FTFC23: Build-ruary by Inq: Inq'd F-8 Crusader with Training Wheels

[Inq]

Progress... or lack there of
I CAD'd up a first cut of a wing, unrolled the surface, paper printed, cut the foamboard pieces and it didn't go very well. I'm mainly finding that the F.T. method of leading edge folding doesn't work very well with 42° leading edge sweep AND anhedral... especially when I tried to get the saw-tooth also. Chocked it up to foamboard design learning curve. I'll take a new stab today. Take out the saw tooth and add those as 3D printed prosthetics.

 

[telnar1236]

Hmm... I thought you guesstimated around 1700 gram, but I assume you're probably used to the nice 12 bladed HO versions.. I was thinking I got what I paid for with 1160.

Looking back on the thread, my guess was between 700g and 1 kg, so you're about 16% above that. I think the 1700g number was the allowable weight for a U-2 with that EDF.

 

[telnar1236]

I didn't even pause to think... I was trying to be true to the scale drawings. And since the F-8 only had them as elevators, I see it was my doings and not the F-8. I'd hope not to add to my handling problems. All tail surfaces use NACA 7 Series since I needed some thickness back further to deal with the cross spar. Uses NACA 5 series around the cross spar.
View attachment 235136

Yeah, if I remember correctly, the F-8 had that dihedral to help make sure some part of the elevator was always out of the turbulence from the wing. Like I said, it should probably be fine with such a small amount of dihedral.

 

[telnar1236]

Progress... or lack there of
I CAD'd up a first cut of a wing, unrolled the surface, paper printed, cut the foamboard pieces and it didn't go very well. I'm mainly finding that the F.T. method of leading edge folding doesn't work very well with 42° leading edge sweep AND anhedral... especially when I tried to get the saw-tooth also. Chocked it up to foamboard design learning curve. I'll take a new stab today. Take out the saw tooth and add those as 3D printed prosthetics.
View attachment 235137
View attachment 235138

Was the issue that the paper was splitting along the seam? That wing honestly looks fine to me apart from that one bit on the leading edge. Extending the lower skin further out along the wing should also help some with any warping.

 

[Inq]

Was the issue that the paper was splitting along the seam? That wing honestly looks fine to me apart from that one bit on the leading edge. Extending the lower skin further out along the wing should also help some with any warping.

No, the busted front-end wasn't what got it axed. I'm using the curved upper surface technique of the Master Series where you take off the paper on the inside instead of the folded breaks of the upper surface as on my Storch. On this wing I was trying to go with only doing about 2/3 span of the lower surface. I wanted just one thickness at the tip and you also mentioned that it would have somewhat washout compensation for tip stalls. Between not having the inner paper and curving the surface, the tip just didn't look like a good idea. It was twisting the wrong way - "Wash-in" At the root (left) you can see the stop more, on the tip... WAY TOO MUCH. It has about 20 DEGREES of twist.

I don't know if you can make it out in the pictures (with the words above, it might make sense).

I finished the CAD work and print the paper dolls this morning. Had some chores to do and I'll work on the wing tonight. It has full span top and bottom and no saw-tooth. The root is scale at 20 mm thick... the tip will be about 2x scale thick at the 9.2 mm. Maybe if I iron the heck out of it, I can reduce that some.

 

[telnar1236]

No, the busted front-end wasn't what got it axed. I'm using the curved upper surface technique of the Master Series where you take off the paper on the inside instead of the folded breaks of the upper surface as on my Storch. On this wing I was trying to go with only doing about 2/3 span of the lower surface. I wanted just one thickness at the tip and you also mentioned that it would have somewhat washout compensation for tip stalls. Between not having the inner paper and curving the surface, the tip just didn't look like a good idea. It was twisting the wrong way - "Wash-in" At the root (left) you can see the stop more, on the tip... WAY TOO MUCH. It has about 20 DEGREES of twist.

I don't know if you can make it out in the pictures (with the words above, it might make sense).
View attachment 235164
View attachment 235165

I finished the CAD work and print the paper dolls this morning. Had some chores to do and I'll work on the wing tonight. It has full span top and bottom and no saw-tooth. The root is scale at 20 mm thick... the tip will be about 2x scale thick at the 9.2 mm. Maybe if I iron the heck out of it, I can reduce that some.

That makes sense. Yeah, I've noticed that a couple times but never came up with an easy solution. Running the back of the lower skin parallel to the TE seems to help, but doesn't fully get rid of it.

 

[Inq]

F-8 Crusader Progress

Did a full re-design on the wing. I'll add the saw-tooth and maybe the wing tip using 3D Printing (if I have time). We're getting down to the wire. It's a lot heavier than I was originally planning.

Building it was a challenge I wanted the rounded tops of the Master Class planes and I'm using foamboard spars... except they're different than the standard fare. They're sized to fill the space and be in full contact with the upper and lower skins (two left pieces). It's pretty much a solid foam wing all said an done. The challenge comes in that the anhedral has to be put in before the spars and then I'm folding over the top surface on the table edge to let the anhedral hang off. It weighs 125.4 grams which bumps up my AUW to 780 grams. I still have the wing mount, fairing over the wing, back to the tailfin and some secondary inlet work to do that will add weight. I'll probably be over 800 grams ready to fly.

