SR-71 build using 64mm EDF or possibility of 70's

kilroy07

Legendary member
Love the idea for rolling the foam 👍

Not sure if I mentioned it or not on my thread, but I used an arrow shaft for the forward fuselage
 

L Edge

Master member
Love the idea for rolling the foam 👍

Not sure if I mentioned it or not on my thread, but I used an arrow shaft for the forward fuselage

Hey, thanks for that suggestion. Keep them coming. Always good to see alternatives.

I have two objectives in mind, 1) To keep the twist down on the long nose and 2) to keep it in one piece if the body slams down hard especially with the battery above.

A number of years ago I designed a fixed landing gear that really holds up great for foam. What it amounts to is a thick piece of balsa that is going down the nose past the 2 carbon re-enforced strip/rod to prevent twisting to the entire fuse. It is the same density as the foam. I am using epoxy to hold it together.

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I am really getting attached to this project. Now I have a problem with one EDF. And I think it is approaching the heavy side of using 64's. I might even rip apart my Viggen to get the other 70. Would love to put fixed landing gear on to take off and land.

I think it will look awesome at the club runway. Especially if you can flare and hold it until the main wheels touch down. Did you see my approach on how to vary the throttle curve so at the low end, so it reduces spool up time in another thread?

I have a multi-engine transport(prop driven) and by playing with the throttle curve, I can actually come in on a landing with it flaired nose up and land main gear only and then pull throttle back causing the nose to drop. All you need to do is flatten a lower sement of the curve and stay within while you flair it. (DX9 radio.)
 

L Edge

Master member
Today was able to use 36" balsa long ,4"wide to reduce twist to nose. It was epoxy to fuse for round 1-


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when dried, put the front end on making sure everything is in line.

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Since it is the XBB(experimental bluebird), no paint or dressing will be added unil it flies. Longest balsa is 36", so it give's you the the size it will be to fly.

Last, put the depron tail on to complete the structure. 2 piece

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At present, the extension inlet ducting is not on till I get both engines working tried and true.

What's left.

1) get engines reliable before flight.
2) since the engines can ingest rocks, dirt, grass ,snow , need to come up with temporary light landing gear so ducting when sliding along on ground doesn't ruin my blades.
3) need to find the CG of this beast. Will be looking for a day whem there will be high winds. no edf's, then edf's running at low speed.
4) tune the gimbal thrust vectoring so it meets my specs.
4a) check out differential thrust and have it under control in yaw axis
5) put my flight jacket on and take a spin (I hope)
 
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L Edge

Master member
After 2 1/2hrs chasing why the 1 EDF kept cutting out with really no pattern, found one of the wires that is soldered to the ESC that goes to the RX, was a poor joint. After doing it right, now I have a reliable setup.

Set up the differential thrust so now steps 1 and 4a are done. Working on setting up of landing gear, hoping to set up stearable nose gear.
 

Grifflyer

WWII fanatic
After 2 1/2hrs chasing why the 1 EDF kept cutting out with really no pattern, found one of the wires that is soldered to the ESC that goes to the RX, was a poor joint. After doing it right, now I have a reliable setup.

Set up the differential thrust so now steps 1 and 4a are done. Working on setting up of landing gear, hoping to set up stearable nose gear.
Nice, are you gonna try to have it ready to fly by next weekend?
 

L Edge

Master member
Always interested!

Currently I had my exhaust down to maybe 85 percent (Ben H. Pretty much said I was probably choking the edf and should go no more than 90. One thing about Pringle’s cans is they have that nice slick foil lining.

I have to redesign my exhaust anyway, I might make them 100% (no taper)

I plan making cheater holes where the blow by doors/vents are. 😉

I have explored not only the exhaust area, but making improvements on the other end. I used a pitot tube, U-tube slated at 10 degrees to explore the exit area. Simply put, don't reduce it below 95 %.
What happens is the P static goes up inside and yes, the exit velocity is increased a %. In examing a problem, you also need to look at the other end, so as the blades turn,it leaks out the front. Yes, go from 5 to 11-12 blades and yes you improve it at the cost of a heavier battery.
Now, you also have leakage between the blades and housing. Guess what, the cheaper fans have quite a gap. Well, I ended up taking Scotch magic tape and layed 1-2 thicknesses between and reduced the leakage and it gives an increase in static thrust. Prove is, hold plane vertical and add power till it hovers with battery at full voltage. Check % of throttle on tx. Now tape, check same voltage charged and hold vertically. Found it took less throttle to hover. Even did this to just the EDF and improved.

