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Cox Engine of The Month
October-2020
Jason_WI's

"Pieces and parts RR-1. New crank, rotary valve, and drive plate. Early #1 cylinder. Drilled out golden bee backplate. Battle hardened crankcase and tank."



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Post  Back to CL on Wed Jul 29, 2020 4:14 pm

I have a  BW on my 1/2A Ringmaster.

I only get about 2 minutes run time. Checked the fuel tube ,spring etc. All seem OK, fuel tube towards outside for CL model. It starts perfect in one or two flips, speed / rpm by shrill noise is good, plenty of power, speed is constant no sagging or speeding. But only lasts under 2 minutes.

A few times ,at the end of the run  hooked up my gas syringe to suck back the remainder fuel. Hardly any , less then half ml fuel left in the tank. Today I opened the tank to really see how much fuel remained back, just a drip , certainly not half a tank.

One thing I did observe is at nears the end of the run, it is still at constant high speed. It does not lean out like my Texaco does.

I am using : 6 by 3 prop, 25 % nitro, 10% castor and 10 % synthetic.  Prop balanced, no funny noise or vibrations.

Thanks for your comments and support in advance.

PS: there is not much fuel sprayed on the wing or the airplane , not more than expected. Hardly any fuel drips behind the tank and firewall when i took it off today. Where else can a leak be?


Last edited by Back to CL on Wed Jul 29, 2020 4:41 pm; edited 1 time in total (Reason for editing : Addition)
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Post  rsv1cox on Wed Jul 29, 2020 6:16 pm

Two things come to mind.

Does the fuel tank leak? Check for clean grooves where it mates with the back plate. Tighten screws equally. Ensure the case gasket is not broken and fits securely around the machine screws.

Are your running it rich?
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Post  Iceberg on Wed Jul 29, 2020 6:48 pm

I have a widow from late 60's #1 cylinder and it absolutely kicks but. My later Blacks are maybe 25% slower. That one only runs 90 seconds and sucks every drop of fuel. I got some APC 6x4 Sport Gas props and tried them. They powered down too much my other motors however my 69 Widow ran wonderful. I run many times the grey Cox 6x4's and they don't load down the motors anything like the APC props. My run time is possibly closer to the 2 minutes you mention. However the plane is screaming.

Try some APC 6x4 Sport Gas Propeller on it and see if it helps your run time? As I said only the one screamer Black I have responded good to the APC.

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Black Widow Run time Empty What about the backplate hole size, Venturi?

Post  happydad on Wed Jul 29, 2020 8:45 pm

Iceberg wrote:I have a widow from late 60's #1 cylinder and it absolutely kicks but. My later Blacks are maybe 25% slower. That one only runs 90 seconds and sucks every drop of fuel. I got some APC 6x4 Sport Gas props and tried them. They powered down too much my other motors however my 69 Widow ran wonderful. I run many times the grey Cox 6x4's and they don't load down the motors anything like the APC props. My run time is possibly closer to the 2 minutes you mention. However the plane is screaming.

Try some APC 6x4 Sport Gas Propeller on it and see if it helps your run time? As I said only the one screamer Black I have responded good to the APC.

Ice

Have you measured the hole thru the backplate diameter? Some of the older BW had a larger diameter hole, newer models had a smaller diameter hole. Some how .085in. dia. for older and .068 for newer BW sticks in my head. Measure and see.

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Post  Iceberg on Thu Jul 30, 2020 12:20 am

Yes any of my performance oriented blocks I always make sure the Venturi is .082" if not I drill it but due to better or worse cylinders some run substantially better than others.

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Post  happydad on Thu Jul 30, 2020 12:56 am

Iceberg wrote:Yes any of my performance oriented blocks I always make sure the Venturi is .082" if not I drill it but due to better or worse cylinders some run substantially better than others.

Ice

Iceman: I’m running back and forth trying to clean the garage, follow ebay and take pics for someone who needs to count the number of threads, turns, on his needle.
   Have you checked the cylinder #‘s ?  A #2 only has 1 bypass port, but a #3 has 2 bypass port on both sides. Huh...  Better performance. A #4 cylinder has 2 bypass ports and 2 boost ports for better performance. Some #3 cylinders I have also have 1 boost port, OR a wider boost port, essentially the same because of it’s location on the edge of the bypass port. See the cylinders on the left panel below the “latest topics”.  Check those cylinders.

