Building Frank's SR-71

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While waiting for the Testors paint to arrive I took some pictures of Frank's SR-71 and the HobbyLab SR-71 together. You can see that Frank's model is slightly larger than the HobbyLab model. I also have a picture of Frank's SR-71 with the old Estes SR-71.

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I glued on the launch lug at the location (bottom left side and off center a little bit so that the guide rail clears the motor mount) given by Frank on his drawing using the foam safe glue. My wing spar sticks out a little bit so I glued the launch lug onto a small thin piece of bass word in order to have a slight stand off to clear the spar. I used a cardboard launch lug that was in my inventory. I believe it came from Loc Precision. It is about 1/4" diameter by 5.5" long. There is some spray paint on the model that was put there before the Krylon can clogged. The Testors paint should be here in about 2 days. Frank told me that he glues the servos on before painting and then puts masking tape around the servos to prevent the chance of any paint getting into the gears and doing damage.

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You just want to be sure that you don't have any binding on the rod. I use a slightly oversize aluminum tube since it doesn't swell when wet and gives less resistance, however now everything I have is converted to rail buttons. Remember, you also need to clear the servo wire with the guide rod so make sure your launch lug standoff accounts for that too.

You should balance it before you paint it so you can glue or inset any nose weight you might need. You may consider flying it too, get it trimmed and working well before you invest a lot of time on finishing.

Frank
 
Frank,
I have spray painted the model. I used a whole can of testors paint, but I have another can for touching up. I need some help with knowing which receiver, battery, and transmitter to buy. I would like to use a transmitter that I bought for the Arcie II (feather weight servo). It is a Hi-Tec Laser 4. I suspect that it is much simpler than what you use, so I may be out of luck. I am including some pictures of the transmitter. The settings in the battery compartment look very simple.


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I see you painted before installing the battery/receiver and wires, I normally install everything and tape the wires down and use velcro to hold the battery and receiver in place and do that before I paint because the tape and self adhesive velcro will just pull off the paint and not stick to it very well,.....I also do that because I can set my CG location and attach any nose weight first before painting. I then pull off the battery and receiver and mask off the velcro spots then paint.... I did mention it in my list in an earlier thread:

Install your receiver and bec as far forward as possible for CG.
Install velcro to mount your battery as far forward as possible.
Tape down all wiring with the hinge tape.
Install a loaded motor, and check CG, add nose weight if needed, or move the battery back if needed.
Remove receiver and bec, tape around servo, and paint the model flat black using model master flat black spray.
Re-install all components and set your trims to neutral for boost, and about 3/16" up for glide.

However back to your question:

It's really preferred to have a radio with mixing capability so you can do elevon.

You can get mixing boards but those add weight. Here is one: https://www.hobbyking.com/hobbyking/store/__6321__TURNIGY_V_Tail_Mixer_Ultra_small.html
If you go that route and can set up the directions, trims and throws the way you want it and be able to set the boost and glide trim the way you need using the tabs you can use whatever receiver will work with your hitec radio and whatever battery gives you the right CG, or use a small battery and add nose weight as needed. I just use self adhesive velcro to attach the receiver and battery.

It's so much easier to set things up with a computer radio,

As for radio/receiver, I use a spektrum radio so use a spektrum receiver, like an AR-610, 6115e, etc...Orange(hobby king carries them) makes spektrum compatible receivers for very little money. Hitec also makes good transmitter/receivers as does turnigy.

A computer radio is nice because you can individually tweak trims and mixing and have dual rate etc, your radio just has reversing. Also, you can then mix your glide trim to a switch instead of having to manually adjust the trim setting after boost.

Here is the orange radio version of my spektrum(sort of)

https://www.hobbyking.com/hobbyking...10_Model_Memory_and_3_Pos_Switch_Mode_2_.html
It can store 10 models, so for a different plane you just get a new receiver and bind it to that model number and you can never get them mixed up...
In general the new non fm/am radios are so much better for interference rejection I would not use an fm/am radio any more. I switched about 10 years ago and sort of forgot folks still have these laying around:)


Here is the receiver

https://www.hobbyking.com/hobbyking...MX_Compatible_6Ch_2_4GHz_Receiver_w_CPPM.html

As you can see prices are not very expensive for what you are getting.