Before, jet didn't take off from table, taped 2 layers and voila!!!


General rule for low airflow . If you choke the exhaust, yes, you increase the exit speed (anybody know what the foward speed amounts to?) but you then reduce the static thrust of the EDF.

I have done projects with my cheap 5 bladers with "thrusters" having 2 carbon tubes pick up total pressure and deliver flow to the wings as well as having a third carbon tube go thru the ducting for strength and have it fly a F-22 with no reduced losses. I do not choke the TV tube down at all. Another way I explored is as the guys came to the flying field, I watch the performance of the jets, ask what size the EDF was, and then measured the exit area. Result was between 95 to 100% the size of the EDF for the good performance jets and the other's had high reduction of exits. That's my experience.

This project has also layers of tape between the blades and housing.
 

L Edge

Master member
Weather is very crappy outside for next 2 days.

1) Checked TV units(2) so they are perpendicular and parellel.
2) Set elevons so deflections are the same for up and down. Adjusted ailerons and elevator by changing end travel.
3) Set differential thrust fairly high because the shape (white depron) is a vertical stab. Will be interesting what happens in flight if i make it.
4) Fasten the electronics down and will balance the plane lateral (by moving battery left or right) for so it roll over while launching.


Being a member of a club, it offers lots of things. Guy brings foam F-86 to field, takes off and gets up to top speed and bends it real tight and totally demolishes it. Trashes plane. Asked him if he wants parts, says no, and you can take. Here is the end result.

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Now have a light gear set with a steerable nose wheel. If I still have enough power, will install.
 

L Edge

Master member
Today(raining), did a number of things to try to ensure it's upcoming maiden flight.

Determined that the length of maiden flight is going to be 2 min. That allows for go-around if needed.
Made a bunch of runs(first was when I had an electrical fire were caseing started to smoke and melt due to high amperage). After replacement, max time was 3min 22secs of run before lack of power. Used a 3300mah 3s system.

Assumed the CG to be near the end of angular fuse joint. Adjusted battery and then held BBX vert and needed to adjust TV so it will stay vert rather than move aft like it did. Now have plenty of power and throttle limits of +/- 150, it hovered at -33 on TX. Tried quick boost of throttle and up it wanted to go vert.

Got real antsy and with light rain went outside to chuck it for CG. I added small amount of throttle and l saw it nose down slowly and stop. No elevon control was used. Result was a muddy mess on the bottom.

So, now is the time to add landing gear. With enough power(I hope) should work. Tommorow it's snow, so gives me a chance to install and do a video with it's taxi around. With TV and steerable nose gear, wonder what the radius will be to do a 180.
 

kilroy07

Legendary member
I have explored not only the exhaust area, but making improvements on the other end. I used a pitot tube, U-tube slated at 10 degrees to explore the exit area. Simply put, don't reduce it below 95 %.
What happens is the P static goes up inside and yes, the exit velocity is increased a %. In examing a problem, you also need to look at the other end, so as the blades turn,it leaks out the front. Yes, go from 5 to 11-12 blades and yes you improve it at the cost of a heavier battery.
Now, you also have leakage between the blades and housing. Guess what, the cheaper fans have quite a gap. Well, I ended up taking Scotch magic tape and layed 1-2 thicknesses between and reduced the leakage and it gives an increase in static thrust. Prove is, hold plane vertical and add power till it hovers with battery at full voltage. Check % of throttle on tx. Now tape, check same voltage charged and hold vertically. Found it took less throttle to hover. Even did this to just the EDF and improved.

Before, jet didn't take off from table, taped 2 layers and voila!!!


General rule for low airflow . If you choke the exhaust, yes, you increase the exit speed (anybody know what the foward speed amounts to?) but you then reduce the static thrust of the EDF.

I have done projects with my cheap 5 bladers with "thrusters" having 2 carbon tubes pick up total pressure and deliver flow to the wings as well as having a third carbon tube go thru the ducting for strength and have it fly a F-22 with no reduced losses. I do not choke the TV tube down at all. Another way I explored is as the guys came to the flying field, I watch the performance of the jets, ask what size the EDF was, and then measured the exit area. Result was between 95 to 100% the size of the EDF for the good performance jets and the other's had high reduction of exits. That's my experience.