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Post  Back to CL on Thu Jul 30, 2020 8:58 am

Thank you all for your quick response and suggestions.

As far as the performance goes, I am happy. Starts fast, runs great no variations, reliable etc..

Just that a 2 minute run seems rather short.

So drilling out the 0.085 hole, does that increase speed or performance (more speed). Please pardon my questions as I am learning Cox. My previous limited experience is OS La 20 and 46 engines .

Wonder what times are people getting in the Mouse Race that primarily uses Black widow. Do they actually get more time at higher nitro and speeds? That would be a nice bench mark. After how many minutes do they expect to get ready to refuel?
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Post  getback on Thu Jul 30, 2020 10:11 am

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Post  crankbndr on Thu Jul 30, 2020 9:25 pm

If you enlarge the venturi it will shorten your run times. Mine only runs about a minute. At the time I was wondering if prop wash was pulling fuel out the filler tube.

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Post  Back to CL on Fri Jul 31, 2020 7:46 am

Thanks for the link . A lot of great stuff in the write-up.
based on that Googled out the results from such races which shows best times for 50 laps on Black Widow is around , let say, two and a half minutes. Assume they are landing dead stick when gas is over, so 2.5 minutes is expected, I think..

So I need my engine to give at least 30 to 45 seconds more.

Hence I will experiment with the metallic fuel tube in the tank and put an extension fuel tubing sleeve on the inlet of the tank to extend it by say 1/2" (?). That may prevent pulling out of the fuel from prop wash. I am happy with the stock performance for my Ringmaster. More than enough power for loops and wing overs. So will not drill the hole out to 0.082 as it will further reduce times and I do not need such high RPM, speed.

Question: so when i replace the fuel line with metal tube, do i still insert the spring for capillary action?
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Post  Ken Cook on Fri Jul 31, 2020 1:52 pm

Reduce your nitro and add another head gasket. You will have to lean the engine out now to get the power you once had which will increase your mileage. It also makes your glow plugs last a bit longer doing so. To answer your question as to where else can a leak be, look at the prop driver where it meets the case to insure it's not leaking out of the nose when running. Not a bad thing actually, but fuel can go out the nose.
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Post  coxaddict on Sat Aug 01, 2020 3:01 am

Hi, are you using a spring starter? The older type spring starter is generally known as drag free. The newer style with the hex shaped drive washer and plastic cam causes drag when running as the starter spring bounces off the plastic cam. Hope you can max out your run time.
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Post  GallopingGhostler on Sat Aug 01, 2020 5:48 am

Back to CL wrote:As far as the performance goes, I  am happy. Starts fast, runs great no variations, reliable etc. Just that a 2 minute run seems rather short.

If you have about a half tank or a touch less left when engine quits, what sounds like is happening is that the venturi gasket (flat rubber washer but sometimes is an O-ring) is missing or bad. It fits on the end of the tank venturi tube and seals the joint between the backplate and tank venturi tube. With fuel present, that joint is more or less sealed by the viscosity of the fuel. When fuel is used up and level drops to the venturi tube, now the joint is exposed to air. Without fuel surrounding, air enters in short cutting your needled fuel draw, ending engine run.

Here is what that flat black (usually black but is possible another color like gray) gasket looks like:

Black Widow Run time Cox20013

coxengines.ca Cox .049 Tanked Bee Tune-up Kit: $1.95 US

Note, the tank venturi gaskets are available separately (3 for $1.95 US) from both Cox Engines International (Canada) and EX Model Engines (US).

Back to CL wrote:So drilling out the 0.085 hole, does that increase speed or performance (more speed). Please pardon my questions as I am learning Cox. My previous limited experience is OS La 20 and 46 engines.

I've never drilled out the venturi on a tanked Bee to increase its diameter. Effect is similar to increasing the diameter of your venturi on the OS LA and other standard engines. You increase the engine's ability to draw in a greater volume of air/fuel mixture, in essence increasing the engine's power (which also increases speed). Caveats are decreased fuel suction draw. If too large then will require going to some form of a pressurized fuel system.

