plans called for a large washer under the screw head - the plans did not call for this at the top attachment point. This is a mistake, as the plastic under the screw will break in the same diameter as the screw head and then your left with the gear door flopping from the lower attachment.

My recommendation for these door covers is the same as for the scale prop - take 'em off when flying. If you are going to use them, beef up the attachment areas, perhaps by using a second layer of the same plastic material (from scrap) at the attachment points - I might use a plastic cement, rather than epoxy - something that'll adhere better. Also, use large washers under the screw heads at both upper and lower attachment points.

Also, the mechanism for opening the front, spring gear door is really bad. Maybe they changed the design, as they were not 'pretty trick' for me. On my plans, they showed a 'C' collar that attached to the strut, and a piece of plastic tubing with threaded rod on each end. One end of the rod/tube threaded into the 'C' collar while a plastic, rounded cone was threaded on to the other end. This rounded cone is supposed to open the front cover when the gear strut come down.

Nice in theory, except the rounded cone is trying to slide on the rough side of the fiberglass gear door cover. It doesn't slide at all - instead, the whole rod/tube/cone thing just breaks off.

Using the same 'C' collar, I lowered its mounting point on the strut. I then took a piece of 1/16" rod about 2 inches long, thread on one end and bent it into an 'L' shape. The short leg of the 'L' threads into the 'C' collar, with the long leg pointing up and laying against the front gear door. This arrangement works very well, with the long leg of the 'L' sliding smoothly over the rough fiberglass back of the door.

Have not flown yet - will be trying the Zinger 24x10 in an attempt to get the RPMs up. Feedback seems to indicate that large Top Flite props tend to load engines more than others.

Also, if I had to do over, I'd throw out the foam stab/elevator and go with a built up(ribbed) design. I shortened the brass tubes used to mount the rudder and elevators - but I could have shortened them all another quarter inch. I threw out the plastic stab tips, replacing them with balsa - this was a good idea, but I'd hollow them out next time. Every ounce you save in the tail lets you take out 4 in the nose - and the foam/balsa sheeted stab/elevator is not the lightest thing.

I'd do the same for the wing panels - at least the ailerons and outer flaps. Also, I'd make a better attempt at getting my aileron servos on the CG line of the aircraft. These panels tend to be rearward heavy - meaning one has to add weight to the nose to counter them.

I've had it recommended to me that one should keep RC aircraft under 40 ozs/sqft wing loading. The instructions I received indicated the plane to come in at 22-24 lbs. At 24 lbs, the wing loading is up around 43 oz/sqft. So before thinking about any details you want to add, think about how you can change the design of the kit to lighten it up. Push everything you can, forward (air bottle, receiver battery, servos, etc.). Its easier to move stuff back later, if needed, or add a few ounces of balance weights inside the rear gear well.

I'm still looking to find someone that has flown this bird at 30-32 lbs. During high speed taxi tests, it seems to have enough power even with the under performing prop at half throttle - but it is moving quite fast at/around its stall speed.

So, build it light as you can!

Iron Bay can get you the prop adapter. If not, go directly to CH. When I called Iron Bay (last Winter?), they did not have any in stock and were a bit unsure as to when they would have any. CH will supply the adapter and the magnet for the ignition. They won't drill/ream the hole in the adapter for you to mount the magnet - unless you send them your engine. If you can get real good, accurate measurements as to where the hole should go relative to the drive shaft key, maybe they will do the drilling/reaming for you without having to in your engine. I have a drill press, so I did this myself.

If you order the adapter from Iron Bay, perhaps it will come with the magnet already installed - I don't know.

I found the assembly of the two fuse halves to be the hardest part. Not so much the assembly, but the filler work afterwards, as the two halves did not fit together as seemlessly as expected. Mine was a Byron built kit - maybe Iron Bay has improved on this.

I found the local auto parts shop to be my new favorite haunt. There, you can find body fillers that adhere very well to fiberglass, apply smoothly and they sand very easily.

And, if you don't have a respirator - get one. I got mine at Home Depot and it comes with cartridges for filtering out organics. The resins, body fillers, etc can all be pretty nasty to work with - both from the fumes and the sanding particulates.

Will be interested to hear your progress.

Thank you - will check this after trying the Zinger 24x10 prop. The engine has less than 2 hours run time, none of it too lean - so I hope that wear is not a factor, yet. I can test a new prop pretty quickly, before tearing into the engine.