This project has also layers of tape between the blades and housing.
As this is my first real design using EDFs (and just so I’m crystal clear on this) you are referencing the fan face area, correct? That is the area of the fan blades minus the center spindle. I hope so, cause I spent a lot of time designing the exhaust using those numbers. 😂

My first run was with the 5 bladed edfs, new build is using 12 blade. I have a thrust meter due to arrive any time so hopefully I can get some real numbers. If you check out my Alpha build maiden video, you can see she “almost” hovered....

I like the tape idea to tune the motors! Might give new life to those 5 blades.
 

L Edge

Master member
As this is my first real design using EDFs (and just so I’m crystal clear on this) you are referencing the fan face area, correct? That is the area of the fan blades minus the center spindle. I hope so, cause I spent a lot of time designing the exhaust using those numbers. 😂

My first run was with the 5 bladed edfs, new build is using 12 blade. I have a thrust meter due to arrive any time so hopefully I can get some real numbers. If you check out my Alpha build maiden video, you can see she “almost” hovered....

I like the tape idea to tune the motors! Might give new life to those 5 blades.

No, I use the dia of the fan in my calcs. I tried that way and one of my designs and it choked in tight turns. Ended up with cheaters slots to get out of problem. This was with 5 blades, when I did a 4s 12 blade, I just still followed the rules as the 5. To me, choking the exit will increase the airflow but what person has done testing to see "How much speed increase there actually is?".
 

L Edge

Master member
Finished off landing gear and getting is set up was real easy. Servo was installed in the gear slot and went back to system setup (DX9) and selected gear and went to Channel Input Config and used RKnb to control directional turning. Now I will be able to trim it out for a straight takeoff and use it for taxing. Snow is out side so did a run in cellar. Trims out nice!! Set up so knob notch goes left, turn is left.

Also tried differential thrust for taxing, works real well.
 

L Edge

Master member
Here is vid of the SR-71 taxing. High winds were encountered.

Decided to punch to see power of EDF's.
Use Differential thrust for high speed turn.
Taxing using nose gear steering.

 

L Edge

Master member
Using high winds to find CG and it's first experimental flight.

Concept is to have a good wind going across the fuse. That way you find the CG is to place the battery at a suppose position, grab the vertical segment by 2 fingers , release yor left hand grip, and see if it goes nose down or nose up. The object is to have it stay level. It took me three trys of moving the battery to find the CG.

I have found if you throw (sling,run,etc) the plane at shoulder high, there is a lot of potential and kinetic energy that either a stall(nose high) or very nose down plane is going to absorb. So I found a different way . If you have a 15-30mph wind going over the fuse, why not take the airplane and do the following and perhaps save it.

1) Grab plane(right hand) at the CG point about 6" from the ground. (Majority of PE and KE are greatly reduced)
2) Place left thumb on throttle on gimbal. Don't touch stick!!!
3) Since flow over wing has velocity, added 1/3 throttle or so.
4) Now release with a forward horizontal movement and the plane should just move forward if CG is close.
5) Very quickly, move the TX so left and right hands are on the stick and fly it. If failure, you got a good chance to ding it , rather then wreck it.

Works for me.

As you can see, it endured it's short maiden flight with no damage. A big gust came around the building and just lifted the nose and I recovered with only a minor ding when I hit the curb.

Present Problems for others who want to build a SR-71.

1) Suggest 70's or 80's size EDF's which means scaling up.
2) Biggest problem is with long!!!!!!!! nose. Very touchy with elevator.
3) Since battery(s) are quite a bit of the total weight and are located on the nose, re-enforcement of fuse will be a necessity.
4) Present feeling is you will need landing gear(lacking good airflow) to get it into the air.

What's left?

Winter is setting in (already snow storms) and feel I could launch easily(full throttle) but landing is the problem. If club runway has no snow, will go for it. If not, 100% sure I will tear away landing gear in the clumpy frozen grass. Hoping for a warm up to occur.

Builders- run this video at .25 speed at 0:40 to watch the action of gusty wind and controls.




 
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