I am more interested in sport stunt, so fuel draw is more important to me. However, in general half-A's particularly in R/C tend to be slightly under-powered, and as such it is more desirable to tweak as much performance as possible out of them. Thus it is common to use 25% nitro fuel instead of the standard 15% nitro. Some use higher nitro, but it tends to shorten the life the glow head when you go above 30%.

The spring starter on later Bee and Sure Start engines is a rachet type, so one does not have to lift the spring end over the back side of the prop to start. Because of the constant rubbing of the rachet, one loses about 300 RPM or so I am told. I never had any problem with this on my .049 R/C Bee (forerunner of the Dragonfly) on my Sterling 36" Minnie Mambo. However, others have simply removed the plastic rachet (don't spring start) or replaced starter with the older style snap spring starter.
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Post  Ken Cook on Sat Aug 01, 2020 7:40 am

If you choose to use the aluminum tubing, may I recommend a few things. The aluminum will try and kink due to the bend radius. To make the piece your going to need a lot more than what you think. The tubing either cracks, kinks. You can anneal the tubing but that's not so easy either. I use K&S tubing which was available in hobby shops when we used to have hobby shops. Remember those?  The spring is not necessary. I never used it when I used the aluminum pickup. I'm not even certain if that's a good idea with two dissimilar metals together in that environment. But, it might prevent kinking during the bending. Something I never tried but I would like to see would be using a piece of weed wacker string in the tubing during bending to prevent kinking. While I won't deny that the spring offers capillary action, it's not necessary and it will work without it. I've never seen a engine suffer performance as a result of not using one. I would try just bending the aluminum for the first try to see if you can do it easily.

            Annealing aluminum is not like copper. Your heat is important as I have melted aluminum tubing just with the flame on my stove top. Unlike copper which turns orange indicating heat temp, aluminum offers no change. My dad suggested putting a Sharpie mark on the tubing and waiting for it to burn off prior to quenching. I never tried this so I can't say it does or doesn't. Copper you heat until orange and let air cool and you will find it's as pliable as putty. Aluminum has to be quenched in water immediately upon being removed from the flame. This will enable it to be bent without cracking or kinking. When you connect the tubing to the backplate after completing the pickup tube, I don't use silicone fuel tubing. I've found it never stays on, it eventually swells losing it's ability to hold. I use the yellow Tygon tubing which is hard and it's a pain in the rear to get it on. I've had good success using it and it stays put. They also make it in mm sizes which fits older metal backplate nipples better. The newer plastic backplate has a much larger nipple. If you find it too hard to get over the tubing or nipple, apply heat from a heat gun and it will push right on.
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Post  Kim on Sat Aug 01, 2020 8:39 am

A short "Redneck Addendum" to George's (GallopingGhostler) excellent tip on on replacing the tiny intake tube gasket:

The gasket is usually pressed tight into the tube, and may require using the tip of a #11 Xacto blade to peel it out. That is a very precise fitting between the tube and backplate, and it's easy to dig scratches into the the soft aluminum area around the gasket.

So, I use a heat gun or small torch to heat the gasket and get it to curl so I can hook it out with minimum contact with the tube.

And yes, new gaskets (venturi, head, and case) are ALWAYS a great idea! I buy them from the "Bulk Sales" section in Matt or Bernie's sites.

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Post  sosam117 on Sat Aug 01, 2020 10:00 am

Here are my modifications on my Black Widow's back plate and fuel line to get more fuel in the tank.
Like it was mentioned here, I made an aluminum fuel line with Tygon connector to the nipple of the back plate to the aluminum fuel line. There is no spring inside the fuel line like on the vinyl fuel line.

I use my Black Widow for free flight, so it needs to suck the fuel at the back of the tank.
So, that is why I removed the extra plastic off the back plate.
On the back plate (for U-control) there are little shelves on the back plate to lay the pickup on when you assemble it.

Also, I added an aluminum tube (extension) to get the time.
I don't use the original (top/bottom) fuel tank. I use a "Texaco fuel tank bowl" and the back plate with the fuel fill/overflow on it.
After I fill the tank, I plug the fill nipple, leaving the overflow the only way for air to come in ( no fuel getting sucked out.