I use a 2 cell 800mah battery because that gives me the right CG typically, it weighs about what the loaded motor weight is, so if I place components right, I just need to place the battery the same distance forward of the CG as the motor and I'm good. I had these batteries available to me so I just designed everything to be CG correct with that same battery. I typically use a castle creations 10amp bec to regulate the battery to the receiver as the servos are speced for 4.8-6v...so a direct 2s input to the rx might burn them out. Hobbyking makes switching bec's for cheap as well.

https://www.e-fliterc.com/Products/Default.aspx?ProdID=EFLB0990

But you don't really need any capacity, flights are short, and drain shouldn't be much, you could use a much smaller two cell battery and just use lead for nose weight if needed.
 
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I tried today sticking the wires with hinge tape and it seems to work well. I will check back and see how it works. I cut a small hole in the depron to get one of the servo wires to the other side. I had a 12" extension wire, but that seems too short to get wires up to where the battery will be. It looks like 19" or 24" wires will work. The hinge tape shows up a little too much and , if it works, I may spray paint over it.

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It took a little while for the receiver and the transmitter to arrive from Hobby King and even longer for me to update this thread. I am puzzled by the power leads to the receiver.

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I would like to order the 800mah battery, but I am wondering do I need to buy a charger, too. Below is the charger that I currently have. It is suppose to charge the small 100mah batteries.

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That charger goes to 5A, so it is plenty powerful to charge an 800mAh battery. Just set it to 0.8A charge rate.
 
You don't have to place your receiver all the way forward, you can just put it as far as your extensions reach, then put the bec up forward closer to the battery. Moving things forward just helps to reduce any lead weight needed. On the one I just built from my kit as a test, I didn't use any servo extensions and only wound up needing 1/4 ounce of nose weight.

Yes, I just poke a hole through the foam and route the wires from one servo accross to the other side to get to the receiver.

Here's a picture of approx where my stuff wound up. What is confusing you on the receiver? The BEC will plug into any of the receiver channels, it will provide power via the plug that looks just like a servo plug. On the receiver board the ground and power rails are all shorted together so plugging in the bec into any channel will power the rest of the servos...only the signal pin is unique accross the channels.

BTW, make sure you put the battery on the side opposite to the launch lug or the launch rod may interfer with it. You may get a bit of dragging on the servo wire, you'll have to test it to be sure. You can always cut a little slit in the foam and push the wire down into it and re-tape it if needed to get clearance.
Frank

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Well, I'm finding out that I am a novice on R/C especially on what I consider to be the new stuff. I wasn't sure what a BEC is and I had some questions on the receiver, so I sent Frank a PM. I'm going to put his answer here:

Bob, yes the short wires are the antennae (Bob's first receiver question)...

The servo connections have a pos wire, neg wire(black or brown), and signal wire...the negative and positive are shorted together (another receiver question).

I had mentioned the bec before but you might have missed it. Servos made now are still made to operate at 4.8 to 6V and not above. The lipo batteries are 8.4v at peak...so you have to convert that. If you are running an electric motor, the speed controls automtically do that for you, when you plug in the esc to the receiver it powers it with 5v, since we don't have a speed control you need a regulator(Battery Eliminator Circuit) to do that. The battery will connect to one end, the other will plug into the receiver and power the receiver and servos.

https://www.graysonhobby.com/catalog/bec-c-52.html I use the castle unit, but the 3 amp grayson is fine and cheaper, it's just heavier.
You will need to get an opposite connector to connect the bec to your battery and will need to solder that onto the bec...they don't come with one because batteries use all sorts of connectors. Unfortunately you can't just plug in the battery to the receiver, it will fry the servos.

Frank
 
The 800mah battery has come in. (The BEC has not arrived yet.) It has 2 connectors; one is 3 pins and one is 2 pins. I noticed that if I take the voltage on the red and black wires of either connector I get about 8 volts. So, I am thinking that the Lipo battery may have come fully charged. Which connector is used for charging (or does it make any difference)?