Here is a dry fit assembly.

 

[FlyerInStyle]

F-8 Crusader Progress

Did a full re-design on the wing. I'll add the saw-tooth and maybe the wing tip using 3D Printing (if I have time). We're getting down to the wire. It's a lot heavier than I was originally planning.

View attachment 235354

Building it was a challenge I wanted the rounded tops of the Master Class planes and I'm using foamboard spars... except they're different than the standard fare. They're sized to fill the space and be in full contact with the upper and lower skins (two left pieces). It's pretty much a solid foam wing all said an done. The challenge comes in that the anhedral has to be put in before the spars and then I'm folding over the top surface on the table edge to let the anhedral hang off. It weighs 125.4 grams which bumps up my AUW to 780 grams. I still have the wing mount, fairing over the wing, back to the tailfin and some secondary inlet work to do that will add weight. I'll probably be over 800 grams ready to fly.

View attachment 235355

Here is a dry fit assembly.
View attachment 235356

looking amazing! I hope it flies as well as it looks!

 

[telnar1236]

F-8 Crusader Progress

Did a full re-design on the wing. I'll add the saw-tooth and maybe the wing tip using 3D Printing (if I have time). We're getting down to the wire. It's a lot heavier than I was originally planning.

View attachment 235354

Building it was a challenge I wanted the rounded tops of the Master Class planes and I'm using foamboard spars... except they're different than the standard fare. They're sized to fill the space and be in full contact with the upper and lower skins (two left pieces). It's pretty much a solid foam wing all said an done. The challenge comes in that the anhedral has to be put in before the spars and then I'm folding over the top surface on the table edge to let the anhedral hang off. It weighs 125.4 grams which bumps up my AUW to 780 grams. I still have the wing mount, fairing over the wing, back to the tailfin and some secondary inlet work to do that will add weight. I'll probably be over 800 grams ready to fly.

View attachment 235355

Here is a dry fit assembly.
View attachment 235356

That looks incredible! Is there some kind of thrust tube in the tail section? If there isn't, you might want to consider making one out of some rolled up poster board. Not having a thrust tube can badly hurt thrust. Also, every gram helps, but 800 grams flying weight is still exceptionally light for an EDF this size. My little F-104 with its 50mm fan (although the same battery) is a similar weight with a much smaller wings and is by no means a particularly fast plane while landing. Making some conservative assumptions of a weight of 850 grams and a max lift coefficient of 1 gives a stall speed of about 20 mph which is very manageable.

 

[Inq]

That was a PITA...

The wing mounting structure ate a full day of design, print... iterate.

My craftsman skills are not living up to my imagination and designs. this one shows the 5 mm bamboo skewer pegs of the front and slider back unit.

Here, mounted on the plane. It'll have to do; time is running out.

 

[Inq]

One thing left...
... to build. I need to add the fake intake near the EDF. However, I want to run some thrust tests so I can do a before and after evaluation. I'd like to see how design decisions affect results. Although a NACA duct would probably be the wise decision, I want to try a movable door. My premise is that at static conditions the tiny scale F-8 inlet is near worthless. It has an area of 1690 sq-mm. The EDF is wanting draw through 3850 sq-mm. Not even realistic.

My simplistic look on aerodynamics. I'm learning something every day from @telnar1236 jets and my DIY Telemetry thread. Anyway... my premise is those numbers will cause a partial vacuum in the fuselage and the door will open up till it balances what it can get through the F-8 inlet and this fake inlet. The door opening should be about 7200 sq-mm. During flight, the front inlet should contribute a larger portion and the door opening will close partially or completely in a self regulated way. It would be nice to figure a cheap/easy way to measure the door position just for my edification.

The door will be hinged off the aft wing mount bulkhead and be nicely place between the two ventral fins that were added to the F-8C in about 1963.

 

[Inq]

An hour later... Dismal...

Is all I can say.
The EDF starts out with 1160 grams here in free air. Note - All these tests are without any cheater inlet... just the scale inlet.

Test 1 - 509 grams
This test was with the wing removed and the nose off. This lets in the maximum air even if the insides are cluttered with equipment... no internal ducting.

Test 2 - 410 grams
This test was with the wing on, but the nose off.


Test 3 - 130 grams
This test was with the wing and nose on.


Not that I had any doubts ahead of time, but I think that is conclusive evidence that a cheater inlet is mandatory!

 

[L Edge]

Just looking at the above diagram, the flap is so close to the EDF that you would have a swirling airflow pattern entering the EDF. So, loss of power.

Using cheater holes on the bottom, the further forward they are, more of a chance to reduce loses. Best I could do was 6 inches on my fighter. Hovering went from 58% throttle to 49%.
Did experiment taking pvc tube with same inlet ducting length with inlet areas the same, EDF in-between, and exhaust length and set cut slots in. Open 2 slots, rest tape and measured exhaust velocity and distribution across the exhaust by drawn glass pitot tube and U-tube. Then moved ahead by one slot and taped the rear. Get it the furthest distance and taper it in without causing structural damage. . Didn't want to cut center section out to insure best airflow pattern across EDF.