Dale

Thank you. Will try the Zingers, first before the Menz. If the performance moves in the right direction with the Zingers, I'll then try the Menz.

Dale

dale,
Don't worry about your wing loading, you can get away with 50 or more oz/sqft on a bird of that size. I am flying a T/F Mustang that is 84"w/s and has a wing loading of 41oz. Flys like a puppy. Actually almost too lite in a strong wind. I can land without flaps with no problems. I did a 110" B-24 that was only 52oz wing loading and it flew very lite as well.
Check with some of the guys in the warbird forum about what kind of wing loading they have on their "Big" birds. I think you will be suprised.

Yea ... maybe I will take the gear fairings off when I fly. Put them on for display only. Those spring loaded gear doors though, work very well for me. I glued some scrap pieces of the fiberglass on the backside ... rough sides of the fiberglass facing each other so that that little platic piece has a smooth surface to slide on.

Looks like you found the same problem, but came up with a different solution.

I picked up a Zinger 24x10 and tested it yesterday. I'm getting an additional 600 RPM out of it vs. the TopFlite 24x10. The Zinger is not as think, front to back, has a narrower blade tip and appears to flex much less. So, now I'm at 5600 RPM, but still short of the spec in the plans which indicate I should be getting 6000 RPM.

Starting to wonder if the spec is wrong....

Others have suggested trying a Zinger Pro or a Menz, or going to a smaller prop. I have a 22x10 that puts out 7000 RPM - would like to find a source for a 23x10.

Thank you. Will check out the warbird forum as you suggest.

Found a Zinger 24x10 and it did help by providing an additional 600 RPM. My 4.2 is up to 5600 RPM, still short of spec and what you are achieving. Have not yet attempted to adjust the mixture settings with this new prop running at the higher RPM. Since these settings were last adjusted using props turning at slower RPMs, I suspect I may have some opportunity to gain a few more by not assuming the settings at the lower RPM are good for the higher RPM.

Its already getting quite cold to stand behind a prop, up here in Michigan.

What fuel mix ratio are you using on your 4.2?

Try the Zinger Pro. I gained substantial rpms over the standard Zinger. This was on a plane I have with a G-62. I havent run my 4.2 yet. My fuse still isnt glued together yet.

I wouldnt worry too much about chasing that 6000 rpm mark though. If youre at 5600 on the ground I bet youre over 6000 during an actual flight. I bet youre getting good thurst. Also .. maybe the 6000 figure on the spec sheet was with that flimsy but scale 3 bladed prop.

chuck

Your 4.2 should turn that standard 24x10 Zinger at at least 6K. I would bet you can tune it to that point. If not, it may be worth you time to put a gasket and diaghram set in the carb. If has set for a long period, they may be a little stiff.

Ahh - that makes some sense. The previous owner hadn't run it since it came back from CH Ignition - it sat in a box, in an apartment basement for probably 4 years before I purchased the plane/engine, still in kit form - then it took me probably another two years before the plane was built to the point where I could run the engine.

Hope I can still find parts - I can't find the exact Walbro carb model number on their web site, but maybe they still have parts for the older carbs.

Will tweak the mixture a bit first.

Thank you.

No, the 6200-6400 mark was actually for the Zinger 24x10. The scale, highly flexible prop was rated lower at 5000-5400 RPM, but I was never able to get to this mark.

I'll tweak the mixture with the new prop. Maybe this will get me to where it ought to be. If not, there was a suggestion that certain carb parts may need to be replaced to their age - the engine sat for years unused by the previous owner. Things may have stiffened/dried out.

Thank you.

Your suggestion to try the warbird forum has given me some confidence. I found a guy that build his own 105" wingspan Hellcat, at 45 lbs. If the wing plan form is the same, then he's got 12 sqft of wing area and this works out to about 60 oz/sqft of wing loading - and he said it didn't "feel heavy" when flying it.

Also, I could take my full length pilot out for the initial test flights, which would allow me to also remove some weight out of the nose. May not get me under 50 oz/sqft, but its alot easier to do then building new, lighter, horizontal surfaces.

Thanks again.

Dale,
You can get the parts for the carb at any chainsaw shop. It should have a Tillotson carb, not sure of the number, but it is stamped on the carb. Just take it to the shop with you. If you dont fell confident to rebuild it, they will do it cheap.