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My battery charger has 5 settings for Lipo batteries. They are as follows:

* LiPo Charge, 0.1 A 3.7v(15)
* LiPo Balance, 4.0 A 7.4v(25)
* LiPo Fast Chg, 0.1 A 3.7v(15)
* LiPo Storage, 0.1 A 3.7v(15)
* LiPo Discharge, 1.0 A 6.0v(25)

If I want to charge the 800mah battery, which setting should I choose? What are the other settings?
 
Bob, the connector with three wires is the balance connector, it allows the charger to charge the cells in parallel for a better charge...the two pin connector is a JST connector that will go to your BEC, you'll need the male connector for your bec and will have to solder that in place.

For your charger balance plug will plug directly into the side of the charger but it also requires you to plug in the two wire lead also into the red/black bannana plugs, I'm not sure if your charger came with any connectors for that...look at page 06 for a picture.....Here is the manual: https://www.pololu.com/file/download/iMAXB6ACmanual.pdf?file_id=0J525

The numbers you are showing below are just the defaults, you should be able to use the increment/decrement buttons and adjust the charge rate.
You should use LiPo balance or fast charge 7.4V and .8 amps(1c or 1 times the capacity of the battery as it shows on the label, this is the recommended charge rate)...

It looks like your charger only comes with a bannana plug/tamiya connector by default, so you may need to get a second male jst plug and solder that to the wires that go to the black/red charger bannana sockets so that you can connect the battery. Boy, this sure seems like I've steered you down a never ending road of little things to buy....it will look like this: https://www3.towerhobbies.com/cgi-bin/wti0001p?&I=LXEBFP&P=M Or sometimes you can find a bundle of a million connectors to fit anything....like this: https://www.all-battery.com/Multipl...22_a_7c80230&gclid=CNiS9If3o8QCFYiVfgodKm8AQw

In the end you will have a great setup and can build a dozen more planes and make it worthwhile:)

Frank


The 800mah battery has come in. (The BEC has not arrived yet.) It has 2 connectors; one is 3 pins and one is 2 pins. I noticed that if I take the voltage on the red and black wires of either connector I get about 8 volts. So, I am thinking that the Lipo battery may have come fully charged. Which connector is used for charging (or does it make any difference)?

View attachment 257625

My battery charger has 5 settings for Lipo batteries. They are as follows:

* LiPo Charge, 0.1 A 3.7v(15)
* LiPo Balance, 4.0 A 7.4v(25)
* LiPo Fast Chg, 0.1 A 3.7v(15)
* LiPo Storage, 0.1 A 3.7v(15)
* LiPo Discharge, 1.0 A 6.0v(25)

If I want to charge the 800mah battery, which setting should I choose? What are the other settings?
 
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Frank,

Thanks for all the information! It really helped. I already had the charger in my inventory from several years ago, so there was no problem there. Either the charger came with many connectors or I ordered a number of connectors at that time. In any case I have the right connector for the battery, so there is no need to make an order. I decided to set the charging rate to 0.8A and I am running it now.

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I put the push rods on yesterday. I was surprised with the toughness of the 0.03" wire. I cut the wire with regular wire cutters and bent the wire with needle nose pliers. It took some force to cut and bend the wires. It was fairly easy to get the right length. I made the bend for the connection to the servo horn first and then just marked the location for the bend at the elevon horn with a black magic marker. It is a little hard to see the bends in the photos, but they are enough so that the push rods will not come out.
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If its the music wire/hardened wire sold in hobby stores under the K&S brand it great stuff, it will however eat regular wire cutters for lunch. Better to use the hard wire cutters made for it or a dremel with cut off disc. The money I spent for the hardwire cutters was well spent.
 
If its the music wire/hardened wire sold in hobby stores under the K&S brand it great stuff, it will however eat regular wire cutters for lunch. Better to use the hard wire cutters made for it or a dremel with cut off disc. The money I spent for the hardwire cutters was well spent.

I took the push rod out of a Du-Bro 20" push-rod system kit. I have a feeling that it is the same stuff.
 