You could do the same for the stock Black Widow tank.
Plug the overflow vent (bottom tube) and leave the top vent open.
A plus on that is then you'll have a uniflow tank and fuel won't get sucked out from the tank.

The venturi hole on mine is .083 and for my free flight run I get just 2:00 minutes on the motor run.
If you don't get the 2 minutes run time.
Purchase another plastic back plate and drill the venturi hole smaller that the one you currently have.
Or, measure your current hole size (with a number drill set -- use the shaft side, not the drilling side to check the size!)
Fill the venturi hole completely, (with JB Weld) then re-drill the venturi with a smaller size number drill.
So, if your original venturi hole fit a #44 drill (.086") then try to use a #48 drill then.
You can fine tune the hole size to optimize the run time to get the run time you want.
Start with a smaller drill and work your way up to the larger drill sizes for the run time.
The larger dia. venturi also increases the RPM as well. ( reducing run time too.)

You'll find the trade off.

sosam117

Original venturi size .086 (#44 drill) with plastic removed from inside back plate. With extended fuel filler nipple.
Black Widow Run time Origin11

Aluminum fuel line with Tygon fuel line as connector to plastic back plate nipple.
Black Widow Run time Alumin10

Aluminum fuel line attached to back plate.
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Black Widow Run time Empty Thanks so much

Post  Back to CL on Mon Aug 03, 2020 9:29 am

Dear All,

Thanks so much. Learnt a lot from your posts.

Ideally would want to make one change at a time. But in the case of impatience and limited fuel, I will do the "give-me's" now and see the outcome.
Will do :
1) Put a second gasket under the glow plug. (one gasket per 10 % nitro)
2) Check for leaks at the prop diver front.
3) Remove the spring starter with plastic clutch. Any way the engine starts in the first spring wound. So should start real soon without it too.
4) At the fuel tank inlet install an extension tube to prevent any loss from prop wash.
5) Will change the venturi gasket.

As of today, Will leave the following as is:
1) NV tubing versus spring. it is quite responsive today.
2) Substitute fuel tubing with K&S metallic tubing. Thanks so much for the detailed explanation and the great close-up photos. This would be my second step.  
3) Stuck with 25 % Nitro as that is what I have for now. Perhaps future order?
4) Keep the back hole size the same. I am not a good machinist at all.

Expecting winds and heavy rains soon. So will complete the experiments and report close to the weekend.

Come to think after all this, I should have considered leaving the Black Widow for future speed flying. Instead should have installed a Cox engine without integral tank and thus a larger external tank would give the needed run time.

Thanks again


Last edited by Back to CL on Mon Aug 03, 2020 9:30 am; edited 1 time in total (Reason for editing : clarity changes)
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Post  Iceberg on Mon Aug 03, 2020 2:44 pm

For bending the aluminum pickup tube. Find the weed eater plastic cord.
Find one that fits snug inside 3/32" aluminum tube then bend to your heart's content. Then when happy with the bend take pliers and pull out the weed eater line and the bend will be PERFCET no kinks.

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Post  Back to CL on Mon Aug 03, 2020 4:12 pm

Thank you for the weed cutter line method and photo. This i can attempt.
Thanks
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Post  dckrsn on Mon Aug 03, 2020 6:51 pm

Thanks for that, Ice. Good stuff.
Now, off to my neighbor's garage!
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Post  coxaddict on Fri Aug 14, 2020 5:08 pm

Just ordered this off  'Bay
Sorry photo not shown. It's a K&S spring tubing bender set
can bend 1/16", 3/32", 1/8", 5/32" and 3/16" tubing.  Aluminum, brass or copper tubing.  I used to have a set like this and it worked fine except when it got stuck. Just spray a little lubricant and twist it off.
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Post  Back to CL on Tue Aug 18, 2020 2:58 pm

Dear All,

Finally had a chance to implement all of the easy changes listed above. Yes big difference (for the better) in both quality of run and increase in time. I am now consistently at a minimum of two and half minutes. Now to get to the three minute mark, must change the the fuel tube to the aluminium as explained wonderfully above.

But here is my opinion that for a half A Ringmaster: One can get away with a simple 049 with an external tank. Will save the BW for later Rat race models.

So once again , thanks so much for your input and helping me learn more about the Black Widow engine.