 

[telnar1236]

One thing left...
... to build. I need to add the fake intake near the EDF. However, I want to run some thrust tests so I can do a before and after evaluation. I'd like to see how design decisions affect results. Although a NACA duct would probably be the wise decision, I want to try a movable door. My premise is that at static conditions the tiny scale F-8 inlet is near worthless. It has an area of 1690 sq-mm. The EDF is wanting draw through 3850 sq-mm. Not even realistic.

My simplistic look on aerodynamics. I'm learning something every day from @telnar1236 jets and my DIY Telemetry thread. Anyway... my premise is those numbers will cause a partial vacuum in the fuselage and the door will open up till it balances what it can get through the F-8 inlet and this fake inlet. The door opening should be about 7200 sq-mm. During flight, the front inlet should contribute a larger portion and the door opening will close partially or completely in a self regulated way. It would be nice to figure a cheap/easy way to measure the door position just for my edification.

The door will be hinged off the aft wing mount bulkhead and be nicely place between the two ventral fins that were added to the F-8C in about 1963.

View attachment 235412

That inlet door seems like a great idea. I expect it will work exactly as you anticipate. I think some of the new EDFs from Freewing have something similar and I haven't heard any complaints.

 

[telnar1236]

An hour later... Dismal...

Is all I can say.
The EDF starts out with 1160 grams here in free air. Note - All these tests are without any cheater inlet... just the scale inlet.

Test 1 - 509 grams
This test was with the wing removed and the nose off. This lets in the maximum air even if the insides are cluttered with equipment... no internal ducting.

Test 2 - 410 grams
This test was with the wing on, but the nose off.
View attachment 235413

Test 3 - 130 grams
This test was with the wing and nose on.
View attachment 235414

Not that I had any doubts ahead of time, but I think that is conclusive evidence that a cheater inlet is mandatory!

Do you have a thrust tube behind the EDF? If the EDF just goes into the 3D printed tail, that's probably the biggest source of losses without the nose on. And going from 1160 grams to 130 grams - yikes - that might be the largest percentage loss I've heard of for an EDF to date.

 

[telnar1236]

Just looking at the above diagram, the flap is so close to the EDF that you would have a swirling airflow pattern entering the EDF. So, loss of power.

Using cheater holes on the bottom, the further forward they are, more of a chance to reduce loses. Best I could do was 6 inches on my fighter. Hovering went from 58% throttle to 49%.
Did experiment taking pvc tube with same inlet ducting length with inlet areas the same, EDF in-between, and exhaust length and set cut slots in. Open 2 slots, rest tape and measured exhaust velocity and distribution across the exhaust by drawn glass pitot tube and U-tube. Then moved ahead by one slot and taped the rear. Get it the furthest distance and taper it in without causing structural damage. . Didn't want to cut center section out to insure best airflow pattern across EDF.

View attachment 235415

The only thing to add here is that this is most true at higher speeds. The closer to the EDF the cheater inlet is, at least to a point, the better it will typically perform at high angles of attack.

 

[Inq]

Do you have a thrust tube behind the EDF? If the EDF just goes into the 3D printed tail, that's probably the biggest source of losses without the nose on. And going from 1160 grams to 130 grams - yikes - that might be the largest percentage loss I've heard of for an EDF to date.

No, I don't have any direct tube. It just empties into the funnel shape of aft fuselage. I should be able to add one after the inlet is done.

 

[L Edge]

Happen to look at the table on the 12th entry.

You show a 4S 1500 mah running your 70 mm EDF?it's
Most 70 mm EDf's use at least 3000+ battery to get a flight of 2-4 mins which depends on throttle management.

How long do you think you can fly with the 1500? Remember as the voltage goes down in the battery, the thrust goes down.
Some ESC's cut off the motor so that the RX functions so you can land it deadstick. You also can't get 1500mah out of the battery
What happens if you need to do a go-around on approach?


What time of flight do you calculate with the 1500?

 

[Inq]

Happen to look at the table on the 12th entry.

You show a 4S 1500 mah running your 70 mm EDF?it's
Most 70 mm EDf's use at least 3000+ battery to get a flight of 2-4 mins which depends on throttle management.

How long do you think you can fly with the 1500? Remember as the voltage goes down in the battery, the thrust goes down.
Some ESC's cut off the motor so that the RX functions so you can land it deadstick. You also can't get 1500mah out of the battery
What happens if you need to do a go-around on approach?


What time of flight do you calculate with the 1500?

Don't know. These LiPO 4S and the ESC came with different connectors than my watt-meter, so I didn't get a draw rate. I'm not too worried about weight carrying capability, so I'll get whatever is needed... after FTFC23. If I get one lap for the maiden video... I'll call it good.

 

[Inq]

A Little Progress...

Working on the other planes more today. Did finish the design, print and sanding of the inlet door, but did not install it.