OKay, I've got all the electronic equipment and soldered the necessary connections. I followed Frank's directions for binding the receiver with the transmitter and also looked at the manual for this operation. Basically, this operation involves putting the shorting plug into the receiver BATT/Bind slot and turning on the transmitter. (The BEC connection was plugged into the AUX slot for this step.) The shorting plug is only used for binding to the transmitter and then removed. I then plugged the BEC into the BATT/Bind port and plugged the two servos into the aileron/elevator slots. I powered everything up and sure enough the servo's move, although, not correctly. This is my first programmable transmitter and I am on a learning curve. I now need to input the correct parameters into the transmitter. I was able to get the name of the model into the transmitter using a little intuition and the manual. (I took Frank's advice later today and used a twist-tie to attach the shorting plug to the transmitter handle. That way if the transmitter ever loses the bind on power-up, the receiver can be bound again.)


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Bob, here is a picture from the manual showing the flap screen, basically you want to edit the elevator setting when the switch is down, so that you have some up elevator(maybe 3/16" or so) when the switch is down and neutral or 0 when the switch is up, the flap column will stay zero because there are no flaps. The flap elevator trim is used to put in up trim for post boost nose heavy condition, otherwise you have to hold the trim lever each flight and put in up trim manually or try to fly it nose heavy with the sticks.

flap setting.png
 
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I took a few pictures of the Aerotech 24-40 plugged case for R/G gliders along side of the standard 24-40 case with the built-in delay charge. I bought my plugged case at Red Arrow. I think they were a little bit cheaper than other vendors. It may take Dave at Red Arrow a little bit of time to get this part in stock, but your patience will be rewarded. In Frank's video on another thread he shows how to reload this motor. It is easier to load than the standard case, because the delay charge and parts are not present.

https://www.rocketryforum.com/showt...and-F-106-Delta-Dart-Rocket-glider-kits/page4

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I took a few pictures of the Aerotech 24-40 plugged case for R/G gliders along side of the standard 24-40 case with the built-in delay charge. I bought my plugged case at Red Arrow. I think they were a little bit cheaper than other vendors. It may take Dave at Red Arrow a little bit of time to get this part in stock, but your patience will be rewarded. In Frank's video on another thread he shows how to reload this motor. It is easier to load than the standard case, because the delay charge and parts are not present.

https://www.rocketryforum.com/showt...and-F-106-Delta-Dart-Rocket-glider-kits/page4[/QUOTE.

Just curious since you have both side-by-side, would the standard 24-40 case work the same as the plugged case if the forward closure was filled with epoxy? I just think it's a bit ridiculous that the plugged case costs more than twice that of the standard case.
 
The rc case is machined from a solid piece, not a tube that is threaded which is why it is more. Epoxy may work if you ignore the fact it isn't an approved motor in that form. A friend of mine made an aluminum plug with two oring grooves I used to use with these loads that fit the standard front closure, but eventually I got a deal on the rc cases, it is a lighter setup using the rc case which helps. You'd have to be sure the inside length was right to get sufficient compression of the o ring. Since these are end burners the front isn't exposed to the flame till the end of the burn. you'd need to run your motor tube longer as well of course to fit the longer case. Not sure on how it might work with a core burner. I know for the 18mm glider reloads they do have you plug the standard case with epoxy. Seems they could make a flat solid front closure that should work...

Frank
 
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I found that I am on a learning curve with regard to the 2-cell 800mah LiPo battery (around 8 volts). At first when my electronics were not responding I thought that the transmitter was bad, then I thought that the BEC was bad, and then I thought that the battery charger was bad. It turned out that the battery had gone bad. In talking to the tech support at Horizon they said that when the 2-cell battery gets down to around 5 volts it is time to recharge it, otherwise you might lose the battery completely. They said that almost any kind of connection can drain the battery. Since the battery was only about a month old, they sent me a new battery free of charge.

I had a written question answered by Horizon and they said that a Hitec charger can possibly bring bad Lipo batteries back to life. I have one 2-cell battery with 4 volts on one cell, but only 2 volts on the other cell. I wonder if I can bring that battery back to life. I saw that one Hitec charger that can charge 4 batteries cost about $200. That is too much for my needs. There was a cheaper Hitec battery charger for about $40 that charges one battery. I wonder if I should buy it.
 