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Post  Ken Cook on Tue Aug 18, 2020 4:24 pm

A Ringmaster needs all the power you can offer it. The wing is too thin, chord too narrow and the wingspan isn't very wide. A Sterling kit built Ringmaster is quite heavy and it builds very nose heavy.  Flying it with a standard Babe Bee is not going to be very exciting unless your just flying in circles. While a Babe Bee can be nursed into loops and eights, the power drops off dramatically stalling the wing and the plane flounders around. If your looking to fly a stunt pattern for instance, you really should be using a external tank. This offers uniform runs back to back and not the idiosyncrasies of a integral tanked bee. They can be extremely problematic even day to day. They can be prone to fuel leaks, air leaks, shutting off at inopportune times.

                    If flying longer is the goal you seek, adding the aluminum fuel tubing to the bee isn't going to offer you that satisfaction. What it will do however is to assist fuel draw insuring that the engine doesn't shut off due to a misaligned fuel pickup. If your burning fuel your making power. If you increase the duration of the run from either lessening nitro, using a larger than normal prop, decreasing venturi intake, your strangling the engine and making less power. The main problem with the Ring and many other commercially offered profiles is that they have no nose length to accommodate a external tank. The nose is too close to the leading edge. many times, I have installed a wing mounted tank directly behind the leading edge. If need be, I remove the second rib that's within the tank area and head it off to install a tank. Generally, a tank will protrude above and below the wing. I cover the wing as needed wrapping into the tank compartment and then I silicone or epoxy the tank into the area. What this equates too is that to you need to rework the stock tank configuration of piping to suit the plane. Keep tanks on the centerline of engine, as close as possible to the engine, and use a longer narrower tank on a profile. When the fuel load is too far outboard, this causes feed issues and poor engine runs.
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Black Widow Run time Empty What is wrong with the built up, or ribbed, wing version?

Post  happydad on Tue Aug 18, 2020 4:46 pm

Ken Cook wrote:A Ringmaster needs all the power you can offer it. The wing is too thin, chord too narrow and the wingspan isn't very wide. A kit Sterling kit built Ringmaster is quite heavy and it builds very nose heavy.  Flying it with a standard Babe Bee is not going to be very exciting unless your just flying in circles. While a Babe Bee can be nursed into loops and eights, the power drops off dramatically stalling the wing and the plane flounders around. If your looking to fly a stunt pattern for instance, you really should be using a external tank. This offers uniform runs back to back and not the idiosyncrasies of a integral tanked bee. They can be extremely problematic even day to day. They can be prone to fuel leaks, air leaks, shutting off at inopportune times.

                    If flying longer is the goal you seek, adding the aluminum fuel tubing to the bee isn't going to offer you that satisfaction. What it will do however is to assist fuel draw insuring that the engine doesn't shut off due to a misaligned fuel pickup. If your burning fuel your making power. If you increase the duration of the run from either lessening nitro, using a larger than normal prop, decreasing venturi intake, your strangling the engine and making less power. The main problem with the Ring and many other commercially offered profiles is that they have no nose length to accommodate a external tank. The nose is too close to the leading edge. many times, I have installed a wing mounted tank directly behind the leading edge. If need be, I remove the second rib that's within the tank area and head it off to install a tank. Generally, a tank will protrude above and below the wing. I cover the wing as needed wrapping into the tank compartment and then I silicone or epoxy the tank into the area. What this equates too is that to you need to rework the stock tank configuration of piping to suit the plane. Keep tanks on the centerline of engine, as close as possible to the engine, and use a longer narrower tank on a profile. When the fuel load is too far outboard, this causes feed issues and poor engine runs.

Ken: so what is wrong with baby BRM with the built up, or ribbed wing? Airfoil, thicker chord and 2inch wider wing if I remember, 22 1/2inch, versus 21inch.
See version I built back in 2012 for nitrosmeller and myself.  See attached.
Have to go to MacBook, will edit
>>>>>>edited 8-18-20 2:52p.m. PST to add a photo

Black Widow Run time Img_1630
Ribbed Baby Ring Master version
and the chord from wing tip is 4 1/4inch to fuselage is 5 1/2inch tapered.

The monokote has loosened over the last 8 or so years.

>>>> edit complete

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