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I've got the 4 battery charger from hitec and really like it, I can charge my transmitter and three flight batteries in parallel in about 25 minutes, so I don't have to leave things charge and can sort of impulse fly...ie by the time the car is loaded my batteries are ready to go. I've also got the simpler hitec single battery charger and it works well too.

I think the guidance they gave you is too optimistic, I don't let my batteries go down much below 7v. The good guideline is only to discharge to about 80% of capacity....For me, batteries are cheap, and I would not risk a flaky battery, 2v I think is dead. Right now I'm flying in a single cell direct to the receiver and got rid of my bec and 2s batteries...

Frank
 
At 6v there is very little usable capacity left and 6.6 is where it falls off. 7v as Frank said is a good safe cut off point. Spending good money to hopefully save bad is only viable if you intend to ruin more batteries. To me it sounds like they were trying to up sell you. :y: It is better and cheaper to buy more batteries and have spares in case of accidents. Make sure to store them at half charge and they will last a lot longer.


Richard
Ps; I fly 1s also.
 
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I launched the SR-71 yesterday in about 5 to 10 mph winds, but things did not go well. At some point at altitude the model shredded into several large pieces. One break is just before the carbon rod cross spar. I had shortened the motor tube and got the c.g. at the right location before flight with the large 7.2 volt battery. Shortly, after lift off the model started arcing over. It seemed like small corrections did not help, so I gave a large nose up stick and shortly thereafter the model shredded.

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Bob, what motor were you using? i would have thought on the e6 it would be hard to pull hard enough to break the neck. This was an early version of my plans and different than the kit, I recommended a carbon rod to support the neck but it sounds like it broke further back, just behind where your carbon neck stiffener stopped, so I probably should have suggested it go full length, but I remember it came broken from your online source and thought it should have been strong enough. I've only had one guy ever break one and that was a pusher with a 1300 mah pack in the neck and he had no carbon neck support and pulled hard out of a dive..

Frank
 
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Frank, it was the E6. Yes, I recall the carbon rod was broke during shipping, so we decided to go with the remaining length towards the front. If you look at the attached pictures closely (everything is in black, so it's hard to see), it can be seen that the axial carbon rod ends before the aft end of the launch lug and there is actually a gap between that axial carbon rod and the transverse rod. The failure is right before the transverse rod. I would like to buy one of your kits (maybe I should buy two) and try this again. Which kit would you recommend?

(As bad luck would have it, I noticed last night that the 24 mm motor is missing. I should have been more careful, when I picked up the pieces. Perhaps, I would have found it. I had put a little bit of masking tape around the motor aft case and I thought that it was in tight. Otherwise, I have all the parts to build one or more models.)

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Bob, I think it was a combination of bad luck when you built from my original plans. I remember you forgot to put the spar in, so you slit through the fuse to do it after the fact, leaving a notch where the fuse could break easier, I don't see the reinforcing tape on the strip spar, and the launch lug didn't support that area, and the broken carbon rod was just a bit short. I'm still surprised it broke from a hard pull on an E-6 but I don't think the kit would have any problem. In the kit version I have a doubler on the top of the fuse, I double the bottom of the fuse as well, and I also put a styrene strip on the bottom in this area. I also use recessed round wing spars instead of a strip spar that doesn't have a slot through the wing, just a groove and I tape those. The kit also has a motor hook to prevent you from losing the casing. The X-15 I think is a great flyer if you want to try something different. You can PM me about kits, I'm happy to help.

I rememer Tom Blakeney had a neck failure as well on his initial F-108 he built a few months ago, and he reinforced it.

Frank
 
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Frank, I think you are right about the cross spar being put in with a notch. I think I can see the remainder of the notch in the wing. Also, I noticed that I put a short section of axial spar on the opposite side of the fuse that goes about 1" aft of the launch lug. Part of the break is exactly where that axial spar ends. I think I will order a SR-71 and the X-15. I will send you an email.
 
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